1.1.9

Ionization Energy

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Ionization Energy

We see trends in ionization energy across the periods and down the groups of the periodic table.

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Periodic trend

  • Ionization energy increases along a period.
    • This is because the electrostatic attraction of each electron to the nucleus increases.
    • The attraction increases because the proton number increases.
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Periodic example

  • In Period 3, chlorine has a greater nuclear charge than sulfur because it has a greater proton number.
  • So the electrostatic charge between electrons and the nucleus in chlorine will be greater.
    • So the ionization energy is greater.
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Group trend

  • Ionization energy decreases down a group.
    • This is because the outer electron is further from the nucleus down the group.
    • The electrostatic attraction of the outer electron to the nucleus decreases down the group.
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Group example

  • In Group 2, magnesium is below beryllium.
    • Magnesium fills up an extra electron shell than beryllium.
    • This means an electron is further from the nucleus in magnesium and so the electrostatic attraction is less.
      • So the ionization energy of magnesium is lower than beryllium.

Jump to other topics

1Structure - Models of the Particulate of Matter

2Structure - Models of Bonding & Structure

3Structure - Classification of Matter

3.1The Periodic Table: Classification of Elements

3.2Periodic Trends

3.3Group 1 Alkali Metals

3.4Halogens

3.5Noble gases, group 18

3.6Functional Groups: Classification of Organic

3.7Functional Group Chemistry

3.8Alkanes

3.9Alcohols

3.10Halogenoalkanes

4Reactivity - What Drives Chemical Reaction?

5Reactivity - How Much, How Fast & How Far?

6Reactivity - The Mechanisms of Chemical Change

7Measurement, Data Processing & Analysis

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