Basic Science Solutions for Class 7 Science Chapter 1 The Language Of Chemistry are provided here with simple step-by-step explanations. These solutions for The Language Of Chemistry are extremely popular among Class 7 students for Science The Language Of Chemistry Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Basic Science Book of Class 7 Science Chapter 1 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Basic Science Solutions. All Basic Science Solutions for class Class 7 Science are prepared by experts and are 100% accurate.

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Formula of a compound or an element represents the type and number of atoms present in one molecule of that compound or element.

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The number of electrons that can be donated, accepted or shared by an atom of an element during a chemical reaction is equal to the valency of that element. It represents the combining capacity of an atom.

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A compound radical is a group of two or more elements that acts as a single atom with a specific valency, in a chemical reaction.

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Two elements having variable valency and compounds formed by them are as follows:

(i) Copper (Cu):
Cuprous oxide [Copper(I)oxide] − Cu2O
Cupric oxide [Copper(II)oxide] − CuO

(ii) Iron (Fe):
Ferrous oxide [Iron(II)oxide] − FeO
Ferric oxide [Iron(III)oxide] − Fe2O3

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A balanced chemical reaction is one in which the number of atoms on the side of the products is equal to the number of atoms on the side of the reactants.
The number of atoms on the side of reactants is always equal to the number of atoms on the side of the products in a chemical reaction, i.e., no atom is lost during a chemical reaction. We balance a chemical reaction to represent this fact.

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 Compound Valency of Underlined Elements of Radicals BaCl2 2 PCl3 3 PCl5 5 NH3 3 MgSO4 2 CaCO3 2 Na2O 1 CaO 2 Ca(OH)2 2 FeSO4 2 FeCl3 3 Fe2O3 3 NaOH 1 Al(OH)3 3 Na2CO3 1

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Compound radical is a group of atoms of different elements that behave as an intact unit during a chemical reaction. Atoms in a compound radical do not break apart revealing the individual atoms but remain together forming an intact group of atoms having a valency. This unit behaves just like an atom or a molecule during a reaction.

Some compound radicals with their valencies are given below:

 Compound Radical Valency OH 1 SO4 2 NO3 1 CO3 2

 Compound Name Compound Radical Valency NaOH Sodium hydroxide OH 1 H2SO4 Sulphuric acid SO4 2 Na2CO3 Sodium carbonate CO3 2 (NH4)2SO4 Ammonium sulphate SO4 2 KNO3 Potassium nitrate NO3 1

#### Page No 7:

1. A symbol is an abbreviation of the name of an element.
2. A molecule of an element or a compound is represented by its formula.
3. The valencies of the two elements of a binary compound are transposed to obtain its formula.
4. Atoms are neither lost nor gained in a chemical reaction.

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(c) Au
Symbol of gold is Au.

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(c) Sulphate
Sulphate $\left({\mathrm{SO}}_{4}^{-}\right)$ is a divalent radical.

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(d) 4
Sulphur dioxide has two atoms of oxygen, each with a valency of 2. To satisfy this, sulphur has a valency of 4 in SO2.

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(b) 3
Valency of N in NH3 is 3, whereas the valency of Cl in HCl is 1. Hence, the valency of N in NH3 is three times greater than that of Cl in HCl.

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 Column A Column B (a) Helium (ii) He (b) Mercury (i) Hg (c) Copper (v) Cu (d) Calcium (vi) Ca (e) Phosphorus (iv) P (f) Lead (iii) Pb

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1. True. The valency of hydrogen is 1.
2. True. The valency of oxygen is 2.
3. False. Symbol of iron is Fe.
4. True. The symbol of silver is Ag.
5. False. Calcium chloride is CaCl2.
6. True. The valency of both zinc and oxygen is 2. So, zinc oxide is ZnO.

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 Compound Formula Water H2O Calcium oxide CaO Carbon dioxide CO2 Carbon monoxide CO Magnesium oxide MgO Hydrogen chloride HCl Sodium chloride NaCl Potassium chloride KCl Magnesium chloride MgCl2 Zinc chloride ZnCl2 Nitric acid HNO3 Sodium nitrate NaNO3 Sodium carbonate Na2CO3 Potassium carbonate K2CO3 Calcium carbonate CaCO3

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