1.3 Electron Configurations

trends in an electromagnetic spectrum

red → blue

increasing wavelength →

increasing energy →

increasing frequency →

how are emissions spectra produced?

by atoms emitting photons when electrons in excited states return to lower energy levels

what does the line emission spectrum of hydrogen provide evidence for?

evidence for the existence of electrons in discrete energy levels, which converge at higher energies

describe the emission spectrum of the hydrogen atom

• consists of discrete lines at specific wavelengths

• when excited electrons fall from higher to lower energy levels, the emit photons with energies equal to the difference between the energy levels

• since the energy levels are quantised, only certain wavelengths are emitted

• n=∞ is the convergence limit

• red - n=3 to n=2

• cyan - n=4 to n=2

• dark blue - n=5 to n=2

• violet - n=6 to n=2

probability with electrons

an electron can be considered to be a particle but also a wave or a wave packet

there is a probability associated with the location of the electron

what is an orbital?

an orbital is a region or volume in which there is a high probability of finding an electron. orbitals can hold up to two electrons of opposite spin (they repel less due to small attraction of their magnetic fields)

shapes of the main orbitals

s orbitals are spherical ◯

p orbitals are dumb-bell shaped ∞

there are also d and f orbitals

how are the main energy levels divided?

the main energy levels are divided into sub-levels of successfully higher energies.

a sub level contains a fixed number of the same type of atomic orbitals

• there is 1 orbital in an s sub-level

• there are 3 orbitals in a p sub-level

• there are 5 orbitals in a d sub-level

• there are 7 orbitals in an f sub-level

how many electrons can orbitals hold?

all orbitals of any type can hold up to 2 electrons

energy levels and their sub-levels

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

quantities of orbitals in each sub level

1 s-orbital in s-sub level e=2

3 p-orbitals in p-sub level e=6

5 d-orbitals in d-sub level e=10

7 f-orbitals in f-sub level e=14

Pauli’s exclusion principle

no 2 electrons can have the same 4 quantum numbers

(a full orbital must contain opposite spin electrons)

Alfbau’s principle

electrons will always enter the lowest available energy level

Hund’s rule

when in orbitals of equal energy, electrons will try to remain unpaired

show the condensed electron configuration for sodium

$$1s²2s²2p^6 3s^1$$

[Ne] $3s^1$

exceptions to Aufbau’s principle

• there are exceptions, particularly in the transition metals, because the $4s$ and $3d$ orbitals have very similiar energies

• k