Atomic Theory

What is the nucleus of an atom composed of?

Protons and neutrons.

In the modern atomic model, where are electrons found?

In orbitals — regions of high probability, not fixed paths.

Define wavelength

The distance between two successive peaks of a wave.

Define frequency

The number of wave cycles per second (s-1" or Hz).

What is a photon?

A packet of quantised light energy.

Arrange these in order of increasing energy: infrared, visible, UV, gamma.

Infrared < Visible < UV < Gamma.

Which has higher frequency: red light or blue light?

Blue light.

What does the principal quantum number (n) describe?

The energy level and size of the orbital.

What values can the angular momentum quantum number (f) take?

From 0 to (n -1).

What is the maximum number of electrons an orbital can hold?

2 electrons.

Which rule states that electrons fill orbitals of lowest energy first?

Aufbau principle.

Which rule states that degenerate orbitals are filled singly with parallel spins before pairing?

Hund's rule.

Which principle states that no two electrons can have the same set of four quantum numbers?

Pauli Exclusion Principle.

Which electrons are lost first when transition metals form ions: 4s or 3d?

4s electrons

Why do Cr and Cu not follow strict Aufbau order?

They gain extra stability from half filed (d5) or fully filled (d10) sub shells.

What is the shape and bond angle of BeCl, according to VSEPR?,

Linear, 180°.

Why are half-filled and fully filled subshells unusually stable?

They minimise electron repulsions and maximise exchange energy, giving lower total energy.

Define "degenerate orbitals" and give an example.

Orbitals with equal energy, e.g. px, py, pz in the p subshell.

An orbital has the quantum numbers n = 3, t = 1. What subshell is it?

3p.

How many orbitals are in the n = 3 shell in total?

3 squared = 9 orbitals (1 s + 3 p + 5 d).