DEFINITIONS IN CHEMISTRY

DEFINITION

AN ACID

Arrhenius definition: An acid is a substance which produces hydrogen ion (H⁺) as the only positive ion in solution.

                                   HCl  → H+  +  Cl-

                                    H2O → H+  + OH-

Bronsted -Lowry’s definition: An acid is a proton donor.

Lewis's acid: An acid is any species that accepts an electron pair.

ACID-ANHYDRIDE: is the oxide of a nonmetal which dissolves in water to yield the corresponding acid.

ABSOLUTE-ZERO-TEMPERATURE: This is the lowest temperature in the Kelvin scale in which the volume of a gas is assumed to be zero.

ACTINADES: The Period 7 elements that forms the second inner transition series (5f block). It includes thorium (Th;Z=90) through lawrencium (Lr; Z=103) 

ACTIVATED COMPLEX: It is the highest energy level in a chemical reaction where the reactants are no longer reactants but are not yet products.

ACTIVATION ENERGY: this is the minimum amount of energy reactant particles must possess before a chemical reaction can occur.    OR it is the energy barrier that reactants must overcome to become products

ACTIVITY: The change in number of nuclei (N) of a radioactive sample divided by the change in time (t)

ALKANES: A hydrocarbon with the general molecular formular CnH2n+2. having only C-C single bonds

ALKENES: A hydrocarbon that contains at least one  carbon-carbon double bond (C=C bond)with the general formula CnH₂n.

ALKYNES: A hydrocarbon that contains at least one carbon-carbon triple bond (C=C ) with general formula CnH_2n-2

ALLOTROPY: This is  when an element occurs in different form but in the same physical state.

ALLOTROPES: These are different forms of an element occurring in the same physical state.

ALPHA (Ἀ) DECAY:  A radioactive process in which an alpha particle is emitted from the  nucleus of a radioactive element.

ALPHA  PARTICLE (ἀ or ⁴₂He).  A  positively charged particle, identical to a helium nucleus.

ANION: A negatively charged ion e.g  Cl^-, O^2-, N^3- .

ANODE: The electrode at which oxidation occurs in an electrochemical cell or an electrolytic cell.

ATOM: this is the smallest particle of an element that can take part in a chemical reaction.

ATOMIC MASS: This is the sum of the protons and neutrons in an atom of an element.

ATOMIC NUMBER: This is the number of protons in one atom an element.

BETA (β) DECAY: This involves the emission of a beta particle by a radioactive isotope.

BOILING POINT OF A LIQUID -: This is the temperature at which the saturated vapour pressure of the liquid is equal to the atmospheric pressure.

CATALYST: This is a substance that alters the rate of a chemical reaction, but itself is not affected by the reaction. 

CARBOHYDRATES:- These are organic compounds that contain carbon, hydrogen and oxygen, where     the hydrogen and oxygen are in the ratio of 2:1

CATHODE :- this is the electrode where reduction occurs in an electrochemical cell or an electrolytic cell.

CHEMICAL CHANGE: this is a change that is not easily reversible and in which a new substance is formed.

CONCENTRATION: this is the amount of a solute in moles per dm³ of   solution.  

COMBINATION REACTION: This is when two or more elements  combine  together to form a single compound       example        

                                     Fe_{(s) +}  S_(s) → FeS_(s)

COVALENT BONDING: this is a type of bonding that involves the sharing of electron pair between two atoms ( usually non-metals)

Cracking: this is the breaking down of higher molecular mass alkanes to lower molecular mass alkanes and alkenes.

   C₁₀H₂₂  → C8H18 +  C2H4

DEGENERATE ORBITALS: These are orbitals that are at the same energy level examples include the  p-orbital, the d-orbital and the f-orbital.

EFFLORESCENCE: this is the phenomenon whereby some salts when exposed to the atmosphere loses part or all of their water of crystallization.

EFFLORECENT SALTS; these are salts which loses part or all of their wate of crystallization when exposed to the atmosphere.

ELECTRON AFFINITY: This is the energy evolved when an electron enters an atom in the gaseous state to form a mole of gaseous negative ions.

ELECTROLYSIS: - This is the decomposition of a compound brought about by the passage of a direct current through either a solution of the compound or its molten form 

ELECTRONEGATIVITY:  Is defined as the power of an atom to attract (shared pair or bonded) electrons in a molecule.

ELECTROVALENT BOND: this is a type of bond that involves the transfer of electrons from one atom (metal) to another (non-metal).           OR             

 it is the electrostatic force of attraction between oppositely charged ions / cations and anions.

EMPIRICAL FORMULA: - This is the simplest formula of a compound; it shows the elements present and the ratio to which they are combined.

ENDOTHERMIC REACTION: This is a reaction during which heat is absorbed from the  surrounding.

END POINT: This is the point at which the chemical reaction is complete during titration. The end point is detected with the help of an indicator.

ENTHALPY: This is the total heat content of a body/substance 

ENTROPY:- This the degree of disorder or randomness of a system.

ESTERIFICATION REACTION: This is the reaction between an alkanoic acid and an alkanol to form an alkanoate (ester) and water only. 

  RCOOH + R'OH  → RCOOR' + H2O

EXOTHERMIC REACTION: This is a reaction during which heat is given off to the surrounding.

FERMENTATION:- This is the breakdown of carbohydrates into ethanol and carbon (IV) oxide by the action of micro-organism.

FUNCTIONAL GROUP: - A functional group may be a bond, an atom or a radical it is common to a homologous series and it  also determines the  chemical property of the series.

HALF-LIFE: - This is the time taken for half the total number of atoms in a given sample of a radioactive substance to undergo decay.

HOMOLOGOUS SERIES: - This is a family of organic compounds that have a regular structural pattern where successive members differs by a -CH2- group.

HYBRIDIZATION:- This is mixing of two or more orbitals to form a set of new and equal number of hybrid orbitals.  the three most common types of hybridization are the sp3, the sp2 and the sp hybridization

HYGROSCOPY: This is a phenomenon whereby some substances when exposed to the atmosphere absorbs moisture and only become sticky or wet.

ION: This is a charged atom (particle) or group of atoms carrying a charged.

IONISATION ENERGY: - This is the energy required to remove an electron from an atom to form a mole of gaseous ions.

IONIC BOND: see electrovalent bond.

ISOMERS: these are organic compounds with the same molecular formula but different structural formula.

ISOMERISM: This is the occurrence of two or more organic compounds with the same molecular formula but different structural formula.

ISOTOPES: These are atoms of the same element with the same atomic number but different mass number.

ISOTOPY: This is the occurrence of atoms of the same element with the same atomic number but different mass number. 

MASS CONCENTRATION: This is the concentration expressed in g/dm3

MOLAR CONCENTRATION: This is the concentration expressed in mols/dm3

MOLAR MASS: - This is the mass of one mole of a substance. the unit is g/mol.

MOLAR SOLUTION: These is a solution that contains one mole (1mol) or the molar mass of a substance in 1dm3 of solution

MOLECULAR FORMULA: -This is the actual formula of a compound; it shows the exact number of atoms present in one molecule of compound.

OXYDATION: This is the loss of electrons from a substance.

OXYDIXING AGENT: A substance that accepts/gains electrons.

PHYSICAL CHANGE: this is a change that is easily reversible and in which no new substance is formed.

POLLUTION:- This is the release of harmful substances into the atmosphere  in concentration that is harmful to man and his environment.

POLYMERIZATION: This is the process whereby two or more small molecules (monomers) link together to form large molecules (polymer).

REDUCTION: This is the gain of electrons 

REDUCING AGENT: A substance that donate/loss electrons 

SATURATED SOLUTION: - This is a solution that contains as much solute particles as it can hold at a particular temperature in the presence of undissolved solute particles.

STANDARD SOLUTION: This is a solution with a known concentration.  

SUPER SATURATED SOLUTION: - This is a solution that contains More than the solute it can normally hold a particular temperature.

SOLUBILITY: - Solubility of a solute in a solvent is the amount of solute in moles or grams that can saturate 1dm3 of solvent (water) at a particular temperature.