Selina Concise Class 7 Chemistry Solution Chapter No. 4- ‘Atomic Structure’ For ICSE Board Students.
1)
a)
Answer : Atoms :
Matter is made up of very tiny and small particles , it cannot break down or divided further, as atoms.
b)
Answer : Molecules :
When two or more same and different elements chemically combine together to form neutral compound known as Molecules .
c)
Answer : Radical :
The chemical particles with unpaired electrons or elements or compound that contains negative and positive charge on it known as radical.
d)
Answer : Valency :
The combining capacity of maximum number of electrons , which an atom loss or gain , known as Valency.
e)
Answer : Periodic Table :
A chart of elements that arrange into rows and columns according to their atomic number or physical and chemical properties.
2)
a)
Answer : Common salt (NaCl) : Sodium (Na) , Chlorine (Cl).
b)
Answer : Ammonia (NH3) :. Nitrogen ( N) , Hydrogen ( H) .
c)
Answer : Sulphuric acid ( H2SO4) : Hydrogen (H) , Sulphur ( S) , Oxygen (O).
d)
Answer : Glucose ( C6H12O6) : Carbon ( C ) , Hydrogen (H) , Oxygen (O).
e)
Answer : Sodium Hydroxide (NaOH) : Sodium (Na) , Hydrogen (H) , Oxygen (O) .
f)
Answer : Acetic acid (CH3COOH) : Carbon ( C) , Hydrogen (H) , Oxygen (O).
3)
a)
Answer : 2CO₂ :
Two molecule of carbon dioxide which contains carbon and oxygen atoms.
b)
Answer : 2H₂S:
Two molecule of hydrogen sulphide which contains Hydrogen and Sulphur atoms .
c)
Answer :5H₂SO₄ :
Five molecules of sulphuric acid which contains Hydrogen, sulphur and oxygen atoms.
d)
Answer : 6NaNO₃ :
Six molecules of sodium nitrate which contains Sodium, Nitrogen, Oxygen atoms.
4)
Answer :
Elements |
Symbol | Valency |
a) Magnesium ion | Mg²⁺ |
2 |
b) Ammonium |
NH₄⁺ | 1 |
c) Carbonate | CO²⁻₃ |
2 |
d) Nitrate |
NO⁻₃ | 1 |
e) Oxide | O²⁻ |
2 |
f) Bisulphate |
HSO⁻₃ | 1 |
g) Aluminium ion | Al³⁺ |
3 |
5)
a)
Answer : SO₄²⁻ – Sulphate
b)
Answer : HCO₃⁻ – Bicarbonate
c)
Answer :OH⁻ – Hydroxide
d)
Answer : Cr₂O₇²⁻ – Dichromate
6)
a) .
Answer : Name the ion for each of the Valency +1,+2,+3 are following .
- Potassium K + =+1
- Calcium Ca 2+ = +2
- Gold Au3+ = +3
b) .
Answer : Name the ion for each of the Valency -1, -2, -3 are following .
- Chloride Cl⁻ = -1
- Oxide O²⁻ = -2
- Nitride N³⁻=-3
7) .
a).
Answer : CaO :
Oxide : O²⁻ = -2
b).
Answer : Ca(OH)2 :
Hydroxide : OH⁻ = 1
c).
Answer : CaCO₃
Carbonate :CO₃²⁻ = 2
d).
Answer : CaCl₂
Chloride. : Cl⁻ = -1
8)
a)
Answer : (NH₄)₂SO₄: Ammonium sulphate
b)
Answer : Ca(NO₃)₂ : Calcium Nitrate
c)
Answer : FeS. :. Iron sulphide
d)
Answer : Na₃PO₄. :. Sodium phosphate
e)
Answer : NH₄OH. :. Ammonium hydroxide
f)
Answer : CuCO₃ : Copper carbonate
g)
Answer : HgO. :. Mercuric oxide
h)
Answer : ZnCl₂. ;. Zinc chloride
i)
Answer : ZnS. :. Zinc sulphide
j)
Answer : H₂S. : Hydrogen Sulphide
9)
a)
Answer : Sodium Sulphide
Molecular formula : Na₂S
b) .
Answer : Magnesium Oxide :
Molecular formula : MgO
c) .
Answer :. Calcium hydroxide :
Molecular formula : Ca(OH)₂
d) .
Answer : Hydrogen chloride :
Molecular formula : HCl
e)
Answer : Sulphuric acid :
Molecular formula : H₂SO₄
f) .
Answer : Iron (II) sulphide :
Molecular formula : FeS
g) .
Answer : Iron(III) Sulphate :
Molecular formula : Fe₂(SO₄)₃
h) .
Answer : Nitric acid :
Molecular formula : HNO₃
i) .
Answer : Calcium phosphate :
Molecular formula : Ca₃(PO₄)₂
j) .
Answer : Aluminium Sulphate
Molecular formula : AlSO₄
k) .
Answer : Magnesium Nitride :
Molecular formula : Mg₃N₂
10) .
a)
Answer : Sodium Oxide :
Molecular formula : Na₂O
b)
Answer :Sodium Sulphate :
Molecular formula : Na₂SO₄
c)
Answer :. Sodium carbonate :
Molecular formula : Na₂CO₃
d)
Answer : Sodium Hydroxide :
Molecular formula : NaOH
e)
Answer : Sodium nitrate :
Molecular formula : NaNO₃
11)
Answer : Variable Valency :
The elements have different combining capacity of maximum number of electrons , which an atom loss or gain or Valency or more than one Valency are Known as variable Valency .
Example :
1) Copper (Cu) :
Copper has two one (1) and two (2) ,Valency when Cu is chemically combine with oxygen , to form cuprous oxide Cu2O , and cupric oxide CuO.
2) Iron (Fe) :
Iron has two Valency +2 and +3 , when iron is combine with oxygen to form ferrous oxide which has the valence +2 and ferric oxide has the valence + 3.
12) .
a)
Answer : Magnesium :
Group number of Magnesium element present in periodic table IIA.
b)
Answer : Carbon :
Group number of Carbon element present in periodic table IVA.
c)
Answer : Sulphur :
Group number of Sulphur element present in periodic table VIA.
d) .
Answer : Neon :
Group number of Neon element present in periodic table Zero.
13)
Answer :Elements belong to group VA has the Valency 3 . Elements present in group VA are Nitrogen , Phosphorus .
14)
Answer : Elements belongs to group II, Valency is 2 .
a) formula of molecule of compound II group element With group VA elements :
- Symbol of Beryllium (Be) and phosphorus (P).
- Valency of Beryllium (Be) is 2 and phosphorus (P) is 3.
- Interchange the Valency of radical.
Symbol : Be²⁺ P³⁻
Charge : 2+ 3–
Valency: 2 3
So, Be2+ and P3- charge is negligible or omitted. By the rules.
- Molecular formula: Be₃P₂ (Beryllium Phosphide)
b) formula of molecule of compound II group element With group VIA elements :
- Symbol of Barium (Ba) and Sulphur (S) .
- Valency of Barium( Ba) is 2 and Sulphur (S) is 2.
- Interchange the Valency of radical.
Symbol : Ba²⁺ S²⁻
Charge : 2+ 2–
Valency: 2 2
So, Be2+ and P3- charge is negligible or omitted, and the reduce the Valency to the lowest ratio by the rules.
- Molecular formula : BaS (Barium Sulphide)
c) formula of molecule of compound II group element With group VIIA elements :
- Symbol of Barium (Ba) and Bromide (Br) .
- Valency of Barium( Ba) is 2 and Bromide (S) is 1.
- Interchange the Valency of radical .
Symbol : Ba²⁺ Br¹⁻
Charge : 2+ 1–
Valency: 2 1
So, Be2+ and P3- charge is negligible or omitted, by the rules.
- Molecular formula : BaBr2 (Barium Bromide )
Objective types questions
1)
a) Atoms are …………..
Answer : neutral
(Atoms are neutral particles because it contain equal number of sub Atomic particles protons positive charge and electron negative charge which make the atom neutral )
b) An ion with positive charge is called
Answer : Cation
(Ion with positive charge is called cation because it loss electrons )
c) An ion with negative charge is called ……..
(Ion with negative charge is called anion because it gain electrons.)
Answer : anion
d) 2H2 means …………atoms of Hydrogen .
Answer : Two
(2H2 means two individuals hydrogen atom .)
e) ……………is triatomic molecule.
Answer : ozone
(When three atoms are chemically combine with each other known as triatomic molecule , so formula of ozone is O3 three oxygen atoms chemically combine with each other.)
f) Metals have ………… Valency .
Answer : variable
(Metals have variable Valency because sometimes chemical reaction occur under different conditions and different electron transition)
g) Chemical name of caustic soda is …………
Answer : Sodium Hydroxide
(The chemical name of caustic soda is sodium hydroxide , sodium hydroxide ( NaOH), the name is given because it is a alkali salt and corrosive in nature ,)
2)
a)
Answer : iii) 3 (✓)
b)
Answer : iii) Carbon (✓)
c)
Answer : iv) CaSO₄ (✓)
d)
Answer : ii) Copper (✓)
3)
a)
Answer : Atomicity
b)
Answer : Molecular formula
c)
Answer : Molecule
d)
Answer : Valency
e)
Answer : Periodic table