Question 15
'Dilute hydrochloric acid is added to sodium hydroxide'. Give a word equation and a molecular equation of the same. Is the equation written, a balanced equation. Give reasons.
Word equation:
Sodium hydroxide + hydrochloric acid ⟶ sodium chloride + water
Molecular equation:
NaOH + HCl ⟶ NaCl + H2O
In the above equation,
| Reactants | Products |
|---|---|
| 1 atom of sodium [Na] | 1 atom of sodium [Na] |
| 1 atom of oxygen [O] | 1 atom of oxygen [O] |
| 1 atom of chlorine [Cl] | 1 atom of chlorine [Cl] |
| 2 atoms of hydrogen [H] | 2 atoms of hydrogen [H] |
As, the number of atoms of each element of reactants = the number of atoms of each element of products. Hence, the equation is balanced.
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
Bright Tutorials | ICSE Class VII Chemistry | Chapter 3: Atomic Structure | Contact: 9403781999