Periodicity and bonding flashcards

Periodicity and bonding explores how atomic structure determines the physical and chemical properties of elements across periods and down groups. Students must understand trends in atomic radius, ionic radius, ionisation energy, electronegativity, and electron affinity, explaining these in terms of nuclear charge, shielding, and distance. Bonding type — ionic, covalent, or metallic — arises from electronegativity differences and determines properties such as melting point, conductivity, and solubility. Students should also understand how bond polarity leads to polar molecules, how molecular geometry relates to VSEPR theory, and how intermolecular forces (London dispersion, dipole-dipole, and hydrogen bonding) influence physical properties. Connecting periodic trends to bonding character and then to observable properties is essential for answering higher-level questions.

1. Card 1

   What happens to atomic radius across a period from left to right?

   Atomic radius decreases because nuclear charge increases while shielding stays roughly constant, pulling electrons closer to the nucleus.

2. Card 2

   Why does atomic radius increase down a group?

   Each successive period adds a new electron shell, increasing the distance between the nucleus and outer electrons, despite greater nuclear charge.

3. Card 3

   Define first ionisation energy.

   The first ionisation energy is the energy needed to remove one mole of electrons from one mole of gaseous atoms in their ground state.

4. Card 4

   Why does ionisation energy generally increase across a period?

   Increasing nuclear charge with similar shielding draws electrons closer and more tightly, making them harder to remove.

5. Card 5

   What is electronegativity and what is the trend across a period?

   Electronegativity is the ability of a bonded atom to attract electron density. It increases across a period as nuclear charge rises and atomic radius falls.

6. Card 6

   How does electronegativity difference determine bond character?

   A large difference gives an ionic bond, a moderate difference gives a polar covalent bond, and a negligible difference gives a nonpolar covalent bond.

7. Card 7

   What is a polar molecule and how does molecular shape affect polarity?

   A polar molecule has an overall dipole moment. Symmetrical arrangements of polar bonds cancel, making the molecule nonpolar despite having polar bonds.

8. Card 8

   State the conditions required for hydrogen bonding to occur.

   Hydrogen bonding requires hydrogen bonded directly to N, O, or F, and a lone pair on N, O, or F in a neighbouring molecule.

9. Card 9

   Why do ionic compounds have high melting points?

   Strong electrostatic attraction between oppositely charged ions in the lattice requires a large amount of energy to overcome.

10. Card 10

    What trend is seen in the melting points of Period 3 elements and why?

    Melting points rise from Na to Si due to stronger metallic or covalent bonding, then drop sharply for P, S, Cl, Ar which have weak London dispersion forces.

11. Card 11

    How does VSEPR theory predict molecular geometry?

    VSEPR theory states that electron pairs around a central atom repel each other and arrange themselves to minimise repulsion, determining shape.

12. Card 12

    Why is the boiling point of water unusually high for its molar mass?

    Water molecules form extensive hydrogen bonds with each other, requiring significantly more energy to separate than molecules of similar mass.

• Students often assume that all molecules containing polar bonds are polar overall, forgetting that symmetrical geometry can cause bond dipoles to cancel, as in CO2 or CCl4.
• A common error is stating that ionisation energy increases smoothly across every period, overlooking the dips at Group 3 and Group 6 caused by sub-shell and electron-pairing effects.
• Many students confuse the trend in ionic radius with atomic radius, not realising that cations are smaller than their parent atoms while anions are larger due to changes in electron-electron repulsion.

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