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Chemistry - Language of Chemistry (Symbols, Formulae, Balancing Equations)

Grade 8ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A Symbol is a short-hand representation of an atom of a specific element. Symbols are often derived from English names (e.g., HH for Hydrogen) or Latin names (e.g., FeFe for Ferrum).

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Valency is defined as the combining capacity of an element or a radical. It is determined by the number of electrons lost, gained, or shared during chemical bond formation.

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Some elements exhibit Variable Valency. For example, Iron can have a valency of +2+2 (Ferrous, Fe2+Fe^{2+}) or +3+3 (Ferric, Fe3+Fe^{3+}).

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A Radical is an atom or a group of atoms that carries a charge and behaves as a single unit in chemical reactions. Examples include the Ammonium ion (NH4+NH_4^+) and the Carbonate ion (CO32−CO_3^{2-}).

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The Chemical Formula represents the actual number of atoms of each element present in a molecule. It is written using the criss-cross method of valencies.

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A Chemical Equation is the symbolic representation of a chemical change. According to the Law of Conservation of Mass, the total mass of reactants must equal the total mass of products, necessitating the balancing of equations.

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Balancing an Equation involves adding coefficients to the reactants and products so that the number of atoms of each element is equal on both sides of the yield sign (ightarrow ightarrow).

📐Formulae

Density=MassVolumeDensity = \frac{Mass}{Volume}

2H2+O2→2H2O2H_2 + O_2 \rightarrow 2H_2O

Ca(OH)2+CO2→CaCO3+H2OCa(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O

Al2(SO4)3 (Molecular Formula of Aluminium Sulphate)Al_2(SO_4)_3 \text{ (Molecular Formula of Aluminium Sulphate)}

FeCl2 (Ferrous Chloride) vs FeCl3 (Ferric Chloride)FeCl_2 \text{ (Ferrous Chloride) vs } FeCl_3 \text{ (Ferric Chloride)}

💡Examples

Problem 1:

Write the chemical formula for Magnesium Nitride.

Solution:

Mg3N2Mg_3N_2

Explanation:

The symbol for Magnesium is MgMg with a valency of 2+2+. The symbol for Nitrogen (as Nitride) is NN with a valency of 3−3-. By using the criss-cross method, the valency of MgMg becomes the subscript for NN, and the valency of NN becomes the subscript for MgMg, resulting in Mg3N2Mg_3N_2.

Problem 2:

Balance the following chemical equation: NH3+O2→N2+H2ONH_3 + O_2 \rightarrow N_2 + H_2O

Solution:

4NH3+3O2→2N2+6H2O4NH_3 + 3O_2 \rightarrow 2N_2 + 6H_2O

Explanation:

Initially, there are 33 Hydrogen atoms on the left and 22 on the right. To balance HH, we use a common multiple of 66. Placing 22 before NH3NH_3 and 33 before H2OH_2O gives 6H6H on both sides. However, balancing OO and NN subsequently requires doubling the coefficients to reach 4NH3+3O2→2N2+6H2O4NH_3 + 3O_2 \rightarrow 2N_2 + 6H_2O.

Problem 3:

Identify the radicals and their valencies in the compound (NH4)2SO4(NH_4)_2SO_4.

Solution:

Ammonium (NH4+NH_4^+) valency 11; Sulphate (SO42−SO_4^{2-}) valency 22.

Explanation:

The compound is Ammonium Sulphate. It consists of the basic radical NH4+NH_4^+ (Ammonium) and the acid radical SO42−SO_4^{2-} (Sulphate). The subscript 22 outside the bracket for NH4NH_4 indicates the valency of the Sulphate radical was 22.

Language of Chemistry (Symbols, Formulae, Balancing Equations) Revision - Class 8 Science ICSE