Class 11 Chemistry – Some Basic Concepts of Chemistry

Vocabulary flashcards summarising essential terms and definitions from the video lecture on basic concepts of chemistry.

Matter

Anything that has mass and occupies space; exists as solid, liquid, gas (plus plasma and Bose-Einstein condensate).

Solid

State of matter with definite shape and definite volume.

Liquid

State of matter with definite volume but no fixed shape; takes shape of its container.

Gas

State of matter with neither definite shape nor definite volume; completely fills its container.

Plasma

High-energy ionised gas regarded as a fourth physical state of matter.

Bose-Einstein Condensate (BEC)

State of matter formed by atoms cooled to near absolute zero, causing them to occupy the same quantum state.

Fusion (Melting)

Process of changing a solid to a liquid by heating.

Freezing (Solidification)

Process of changing a liquid to a solid by cooling.

Vaporization (Boiling)

Change of a liquid to a gas on heating.

Condensation

Conversion of a gas to a liquid on cooling.

Sublimation

Direct change of a solid to a gas without passing through the liquid state.

Deposition

Direct change of a gas to a solid without becoming liquid.

Mixture

Physical combination of two or more substances in any proportion; components are not chemically bonded.

Homogeneous Mixture

Mixture with uniform composition throughout; components are completely miscible (e.g., air, sugar solution).

Heterogeneous Mixture

Mixture with non-uniform composition where different parts can be observed (e.g., sand and salt).

Pure Substance

Material with fixed composition; components cannot be separated by simple physical methods; includes elements and compounds.

Element

Pure substance consisting of only one type of atom; cannot be broken down by chemical means.

Molecule

Group of two or more atoms held together by chemical bonds; can represent an element (O₂) or a compound (H₂O).

Compound

Pure substance formed when atoms of different elements chemically combine in a fixed ratio; properties differ from constituent elements.

Allotropy

Existence of an element in two or more physical forms with identical chemical composition but different properties (e.g., diamond and graphite).

Law of Conservation of Mass

In any physical or chemical change, total mass of reactants equals total mass of products; matter is neither created nor destroyed.

Law of Definite Proportions

A given compound always contains the same elements combined in the same fixed mass ratio.

Law of Multiple Proportions

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple whole-number ratios.

Gay-Lussac’s Law of Gaseous Volumes

When gases react at constant temperature and pressure, their volumes combine in simple whole-number ratios.

Avogadro’s Law

Equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules.

Mole

SI amount of substance containing exactly 6.022 × 10²³ elementary entities (Avogadro number).

Avogadro Number (Nₐ)

6.022 × 10²³; number of particles present in one mole of any substance.

Molar Mass

Mass (in grams) of one mole of a substance; numerically equal to its relative molecular or atomic mass.

Stoichiometry

Quantitative relationship between reactants and products in a chemical reaction based on balanced equations.

Limiting Reagent

Reactant that is completely consumed first, thus limiting the amount of product formed in a reaction.

Empirical Formula

Chemical formula showing simplest whole-number ratio of atoms in a compound.

Molecular Formula

Formula indicating the actual number of each type of atom present in one molecule of a compound.

Mass Percentage (w/w)

Grams of solute per 100 g of solution, expressed as a percentage.

Volume Percentage (v/v)

Millilitres of solute per 100 mL of solution, expressed as a percentage.

Mass by Volume Percentage (w/v)

Grams of solute per 100 mL of solution.

Parts Per Million (ppm)

Concentration unit representing mass of solute per 10⁶ parts of solution; useful for trace quantities.

Mole Fraction (x)

Ratio of moles of a component to total moles of all components in a solution; unitless.

Molarity (M)

Number of moles of solute per litre of solution (mol L⁻¹); temperature dependent.

Molality (m)

Number of moles of solute per kilogram of solvent (mol kg⁻¹); temperature independent.

Atomic Mass Unit (amu or u)

One-twelfth the mass of a carbon-12 atom; 1 u = 1.66056 × 10⁻²⁴ g.

Unified Mass (u)

Modern term replacing amu for atomic masses; numerically identical to amu.

Dalton’s Atomic Theory

Early theory stating that matter is composed of indivisible atoms, atoms of an element are identical, and chemical reactions involve rearrangement of atoms.

Limitations of Dalton’s Theory

Failed to explain gaseous volume relationships, atomic forces, and variations in atomic masses or bonding characteristics among elements.