Kerala SSLC Chemistry key terms

The number of protons in the nucleus of an atom. It identifies the element and equals the number of electrons in a neutral atom, fixing its position in the periodic table.

The total count of protons plus neutrons in one atom's nucleus, written as a whole number. Electrons are ignored because their mass is negligible compared with nucleons.

Atoms of the same element with equal proton numbers but different neutron numbers, so their mass numbers differ. They share chemical properties but may differ in nuclear stability and physical behaviour.

An electron in the outermost shell of an atom that is available for bonding. The count of valence electrons mainly decides an element's group and its combining capacity.

The combining capacity of an element, expressed as the number of hydrogen atoms or equivalent units it can bond with, or the electrons it gains, loses or shares.

The tendency of atoms to gain, lose or share electrons until eight electrons occupy their outermost shell, giving the stable configuration of a noble gas.

The minimum energy needed to remove the most loosely held electron from an isolated gaseous atom. It generally increases across a period and decreases down a group.

A measure of how strongly an atom in a molecule attracts the shared electron pair of a bond. Larger values mean a greater pull, producing more polar bonds.

A measure of the size of an atom, usually half the distance between neighbouring nuclei in an element. It decreases across a period and increases down a group.

A chart arranging elements in order of increasing atomic number, with elements of similar properties placed in the same vertical group and horizontal periods showing trends.

A vertical column of the periodic table. Elements in one group have the same number of valence electrons and therefore similar chemical behaviour and valency.

A horizontal row of the periodic table. Across a period the number of shells stays the same while protons increase, so metallic character falls and non-metallic character rises.

The electrostatic attraction formed when one atom transfers electrons to another, creating oppositely charged ions that pack into a crystal lattice.

A bond formed when two atoms share one or more pairs of electrons. Each shared pair counts toward both atoms' outer shells, holding the atoms together.

A covalent bond in which the shared electrons are pulled towards the more electronegative atom, giving it a partial negative charge and the other atom a partial positive charge.

A positively charged ion produced when an atom or group loses one or more electrons. Metals typically form cations, which migrate to the cathode during electrolysis.

A negatively charged ion produced when an atom or group gains one or more electrons. Non-metals commonly form anions, which move towards the anode in electrolysis.

The number of electrons an atom gains or loses to become an ion, equal to the magnitude of the charge on the resulting ion, such as 1 for sodium and 2 for magnesium.

The amount of substance containing as many particles as there are atoms in 12 g of carbon-12, that is 6.022 × 10²³ particles. It links mass and particle count.

The number of particles in one mole of a substance, approximately 6.022 × 10²³ per mole. It converts between counted particles and amounts in moles.

The mass of one mole of a substance in grams per mole, numerically equal to its relative molecular or formula mass. It converts mass to moles in calculations.

The volume occupied by one mole of a gas. At standard temperature and pressure it is 22.4 litres per mole for any ideal gas, regardless of identity.

The simplest whole-number ratio of atoms of each element in a compound, such as CH₂O for glucose. It may be a multiple smaller than the molecular formula.

The actual number of atoms of each element present in one molecule of a compound, such as C₆H₁₂O₆ for glucose. It is a whole-number multiple of the empirical formula.

The mass percentage of each element in a compound, found by dividing the total mass of that element in one mole by the molar mass and multiplying by 100.

The calculation of quantities of reactants and products from a balanced chemical equation, using mole ratios shown by the coefficients in that equation.

The reactant that is used up first in a reaction and therefore limits how much product can form. Other reactants are said to be in excess.

A chemical equation in which the number of atoms of each element is equal on both sides, satisfying conservation of mass. Coefficients show the reacting mole ratios.

A symbolic representation of a compound using element symbols and subscript numbers to show which elements are present and in what proportion.

A substance that donates hydrogen ions (protons) to another species, turns blue litmus red, and reacts with bases to form salt and water.

A substance that accepts hydrogen ions, or releases hydroxide ions in water, turns red litmus blue, and reacts with acids to give salt and water.

A logarithmic scale from 0 to 14 measuring hydrogen ion concentration. Values below 7 are acidic, 7 is neutral, and above 7 is basic at room temperature.

The reaction between an acid and a base producing salt and water. Hydrogen ions and hydroxide ions combine, so the solution moves towards pH 7.

An ionic compound formed when the hydrogen of an acid is replaced by a metal or ammonium ion, for example sodium chloride from hydrochloric acid and sodium hydroxide.

A dye that changes colour over a particular pH range, used to detect acidity or alkalinity or to mark the end point of a titration.

A procedure in which a solution of known concentration is added from a burette to a measured volume of another until the end point, allowing concentration to be calculated.

The concentration of a solution expressed as moles of solute per litre of solution, abbreviated M. It is widely used in volumetric calculations.

The decomposition of an electrolyte by passing direct current through its molten state or aqueous solution, causing oxidation at the anode and reduction at the cathode.

A substance that conducts electricity when molten or dissolved in water because it yields mobile ions, unlike metals, which conduct as solid electron conductors.

The electrode at which reduction occurs. In electrolysis it is the negative electrode, where cations gain electrons; in a cell it is the positive terminal.

The electrode at which oxidation occurs. In electrolysis it is the positive electrode, where anions lose electrons; in a cell it is the negative terminal.