Important Definitions in High school Chemistry

Matter is anything that occupies space and has mass and made up of tiny particles.

ATOM is the smallest particle of a substance or the fundamental unit of the matter.

Atom may or may not exist independently.

An atom is composed of sub-atomic particles called proton, electrons and Neutrons.

MOLECULE: A molecule is formed when two or more atoms of same or different kind combine chemically.

ELEMENT: An element is a pure substance made up of identical atoms.

COMPOUND: Two or more atoms of different kind combine chemically in a fixed proportion to form a compound.

ATOMICITY: The number of atoms present in a molecule of an element is called its atomicity.

ATOMIC NUMBER (Z): The number of protons present in the nucleus of an atom of an element is called its Atomic number.

MASS NUMBER (A): The total number of protons and neutrons present in the nucleus of an atom of an element.

ELECTRONIC CONFIGURATION: The distribution of electrons in the shells (or) orbits in atom is

called electronic configuration.

STABLE ELECTRONIC CONFIGURATION:

                If an element has completely filled valence shell or 8 valence electrons then it is said to have stable electronic configuration.

OCTET CONFIGURATION: If an element has 8 valence electrons it is called Octet configuration.

VALENCY:

ELECTRO-VALENCY: The number of electrons that an atom of an element loses or gains to attain stability is called the electro-valency of that element.

COVALENCY: The number of electron pairs which an atom of an element shares with atoms of the same or different kind to attain stability.

ION:  An ion is an atom or a group of atoms carrying a charge (positive or negative).

Positively charged ions are termed as Cations and those which are negatively charged as Anions.

CHEMICAL BOND: The force of attraction by which two or more atoms of same or different kind are held together is a chemical bond.

ELECTROVALENT BOND: The strong electrostatic force of attraction that holds two oppositely charged ions together which are formed as a result of transfer of electron/s.

COVALENT BOND: A covalent bond is formed due to the mutual sharing of electron pairs between two non-metallic atoms.

CO-ORDINATE COVALENT BOND: It is a covalent bond in which both the electrons in the bond coming from the same atom.

ATOMIC RADIUS: The distance between the center of the nucleus and the valence shell of an atom.

ELECTRONEGATIVITY: The tendency of an element to attract the bond pair of electrons towards itself .

ELECTRON AFFINITY: The amount of energy released when an atom accepts an electron to form an anion.

IONISATION POTENTIAL: The minimum amount of energy required to remove an electron from the valence shell of an atom in gaseous state.

ACID : An acid is a chemical compound which dissolves in water to produce hydronium ions (H₃O⁺) as the only positively charged ions.

BASE : A base is an oxide or hydroxide of a metal which reacts with an acid and gives salt and water only.

ALKALI : An alkali is a chemical compound which when dissolved in water produces hydroxyl ions (OH^-) as the only negatively charged ions.

BASICITY OF AN ACID: The number of hydronium ions that one molecule of an acid produces in its aqueous solution (or) The number of replaceable hydrogen ions present in one molecule of an acid is called the Basicity of that acid.

ACIDITY OF A BASE: The number of hydroxyl ions produced per one molecule of an alkali in its aqueous solution (or) the number of replaceable hydroxyl ions present in one molecule of a base is called the acidity of that base.

NORMAL SALT : The salt which is formed due to the complete neutralization of an acid by a base.

ACID SALT : An acid salt is formed when a dibasic or tri basic acid is partially neutralized by a base.

BASIC SALT : A basic salt is formed when a di acidic or tri acidic base is partially neutralized by an acid.

HYDRATED SALT : The salt which contains a definite number of water molecules.

WATER OF CRYSTALLISATION :  The number of water molecules that a hydrated salt holds with week force of attraction