AIIMS Nursing (BSc) Entrance Chemistry Flashcards

24 sample cards from the Chemistry deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Define electronegativity and name the most electronegative element.

   Electronegativity is the tendency of an atom to attract a shared pair of electrons in a bond. Fluorine is the most electronegative element.

2. State the octet rule.

   Atoms tend to gain, lose, or share electrons to achieve a stable configuration of eight electrons in their valence (outermost) shell, like a noble gas.

3. What is the difference between sigma (σ) and pi (π) bonds?

   A σ bond forms by head-on (axial) overlap of orbitals and is stronger; a π bond forms by sideways (lateral) overlap of p-orbitals and is weaker. Single = 1σ; double = 1σ+1π; triple = 1σ+2π.

4. Predict the hybridization and shape of methane (CH₄).

   sp³ hybridization, tetrahedral shape, bond angle 109.5°.

5. According to VSEPR theory, what shape and bond angle does a water molecule have and why?

   Bent/angular shape with bond angle ~104.5°; the two lone pairs on oxygen repel the bonding pairs more strongly, reducing the angle from the ideal 109.5°.

6. What is hydrogen bonding? Give one example.

   An electrostatic attraction between a hydrogen atom bonded to a highly electronegative atom (F, O, N) and a lone pair on another electronegative atom. Example: hydrogen bonding in water (H₂O).

7. Why are alkali metals (s-block Group 1) strong reducing agents?

   They have low ionization energy and readily lose their single valence electron to form +1 ions, making them powerful reducing agents.

8. What is the diagonal relationship? Give the classic pair.

   Similarity in properties between an element and the element diagonally placed to it in the next period/group. Classic example: lithium and magnesium (also Be–Al, B–Si).

9. Why do noble gases (Group 18) have very low reactivity?

   They have completely filled valence shells (stable octet, or duplet for He), giving very high ionization energy and no tendency to gain, lose or share electrons.

10. Why are transition (d-block) elements typically coloured and good catalysts?

    Colour arises from d–d electronic transitions (partially filled d-orbitals); their variable oxidation states and ability to form intermediates/adsorb reactants make them effective catalysts.

11. What causes the lanthanide contraction and one of its consequences?

    The steady decrease in atomic/ionic size across the lanthanide series due to poor shielding by 4f electrons. Consequence: 2nd and 3rd row transition elements (e.g., Zr & Hf) have nearly identical sizes.

12. Define a coordination compound and give an example.

    A compound containing a central metal atom/ion bonded to ligands by coordinate (dative) bonds, often forming a complex ion. Example: K₄[Fe(CN)₆] / [Cu(NH₃)₄]²⁺.

13. Define ligand and coordination number.

    A ligand is an ion or molecule that donates a lone pair to the central metal. Coordination number = number of ligand donor atoms directly bonded to the central metal ion.

14. Determine the oxidation state of iron in K₄[Fe(CN)₆].

    K = +1 (×4 = +4), CN = −1 (×6 = −6). Let Fe = x: 4 + x − 6 = 0 → x = +2. Iron is in the +2 oxidation state.

15. Define the terms catenation and tetravalency of carbon.

    Catenation: the ability of carbon to form long chains/rings by bonding with other carbon atoms. Tetravalency: carbon has 4 valence electrons and forms 4 covalent bonds.

16. What is the difference between inductive effect and resonance effect?

    Inductive effect is the permanent polarization of σ-bonds due to electronegativity difference, transmitted through the chain and decreasing with distance. Resonance (mesomeric) effect is the delocalization of π/lone-pair electrons through conjugated systems.

17. State Markovnikov's rule for addition of HX to an unsymmetrical alkene.

    When HX adds to an unsymmetrical alkene, the hydrogen attaches to the carbon already bearing more hydrogen atoms, and X goes to the carbon with fewer hydrogens (richer get richer).

18. Compare the reactivity of alkanes, alkenes and alkynes towards addition reactions.

    Alkanes are saturated and largely unreactive (undergo substitution); alkenes (C=C) and alkynes (C≡C) are unsaturated and readily undergo addition reactions, alkynes being even more unsaturated.

19. Why are haloarenes less reactive than haloalkanes towards nucleophilic substitution?

    In haloarenes the C–X bond has partial double-bond character due to resonance with the ring, and the sp² carbon holds the halogen more tightly, making nucleophilic substitution difficult.

20. Name the functional groups: −OH, −CHO, >C=O, −COOH.

    −OH = alcohol (hydroxyl); −CHO = aldehyde; >C=O = ketone (carbonyl); −COOH = carboxylic acid.

21. Which gives a positive Tollens' (silver mirror) test, an aldehyde or a ketone, and why?

    Aldehydes give a positive Tollens' test (forming a silver mirror) because they are easily oxidized; ketones are not oxidized by Tollens' reagent and give a negative test.

22. Name the four classes of biomolecules and one example of each.

    Carbohydrates (glucose), proteins (insulin/enzymes), lipids/fats (triglycerides), and nucleic acids (DNA/RNA).

23. What is the greenhouse effect and name two greenhouse gases.

    The trapping of infrared radiation by atmospheric gases, warming the Earth's surface. Greenhouse gases include carbon dioxide (CO₂) and methane (CH₄) (also water vapour, CFCs, N₂O).

24. Distinguish between addition and condensation polymers, with one example each.

    Addition polymers form by repeated addition of monomers with no by-product (e.g., polythene from ethene); condensation polymers form by combination of monomers with loss of small molecules like water (e.g., nylon-6,6).

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