Atomic orbitals, electronic configurations and the periodic table

Question 1

How can the discrete lines observed in atomic spectra can be explained

Answer 1

If electrons, like photons, also display the properties of both particles and waves.

Question 2

How do electrons behave in an atom ?

Answer 2

Electrons behave as standing (stationary) waves in an atom. These are waves that vibrate in time but do not move in space. There are different sizes and shapes of standing wave possible around the nucleus, known as orbitals. Orbitals can hold a maximum of two electrons.

Electrons within atoms have fixed amounts of energy called quanta

Question 3

What are the four quantum numbers ?

Answer 3

-The principal quantum number, n, indicates the main energy level for an electron and is related to the size of the orbital

-The angular momentum quantum number l determines the shape of the subshell and can have values from zero to n −1 (s, p, d, f)

-The magnetic quantum number ml determines the orientation of the orbital and can have values between−l and + l

-The spin magnetic quantum number ms determines the direction of spin and can have values of +1/2 or -1/2

Question 4

What is the Aufbau principle ?

Answer 4

Electrons fill orbitals in order of increasing energy

Question 5

What is Hund’s rule ?

Answer 5

When degenerate orbitals are available, electrons fill each singly, keeping their spins parallel before spin pairing starts

Question 6

What is the the Pauli exclusion principle

Answer 6

No two electrons in one atom can have the same set of four quantum numbers, therefore, no orbital can hold more than two electrons and these two electrons must have opposite spins

Question 7

When are electrons degenerate

Answer 7

In an isolated atom the orbitals within each subshell are degenerate (have equal energy)

Question 8

How are electron pairs arranged (in molecules) ?

Answer 8

Electron pairs are negatively charged and repel each other.

They are arranged to minimise repulsion and maximise separation.