1. What is a symbol ? What information does it convey?
2. Why is the symbol S for sulphur, but Na for sodium and Si
for silicon ?
3. Write the full form of IUPAC. Name the elements
represented by the following symbols :
Au, Pb, Sn, Hg
4. If the symbol for Cobalt, Co, were written as CO, what
would be wrong with it?
5. What do the following symbols stand for?
(a) H (b) H (c) 2H
(d) 2H2
6. What is meant by atomícity ? Name a diatomic element,
7. (a) Explain the terms 'valency' and 'variable valency'.
(b) How are the elements with variable valency named ?
Explain with an example.
8. Give the formula and valency of:
(a) aluminate
(b) chromate
(c) aluminium
(d) cupric
9. (a) What is a chemical formula ? (b) What is the
significance of a formula ? Give an example to illustrate.
10. What do you understand by the following terms ?
(a) Acid radical (b) Basic radical
11. Select the basic and acidic radicals in the following
compounds.
(a) MgSO4
(b) (NH22504
(c) Al(SO4)3
(d) ZnCo
(e) Mg(OH)2
12. Write chemical formulae of the sulphates of Aluminium,
Ammonium and Zinc.
13. The valency of an element A is 3 and that of element B
is 2. Write the formula of the compound formed by the
combination of A and B.
Answers
Answer:
1. A symbol is the short form which stands for the atom of a specific element or the abbreviations used for the names of elements. A symbol represents how many atoms are present in its one gram (gm) atom.
2.While naming an element first letter of the elements is taken and written in capitals(e.g. for sulfur, we use the symbol S). (e.g. for sodium/Natrium, we use the symbol Na).
3.International Union of Pure and Applied Chemistry (IUPAC).
Au-gold, pv-lead, sn-tin, H-Mercury
two non-metals namely Carbon and Oxygen and it would represent Carbon-monoxide but not Cobalt.
5.a) hydrogen atom
b) hydrogen gas
c) two hydrogen atom
d) two dihydrogen atom
6.Atomicity of an element is the number of atoms in a molecule of a substance.
example of a diatomic element is h2O.
7. a)Valency is defined as the combining capacity of an element. ... Some elements differ in their capacity to combine with other elements depending on the nature of the reaction; this property is called variable valency. For example, Iron (Fe) can have a valency of both 2 and 3.
b) the suffix “ous” is used to show the lower valency.
8. a) Alo2 - (- 2) b) CrO42− and valency is2 c) Al and valency is 3 d) cu and valency is 2
9. A chemical formula is a symbolic representation of the number of atoms present in a molecule of that substance. Example - Salt - NaCl, ethanol C2H6O because the molecule of ethanol contains two Carbon, 6 Hydrogen and 1 Oxygen atom.
10.Acidic radical: The ion formed after the removal of hydrogen ion (H+) from an acid is known as acidic radical. Basic radical: The ion formed after the removal of hydroxide ion (OH−) from a base is known as basic radical.
11.Acid radical Basic radical
a) MgSO 4. SO
4
Mg
+
b) (NH
4
)
2
SO
4
SO
4
−
NH
4
+
c) Al
2
(SO
4
)
3
SO
4
−
Al
+3
d) ZnCO
3
CO
3
−
Zn
+2
e) Mg(OH)
2
OH
−
Mg
+2
12.Al2(SO4)3, (NH4)2SO4 and ZnSO4.
13.Formula of compound whose valency is 3 and 3 is A
2
B
3
.