10
Question Question 9
Write the molecular formula of:
(a) Sodium sulphide
(b) Magnesium oxide
(c) Calcium hydroxide
(d) Hydrogen chloride
(e) Sulphuric acid
(f) Iron (II) sulphide
(g) Iron (III) sulphate
(h) Nitric acid
(i) Calcium phosphate
(j) Aluminium sulphate
(k) Magnesium nitride
(a) Na2S
(b) MgO
(c) Ca(OH)2
(d) HCl
(e) H2SO4
(f) FeS
(g) Fe2(SO4)3
(h) HNO3
(i) Ca3(PO4)2
(j) Al2(SO4)3
(k) Mg3N2
ICSE Class VII Chemistry Chapter 3 15 Marks
Atomic Structure — Quick Study Guide
Atoms are the building blocks of all matter. Understanding atomic structure is essential for all of chemistry.
Key Definitions
- Atom: Smallest particle of an element with its chemical properties
- Molecule: Group of two or more atoms bonded together
- Element: Pure substance with only one type of atom
- Compound: Two or more different elements chemically combined
- Atomic number (Z): Number of protons = Number of electrons
- Mass number (A): Protons + Neutrons
- Valency: Combining capacity of an element
- Isotopes: Same element, different mass numbers
Electronic Configuration Rules
K shell = max 2 electrons, L shell = max 8, M shell = max 8 (for first 20 elements). Fill inner shells first.
Exam Tips
- Memorise symbols of first 20 elements
- Practice calculating protons, neutrons, electrons from Z and A
- Practice drawing Bohr diagrams
- Valency: if outermost ≤ 4, valency = outermost; if > 4, valency = 8 - outermost
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