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MYP Chemistry

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A.1 Atomic Structure

Practice Worksheet — name: ______________________ date: ____________

Formulas for this topic

Mass number A=Z+NA = Z + N

Section A — Multiple choice

A1. An atom has 11 protons, 12 neutrons and 11 electrons. Its electron arrangement is:

  1. A 2, 8, 1
  2. B 2, 9
  3. C 11
  4. D 2, 8, 2

A2. Chlorine-35 and chlorine-37 differ in their number of:

  1. A Protons
  2. B Electrons
  3. C Neutrons
  4. D Shells

A3. When a magnesium atom (2, 8, 2) becomes an ion it:

  1. A Gains 2 electrons to form Mg²⁻
  2. B Loses 2 electrons to form Mg²⁺
  3. C Loses 2 protons to form Mg²⁻
  4. D Gains 6 electrons to form Mg⁶⁻

Section B — Short answer

B1. Copy and complete: the ion 816O2−^{16}_{8}\text{O}^{2-} contains ___ protons, ___ neutrons and ___ electrons. Explain each number. [3 marks]

B2. Explain why isotopes of an element have identical chemical properties. [2 marks]

B3. Describe the experimental evidence that led to the nuclear model of the atom. [3 marks]

Answer key

For worked explanations, interactive practice and more free resources, visit www.newtonine.com

Section A

A1: 2, 8, 1 — Eleven electrons fill the shells in order: 2 in the first, 8 in the second, leaving 1 in the third — sodium's arrangement, and the reason it reacts by losing that lone outer electron.

A2: Neutrons — Isotopes share the same proton number (17 for chlorine — otherwise they would be different elements) but have different neutron counts: 18 versus 20. Chemical behaviour, set by electrons, is identical.

A3: Loses 2 electrons to form Mg²⁺ — Losing the 2 outer electrons leaves the stable arrangement 2, 8 and a 2+ charge (12 protons versus 10 electrons). Metals lose electrons; the nucleus is never involved in chemical changes.

Section B

B1: 8 protons (atomic number), 8 neutrons (16 − 8), and 10 electrons (8 for a neutral atom, plus 2 gained to give the 2− charge). The oxide ion has the stable arrangement 2, 8.

B2: Chemical behaviour is determined by the electron arrangement, which depends on the proton number. Isotopes have the same protons and therefore the same electrons and arrangement — only the neutron count (and hence mass) differs.

B3: In the Geiger–Marsden experiment, alpha particles were fired at thin gold foil. Most passed straight through (atoms are mostly empty space), but a tiny fraction deflected at large angles or bounced back (the positive charge and mass are concentrated in a tiny, dense nucleus) — replacing the plum-pudding model.