ICSE Class 10 Chemistry • Chapter 02
Chemical Bond: The attractive force that holds atoms together in a molecule or compound.
Why do atoms form bonds? To achieve a stable electronic configuration (complete octet or duplet) and lower their energy.
Octet Rule: Atoms tend to gain, lose, or share electrons to achieve 8 electrons in their valence shell.
Duplet Rule: For H, Li, Be → achieve 2 electrons in valence shell.
| Bond Type | Formation | Formed Between |
|---|---|---|
| Electrovalent (Ionic) | Transfer of electrons | Metal + Non-metal |
| Covalent | Sharing of electrons | Non-metal + Non-metal |
| Coordinate (Dative) | One-sided sharing | Special cases (lone pair donation) |
Definition: A bond formed by the complete transfer of one or more electrons from a metal atom to a non-metal atom, resulting in the formation of ions held together by electrostatic attraction.
Metal → Loses electrons → Forms Cation (+)
Non-metal → Gains electrons → Forms Anion (-)
Example 1: Formation of NaCl (Sodium Chloride)
Na (2,8,1) → Na⁺ (2,8) + e⁻
Cl (2,8,7) + e⁻ → Cl⁻ (2,8,8)
Electrostatic attraction between Na⁺ and Cl⁻ forms NaCl
Example 2: Formation of MgCl₂ (Magnesium Chloride)
Mg (2,8,2) → Mg²⁺ (2,8) + 2e⁻
2 Cl atoms accept 1 electron each → 2 Cl⁻
Example 3: Formation of CaO (Calcium Oxide)
Ca (2,8,8,2) → Ca²⁺ (2,8,8) + 2e⁻
O (2,6) + 2e⁻ → O²⁻ (2,8)
| Property | Explanation |
|---|---|
| High Melting & Boiling Point | Strong electrostatic forces between ions require high energy to break |
| Solid at Room Temperature | Ions arranged in rigid crystal lattice |
| Conduct Electricity (molten/aqueous) | Free mobile ions carry charge; NOT in solid state |
| Soluble in Water | Polar water molecules dissociate ionic compounds |
| Not Soluble in Organic Solvents | Non-polar solvents cannot break ionic bonds |
Definition: A bond formed by mutual sharing of electrons between two non-metal atoms to achieve stable configuration.
Shared Pair: The pair of electrons shared between atoms.
Lone Pair: Non-bonding electron pairs on an atom.
| Type | Electrons Shared | Bond Representation | Examples |
|---|---|---|---|
| Single Bond | 1 pair (2 e⁻) | A — B | H₂, Cl₂, H₂O |
| Double Bond | 2 pairs (4 e⁻) | A = B | O₂, CO₂, C₂H₄ |
| Triple Bond | 3 pairs (6 e⁻) | A ≡ B | N₂, C₂H₂ |
Hydrogen (H₂) - Single Bond
Each H has 1 electron, needs 1 more for duplet.
Chlorine (Cl₂) - Single Bond
Each Cl has 7 electrons, needs 1 more for octet.
Oxygen (O₂) - Double Bond
Each O has 6 electrons, needs 2 more for octet.
Nitrogen (N₂) - Triple Bond
Each N has 5 electrons, needs 3 more for octet.
Water (H₂O)
O shares 1 electron with each H. O has 2 lone pairs.
Ammonia (NH₃)
N shares 1 electron with each of 3 H atoms. N has 1 lone pair.
Methane (CH₄)
C shares 1 electron with each of 4 H atoms. No lone pairs on C.
Carbon Tetrachloride (CCl₄)
C shares 1 electron with each of 4 Cl atoms.
| Polar Covalent | Non-Polar Covalent |
|---|---|
| Unequal sharing of electrons | Equal sharing of electrons |
| Difference in electronegativity | Same electronegativity (same atoms) |
| Examples: HCl, H₂O | Examples: H₂, Cl₂, O₂, N₂ |
| Property | Explanation |
|---|---|
| Low Melting & Boiling Point | Weak intermolecular forces (easy to break) |
| Exist as Gases/Liquids/Soft Solids | Weak forces between molecules |
| Do NOT Conduct Electricity | No free ions or electrons |
| Insoluble in Water | Non-polar molecules don't interact with polar water |
| Soluble in Organic Solvents | "Like dissolves like" |
Definition: A covalent bond where both electrons of the shared pair are contributed by ONE atom only (donor), while the other atom accepts them (acceptor).
Represented by: Arrow (→) pointing from donor to acceptor.
Ammonium Ion (NH₄⁺)
NH₃ has a lone pair on N. H⁺ has empty orbital.
N donates its lone pair to H⁺ → Coordinate bond formed.
Hydronium Ion (H₃O⁺)
H₂O has lone pairs on O. H⁺ has empty orbital.
O donates lone pair to H⁺ → Coordinate bond formed.
Key Point: In coordinate bonding, once formed, the coordinate bond is indistinguishable from a normal covalent bond!
| Property | Ionic | Covalent |
|---|---|---|
| Formation | Electron transfer | Electron sharing |
| Between | Metal + Non-metal | Non-metals |
| State | Solid | Gas/Liquid/Soft solid |
| M.P./B.P. | High | Low |
| Conductivity | Yes (molten/aqueous) | No |
| Solubility | Water soluble | Organic solvent soluble |
BOARD Draw electron dot structures showing formation of: (i) MgO (ii) CaCl₂
BOARD Give two differences between electrovalent and covalent compounds. Give one example of each.
HOTS Explain with electron dot diagram how a coordinate bond is formed in ammonium ion.