2.2.1 Electron Structure

What does the Bohr model of the atom describe?

Electrons in fixed spherical shells (2,8,8) around the nucleus.

What is the limitation of the Bohr model?

It does not explain sub-shells or the shapes of orbitals.

What are the four sub-levels and their electron capacities?

s (2), p (6), d (10), f (14).

What is an orbital?

A region of space where there is a high probability of finding an electron.

How many electrons can each orbital hold?

2 electrons with opposite spins.

What is the shape of an s-orbital?

Spherical.

What is the shape of a p-orbital?

Dumbbell-shaped.

What is Hund’s rule?

Orbitals in the same sub-level are filled singly before pairing.

What is the order of filling orbitals up to 5p?

1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p.

Why does 4s fill before 3d?

Because the 4s sub-level is lower in energy than 3d.

Which electrons are lost first when transition metals form ions?

The 4s electrons.

How many orbitals are in the 2p sub-level?

3 orbitals (each holding 2 electrons).

How many orbitals are in the 3d sub-level?

5 orbitals (each holding 2 electrons).

What determines the block (s, p, d, f) of an element in the periodic table?

The type of orbital that the highest energy electron occupies.

Why are noble gases chemically unreactive?

They have a full outer electron shell (stable configuration).

Exam Q: Which sub-level is filled after the 5s orbital?

4d.

Exam Q: Why do electrons in the same orbital have opposite spins?

To reduce repulsion between them (Pauli exclusion principle).