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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 (→\rightarrow).

📐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.