TOPIC: PARTICULATE NATURE OF MATTER
CONTENT
- ATOMS AND MOLECULES
- IONS
- DALTON’S ATOMIC THEORY
- MODIFICATIONS OF DALTONS ATOMIC THEORY
ATOMS AND MOLECULES
Matter is made up of discrete particles. The main ones are atoms, molecules, and ions.
An atom is the smallest part of an element which can take part in a chemical reaction.
A molecule is the smallest particle of a substance that can exist alone and still retains the chemical properties of that substance.
Molecules are made up of atoms. These atoms may be the same or may be different
ATOMICITY: - This is the number of atoms in one molecule of an element or a compound
We have monatomic, diatomic and triatomic for those elements that contain one atom, two atoms and three atoms respectively in their molecules.
Examples:
Element Atomicity
Neon Monoatomic Ne
Helium Monoatomic He
Argon Monoatomic Ar
Hydrogen Diatomic H2
Oxygen Diatomic O2
Nitrogen Diatomic N2
Ozone Triatomic O3
Sulphur Polyatomic S8
Water triatomic H2O
Limestone pentatomic CaCO3
IONS
An ion is an atom or group of atoms which carries an electric charge. They are formed when atoms loss or gain electrons.
Generally, ions are grouped as cations and anions.
Cations are positively charged ions e.g. Ca2+, Na+, NH4+ etc.
Anions are negatively charged ions e.g. C032-, S042-, Cl-, OH-, etc.
We also have group of atoms that carry a single charge, whether positive or negative charge, they are called RADICALS.
An acid radical is thus a small group of atoms carrying a negative charge that keeps,
Examples include S042-, N03- e.t.c
DALTON’S ATOMIC THEORY
John Dalton, a British Physicist and Chemist (1808) proposed the atomic theory thus:
1. All elements are made up of small indivisible particles called atoms.
2. Atoms can neither be created nor destroyed in any chemical reaction.
3. Atoms of a particular element are exactly alike in all aspect and are different from atoms of all other elements.
4. Atoms of different elements combine in simple whole number ratios to form compounds.
5. All chemical changes result from the combination or separation of atoms
MODIFICATIONS OF DALTON’S ATOMIC THEORY
Due to new discoveries in the twentieth century, Dalton’s atomic theory cannot hold in its totality. setting new modifications have been made There is need for its modification.
i. Due to the discovery of the sub-atomic particles, (protons and electrons) the atom is no longer believed to be indivisible.
ii. Due to the discovery of radioactivity and radioisotopes which involves the destruction of atoms and formation of new elements during nuclear reactions, the atom is no longer believed to be indestructible. however. This second statement still holds good for ordinary chemical reactions
iii. Due to the discovery of isotopes and isotopy, the third statement is no longer acceptable.
iv. Due to the discovery of very large organic molecules such as proteins, starch and fats which contain thousands of atoms. The fourth statement is no longer true for organic compounds but still remains true for inorganic compounds which contain a few atoms per molecule.
Objective Questions
1. Which of the following is not a constituent of the atom
(a) proton
(b) electron
(c) neutron
(d) isotope
2. Which of the following statement about an atom is not correct?
(a) it is indivisible
(b) it is destructible in some cases
(c) it is the smallest part of a substance that takes part in a reaction
(d) it is made up of protons, neutrons and electrons
3. Which of the following is a liquid at room temperature?
(a) copper (b) gold (c) mercury
(d) silver
4. What is the atomicity of neon? (a) monoatomic (b) diatomic (c) triatomic (d) polyatomic
THEORY
1.(a)i State any two postulates of the Dalton’s atomic theory.
ii. state the modification of the postulates mentioned above
2.(a)i. Differentiate an atom from a molecule.
ii. How will an atom become an ion?
1. Define an atom.
2. Give two examples of diatomic molecules.
EVALUATION
- What are ions?
- State the cation and anion present in (I) H2S04 (ii) NaCl (iii) FeS04
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