or some compounds containing compound radicals
Elements or radicals
with valencies
Compound formed
Formula
Name
1
Na
OH
1
NaOH
K
NO
ŠO
ΝΗ,
Sodium hydroxide
Potassium nitrate
Ammonium sulphate
Sodium carbonate
4
Na
1
KNO,
(NH4)2SO4
Na,CO3
HNO,
H2SO4
Cog
NO3
NO
H
Nitric acid
H
šo,
Sulphuric acid
Answers
Answer:
Formula of a compound or an element represents the type and number of atoms present in one molecule of that compound or element.
Page No 6:
ANSWER:
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.
Page No 6:
ANSWER:
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.
Page No 6:
ANSWER:
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
Page No 6:
ANSWER:
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.
Page No 6:
ANSWER:
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
Page No 6:
ANSWER:
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
Some compounds containing compound radicals:
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:
ANSWER:
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.
Page No 7:
ANSWER:
(c) Au
Symbol of gold is Au.
Page No 7:
ANSWER:
(c) Sulphate
Sulphate (SO−4)SO4- is a divalent radical.
Page No 7:
ANSWER:
(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.
Page No 7:
ANSWER:
(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.
Page No 7:
ANSWER:
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
Page No 7:
ANSWER:
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.
Page No 7:
ANSWER:
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
Answer:
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