AeroLab Reading room

CHEM / AS level

Atomic structure and chemical bonding

Electron orbitals describe quantum states rather than planetary paths. Successive ionisation energies provide evidence for shells, while electron configurations explain periodic patterns.

Learning objectives

The big idea

Electron orbitals describe quantum states rather than planetary paths. Successive ionisation energies provide evidence for shells, while electron configurations explain periodic patterns.

Bond polarity depends on electronegativity, and molecular shape determines whether bond dipoles cancel. Electron-pair repulsion predicts shapes; intermolecular forces differ from the covalent bonds within molecules.

Worked example

What is the shape of methane around carbon?

Follow the solution

Four bonding pairs repel into a tetrahedral arrangement with angles near 109.5°.

Investigate and explain

Predict the worked result before calculating. Change one input, record the new result, and explain which assumptions still hold.

Related interactive model. Compare its assumptions with the explanation; it is not a complete syllabus lesson.

Open the interactive investigation

Check your understanding

1. What does first ionisation energy remove?

  1. One proton from each solid atom
  2. One electron from each gaseous atom
  3. All electrons at once
Check the answer and reasoning

One electron from each gaseous atom

The definition specifies gaseous atoms forming gaseous +1 ions per mole.

2. What is the shape of methane around carbon?

  1. Square planar
  2. Linear
  3. Tetrahedral
Check the answer and reasoning

Tetrahedral

Four bonding pairs repel into a tetrahedral arrangement with angles near 109.5°.

3. Is CO₂ necessarily polar because its bonds are polar?

  1. No
  2. Yes
  3. Only when liquid
Check the answer and reasoning

No

Its linear symmetric geometry makes the two bond dipoles cancel.