General Science Chemistry

🟢 Lite — Quick Review (1h–1d)

Rapid summary of Chemistry for NDA GAT paper.

Chemistry contributes approximately 12–15 questions to the NDA GAT General Science section. Focus your quick revision on these high-yield areas:

Must-Know Facts:

• Atomic number = number of protons; Mass number = protons + neutrons
• 18 groups and 7 periods in the Modern Periodic Table
• pH scale: 0 (strongly acidic) to 14 (strongly alkaline); pH 7 = neutral
• Common indicators: litmus (red in acid, blue in base), phenolphthalein (colourless in acid, pink in base)
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au
• Four primary food components: carbohydrates, proteins, vitamins, fats
• Combustion requires: fuel + oxygen + ignition temperature (fire triangle)

Exam Tip: Focus on periodic table trends (electronegativity, atomic size across periods and down groups) — these are frequently tested in conceptual questions. The pH scale and indicators appear in almost every NDA chemistry paper.

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🟡 Standard — Regular Study (2d–2mo)

For students who want genuine understanding of Chemistry for NDA.

Atomic Structure

All matter consists of atoms, which contain:

• Protons (p⁺): positively charged, mass ≈ 1 atomic mass unit (amu). Number of protons = atomic number (Z) — defines the element.
• Neutrons (n⁰): electrically neutral, mass ≈ 1 amu. Number of neutrons = mass number (A) – atomic number (Z).
• Electrons (e⁻): negatively charged, mass ≈ 1/1836 amu (negligible for mass calculations). Number of electrons = number of protons in a neutral atom.

Isotopes: Atoms of the same element with different mass numbers (different number of neutrons). Example: ¹₂H (protium), ²₁H (deuterium), ³₁H (tritium). Isotopes have the same chemical properties but different physical properties.

Isobars: Atoms of different elements with the same mass number. Example: ₄₀Ca and ₄₀Ar both have mass number 40.

Electronic Configuration: Electrons occupy shells (K, L, M, N…). Maximum electrons per shell: 2n². K (n=1): 2, L (n=2): 8, M (n=3): 18. Elements in the same group have the same number of valence electrons.

The Modern Periodic Table

Dmitri Mendeleev’s periodic table arranged elements by atomic mass. The Modern Periodic Law (Moseley): properties of elements are periodic functions of their atomic number.

• 18 vertical groups: Elements in the same group have similar chemical properties (same valence electrons).
• 7 horizontal periods: Elements in the same period have the same number of electron shells.
• s-block (Groups 1, 2): Alkali and alkaline earth metals. Highly reactive, good conductors.
• p-block (Groups 13–18): Includes metals, metalloids, and non-metals. Boron (B) to Astatine (At) in this block.
• d-block (Groups 3–12): Transition metals — iron, copper, silver, gold, etc. Good conductors, form coloured compounds, have multiple oxidation states.
• f-block (Lanthanides and Actinides): The inner transition metals, placed separately below the main table.

Periodic Trends:

• Atomic size: decreases across a period, increases down a group
• Electronegativity: increases across a period, decreases down a group
• Ionisation energy: generally increases across a period
• Metallic character: decreases across a period, increases down a group

Chemical Bonding

Atoms bond to achieve stable octet (8 electrons in outermost shell, like noble gases).

1. Ionic (electrovalent) bonding: Transfer of electrons from metal to non-metal. Example: NaCl (sodium chloride). Properties: high melting/boiling point, soluble in water, conduct electricity in aqueous solution.
2. Covalent bonding: Sharing of electron pairs. Example: H₂O, CO₂, CH₄. Types: single bond (H₂), double bond (O₂), triple bond (N₂). Properties: low melting points, generally insoluble in water.
3. Metallic bonding: Sea of delocalised electrons among positive metal ions. Explains electrical conductivity, malleability, and ductility of metals.

Lewis structures show valence electrons as dots around the element symbol. Dots represent electrons, and lines represent bonds.

Octet rule exceptions: Phosphorus (P) has 10 electrons in PCl₅; Sulfur (S) has 10 in SF₆; Boron (B) has only 6 in BF₃.

Acids, Bases, and Salts

• Acids: Produce H⁺ ions in water. Properties: sour taste, turn blue litmus red, react with metals to produce hydrogen gas, neutralise bases.
• Bases: Produce OH⁻ ions in water. Properties: bitter taste, slippery feel, turn red litmus blue, neutralise acids.
• Salts: Produced from neutralisation of acid + base. Examples: NaCl, K₂SO₄, NH₄NO₃.

pH Scale:

• pH 0–6: Acidic (lower pH = stronger acid)
• pH 7: Neutral (pure water)
• pH 8–14: Basic/alkaline

Common indicators: Litmus (red in acid, blue in base), phenolphthalein (colourless in acid, pink in base), methyl orange (red in acid, yellow in base).

Oxidation and Reduction (Redox)

• Oxidation: Loss of electrons, increase in oxidation number, gain of oxygen or loss of hydrogen
• Reduction: Gain of electrons, decrease in oxidation number, gain of hydrogen or loss of oxygen
• Oxidising agent: Accepts electrons (gets reduced)
• Reducing agent: Donates electrons (gets oxidised)

Example: 2Mg + O₂ → 2MgO. Magnesium is oxidised (loses electrons), Oxygen is reduced (gains electrons).

Important Chemical Formulas

Name	Formula	Use
Water	H₂O	Essential for life, solvent
Carbon dioxide	CO₂	Photosynthesis, fire extinguisher
Sulfuric acid	H₂SO₄	Car batteries, fertilisers
Hydrochloric acid	HCl	Stomach acid, cleaning
Sodium chloride	NaCl	Table salt, food preservation
Sodium hydroxide	NaOH	Drain cleaner, soap making
Calcium carbonate	CaCO₃	Chalk, marble, antacid
Ammonia	NH₃	Fertilisers, refrigeration
Methane	CH₄	Natural gas, fuel
Acetic acid	CH₃COOH	Vinegar

Metals and Non-Metals

Metals: malleable, ductile, good conductors of heat and electricity, lustrous, sonorous (ring when struck), generally solids at room temperature (except mercury).

Non-metals: generally brittle, poor conductors, may be solids/liquids/gases at room temperature.

Reactivity Series (most reactive to least): K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Hg > Ag > Au > Pt

• Metals above hydrogen react with acids to produce hydrogen gas
• More reactive metals displace less reactive metals from their salts
• Gold and platinum are very unreactive (found in native form)

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🔴 Extended — Deep Study (3mo+)

Comprehensive theory for Chemistry mastery in NDA GAT.

Carbon and Its Compounds

Carbon is unique because:

• It forms four covalent bonds (tetravalency)
• Carbon atoms can link to each other forming long chains, rings, and branched structures
• It forms single, double, and triple bonds

Hydrocarbons:

1. Saturated hydrocarbons (alkanes): Only single bonds. General formula: CₙH₂ₙ₊₂

   • Methane (CH₄): Simplest alkane, main component of natural gas
   • Ethane (C₂H₆): Two-carbon chain
   • Propane (C₃H₈): Three-carbon chain
   • Butane (C₄H₁₀): Used as fuel (lighter gas)

2. Unsaturated hydrocarbons:

   • Alkenes (contain C=C double bond): CₙH₂ₙ. Example: Ethylene (C₂H₄) — used for ripening fruit
   • Alkynes (contain C≡C triple bond): CₙH₂ₙ₋₂. Example: Acetylene (C₂H₂) — used in welding

Combustion Reactions:

• Complete combustion (excess oxygen): Fuel + O₂ → CO₂ + H₂O + Heat + Light Example: CH₄ + 2O₂ → CO₂ + 2H₂O
• Incomplete combustion (limited oxygen): CO + C + H₂O produced instead; releases less heat; dangerous (produces carbon monoxide — toxic)

Food Components — Biochemistry Basics

1. Carbohydrates: Primary energy source. Composed of carbon, hydrogen, and oxygen (general formula: CₙH₂ₙOₙ).

   • Simple carbohydrates (glucose, fructose, sucrose): Quick energy, found in fruits, sugar
   • Complex carbohydrates (starch, cellulose, glycogen): Slow release energy, found in grains, potatoes
   • Glucose (C₆H₁₂O₆) — blood sugar, primary fuel for cells

2. Proteins: Made of amino acids (polymer = polypeptide chain). Essential for growth, repair, and maintenance of body tissues.

   • Sources: meat, eggs, pulses, milk
   • Protein deficiency causes kwashiorkor and marasmus
   • Denaturation: proteins lose structure when heated (cooking eggs)

3. Vitamins: Organic compounds essential in trace amounts. Two categories:

   • Fat-soluble (A, D, E, K): Stored in body fat
   • Water-soluble (B-complex, C): Not stored; need regular dietary intake
   • Vitamin C deficiency → scurvy; Vitamin A deficiency → night blindness

4. Fats (Lipids): Concentrated energy source (9 kcal/g vs 4 kcal/g for carbs/proteins).

   • Saturated fats (butter, ghee): Solid at room temperature; linked to heart disease
   • Unsaturated fats (vegetable oils): Liquid at room temperature; healthier option
   • Stored in adipose tissue as energy reserve

5. Minerals: Inorganic nutrients (calcium, iron, iodine, sodium, potassium). Essential for bone health (calcium), blood oxygenation (iron), thyroid function (iodine).

6. Water: Constitutes 60–70% of human body weight. Essential for all metabolic processes, transportation of nutrients, temperature regulation.

Periodic Table — Elements to Memorise for NDA

Group	Element	Symbol	Atomic Number
1	Hydrogen	H	1
1	Sodium	Na	11
1	Potassium	K	19
2	Calcium	Ca	20
2	Magnesium	Mg	12
13	Boron	B	5
14	Carbon	C	6
14	Silicon	Si	14
15	Nitrogen	N	7
15	Phosphorus	P	15
16	Oxygen	O	8
16	Sulfur	S	16
17	Chlorine	Cl	17
17	Fluorine	F	9
18	Helium	He	2
18	Neon	Ne	10
18	Argon	Ar	18
Transition	Iron	Fe	26
Transition	Copper	Cu	29
Transition	Silver	Ag	47
Transition	Gold	Au	79

NDA Chemistry Question Patterns:

Topic	Questions	Common format
Atomic structure	2–3	MCQ on protons/neutrons/electrons, isotopes
Periodic table	2–3	Trends, group/period identification
Chemical bonding	2–3	Ionic vs covalent, oxidation numbers
Acids, bases, salts	3–4	pH, indicators, neutralisation
Metals and non-metals	2–3	Reactivity series, properties
Carbon compounds	2–3	Hydrocarbons, combustion
Food components	1–2	Identification, deficiency diseases
General chemistry	2–3	Chemical equations, valency

Key Exam Strategies:

1. Balancing chemical equations is a common question type — practice simple equations first.
2. Valency determines combining capacity — elements with valency 1 can replace one hydrogen atom.
3. In redox reactions, remember OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).
4. pH calculation questions: pH = –log[H⁺]. Higher [H⁺] = lower pH.
5. Elements in the same group have similar properties because they have the same number of valence electrons.