Electron configurations

A tiny **packet of light energy**; its energy is given by E = hf (higher frequency → more energy).

A **fixed, allowed energy** an electron can have in an atom; energy levels are **discrete (quantised)**.

Continuous = an **unbroken rainbow** (all wavelengths). Line = a few **discrete bright lines** on black, from an excited element.

An excited electron **falls** from a higher to a lower energy level, emitting a photon of fixed energy (one line per allowed jump).

That the electron's energy levels are **discrete (quantised)** — fixed lines mean only fixed energy gaps are allowed.

The spectral lines get **closer together** toward **high frequency/energy**, because the energy levels bunch up at higher n.

The **biggest energy gap** — an electron falling **to n = 1** (the ground state).

$c = \lambda f$ — speed of light = wavelength × frequency, so **high f means short λ**.

$E = hf$ — photon energy = Planck's constant × frequency (higher f → higher E).

**Radio < red < violet** in frequency, so radio is lowest energy and violet is highest.

The lines merge; the electron gains just enough energy to **leave the atom** — this gives the **ionisation energy**.

The major 'shell' of an atom (n = 1, 2, 3, …); higher n means **higher energy** and **further** from the nucleus.

A subdivision of a main level, labelled **s, p, d, f**, differing slightly in energy (s < p < d < f).

A region around the nucleus that can hold up to **2 electrons**.

A **sphere** centred on the nucleus.

A **dumbbell** — two lobes pointing in opposite directions through the nucleus.

s = **1**, p = **3**, d = **5**, f = **7** orbitals.

s = **2**, p = **6**, d = **10**, f = **14** (2 electrons per orbital).

**2n²** — so n = 1 → 2, n = 2 → 8, n = 3 → 18, n = 4 → 32.

**4s** fills first — it is slightly lower in energy than 3d.

Electrons occupy orbitals of a sublevel **singly** (parallel spins) before any pairing up.

**s < p < d < f** (s is lowest, f is highest).

**3s, 3p and 3d** (max 18 electrons).

Electrons fill the **lowest-energy** sub-shell available first (build up: 1s, 2s, 2p, 3s, …).

Each orbital holds **at most 2 electrons**, and they must have **opposite spins**.

Within a sub-shell, electrons occupy orbitals **singly with parallel spins** before any pairing occurs.

1s, 2s, 2p, 3s, 3p, **4s, 3d**, 4p — note **4s fills before 3d**.

**s = 2**, **p = 6**, **d = 10** (each orbital holds 2).

1s² 2s² 2p⁶ 3s² 3p⁴.

Replace the inner electrons with the **previous noble gas** in [ ], then list the outer electrons — e.g. Ca = [Ar] 4s².

Start from the atom and **remove electrons from the highest main shell (largest n) first** — for transition metals, **4s before 3d**.

**[Ar] 3d⁶** — the two **4s** electrons are removed first, not the 3d.

**Add** the gained electrons to the next available sub-shell — e.g. O²⁻ = 1s² 2s² 2p⁶.

A **half-full** 3d⁵ sub-shell is extra stable, so one 4s electron promotes to 3d.

A **full** 3d¹⁰ sub-shell is extra stable, so one 4s electron promotes to 3d.

The energy to remove one mole of electrons from one mole of **gaseous +1 ions**: X⁺(g) → X²⁺(g) + e⁻.

The electron leaves an **increasingly positive ion** — the same protons pull on **fewer electrons**, so each remaining electron is held more strongly.

The next electron is removed from a **new, inner main energy level (shell)** that is closer to the nucleus and less shielded — evidence for **electron shells**.

A change of **sub-shell** (e.g. p → s) within the same main shell — finer evidence for **sub-shells**.

Count the electrons removed **before the first big jump** — that equals the number of **outer electrons = the group** (for a main-group element).

**Group 1** — one easily-removed outer electron, then the big jump into the inner shell.

**Group 13** — three outer electrons leave before the inner shell is reached.

Because the values span a **huge range** (hundreds to hundreds of thousands of kJ mol⁻¹); **log₁₀(IE)** fits them all on one axis as steps.

The number of **outer electrons**, and so the **group** of a main-group element.

Between the **1st and 2nd** (1 → 8) and between the **10th and 11th** (8 → 2) — the two jumps reveal three shells.

The **position** — after how many electrons the jump falls. The electrons removed before it are the outer electrons.

The **gaseous** atoms / ions — each step is X^{n+}(g) → X^{(n+1)+}(g) + e⁻.