Electronic configuration

1. Electronic configuration Review

2. The maximum number of electrons in shell in an atom is? 2n2 Shell number =1 so 2 electrons Shell number =2 so 8 electrons Shell number =3 so 18 electrons Shell number = 4 so 32 electrons

3. Lets look at some examples: Li – Atomic number of 3 We know the first shell can only have 2 electrons so this leaves 1 electron in the second shell. So electronic structure 2,1 K – Atomic number of 19 We know the first shell can only have 2 electrons in the first shell, so we need to place 17 electrons. The 2nd shell can contain 8 electrons, this leaves 9 electrons, 8 can go into the third shell and 1 in the 4th shell. So electronic structure 2,8,8,1

4. So if we look at Li we see that there is only 1 electron in the outer shell – Li is in group 1 • When we look at K we see that there is 4 shells – K is in period 4 This shows how the period relates to the number of shells that will be present for the element.

5. Shells and subshells • We have looked at shells. Within shells there are energy levels of similar energy called subshells; these are labelled s<p<d<f • S subshells contain 1 orbital • P subshells contain 3 orbitals • D subshells contain 5 orbitals • F subshells contain 7 orbitals

6. First shell contains one subshell -1s. This contains 1 orbital • Second shell contains two subshells the 2s and 2p subshells. The 2s subshell is the lower energy subshell and contains one 2s orbital. The 2p subshell contains three 2p orbitals • Third shell contains three subshells the 3s, 3p and 3d subshells. The 3s subshell is the lowest energy subshell and contains one 3s orbitals. The 3p subshell contains three 3p-orbitals. The 3d-subshell has the highest energy and contains five 3d-orbitals

7. Na - Sodium Atomic Number = 11 so an uncharged sodium atom has 11 electrons Look at the group Na falls in 1s22s22p63s1 Look at the period Na falls in 3d 16 electrons 3p 3s 2p 8 electrons 2s 1s – 2 electrons

8. F - Fluorine Atomic Number = 9 so an uncharged sodium atom has 9 electrons Look at the group F falls in 1s22s22p5 Look at the period F falls in 3d 16 electrons 3p 3s 2p 8 electrons 2s 1s – 2 electrons

9. Let’s look at a transition element: Fe Atomic Number = 26 so an uncharged sodium atom has 26 electrons Number of shells =? 1s22s22p63s23p63d64s2 1st shell – 2 2nd shell – 8 3rd shell -18 4p 3d 4s 3p 16 electrons 3s 2p 8 electrons 2s 1s – 2 electrons

11. Order of energy levels in atoms can be remembered using this geometric pattern. 1s 2p 2s 3s 3p 3d 4s 4d 4p 5f 5d 5f 5p 5s 6s 6p 6d 7s 7p