NDA Chemistry · Free notes
Chemical Bonding — NDA Chemistry
Chemical bonding is a small but concept-dense chapter in NDA Chemistry — about a dozen PYQs, mostly EASY and MODERATE, and almost all answerable from a few core ideas held firmly. The whole chapter rests on one driving force: every atom (except the noble gases) wants a full outer shell, so it bonds — by transferring electrons (ionic), by sharing them (covalent), or by one atom donating both shared electrons (coordinate). Metals pool their electrons in a sea (metallic). The chapter teaches in three movements, building from why atoms bond up to counting the bonds in a molecule: (1) Ionic and covalent bonding — the octet rule, the four bond types, ionic-vs-covalent character, bond polarity, and the lattice properties (melting point, conductivity) the bank tests as 'which is NOT correct' traps; (2) Valency, oxidation states and molecular formula — combining capacity, how to read valency from the group, oxidation states, and writing a formula by crossing valencies; (3) Bond counting and molecular structure — counting the covalent bonds in a small molecule, and odd-electron molecules that dimerize. Lewis-structure diagrams are kept for a later pass; this chapter teaches the bonding rules in words. Every PYQ is tagged — know the bond-type table and the valency rules cold, and the marks follow.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Ionic and Covalent Bonding
7 PYQsAtoms bond to complete their outer shells — metals give electrons to non-metals (ionic), non-metals share electrons (covalent), one atom can donate both shared electrons (coordinate), and metals pool their electrons (metallic).
Valency, Oxidation States and Molecular Formula
4 PYQsValency is an element's combining capacity — the number of bonds it forms; the oxidation state is the charge it would carry if every bond were ionic; and crossing valencies turns the two into the formula of a compound.
Bond Counting and Molecular Structure
3 PYQsOnce you know how many bonds each atom forms, you can count every covalent bond in a small molecule by adding up the C–C, C–H and C–X links — and you can spot odd-electron molecules that pair up (dimerize) to satisfy the octet.
Formula & revision sheet
4 formulas · 3 reference tables · 11 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
4 formulas · 3 reference tables · 11 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (3)
The octet rule and the four types of chemical bond4 rows
| Bond type | How the octet is reached | Formed between | Example |
|---|---|---|---|
| Ionic (electrovalent) | Electrons transferred (lost / gained) | Metal + non-metal | Na⁺Cl⁻, MgO |
| Covalent | Electrons shared (one pair from each atom) | Non-metal + non-metal | H₂O, CH₄, SiC |
| Coordinate (dative) | Shared pair donated by one atom only | Donor with a lone pair | NH₄⁺, H₃O⁺ |
| Metallic | Valence electrons pooled in a 'sea' | Metal atoms | Na, Fe, Cu Metallic bonding (mobile electron sea) is why metals conduct electricity and are malleable. |
Properties of ionic versus covalent compounds5 rows
| Property | Ionic compounds | Covalent (molecular) compounds |
|---|---|---|
| Melting / boiling point | High (strong lattice) | Low (weak intermolecular forces) Among Na₂O, MgO, Fe₂O₃, CuO the highest melting point is MgO (~2852°C) — the small, doubly-charged Mg²⁺O²⁻ lattice. |
| Electrical conductivity | Conducts when molten or dissolved (not solid) | Does not conduct |
| Solubility | Usually soluble in water | Soluble in organic solvents |
| Physical state | Hard crystalline solids | Gases, liquids or soft solids |
| NaCl lattice coordination number | 6 : 6 (each ion surrounded by 6 of the opposite) | —Q |
Bond polarity and polar molecules4 rows
| Statement about water | True or false |
|---|---|
| Water is a polar molecule | TRUE — it is bent, so the O–H dipoles don't cancel The bank's trap: the FALSE option is 'water is a non-polar molecule'. Water is polar. |
| Water has a bent (V-shaped) geometry | TRUE — bond angle ≈ 104.5° |
| Water is a good solvent for ionic compounds | TRUE — its polarity pulls ions apart |
| Water is a non-polar molecule | FALSE — this is the statement the bank wants flagged |
Watch out for (6)
- Metal + non-metal is ionic; non-metal + non-metal is covalent→ The octet rule and the four types of chemical bond
- A coordinate bond is still a covalent bond→ The octet rule and the four types of chemical bond
- Ionic solids do NOT conduct — only when molten or dissolved→ Properties of ionic versus covalent compounds
- Higher charge → higher melting point→ Properties of ionic versus covalent compounds
- Water is polar, not non-polar→ Bond polarity and polar molecules
- Polar bonds don't always make a polar molecule→ Bond polarity and polar molecules
Formulas (3)
Watch out for (3)
- Nitrogen's valency is 3, and nitride is N³⁻→ Valency — combining capacity from the outer shell
- Let the known atoms force the unknown→ Oxidation state — the charge if every bond were ionic
- Bracket a polyatomic ion before adding a subscript→ Writing a molecular formula by crossing valencies
Watch out for (2)
- Count every link, including the O–H in an alcohol→ Counting the covalent bonds in a molecule
- NO₂ dimerizes because it is a radical, not N₂O or N₂O₅→ Odd-electron molecules and dimerization
PYQ weightage by concept
8 concepts · 14 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
8 concepts · 14 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Properties of ionic versus covalent compounds | 3 | 21% |
| The octet rule and the four types of chemical bond | 2 | 14% |
| Bond polarity and polar molecules | 2 | 14% |
| Concept | PYQs | Share |
|---|---|---|
| Valency — combining capacity from the outer shell | 2 | 14% |
| Oxidation state — the charge if every bond were ionic | 1 | 7% |
| Writing a molecular formula by crossing valencies | 1 | 7% |
| Concept | PYQs | Share |
|---|---|---|
| Counting the covalent bonds in a molecule | 2 | 14% |
| Odd-electron molecules and dimerization | 1 | 7% |
Test yourself on a real paper
Sit a past NDA paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.