MYP Chemistry: The Periodic Table & Trends — Frequently Asked Questions

You need four trends: atomic radius (decreases across a period, increases down a group), ionisation energy (increases across, decreases down), metallic character (decreases across, increases down) and reactivity (opposite patterns for metals versus non-metals). Each links back to electron configuration and nuclear charge — that's the explanation examiners actually want.

Atomic radius shrinks across a period because protons are added to the nucleus while electrons join the same energy level. The extra positive charge pulls the electron cloud in tighter — a stronger nuclear charge acting on roughly the same shielding, not a new shell being added.

Group 1 metals react by losing their outer electron — going down the group, that electron sits further from the nucleus and is easier to remove, so reactivity rises. Group 17 non-metals react by gaining an electron — going down, the nucleus attracts an incoming electron less strongly, so reactivity falls.

A group is a vertical column — elements in it share the same number of outer-shell electrons and similar chemical behaviour. A period is a horizontal row — elements across it have the same number of electron shells but an increasing number of outer electrons and protons.

This topic mainly falls under Criterion A: Knowing and Understanding, where you explain trends using scientific reasoning, and Criterion C: Processing and Evaluating if you're analysing data like ionisation energy tables. According to the IB, each MYP Sciences criterion is marked out of a maximum of 8, combining to a total out of 32.

Always link the trend to three things: number of shells, number of outer (valence) electrons, and effective nuclear charge. A strong Criterion A answer names the specific electrons involved — 'chlorine has 7 valence electrons in shell 3, pulled in by 17 protons' — rather than a vague 'more protons, smaller atom'.

The biggest one I see marking these tasks: students describe a trend ('radius decreases across a period') without explaining WHY, which caps you at the lower Criterion A bands. The second: mixing up 'shielding' with 'nuclear charge' — they're opposite forces, and examiners check you know which one is increasing.

A level 7-8 Criterion A answer explains trends with correct scientific terminology, links cause to effect explicitly, and applies the trend to an unfamiliar element or scenario rather than one you've memorised. Practising with elements outside the common examples — like explaining a trend for astatine or francium — is what separates level 5-6 from level 7-8.

Not conceptually hard, but it's a topic where marks are lost through weak explanation rather than wrong facts. Most MYP 4-5 students can recite the trends within a lesson; the challenge is writing a Criterion A response that reasons from electron configuration rather than just stating the pattern.

Periodic trends return in DP Chemistry's Structure 1 (Models of the Particulate Nature of Matter), where you'll need the same reasoning applied to more elements and quantitative data, including graphs of ionisation energy. According to the IB, first exams for the current DP Chemistry guide were 2025, and periodicity is assessed from the first year of the course.

Look for resources that make your child explain trends aloud or in writing, not just highlight a periodic table — that's where the real MYP marks sit. On RevisionPrep, the Chemistry Revision Notes cover each trend with worked reasoning, and the Topical Worksheets give practice questions marked against the actual Criterion A descriptors.