Flashcards · 9620 · AS Topic 1

Atomic structure (AS Level) flashcards

19 cards on AS Topic 1, subtopics 3.1.1.1 to 3.1.1.3. Pick a subtopic or study them all.

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Relative charge and relative mass of a proton, a neutron and an electron: Proton: charge +1, mass 1. Neutron: charge 0, mass 1. Electron: charge −1, mass about 1/1840 (very small).
Where are protons, neutrons and electrons found in an atom?: Protons and neutrons are in the nucleus. Electrons are in shells around the nucleus.
What did the gold foil (alpha particle scattering) experiment show?: Nearly all alpha particles passed straight through, but a few bounced back at large angles. So an atom has a tiny, dense, positive nucleus with mostly empty space around it, replacing the plum pudding model.
Why do models of atomic structure change over time?: A model is kept until new evidence appears that it cannot explain; then it is revised (for example, solid spheres → plum pudding → nuclear atom → shells, sub-shells and orbitals).

Mass number (A) and atomic (proton) number (Z): A: the number of protons + neutrons. Z: the number of protons.
How do you find the numbers of protons, neutrons and electrons in an ion?: Protons = Z. Neutrons = A − Z. Electrons = Z − charge (a 3+ ion has lost three electrons; a 2− ion has gained two).
Protons, neutrons and electrons in ⁵⁶Fe³⁺ (Z = 26): 26 protons, 30 neutrons, 23 electrons.
Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons (so different mass numbers). Same electron arrangement, so the same chemical properties; mass-dependent properties such as density differ slightly.
The four stages of a time of flight (TOF) mass spectrometer: Ionisation (sample vaporised, positive ions formed), acceleration (an electric field gives all ions the same kinetic energy), ion drift (lighter ions move faster and arrive sooner), detection (ions gain electrons, making a current).
Why is a TOF mass spectrometer kept under a vacuum?: So that the ions do not collide with air particles.
Formula for relative atomic mass from a mass spectrum: Ar = Σ(isotopic mass × abundance) ÷ Σ(abundance) Example: (35 × 3 + 37 × 1) ÷ 4 = 35.5
In the mass spectrum of a compound, what does the peak at the highest m/z show?: The molecular ion. Its m/z gives the relative molecular mass.

Number of orbitals and maximum electrons in s, p and d sub-shells: s: 1 orbital, 2 electrons. p: 3 orbitals, 6 electrons. d: 5 orbitals, 10 electrons. Each orbital holds at most two electrons.
Electron configurations of Cr (Z = 24) and Cu (Z = 29): Cr: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹ Cu: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹ The two exceptions up to Z = 36.
Which electrons are lost first when a d-block atom forms a positive ion? Give Fe³⁺.: The 4s electrons are lost first (before 3d). Fe³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵
First ionisation energy: The energy change when one mole of gaseous atoms each lose one electron to form one mole of gaseous 1+ ions. For example: Ba(g) → Ba⁺(g) + e⁻
Why does first ionisation energy decrease down Group 2?: The outer electron is in a shell further from the nucleus and more shielded by inner electrons. This outweighs the greater nuclear charge.
Explain the dips in first ionisation energy from Mg to Al and from P to S: Mg → Al: Al’s outer electron is in 3p, slightly higher in energy and further out than 3s (evidence for sub-shells). P → S: in S one 3p orbital holds a pair of electrons that repel, so one is removed more easily.
How do successive ionisation energies show an element’s group?: Find the largest jump between consecutive values. The number of electrons removed before the jump is the number of outer-shell electrons, which gives the group.