Atoms and Molecules - NCERT Corner & Exercises

Vocabulary practice flashcards covering fundamental laws, definitions, chemical formulas, and mass calculations from Chapter 3: Atoms and Molecules.

Law of Conservation of Mass

A fundamental law stating that the total mass of the reactants must equal the total mass of the products in a chemical reaction; Dalton's atomic theory explains this by stating that atoms can neither be created nor destroyed.

Law of Definite Proportions

A law of chemical combination stating that in a chemical compound, elements combine in a constant proportion by mass (such as hydrogen and oxygen combining in a $1:8$ mass ratio in water); explained by Dalton's postulate that the relative number and kinds of atoms in a given compound remain constant.

Atomic Mass Unit (amu)

A unit of mass defined as equal to $\frac{1}{12}\text{th}$ the mass of one carbon-12 atom.

Chemical Formula

A symbolic representation of a molecule of an element or compound that reveals the proportion of atoms or ions present.

Polyatomic Ion

A group of two or more atoms carrying an overall net electric charge, such as the ammonium ion ($NH_4^+$) or carbonate ion ($CO_3^{2-}$).

Molecular Mass

The sum of the atomic masses of all atoms present in a single molecule of a substance, expressed in unified atomic mass units ($u$).

Formula Unit Mass

The sum of the atomic masses of all atoms in a single formula unit of a compound, such as $81\,u$ for zinc oxide ($ZnO$) or $62\,u$ for sodium oxide ($Na_2O$).

Molar Mass

The mass of one mole of a substance expressed in grams, such as $26\,g$ for ethyne ($C_2H_2$), $256\,g$ for sulphur ($S_8$), or $124\,g$ for phosphorus ($P_4$).

Quick Lime

The common chemical name for calcium oxide ($CaO$), containing the elements calcium and oxygen.

Baking Powder

A compound with the chemical formula $NaHCO_3$, composed of the elements sodium, hydrogen, carbon, and oxygen.

Hydrogen Bromide

A compound with the chemical formula $HBr$, composed of the elements hydrogen and bromine.

Sodium Oxide

An ionic compound with the chemical formula $Na_2O$, having a formula unit mass of $62\,u$.

Aluminium Chloride

A chemical compound represented by the formula $AlCl_3$.

Sodium Sulphide

An ionic compound represented by the chemical formula $Na_2S$.

Magnesium Hydroxide

A base represented by the chemical formula $Mg(OH)_2$.

Potassium Sulphate

A compound with the chemical formula $K_2SO_4$, composed of potassium, sulphur, and oxygen, with a formula unit mass of $138\,u$.

Copper Nitrate

A chemical compound represented by the formula $Cu(NO_3)_2$.

Calcium Carbonate

A chemical compound represented by the formula $CaCO_3$, composed of calcium, carbon, and oxygen.