Answers: BONDING, FORMULA AND NOMENCLATURE

Answers: BONDING, FORMULA AND NOMENCLATURE

Chemistry Form II Revision Questions

01.  

i	Ii	iii	iv	v
D	C	B	A	B

02.  

i)                Chemical formula is a representation that uses symbols to show the proportions of the elements in a chemical compound.

ii)               A radical is a group of atoms with unpaired electrons. OR A radical is a group of atoms which act as a single element in bonding.

iii)             Electrovalent bond is a chemical bond formed between metal and non-metal by transfer of electrons.

iv)             Covalent bond is a chemical bond formed between non-metals by sharing of electrons.

 

03. Differences between electrovalent and covalent bond

 

Electrovalent (ionic) bond	Covalent bond
It is formed between metals and non-metals by transfer of electron(s)	It is formed between non-metals by sharing of electrons.
It is held by electrostatic force of attraction	It is held by the weak Van der Waal force
Ionic compounds are good conductor of electricity	Covalent compounds are poor conductor of electricity
They have high boiling and melting points	They have low melting and boiling points
Ionic compounds are soluble in water	Covalent compounds are soluble in polar solvents

 

04. (a) Oxidation number is the measure of the electron control that an atom has in a compound compared to the atom in the pure element.

(b)

                  i.     Cr₂O₇^2-

 

2Cr + (-2 x 7) = -2

2Cr – 14 = -2

2Cr = -2 + 14

2Cr = +12 (dividing by 2 both sides)

Cr = +6

The oxidation number of Cr is +6

 

                ii.     SO₃^2-

S + (-2 x 3) = -2

S -6 = -2

S = -2 + 6

S = +4

The oxidation number of S is +4

 

              iii.     KClO₃

+1 + Cl + (-2 x 3) = 0

Cl -5 = 0

Cl = +5

The oxidation number of Cl is +5

 

                iv.     NO₂^-

N + (-2 x 2) = -1

N – 4 = -1

N = -1 +4

N = +3

The oxidation number of N is +3

 

                  v.     NaCl

+1 + Cl = 0

Cl = -1

The oxidation number of Cl is -1

 

05.  

i)                FeCl₃ – Iron (III) chloride

ii)               FeCl₂ – Iron (II) chloride

iii)             Cu₂S – Copper (I) sulphide

iv)             N₂O₄ – Dinitrogen tetraoxide

v)               SF₆ – Sulphur hexafluoride

 

06.  

Common name	Chemical name	Chemical formula
Common salt	Sodium chloride	NaCl
Baking soda	Sodium hydrogencarbonate	NaHCO3
Soda ash	Sodium carbonate	Na2CO3
Chalk	Calcium carbonate	CaCO3

 

07. (a)

i)                Empirical formula is the formula which represent a smallest ratio of the atoms or ions in a compound.

ii)               Molecular formula is the formula which shows the actual number of each different atom in a molecule.

 

 

 

(b)

Element’s symbol	C	S
Percentage composition   Percentage composition divided to relative atomic mass Divide each value to smallest ratio	15.8   15.8/12   1.32 1.32/1.32   1	84.2   84.2/32   2.63 2.63/1.32   1.992 ≈ 2

 

The empirical formula is CS₂

 

From,

(Empirical formula)n = Molecular formula

(CS₂)n = 152

76 n = 152

n= 2

 

(CS₂) x 2 è C₂S₄

The molecular formula is C₂S₄

Answers: PERIODIC CLASSIFICATION

Answers: PERIODIC CLASSIFICATION

Chemistry Form II Revision Questions

01.  

i	Ii	iii	iv	v
C	C	A	D	D

02.  

i)                Melting point is the temperature at which a solid melts to form a liquid.

ii)               Boiling point is a temperature at which a liquid boils to form a vapour.

iii)             Density is the degree of compactness of a substance, which means it is the mass per unit volume of a substance.

iv)             Electronegativity is the ability of an atom to attract electron(s) towards itself.

v)               Ionization energy is the energy required to remove electrons from an atom or ion.

vi)             Atomic radius is the distance between the nucleus of an atom and the outermost shell.

 

03.  (a)

i)                 Group I elements are called alkali metals because they react with water to form an alkaline solution.

ii)               Sodium (Na) is stored under kerosene to prevent it from reacting with air since it is more reactive.

 

(b) Physical properties of members of first group elements (Li, Na and K)

§  They are good conductors of heat and electricity

§  They are soft metals

§  They have low density

§  They have shining surfaces when freshly cut

 

 

04.  (a) when group I metals react with oxygen, a metal oxide is formed

Example: 2Na _(s) + O_{2 (g)} à Na₂O _(s)

            (b) Alkali metals react with water to form alkaline solution and hydrogen gas.

                        Example: 2Na _(s) + 2H₂O _(l) à 2NaOH _(aq) + H_{2 (g)}

05.  

i)                The element in Group II, period 2 is Beryllium (Be)

ii)               W = 2 : 2

  I = 2: 4

 C = 2: 6

 K = 2: 8

 L = 2: 8: 3

N = 2: 8: 5

F = 2: 8: 7

 

iii)             ³⁹₁₉K

From:

A = P + n

Where:

 A = atomic mass

P = Number of proton/ number of electrons/ atomic number

n = number of neutron

 

39 = 19 + n

n = 20

The number of protons = number of electrons = 19

The number of neutron is 20.

 

iv)             (a) Alkali metal is B

(b) Alkali earth metals are W and E

(c) Metalloid is I

(d) Noble gas is K

(e) Halogen is F