Electron structure

Question 1

What are shells?

Answer 1

• Shells are regarded as energy levels.
• Energy increases as shell number increases.
• Shell number or energy level number is called the PRINCIPLE QUANTUM NUMBER ‘n’.

Question 2

Atomic orbitals

Answer 2

• Shells are made up of atomic orbitals.
• An atomic orbital is a region around the nucleus that can hold up to two electrons, with opposite spins.
• There are diff. types of orbitals: s-,p-,d- and f-
• Each has diff. shape.
• Models show orbitals as a region in space where there is high probability of finding an electron.

Question 3

Types of sub-shells

Answer 3

s-orbital:

• Sphere shape
• No. of orbitals: 1
• Max no. of electrons: 2

p-orbital:

• Dumb-bell shape
• No. of orbitals: 3
• Max no. of electrons: 6

d-orbital:

• No. of orbitals: 5
• Max no. of electrons: 10

f-orbitals:

• No. of orbitals: 7
• Max no. of electrons: 14

Question 4

Rules for how orbitals are occupied by electrons

Answer 4

• Orbitals fill in order of increasing energy.
• Electrons pair with opposite spins:
  > Electrons can spin up or down and arrows show these.
  > 2 electrons in an orbital must have opp. spins.
  > Opposite spins counteract repulsion between the neg charges.
• Orbitals with the same energy (e.g p- or s-) are occupied singly firs before pairing:
  > Orbitals can’t be left empty.

Question 5

Electron configuration

Answer 5

• 4s sub shell FILLS before 3d sub shell.

- 4s sub shell also EMPTIES before 3d.