RADIOACTIVITY at a glance

 

TOPIC: RADIOACTIVITY AND NUCLEAR ENERGY

Radioactivity

Radioactivity is the spontaneous emission of radiation by an element. Such an element is called a radioactive element.

Discovery of radioactivity

Radioactivity was discovered by Henri Becquerel, a Physicist,  and the phenomenon was named by Marie Curie who also discovered  the elements thorium, polonium and radium. Presently more than 40 naturally occurring radioactive elements have been discovered.

Radioactive reactions are also called nuclear reactions

Differences between nuclear reactions and ordinary chemical reaction.

	Nuclear reaction	Chemical reaction
1.	It involves the nucleus (nuclear particles) of the atom	It involves the valence electrons of the atom
	Large amount of energy change is involved	It involves low amount of energy change
	It involves the decomposition of the nucleus	It involves the transfer, loss, gain and sharing of electrons
	The rates of reactions are not affected by temperature and pressure	The rates of reactions are affected by temperature and pressure
	Does not involve the breaking or forming of bonds involved	It involves the breaking of old bonds and formation of new ones
	The reactions are irreversible	They could be reversible or irreversible

TYPES OF RADIATION

There are three major types of Radioactive radiation

1.  alpha(α-) radiation 

2. beta(β-) radiation and 

3. gamma(γ) radiation/rays. 

1. Alpha rays/radiation

These are fast moving stream of positively charged particles, that resembles the helium nucleus.

Properties of alpha rays

1. They are positively charged particles 

2. They have low penetrating power (they can be stopped by a thin sheet of paper)

3. They have strong ionizing power (ionizing any gas through which they pass).

4. They cause fluorescence in some materials e.g ZnS

5. They have a mass number of 4 and atomic number of 2 

 

2.Beta Rays

These are very fast moving streams of electrons. 

They have velocities close to that of visible light.

Properties

1.     They are negatively charged.

2.     They have higher penetrating power than alpha particles ( can be blocked by a thin sheet of aluminum foil)

3.     They have lower  ionizing power than alpha particles.

4.     They cause florescence in substances like anthracence but not zinc sulphide.

5. They are deflected toward the positive plates in an electrostatic field 

Gamma Rays

Gamma rays/radiations are electromagnetic waves similar to visible light but with shorter wavelengths.

Properties

1.  They have the highest penetrating power of the three particles ( they can be blocked by a thick block of Lead)

  2. They travel with the speed of light.

3.     They are not affected by an electrostatic field.

4   They do not have charge nor mass.    

5.     They have the least ionizing power among the three particles.

Summary of the properties of alpha, beta and gamma rays

	Alpha ray	Beta ray	Gamma ray
Nature Electrical Charge Mass Velocity Relative penetration Absorber	Helium nuclei 42He +2 4 units About 1/20 the speed of light 1 Thin paper	Electron o-1e -1 1/1840  units Varies (from 3 – 99% of the speed of light) 100 Metal plate	Electromagnetic radiation No charge No mass Speed of light 10,000 Large lead Block

Other types of radiations include 

X – rays

X – rays are electromagnetic waves, that resembles visible light, but with a shorter wavelength. They are produced when fast moving electron knock out electrons from the inner shells of metal atoms and electrons from a higher/outer shell then falls down to replace the knocked – out electrons. This movement of electrons is accompanied by the emission of x – rays.

Properties and uses of x – rays

1. X – rays can penetrate readily through most solid substances such as wood, foils, flesh and paper, which are opaque to visible light. 

Hard x – rays have greater penetrating power than soft x – rays.

2. Soft x – rays are used in medicine to photograph human parts while hard x – rays are used for destroying cancerous cells.

3. X – rays are used to study the arrangement of particles in crystal lattices in chemistry and in big organic molecules like proteins.

DETECTION OF RADIATIONS 

Different types of devices have been developed over the years for detecting radiation. The most commonly used detectors are:

i.  Geiger-Muller counter,

ii.   the scintillation counter and

iii. photographic plate or solution,

iv. Diffusion cloud chambers 

Others include:

4. The pulse (wulf) electroscope

5. Solid state detector

6. Photographic plate or solution

7. Dekatron counter.

When a certain quantity of a radioactive material disintegrates spontaneously the word decay is used. During the decay, there is usually an emission of alpha – or beta particles. Sometimes, gamma rays also accompany the emission of these particles. The outcome of the disintegration is that the parent nucleus (nucleus undergoing disintegration) undergoes a change in the atomic number and become the nucleus of a different element. 

TYPES OF DECAY 

Alpha Decay: When the nucleus of an atom loses an α-particle. i.e. a helium nucleus (⁴₂He) during disintegration, the atomic number of the atom is reduced by two units and its mass number by four units, e.g.

when an atom of uranium 238, loses an alpha particle, it will become an atom of thorium Tℎ.  The nuclear reaction is written thus:

  ²³⁸₉₂U →²³⁴₉₀Th + ⁴₂He (α-partcle)

The atom undergoing decay is called the parent cell while the new element (atom) formed is called the daughter cell.

Beta Decay: this kind of radioactive change is equivalent to the splitting of a neutron in the atomic nucleus of the radioactive element into an electron and a proton. The proton remains in the nucleus while the electron is expelled out of the nucleus as beta particles. The mass number does not change but the atomic number increases by one.

For example, if a thorium nucleus Th emits a β particle, its nucleus changes into a nucleus of the element protactinium whose mass number is the same as that of thorium but whose atomic number is increased by one unit from 90 to 91.

²³⁴₉₀Tℎ →²³⁴₉₁Pa + ⁰_-1β-particle

Gamma Decay: Gamma decay involves only the release of large amount of energy and does not involve change in the mass number or atomic number. It always accompanies an α or β decay.

         α + β-particle + γ-rays.

Radioactive decay series

The nucleus of the daughter element formed most times by transmutation is itself unstable, and will undergo further disintegration after some time. This time may vary from few microseconds to millions of years and it is known as HALF-LIFE. This series of changes may occur until a stable nucleus is finally formed. Examples is the uranium series, the thorium series and actinium series, each of which is named after the longest-lived element in the series.

Element and radiation emitted Isotope Half-life

Uranium

     ↓    α        4.5×106years

Thorium

      ↓    β       ℎ 24.1 days

Protactinium

       ↓  β       1.18 minutes

Uranium

       ↓  α       2.5×105years

Thorium

       ↓    α       ℎ 8.0×104years

Radium

       ↓     α     1622 years

Radon

      ↓       α    3.8 days

Half Life as a Factor of Stability of Nucleus

The half-life of a radioactive element is the time taken for half of the total number of atoms in a given sample of the elements to decay.

 For example, the half-life of radium-226 is 1622 years. This means that if we have one thousand radium atoms at the beginning, then at the end of 1622 years, 500 atoms would have disintegrated, leaving 500 undecayed radium atoms. In the next 1622 years, half the remaining atoms i.e. 250 would have disintegrated, leaving 250 undecayed atoms of radium and so on. 

The stability of an atomic nucleus is related to the ratio of neutrons to protons in the nucleus. Atoms with neutron-proton ratio less than 1 or greater than 1.5 tend to be unstable and undergo radioactive radiation.

Nuclear Chemistry and Reactions

Nuclear chemistry is concerned with reactions that involve the nucleus. When nuclear particles like proton, neutrons, alpha and beta particles as well as electrons and gamma rays are used as bullets for bombarding the nuclei of some atoms, one or two of the following events may take place:

a) Artificial radio isotopes may be created

b) Atomic transmutation may occur

This transmutation is the process by which radioactive elements change into different elements.

Artificial Transmutation

Because large amount of heat is released from radioactive disintegration, scientists, devised a means of tapping, harnessing, controlling,  and using this large amount of energy. This results in artificial transmutation since the natural transmutation is not subject to human control i.e. spontaneous. In 1919, Ernest Rutherford succeeded in transmuting a nitrogen isotope into an oxygen isotope by bombarding the nitrogen isotope with alpha particles.

147N+ ⁴₂α → ¹⁷₈O + ¹₁P

                                      ^Proton

Many atomic transmutations can be carried out by bombarding different elements with fast-moving atomic particles like neutrons, protons, deuterons (nuclei of deuterium atoms) and alpha particles. The neutron is a very effective bombarding particle because it is heavy and has no charge.

Generally, when light elements are bombarded by neutrons, new elements are formed by ejecting charged particles.

But, if the nucleus being bombarded is heavy, it captures the neutron to produce an isotope of the original

element. +

Nuclear Fission

Nuclear fission is a process in which the nucleus of a heavy element is split into two nuclei of nearly equal mass with a release of energy and radiation.

Nuclear Fusion

Nuclear fusion is a process in which two or more light nuclei fuse or combine to form a heavier nucleus with the release of energy and radiation.

It is the opposite of nuclear fission. The energy released during nuclear fusion is greater than the energy released during nuclear fission because of the differences in the binding energies of the isotope.

This  principle is  applied in the making of hydrogen bombs. The sun and stars also obtain their energy from nuclear fusion reactions.

1n 1939, a German nuclear scientist (Halm) discovered that atomic nucleus of isotopes of uranium could absorb a neutron and then break into two (atomic fission) e.g.

He noticed that the total products of fission have a slightly different mass from that of the total initial material. This difference in mass is radiated as energy, and the amount of energy is given by Einstein in the equation E = mc² 

where E= energy in joules, 

m= mass in Kg 

and c = velocity of light in s-1.

 A large amount of energy is released during nuclear fission This energy released can now be harnessed during nuclear reactions and are used in power stations to generate electricity and nuclear submarines.

Uses Of Radioactive Isotopes

1. Medical Uses:

a. It is used for the treatment of cancer, radioactive isotopes like 

(i). cobalt 60  for treating tumors and destroying cancerous cells

(ii). Iodine – 131 for  treating cancer of the thyroid gland and

(iii).  phosphorus -32 for treating leukemia

b. Alpha rays are used in the sterilization of hospital equipment and in the pasteurization of foods.

2. Agricultural purposes: radiation is used in insect and pest control. This is done by sterilizing the male pupae of an undesirable insect by radiation, so that sterile male adults are produced. They are then released in large numbers to mate with the native female adults which will lay unfertilized eggs.

3. Radioactive tracers: due to continuous emission of radiation by a radioactive isotope it is possible to trace its position  and also to  measure its concentration using a sensitive counter. And so when a small quantity of a radioactive isotope is mixed with its stable isotope it is possible to follow its path through a series of changes or reactions . This technique has been used to study many metabolic processes in both plants and animals e.g. 

(i). the uptake of iodine by the thyroid gland using iodine-131 

(ii). photosynthesis using carbon-14 in the form of carbon (IV)oxide. 

(iii). In medicine for  tracing the movement of materials or food through the alimentary canal.

4. It is used in generating electricity from nuclear reaction occurring in nuclear power stations/ plants.

5. In Radiological Dating: Radioactive carbon-14 isotope (with half-life of about five thousand years) is used for determining the age of organic materials. The process involves measuring the amount of carbon-14 present in the specimen and the age is determined from this value and the half-life of the isotope. 

The presence of very long – lived radioisotope ( e.g uranium 238 with a half-life of 4.5×10⁹  years) present in the earth crust is utilized by geologists to estimate the age of rocks and archaeological objects. It is also used in distinguishing genuine antiquities from fake ones.

OBJECTIVE QUESTIONS

 1.      Equation? ²³⁴₉₀Th → ^y_xPa + β- particle

           X           Y

a.        91          234

b.        92          235

c.       89           235

d.        88          238

2.  A radioactive solid is best stored 

a. Under paraffin oil 

b. Under ultraviolet light 

c. In a cool, dark cupboard

d. In a box lined with lead

3. 

Briefly discuss the following

- Atomic pile and atomic bomb

- Binding energy

- Nuclear energy for power

Isotopy

Isotopy is the existence of atoms of the same element having the same atomic number but different mass number or atomic mass. 

The different atoms are called isotopes. Hence

Isotopes are atoms of a particular element with the same atomic number but different mass number.

Examples of isotopes are

i.      ³⁵₁₇Cl and ³⁷₁₇Cl

ii.      ¹⁵₈O, ¹⁶₈O, ¹⁷₈O and ¹⁸₈O

iii.    ¹₁H, ²₁H and ³₁H

Relative Abundance: - when atoms exist naturally in isotopic mixture, they do so in a particular amount, when this amount is expressed in percentage, it is known as relative abundance. Hence, 

The relative abundance of an element is the amount (expressed in %) in which a particular isotope occurs in nature

Examples of isotopes are

i.     Cl and ³⁵₁₇Cl with relative abundance of 75% and ³⁷₁₇Cl with relative abundance of 25%.

ii.    ¹⁵₈O with relative abundance of 0.17, ¹⁶₈O with relative abundance of 99.76%, ¹⁷₈O with abundance of 0.05% and ¹⁸₈O with abundance of 0.02%

 RELATIVE ATOMIC MASS: - The relative atomic mass of an element is the number of times the average mass of one atom of the element is as heavy as 8one-twelfth the mass of carbon-12.

DETERMINATION OF RELATIVE ATOMIC MASS OF AN ELEMENT GIVEN THE RELATIVE ABUNDANCE

The relative abundance of an element can be calculated from their various isotopic masses and their relative abundance as follows: -

1.  1.     Naturally occurring exist in two isotopic mixtures ³⁵₁₇Cl with relative abundance of 75% and ³⁷₁₇Cl with relative abundance of 25% respectively. Calculate the relative atomic mass of Cl

            SOLUTION

    75 x 35 + 25 x 37 =
   100           100   

  
     26.25 + 9.25
          = 35.5

2.    2.   An element Q has two isotopes ⁶³₂₉Q and ⁶⁵₂₉Q with relative abundance of 70% and 30% respectively. Calculate the relative atomic mass of Q

SOLUTION

70 x 63 + 30 x 65 =
100         100
  44.2 +   19.5
      = 63.70

3. X is an element which exists as an isotopic mixture containing 90% of ³⁹₁₉Xand 10% of ⁴¹₁₉X

a. How many neutrons are present in ⁴¹₁₉X isotope

b. Calculate the mean relative atomic mass of X

Solution

a. Neutrons in ⁴¹₁₉X

= 41-19 = 22

b. R.A.M =

               90 x 39 + 10 x 41 =
              100           100
                

                35.10 + 4.10 

                   = 39.2

 

CALCULATIONS

1. The following are more examples of calculations of relative atomic masses of elements.

2. An element Y exist in two isotopic forms ³⁹₁₈R and ⁴⁰₁₈Rin the ratio 3:2 respectively. What is the relative atomic mass of the element?

SOLUTION

First you add the ratio together, that is, 3+2 =5

R.A.M of Y
    = 3 x 39 + 2 x40 = 
       5             5

    0.6 x 39 + 0.4 x 40 =
      23.4 + 16 =
        = 39.4   

3. An element with relative atomic mass 16.2 contains two isotopes ¹⁶₈R with relative abundance 90% and ^m₈R with relative abundance 10%. What is the value of m?

SOLUTION 

   16.2 = 90 x 16 + 10 x m
             100           100
   16.2 = 0.9 x 16 + 0.1m
   16.2 = 14.4 + 0.1m
   16.2 – 14.4 = 0.1m
   1.8 = 0.1 m
   m = 1.8 = 18
          0.1
  The value of m is 18

OBJECTIVE QUESTIONS

1. The atomic number of an element is precisely

(a) the number of protons in the atom

 (b) the number of electrons in the atom 

(c) the number of neutrons in the atom

(d) 

2. An atom can be defined more accurately as 

(a) the smallest indivisible parts of an element that can take part in a chemical reaction 

(b) the smallest part of an element that can take part in a chemical reaction

 (c) a combination of protons, neutrons

(d)

3. The mass number is 

(a) proton number + neutron number 

(b) electron number + proton number 

(c) neutron number + electron number

(d) 

4. Calculate the relative atomic mass of an element having two isotopes ¹⁰⁷Ag and ¹⁰⁹Ag in the ratio 1:1

 (a)106 

(b)107 

(c)108

(d) 

5. An element X has two isotopes ^18.8X and ^15.8X in the proportion of 1:9 respectively. Find the relative atomic mass of X 

(a)16.1 

(b)13.6 

(c)16.8

(d) 

THEORY

1. (a) Define the term isotopy.

(b) Determine the number of electrons, protons and neutrons in each of the following:

  i.³⁹₁₉K    ii. ⁶³₂₆Cu    iii. ²³₁₁Na

2. If an element R has isotopes 60% of ¹²₆Qand 40% ^x₆Q and the relative atomic mass is 12.4, find x.

3. Consider the atoms represented below: ^q_rX and ^s_rX

a. State the relationship between the two atoms.

b. What is the difference between them?

c. Give two examples of other elements which exhibit the phenomenon illustrated.

4. State the number of electrons, protons and neutrons present in the following atoms/ions

(a) ₂₀Ca (b) ₁₆S^2- (c) ₁₃Al³⁺ (d) ₁₅P

IUPAC NOMENCLATURE at a glance

          IUPAC NOMENCLATURE

This is a systematic method of naming organic compounds using IUPAC system. That is, the International Union of Pure and Applied Chemistry.  

The IUPAC system of naming organic compounds, the following rules are to be followed.

Every organic compound has 2 or three parts to its name, 

**the root and the suffix or 

**the prefix, the root and thwe suffix  

Organic Compounds without branches or that does not have any subtituents apart from the main the main functional group will have only two parts to their name.

While those with branches will have three parts to their names.

***The ROOT: - This is got from the longest continuous carbon chain in the molecule. We use the Greek system of numbering to indicate the root as follows

Number of C-atom	Name
one C-atom	Meth-
two C-atoms	Eth-
Three C-atoms	Prop
Four C-atoms	But-
Five C-atom	Pent -
Six    C-atoms	Hex-
Seven C-atoms	Hept-
Eight C-atoms	Oct-
Nine   C-atoms	Non-
Ten     C-atoms	Dec-

*** The SUFIX: - This is usually added after the root hydrocarbon, it indicates the family or homologous series that the organic compound belongs to. 

***PREFIX / PREFIXES: - These are usually hanging atoms or groups that are not the main functional group of the compound. They are usually named before the root hydrocarbon. Their positions are usually mentioned (using arithmetic integers like 1,2,3,...)  before their names, and where you have more than one of the same types, we use mono -, di-, tri-, tetra- to indicate the number.  

when we have more than one functional group in a compound, then one is named as the prefix and the other the sufix. In this case we will not use the name as a suffix but as a prefix. (see functional groups)

RULE 1: Select the longest continuous carbon chain in the molecule and use it as the root or the parent hydrocarbon name of this chain.

RULE 2: Every branch off the main chain should be considered as a substituent derived from a corresponding hydrocarbon or any other hanging group that is not a hydrogen 

 CH₄ -methane      CH₃ –   methyl, 

C₂H₆-ethane         CH₃CH₂- ethyl, 

C₃H₈ - propane      C₃H₇ - propyl  

All of these functions as prefix

RULE 3: Number the carbon atoms of the continuous chain from a direction that gives the Carbon atom carrying the substituent ( i.e the Carbon atom carrying anything other than a H-atom will have a lower number) a small number

RULE 4: Give each substituent a name and number

RULE 5: For identical substituents, use di, tri, tetra, penta, hexa, and so on to indicate the number of identical substituents.

RULE 6: Where you have more than one substituent that are different, name them alphabetically

RULE 7: Give the lowest possible number to the functional group.

NOTE: Halogen when they occur in organic compounds are named thus, chlorine = chloro, fluorine = fluoro, bromine = bromo, iodine = iodo.

Always show your bonds when you write or draw structures of organic compounds 

 E.g .1 write the structure of 2-methyl butane. This should be written as shown below:

                       

H  H  H  H                 ׀   ׀   ׀    ׀            H-C-C-C-C-H                 ׀   ׀    ׀    ׀                H   ׀   H  H                 H-C-H                      ׀                     H

                         

Following strictly the above rules, one can then name perfectly any organic compound with ease. For example, in naming the compound below, following the rules

 

                                          CH₃ 
                                                    |                                                                         
                                 C¹H₃C²H₂C³H₂C⁴H₂C⁵H₂C⁶H₃
                                                    |
                                                    CH₃ 

In the above structure, there are six carbon atoms in the longest continuous chain. Therefore, the parent or the ROOT hydrocarbon has a name Hex (RULE 1). There are 2 methyl substituents derived from another hydrocarbons (RULE 2)

Counting the position of the substituents on the continuous root chain, they both stand on the 4^th carbon atom when counting from left to right, but when counting from right to left, they appear on the 3rd carbon atom, hence the lowest position of 3rd carbon atom is considered (RULE 3)

Since the two substituents are similar, they are named dimethyl (RULE 4), hence the two substituents have a number 3 and name 3 and so can be named as 3,3-dimethyl (RULE 5). When this is combined with the parent hydrocarbon (RULE 1), the name of the compound becomes 3,3-dimethylhexane.

Other examples with their names are shown below following the stated rules.

                       CH₃                                                             CH₃
(i)                    |                                                                   |
              C1H₃-C2-C3H₂-C4H-C5H₃              (ii)        C1H₃C2H₂C3H-C4HC5H2C6H₃      
                       |            |                                                             |
                      CH₃     CH₃                                                        CH₃                                       
            2,2,4-trimethylpentane                                 3,4-dimethylhexane

                               CH₂CH₃                                                 CH₃
                                      |                                                               |
(iii)       C1H₃C2H₂-C3-C4H₂C5H₃                   (iv)       C1H₃-C2-C3H₃
                                      |                                                               |
                               CH₂CH₃                                                 CH₃
             3,3-diethylpentane                              2,2-dimethylpropane
                                                                                   

                                                                                                           CH₃      CH₃
                                                                                                            |            |
(v)        CH₃CH₂CHCH₃                         (vi)       CH₃—C−CH2-CHCH₃
                     |                                                                    |
                    CH₃                                                              CH₃    
            2-methylbutane                                  2,2,4-trimethylpentane

(vii)      CH₃CH₂CH—CHCH₃                      (viii)     CH₃CH₂CHCH₃
                              ׀                                                          ׀       ׀               
                            CH₃  CH₃                                                    CH₃

             2,3-dimethylpentane                          2-methylbutane

                   

                       CH₃                                                                                    CH₃ 

(ix)       CH₃ − C −CH− CH2−CH2 CH2CH3                     (x)        CH₃CH₂CHCH₂CHCH₂CH₂CH₃ 

                     CH₃     CH₂CH₃                                                                               CH₂CH₃  

            2,2-dimethyl, 3-ethylheptane                                        5-ethyl, 3-methyloctane

                                                                                 Cl

(xi)       CH₃CH₂CHCH₃                         (xii)      CH₃-C-CH₂CH₃ 

                          Cl                                                     Cl

            2-chlorobutane                                   2,2-dichlorobutane

(xiii)     CH₃CH₂CHCH₂CHCH₃              (xiv)     CH₃CHCH₂CHCH₃  

                         Cl         Br                                          Cl        Cl

            2-bromo, 4-chlorohexane                   2,4-dichloropentane

                            Cl         Br                                                 Cl

(xv)      C1H₃CH₂-C-CH₂-C-CH₃              (xvi)     CH₃CHCH₂-C-CH₃  

                            Cl         Br                                       Cl         Cl

            2,2-dibromo, 4,4-dichlorohexane       2,2,4-trichloropentane

                        CH₃ H     H    CH₃                                                               CH₃  H      H    CH₃ 

(xvii)    CH₃ – C –  C –   C – C – CH₃                  (xviii)   CH₃ – C –   C –   C – C – CH₃    

                       CH₂ CH₂ CH₂ CH₂                                                  CH₂  CH₂ CH₂ CH₂

                       CH₃  CH₃ CH₃ CH₃                                                       CH₂  CH₃ CH₃ CH₂

            4,5-diethyl,3,3,6,6-tetramethyloctane                      CH₃                  CH₃

                                                                                    5,6-diethyl,4,4,7,7-tetramethyldecane

(xix)     CH₃ – CH₂ – CH – CH₃

                                    CH₂Cl

            1-chloro – 2-methylbutane

ALKANES

ALKANES 

The alkanes are a homologous series of saturated aliphatic hydrocarbons with a general molecular formula of CnH2n+2.  The are the only saturated hydrocarbons because they contain only single bonds. The are found mainly in petroleum. The carbon atoms in the alkanes exhibit sp³ hybridization. There is a gradual change in the physical properties of the members from the gaseous state (for the lighter members) to the liquid state and then the solid state for the heavier compounds.

The first ten members of the series are.

1.       methane          CH₄

2.       Ethane             C₂H₆

3.       Propane           C₃H₈

4.       Butane             C₄H₁₀

_5.         Pentane           C₅H₁₂

6.        Hexane           C₆H₁₄

7.        Heptane          C₇H₁₆

8.        Octane            C₈H₁₈

9.        Nonane           C₉H₂₀

10.     Decane            C₁₀H₂₂

Chemical properties 

The alkanes undergo only two reactions, combustion and substitution reactions

1. Combustion Reaction: - this is a general property for all hydrocarbons. The alkanes burn in air or oxygen to yield Carbon (iv) oxide and water.

    CH_4(g) + O_2(g) → CO_2(g) + H₂O_(g)

2. Substitution Reaction: - Substitution reaction is the only other reactions that the alkanes can undergo because they are saturated.

A Substitution reaction is a reaction where one element (atom) replaces one or more of the hydrogen atoms in an alkane molecule.

METHANE: - This is the first and the simplest member of the alkane family. It has a molecular formula of CH₄ and a structural formula of

 

              H
               ׀
       H − C − H
               ׀
              H

It is found naturally in swamps or swampy areas when vegetations and dead organic matter decompose. It is also one of the major components in natural gas

Laboratory Preparation 

Methane is prepared in the laboratory by the action of sodium ethanoate on soda- lime.  (soda-lime is sodium hydroxide that has been slaked with lime CaO).

Soda- lime is preferred to caustic soda because 

1. It is not Deliquescent and 

2. It does not attack glass.

                                       Laboratory Preparation of methane 

CH₃COONa(S) + NaOH(s) → Na₂CO_3(s) + CH_4(g)  

Physical properties 

i.  It is a colourless gas. 

ii. It is less dense than air.

iii. It is insoluble in water.

Chemical properties 

I. Combustion: - methane burns with a pale blue flame in air or oxygen

CH_4(g) + O_2(g) → CO_2(g) + H₂O_(l) 

2. Substitution reaction: - Methane combines with Chlorine to produce various products.

The reaction is faster in the presence of light (photochemical reaction) and it occurs in stages.

I. CH_4(g) + Cl_2(g) → CH₃Cl + HCl

                             Mono chloromethane

II. CH₃Cl + Cl_2(g) → CH₂Cl₂ + HCl

                             dichloromethane

III. CH₂Cl₂ + Cl_2(g) → CHCl₃ + HCl

                            trichloromethane

IV.  CHCl₃ + Cl_2(g) → CCl₄ + HCl

                             tetrachloromethane

Uses of Methane 

I. It is used mainly as fuel sometimes mixed with other fuels

2. It is used to make hydrogen

3. It is used to make carbon black

4. When refined it is can be used as a rocket fuel

OBJECTIVE QUESTIONS 

1. What is the IUPAC name of the compound with this structure 

         H     H    H     H
         |        |      |        |   
H— C — C — C — C — H
         |        |       |         | 
         H      |      H       H
                  | 
          H —C—H
                  | 
                 H 
a. 3-methylbutane

b. 3-methylpentane

c.2-methylbutane 

d.2-methylpropane 

2.  Which of the following compounds is the structural isomer of the compound above?

a. 2,2-dimethylpropane 

b. 2-ethylpropane

c. 1,2-methylbutane 

d. 2-methylpentane

3. the energy value of petrol can be determined by a 

a. bomb calorimeter

b. catalytic cracker

c. fractionating column

d. thermometer

4. C8H18 will undergo the following reactions except 

a.  Cracking 

b. Combustion 

c. Substitution

d. Addition

5. One of the products of pentane in excess air 

a. pentanol 

b. pentene

c. nitrogen (II) oxide 

d. carbon (IV) oxide 

6. The gas produced when a mixture of sodium propanoate and soda lime is heated is 

a. Methane.

b. Pentane

c.. Ethane

d. Butene

 

THEORY QUESTIONS 

1. Methane reacts with chlorine under certain conditions to produce tetrachloromethane 

i.). State the condition for the reaction 

ii). Name the type of reaction

iii). Give two uses of methane 

iv). Name one natural source of methane.

                                                                                           ANSWERS

                                                                                           1. C 

                                                                                           2.  A

NITROGEN AND ITS COMPOUNDS at a glance

NITROGEN

Nitrogen occurs mainly as a free element in the air/ atmosphere, about 78% by volume of the atmosphere. It also found in the combined state in many compounds such as ammonia, urea, proteins and trioxonitrates (V) salts. it does not exhibit allotropy and is a diatomic gas 

LABORATORY PREPARATION

From Air

It can be prepared from air by first passing air through caustic soda to remove CO₂ and then over heated copper turnings to remove and O₂ [ the oxygen can equally be removed by passing the air through alkaline pyrogallol]. The nitrogen obtained is not pure and is denser than air because it contains about 1% by volume of rare/ noble gases.

Pure nitrogen is obtained in the laboratory by any of the following method below:

1.  Thermal decomposition of ammonium dioxonitrate (III)

a.  NaNO_2(aq) + NH₄Cl_(aq) → NH₄NO_2(aq) +NaCl_(aq)

b. NH₄NO_2(aq) →2H₂O_(l) + N_2(g)              

2.       Thermal decomposition of ammonium heptaoxodichromate (VI)

                       (NH₄)₂Cr₂O_7(s) → Cr₂O_3(s) + 4H₂O_(l) + N_2(g)

3.       Oxidation of ammonia by hot Copper (II) oxide

                        2NH_3(g)+3CuO_(s) → 3Cu_(s) + 3H₂O_(g)+ N_2(g)

4.             Reduction of dinitrogen (I) oxide by red-hot copper.

N2O_(g) + Cu_(s) → CuO_(s) + N_2(g)

INDUSTRIAL PREPARATION

Industrially, nitrogen is obtained by fractional distillation of liquid air.  (see industrial preparation of Oxygen)

PHYSICAL PROPERTIES

1.         It is colourless gas.

2.          It is an odourless.

3.          It is a  tasteless

4.         Pure nitrogen is lighter than air.

5.         Slightly soluble in water

6.         Melting point -210⁰C and   boiling point is -196⁰C

CHEMICAL PROPERTIES

1.       It reacts with very electropositive metals to form nitrides

      3Mg_(s) + N_2(g) → Mg₃N_2(s)

2.       It reacts with non – metals like hydrogen and oxygen to form ammonia and oxides respectively.

     N_2(g)+ 3H_2(g) → 3NH_3(g)

                 N_2(g) + 2O_2(g) → 2N₂O_(g)

USES

1.       It is used industrial manufacture of ammonia.

2.       Liquid nitrogen is used as a cooling agent.

3.       It is used as preservative in packaged foods to prevent rancidity.

The stages in which nitrogen from the atmosphere is converted into soil nitrogen and back to atmospheric nitrogen is summarized below.

1.   Oxidation of atmospheric nitrogen:

N_2(g) + O_2(g) →2NO_(g)

2NO_(g) + O_2(g)→ 2NO_2(g)

4NO_(g)+O_2(g)+2H₂O_(l)→4HNO_2(q)

 4NO_(g)+O_2(g)+2H₂O_(l)→4HNO_3(aq)

2.   Action of nitrogen-fixing bacteria: 

3. Nitrification by nitrifying bacterial.

4. Denitrification by denitrifying bacteria 

COMPOUNDS OF NITROGEN

OXIDES OF NITROGEN

1. NITROGEN (I) OXIDE, N₂O

Nitrogen (I) oxide also known as laughing gas. (it can cause uncontrollable laughter when inhale).

LABORATORY PREPARATION

It is prepared in the lab by thermal decomposition of ammonium trioxonitrate (V). Ammonium trioxonitrate (V) can not heated directly because the reaction being highly exothermic and may become uncontrollable leading to an explosion. 

a.  KNO_3(s) + NH₄Cl_(s) → KCl_(s) + NH₄NO_3(s)

b  NH₄NO_3(s) → 2H₂O_(g) + N₂O_(g)

PHYSICAL PROPERTIES

1.    It is a colourless gas 

2.   It has faintly sickly sweet smell.

3.      It has a sweetish taste.

4.  It is fairly soluble in cold water.

6.   It is a neutral gas

CHEMICAL PROPERTIES

1.       It decomposes on strong heating to form nitrogen and oxygen.

      2N₂O_(g)→ O_2(g)+2N_2(g)

2.     It  burns in any  substance which is hot enough to decompose it.

    Mg_(s)+ N₂O_(g)→ MgO_(s)+ N_2(g)

3. it is reduced to nitrogen when in contact with very hot iron or copper. 

 Cu_(s) + N₂O_(g)→ N_2(g)+ CuO_(s)

TEST FOR N₂O

When a glowing splinter is inserted into the jar containing the unknown gas and it  rekindles, then the gas is either oxygen or nitrogen (I) oxide. If the gas has a pleasant smell and does not produce brown fumes of nitrogen (IV) oxide when burnt in air; then the gas is nitrogen (I) oxide.

USE: Nitrogen (I) oxide is used as anesthetic for minor surgical operations.

NITROGEN (II) OXIDE, NO

LABORATORY PREPARATION

Nitrogen (II) oxide is prepared by reacting combining copper with 50% trioxonitrate (IV) acid.

3Cu_(s) + 8HNO_3(aq)→ 3Cu(NO₃)_2(aq)+ 4H₂O_(l) + 2NO_(g)

 brown fumes of nitrogen (IV) oxide produced by some of the nitrogen (II) oxide as they react with oxygen is removed as the gas is pass through water.

PHYSICAL PROPERTIES

1. It is a colourless gas 

2. It is a poisonous gas.

3.  It is a sp7aringly soluble in water.

3.  It is slightly denser than air.

4.  It is neutral to litmus.

CHEMICAL PROPERTIES

1.  It combines readily with oxygen to form brown fumes of nitrogen (IV) oxide

         2NO_(g) + O_2(g) → 2NO_2(g)

2.   At high temperature, it decomposes to form equal volume of nitrogen and oxygen

         2NO_(s)→ N_2(g) + O_2(g)

3.   It is reduced to nitrogen by hot metals

 2Cu_(s)+ 2NO_(g) → 2CuO_(g) + N_2(g)

4.  It decolourizing acidified potassium tetraoxomanganate (VI) slowly ( reducing agent)

3MnO₄^-_(aq)+ 4H⁺_(aq) + NO_(g)→3Mn²⁺_(aq) 5NO₃^-

Test for NO

1. With acidified  iron (II) tetraoxosulphate (VI): A solution of acdified FeSO₄ is poured into the gas jar containing the unknown gas. If the solution turns dark brown, then the gas is NO.

NITROGEN (IV) OXIDE, NO₂

LABORATORY PREPARATION

It is prepared by thermal decomposition of lead (II) trioxonitrate (V) Pb(NO3)2. 

Pb(NO3)2 is preferred because it does not contain water of crystallization which can interfere with the preparation.

          

Dig

Pb(NO₃)_2(s) → 2PbO_(s) + O_2(g)+ 4NO_2(g)

The gaseous mixture obtained is passed through a U- tube dipped in ice, Nitrogen (IV) oxide liquefies as a green liquid (yellow if pure) in the tube while oxygen escapes out.

PHYSICAL PROPERTIES

1.  It is a reddish – brown gas.

2.  It has an irritating smell 

3. It  is a poisonous gas 

4.  It liquefies into yellow liquid at 21^oC.

5.  It is denser than air.

CHEMICAL PROPERTIES

1. It turns damp blue litmus paper red

2.  Nitrogen (IV) oxide exists mainly as dinitrogen (IV) oxide, N₂O₄ at low temperature. It decomposes on heating as follows.

N₂O_4(g) + 2O_2(g) → 2NO2_(g) + O_2(g)

•  Pale                    Reddish         
•  yellow                 brown                 

2.     It decomposes on heating to nitrogen and oxygen and so supports combustion 

  2NO_2(g) → N_2(g)+ 2O_2(g)

3.  With reducing agents it is reduced to nitrogen.

  4Cu_(s) + NO2 → 4CuO_(s) + N_2(g)

4.  With dissolved in water it forms two acids, dioxonitrate (III) and trioxonitrate (V) acids, hence, It is a mixed acid anhydride.

  H₂O_(l)+ 2NO_2(g) → HNO_2(aq)+ HNO_3(aq)

5.  It reacts with alkalis to form a mixture of dioxonitrate (III) and trioxonitrate (V) salts

  2KOH_(aq)+ 2NO_2(g) → KNO_3(aq) + KNO_2(aq) + H₂O_(l)

AMMONIA

Ammonia is a hydride of nitrogen. It is found in traces in the atmosphere from the decomposition/ decay of nitrogenous matter in the absence. Because is very soluble in water, it dissolves in rainwater and is washed down into the soil.     

LABORATORY PREPARATION OF AMMONIA

Ammonia is prepared in the laboratory by heating calcium hydroxide, Ca(OH)₂ (slaked lime) with ammonium chloride.

Ca(OH)_2(s)+ 2NH₄Cl_(s)→CaCl_2(s) +2H₂O_(l)+2NH_3(g).

It is dried using calcium oxide, CaO. Because it will react with drying agents like Conc. H₂SO₄ or fused CaCl₂, since it is an alkaline gas.

            

INDUSTRIAL PREPARATION

Ammonia is manufactured by the Haber process from nitrogen and hydrogen. In this process  nitrogen and hydrogen are reacted  in ratio 1:3 by volume. The reaction is reversible. The conditions for optimum yield of ammonia are 

i. A temperature of 450^Oc 

ii. A pressure of about 200atm and 

iii. Finely divided iron catalyst   

N_2(g) +3H_2(g) →2NH_3(g) + heat

PHYSICAL PROPERTIES

i.   It is a colorless gas 

ii. It has  a characteristic choking/ pungent smell.

iii. When inhaled in large quantity it is poisonous 

3. It is the only known alkaline gas.

4. It is about less dense than air.

CHEMICAL PROPERTIES

1. Ammonia burns readily in oxygen to yield and nitrogen and water vapour 

 4NH_3(g)+3O_2(g)→6H₂O_(g)+ 2N_2(g)

2. As a reducing agent, it reduces most metallic oxides to their metals. 

 i. 3CuO_(s) + 2NH_3(g) → 3Cu_(s) + 3H₂O_(l) + N_2(g)

ii.   With Chlorine it yields NH4Cl

  3Cl_2(g) + 8NH_3(g) → 6NH₄Cl_(s) + N_2(g)

3.  Ammonia reacts with carbon IV oxide to form Urea and water vapour.

 2NH_3(g)+ CO_2(g) → (NH₂)₂CO_(s) + H₂O_(l)

                        ^urea

4. With acids it form ammoniums salts.  

 2NH_3(g) + H₂SO_4(g)→(NH₄)₂SO_4(s)

TEST FOR AMMONIA

Ammonia has a choking and a pungent smell. It can be confirmed using:

1. Litmus paper: It turns damp red litmus paper blue

2.  Hydrochloric acid: it forms dense white fumes with a concentrated on a glass rod 

USES OF AMMONIA

1.  Is is one of the raw materials in the Solvay process for the   manufacture trioxonitrate (V) acid and Sodium trioxocarbonate (IV).

2. Liquid ammonia is used as a refrigerant.

3. Aqueous ammonia is used in softening temporary hard water.

4.    Aqueous ammonia is also used in laundries as a solvent for removing grease and oil stains.

TRIOXONITRATE (V) ACID, HNO₃

LABORATORY PREPARATION

Trioxonitrate (V) acid is a volatile acid. It is prepared in the laboratory by  displacement of the HNO3 from any trioxonitrate salt by concentrated H₂SO₄ which is less volatile. Trioxonitrate (V) of potassium or sodium is usually used because they are cheap.

KNO_3(s)+ H₂SO_4(aq)→ KHSO_4(aq)+HNO_3(aq)

NOTE: we use an  all-glass apparatus for this preparation because the hydrogen trioxonitrate (V) acid vapour will attack cork or rubber.

INDUSTRIAL PREPARATION

It is prepared by the catalytic oxidation of ammonia:

-    Ammonia is treated with excess air using Platinum-rhodium catalyst at 700^oC to produce

4NH_3(g)+ 5O_2(g)→ 4NO_(g)+ 6H2O the nitrogen (II) oxide formed is cooled and mixed with excess air to produce nitrogen (IV) oxide.

2NO_(g) + O_2(g) →2NO₂(g)

-    Nitrogen (IV) oxide formed is dissolved with excess air in hot water to yield trioxonitrate (V) acid solution of up to 50% concentration. 

4NO_2(g)+ 2H₂O_(l)+ O_2(g) → 4HNO_3(aq)

PHYSICAL PROPERTIES

1.  Pure HNO3 acid is a colourless liquid with sharp choking smell. It fumes in air. The acid decomposes to give NO2 gas which redissolves in the acid turning it yellow after a while.

2. The density of the pure acid is 1.52 gcm^-3

3.  The pure acid boils at 86⁰C and melts at -47^oC  

4.   The pure acid dissolves in water in all proportions 

5.  The concentrated form of the acid is corrosive.

CHEMICAL PROPERTIES

1.  As an acid 

I. The dilute acid turns blue litmus red.

 ii.  it neutralizes bases and alkalis to form metallic trioxonitrate (V) and water only

NaOH_(aq)+HNO_3(aq) → NaNO_3(aq)+ H₂O_(l)

iii. it reacts with trioxocarbonate (IV) to liberate carbon (II) oxide 

 CaCO_3(s) + HNO_3(aq) → Ca(NO₃)_2(aq)+ H₂O_(l)+ CO_2(g)

3.  Unlike other acids, it rarely gives out hydrogen with metals except when very dilute solution is reacted with Ca, Mg or Mn.

4.    As an oxidizing agent, 

it oxidizes non–metal like Sulphur to form the corresponding oxides of the non – metals.

  S_(s)+ 6HNO_3(aq)→H₂SO_4(aq) + 2H₂O_(l) + 6NO_2(g)

ii.   it oxidizes least reactive metals like Cu, Pb, Hg and Ag to yield the respective trioxonitrate (V) and nitrogen (IV) oxide.  With moderate  concentration  it yields nitrogen (II) oxide.

Aluminum and iron are not oxidized by the acid, because of the  formation of a thin  coating of the oxide on the surface of the metal which is lmpervious to further attack on the metals. 

Hence, containers lined with aluminum and iron can be used to transport concentrated HNO_3(aq)

5.As an oxidizing agent, it oxidizes hydrogen sulphide to sulphur

  H₂S_(g) + 2HNO_3(aq) → S_(s)+ 2H₂O_(l)+2NO_2(g)

6.  it oxidizes iron (II) salts to iron (III) salts

 6Fe²⁺_(aq) + 8H⁺_(aq) + 2NO₃^-_(aq) →   6Fe³⁺_(aq) + 4H₂O_(l) + 2NO_(g)

USES

1.  It is used as an acid, oxidizing agent and nitrating agent in the laboratory.

2. It is as rocket fuel

3. It is used in producing nylon and Terylene.

4.  It is used to produce fertilizers, dyes, drugs and explosives.

OBJECTIVE QUESTIONS 

1.  In which group of the periodic table is nitrogen found? 

(a) 2

 (b) 5 

(c) 7

(d) 6

2. The boiling point of nitrogen in ⁰C is

 (a) -183

 (b) -196

 (c) 200

 (d) 240

3.   The percentage of nitrogen in air is

 (a) 78 

(b) 75 

(c) 71

 (d) 67

4. The following are uses of nitrogen except a. as a cooling agent b. to prevent rancidity c. in the manufacture of fertilizers d. in laundry.

5. The atomicity of nitrogen is 

(a) 1

(b) 2

 (c) 3

 (d) 4

6.  Which of the following compound will leave a metal residue when heated 

a. Cu(NO₃)₂

b. AgNO₃

c. K₂CO₃

4.CaCO₃

7.  The gas given off when NH4Cl is heated with an alkali is 

a. H₂

b. Cl₂

c. N₂ 

d. NH₃

8. 

9. 

10.

11. 

12.

THEORY

 

1a.   State TWO physical properties and TWO chemical properties of nitrogen.

1b   Mention THREE uses of nitrogen.

1c(i) Briefly describe the preparation of nitrogen from air in the laboratory. 

2a(i)   Give an equation to show the laboratory preparation of nitrogen (II) oxide.

2b. Describe a test to distinguish between nitrogen (I) oxide and oxygen gas.                    

2c(iii) Briefly describe the laboratory preparation of ammonia.

3a   State TWO physical and THREE chemical properties each of ammonia.                                       

3b.  Describe the laboratory preparation of trioxonitrate (V) acid.

3c  Write TWO equations of reactions in which trioxonitrate (V) is acting as an acid.

4a. Write an equation to show the reaction of nitrogen (IV) oxide as a mixed anhydride.

4b.  Describe the electrolysis of CuSO₄ solution using platinum electrodes.

4c. Classify the following oxides: CuO, Na₂O, PbO, NO₂, N₂O