CHEM1201 Lecture Notes - Lecture 3: Valence Electron, Alkali Metal, Noble Gas
7 Jun 2018
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Periodic table – simple configurations
- First period
o n = 1 can hold 2 electrons
o 2n2 true, ut an’t see it
- Second period
o n = 2 can hold 8 electrons
- Third period
o n = 3 can hold 8 electrons
- Fourth period
o n = 4 can hold 18 electrons
- Fifth period
o n = 5 can hold 18 electrons
E.g. lithium – three electrons – 2 1
Sodium – eleven electrons – 2 8 1
Potassium – nineteen electrons – 2 8 8 1
What do these configurations tell us?
Group 8A – Noble Gases
- helium – two electrons – 2
- neon – ten electrons – 2 8
- argon – eighteen electrons – 2 8 8
- krypton – thirty six electrons – 2 8 8 18
- xenon – fifty four electrons – 2 8 8 18 18
*all shells are filled, very stable (unreactive). Stability of a noble gas is related to its
electronic configuration
Group 1A Alkali metals
- lithium – three electrons – 2 1
- sodium – eleven electrons – 2 8 1
- potassium – nineteen electrons – 2 8 8 1
- rubidium – thirty seven electrons – 2 8 8 18 1
Simple electron configurations of ions:
- chlorine atom and chloride ion
o Cl – 17 electrons – 2 8 7
o Cl- - 18 electrons – 2 8 8
- Potassium atom and potassium ion
o K – 19 electrons – 2 8 8 1
o K+ - 18 electrons – 2 8 8
- Sulphur atom and sulphide ion
o S – 16 electrons – 2 8 6
o S2- - 18 electrons – 2 8 8
Valence electrons:
- Outer shell, these are the electrons that are gained or lost when forming ions
- Atoms in the same groups of the periodic table show the same valencies
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Document Summary
First period: n = 1 can hold 2 electrons, 2n2 (cid:894)true, (cid:271)ut (cid:272)an"t see it(cid:895) Second period: n = 2 can hold 8 electrons. Third period: n = 3 can hold 8 electrons. Fourth period: n = 4 can hold 18 electrons. Fifth period: n = 5 can hold 18 electrons. Sodium eleven electrons 2 8 1. Potassium nineteen electrons 2 8 8 1. Neon ten electrons 2 8. Argon eighteen electrons 2 8 8 krypton thirty six electrons 2 8 8 18 xenon fifty four electrons 2 8 8 18 18. Stability of a noble gas is related to its electronic configuration. Group 1a alkali metals lithium three electrons 2 1 sodium eleven electrons 2 8 1. Potassium nineteen electrons 2 8 8 1 rubidium thirty seven electrons 2 8 8 18 1. Simple electron configurations of ions: chlorine atom and chloride ion: cl 17 electrons 2 8 7, cl- - 18 electrons 2 8 8.
