Atomic structure and bonding flashcards

Atomic structure and bonding underpins almost all of A-Level Chemistry. Students must understand the arrangement of protons, neutrons and electrons within atoms, how isotopes arise and how mass spectrometry determines relative atomic mass. Electronic configuration using shells, subshells and orbitals explains periodic trends and reactivity. Ionic bonding involves electron transfer to form oppositely charged ions held by electrostatic attraction, while covalent bonding involves electron pair sharing, with dative bonds as a special case. Electronegativity differences determine bond polarity, and molecular shape is predicted using VSEPR theory by counting bonding and lone pairs. Metallic bonding involves delocalised electrons in a lattice. Understanding the relationship between structure, bonding and physical properties such as melting point, conductivity and solubility is essential throughout the course.

1. Card 1

   What is the mass number of an atom?

   The mass number is the total number of protons and neutrons in the nucleus of an atom.

2. Card 2

   Define isotopes.

   Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, giving different mass numbers.

3. Card 3

   How is relative atomic mass calculated from isotope data?

   Relative atomic mass is the weighted mean mass of all naturally occurring isotopes of an element relative to 1/12 the mass of carbon-12.

4. Card 4

   What is the order of subshell energy levels for the first four shells?

   The order is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p. The 4s subshell fills before 3d because it is at a lower energy level.

5. Card 5

   State the Pauli exclusion principle.

   The Pauli exclusion principle states that each orbital can hold a maximum of two electrons, which must have opposite spins.

6. Card 6

   What is a dative covalent bond?

   A dative covalent bond (coordinate bond) forms when both electrons in the shared pair are donated by the same atom, as in NH4+.

7. Card 7

   What does electronegativity measure?

   Electronegativity measures the ability of an atom to attract the shared pair of electrons in a covalent bond towards itself.

8. Card 8

   Explain why a molecule can have polar bonds but be non-polar overall.

   If the molecule is symmetrical, the individual bond dipoles cancel out, giving a zero net dipole moment, as in CO2 or CCl4.

9. Card 9

   What shape and bond angle does a molecule with 4 bonding pairs and no lone pairs have?

   It is tetrahedral with bond angles of 109.5 degrees, as lone pairs are absent and all four bonding pairs repel equally.

10. Card 10

    How does a lone pair affect bond angles compared to a bonding pair?

    A lone pair exerts greater repulsion than a bonding pair, compressing bond angles, e.g. NH3 has 107 degrees rather than 109.5 degrees.

11. Card 11

    Why do ionic compounds have high melting points?

    Ionic compounds have strong electrostatic attraction between oppositely charged ions in a giant lattice, requiring large amounts of energy to overcome.

12. Card 12

    Why do metals conduct electricity as solids?

    Metals contain a lattice of positive ions surrounded by delocalised electrons that are free to move and carry charge through the structure.

• Many students confuse mass number with relative atomic mass, forgetting that relative atomic mass is a weighted average across all isotopes and is therefore often not a whole number.
• Students frequently write electronic configurations with 3d filled before 4s, not realising that 4s is at a lower energy and fills first, though 4s electrons are lost first when transition metal ions form.
• A common error in VSEPR questions is ignoring lone pairs on the central atom when predicting molecular shape, leading to incorrect bond angles and shape names.

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