A.2 The Periodic Table & Trends

UNIT SYLLABUS

MYP

The periodic table is chemistry's greatest organising achievement: arrange elements by atomic number and their properties repeat in predictable columns. Groups share outer-electron counts and therefore chemistry — the alkali metals grow more reactive down the group, the halogens less; the noble gases barely react at all. Metals sit left, non-metals right, with a staircase of semi-metals between. Once you can read the table's patterns, you can predict the behaviour of elements you have never met — which is exactly what Mendeleev did, leaving gaps for elements yet to be discovered.

Guiding Questions

? Why do sodium and potassium behave like chemical siblings?
? How could Mendeleev predict the properties of elements nobody had discovered?

✓ What the IB expects you to master

Describe the structure of the periodic table: groups (columns), periods (rows), metals and non-metals.
Relate group number to the number of outer electrons, and period to the number of shells.
Describe the properties and reactivity trend of Group 1 (alkali metals) — reactivity increases down the group.
Describe the properties and reactivity trend of Group 7 (halogens) — reactivity decreases down the group.
Explain the unreactivity of Group 0 (noble gases) by their full outer shells.
Explain reactivity trends in terms of how easily outer electrons are lost or gained.
Compare typical properties of metals and non-metals (conduction, malleability, oxide character).

1 Key Formulas

2 Exam Preparation & Topic Explanations

Explaining trends, not just stating them (Criterion A)

Stating "reactivity increases down Group 1" earns one mark; explaining it earns the rest. The explanation chain: more shells → outer electron further from the nucleus and more shielded → weaker attraction → electron lost more easily → more reactive. For halogens, run the chain in reverse (gaining an electron is easier when the shell is closer).

Displacement reactions turn the trend into evidence — know the colour changes.

Pro Exam Strategy

Group 1 metals are stored under oil — expect a "suggest why" question (they react with air and moisture).
Down Group 7: fluorine (pale yellow gas) → chlorine (green gas) → bromine (orange liquid) → iodine (grey solid). Know states and colours.
Mendeleev credit: he left gaps and predicted missing elements — a favourite Criterion D/history question.
Semi-metals (metalloids) like silicon sit on the staircase — useful in electronics as semiconductors.

3 MCQ Practice

Q1. Potassium reacts more violently with water than sodium because potassium:

Has more protons attracting the water
Has its outer electron further from the nucleus, so it is lost more easily
Has more outer electrons
Is denser than sodium

Q2. An element is in Group 6, Period 3. Its electron arrangement is:

2, 8, 6
2, 6, 8
6, 8, 2
2, 8, 8, 6

Q3. Which observation shows chlorine is more reactive than bromine?

Chlorine is a gas while bromine is a liquid
Chlorine displaces bromine from potassium bromide solution
Bromine is darker in colour
Chlorine has a lower boiling point

4 Short Answer Questions

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