MYP Chemistry: Ionic & Covalent Bonding (Intro)

Three things examiners actually check:

1. Can you draw a dot-and-cross diagram correctly (outer shell electrons only)?
2. Can you explain why the bond forms (achieving a full outer shell / stability)?
3. Can you predict a property from the structure, not just recall it?

Most MYP Chemistry courses build this under Criterion A (Knowing and Understanding) and Criterion C (Communicating), so accuracy of diagrams and correct scientific vocabulary both matter.

Worked example — sodium chloride (NaCl):

1. Sodium has 1 outer electron; draw it as a single dot.
2. Chlorine has 7 outer electrons; draw seven crosses in its outer shell.
3. Move sodium's dot into chlorine's outer shell — sodium now has an empty outer shell, chlorine has 8.
4. Enclose Na in brackets as Na⁺ (no electrons shown) and Cl in brackets as [Cl]⁻ with 8 electrons.

Quick tip: examiners deduct marks if you forget the square brackets and charges — the diagram alone isn't enough.

Worked example — water (H2O):

1. Oxygen has 6 outer electrons (dots); each hydrogen has 1 electron (crosses).
2. Each hydrogen shares its single electron with one of oxygen's electrons, forming two shared pairs.
3. Oxygen ends with 8 electrons around it (2 shared pairs + 2 lone pairs); each hydrogen ends with 2.

Common mistake: students forget oxygen's two lone (non-bonding) pairs — leaving them off costs marks under Criterion A.

Hydrogen and helium are the exception — they're stable with just 2 outer electrons, not 8. Students who quote 'octet rule' without checking for hydrogen usually lose a mark on unit tests.

The reasoning matters more than the fact itself. Ionic compounds need huge amounts of energy to break the strong electrostatic forces holding a giant ionic lattice together — that's why melting points are high. Covalent molecules only need to overcome weak intermolecular forces between molecules (not the strong covalent bonds within them) to melt or boil, which is why they melt at far lower temperatures.

According to the International Baccalaureate's MYP: Sciences guide, Criterion A commonly asks students to 'explain scientific knowledge' and 'apply scientific knowledge to solve problems' — for bonding, that means going beyond definitions to justify why a given property occurs.

Quick tip: if a question says 'explain why NaCl has a high melting point,' a description of the lattice structure alone won't score full marks — you need the reason (strong electrostatic forces requiring lots of energy to break).

In my experience marking unit tests, the second most common error is drawing correct dot-and-cross diagrams but then failing to state the charge or brackets for ions — an easy, avoidable mark loss under Criterion C for using correct scientific conventions.

A study routine that works:

1. Redraw 5 diagrams (2 ionic, 3 covalent) without looking at notes.
2. Cover the property column of a comparison table and try to predict it from structure alone.
3. Attempt one 'explain why' question and check it against mark scheme language.

revisionprep.com's Topical Worksheets for MYP Chemistry give short, focused bonding practice sets exactly for this kind of repetition.

For parents: a 15-minute daily worksheet habit over a week tends to fix bonding diagram mistakes faster than a single long revision session the night before a test.

According to the IB, the current DP Chemistry guide (first exams 2025) builds directly on structure-and-bonding foundations, expecting students to already be comfortable with ionic versus covalent distinctions before introducing quantitative bonding concepts like lattice enthalpy.

What usually helps: physical modelling (using beads or magnets to represent electron transfer/sharing) alongside written diagrams. Students who only read definitions tend to struggle more than those who physically build a model at least once.