# Chemistry AS ES CI 2.4

• Created by: A.B.
• Created on: 19-02-14 10:14
• ES Electronic structure: sub-shells and orbitals CI 2.4
• Electrons exist in shells that are designated n = 1, n = 2, n = 3.
• The further away the shell is from the nucleus, the larger its 'n' number.
• These shells are sub-divided into sub-shells
• labelled s, p, d and f
• Each sub-shell is further divided into atomic orbitals
• Each orbital can hold a maximum of two electrons. These two electrons MUST have opposite (paired) spins
• Arrows in boxes are a good way of representing the filling up of orbitals by electrons
• Distribution of electrons in atomic orbitals
• first shell only has one sub shell: 's'
• second shell has two sub shells: 's' and 'p'
• third has three sub shells: 's', 'p' and 'd'
• fourth shell has 4 sub-shells: 's', 'p', 'd' and 'f'
• An 's' sub shell has 1 orbital holding a maximum of 2 electrons
• A 'p' sub-shell has 3 orbitals holding a maximum of 6 electrons
• A 'd' sub-shell has 5 orbitals holding a maximum of 10 electrons
• 1. The orbitals are filled in order of increasing energy.
• 2. Where there is more than one orbital at the same energy, the orbitals are first occupied singly by electrons. When each orbital is singly occupied, then electrons pair up in orbitals.
• 3. Electrons in singly occupied orbitals have parallel spins.
• 4. Electrons in doubly occupied orbitals have opposite spins.
• Representing electron distribution
• Each orbital can be represented by a box, and each electron as an arrow. The   electronic configurations for nitrogen and sodium can be represented as follows.
• Nitrogen
• Sodium
• Deducing electronic configurations
• 1. Find the atomic number, and therefore number of electrons
• 2. Work out how many in each shell
• 3. Then calculate the number in each sub-shell
• 's', 'p' and 'd' blocks
• Group 1 and 2 elements all have one or two electrons, respectively, in their outermost sub shell, which is an s orbital/. They are known as the s block elements
• Group 3, 4, 5, 6, 7 and 0 elements all have that number of electrons (0=8)
• Outermost electrons in 'p' orbitals. Known as the p block elements
• The first transition block elements have electrons which are filling the d sub-shell. Known as thee d block elements.
• Further transition metals have electrons which are filling the f sub shell. These are known as f block electrons.