Periodicity of other elements
Introduced| English | Meaning |
|---|---|
| reactive metal/rɪˈæktɪv ˈmetl/ | reactive metal |
| displace/dɪˈspleɪs/ | To replace another element in a compound during a chemical reaction. |
| periodicity/ˌpɪərɪˌɒˈdɪsɪti/ | A repeating pattern in element properties across the periodic table. |
| ionisation energy/ˌaɪənaɪˈzeɪʃn ˈenədʒi/ | The energy required to remove an electron from a specified gaseous atom or ion, under the stated ionisation process. |
Patterns that repeat
- The same patterns work for any group or period.
- Knowing the trends lets you predict and deduce an element's behaviour.
- This is the real power of the Periodic Table — you can reason about elements you've never met.
The same periodic patterns apply to any group or period, not just Period 3.
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Periodicity is general — once you know the trends, they apply across the whole table.
Across a period, elements change from metallic to ______.
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Metallic character decreases across a period.
Electronegativity generally increases across a period.
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Greater nuclear charge attracts bonding electrons more strongly.
Predict from position
- From an element's position, you can predict its properties.
- A Group 1 element is a reactive metal 活泼金属 that forms a +1 ion.
- A Group 17 element is a reactive non-metal forming a −1 ion.
Period 3 elements show clear trends across the periodic table
Periodic trends
Step across Period 3 to see a property rise or fall, then repeat in the next period — that recurring pattern is periodicity.
From its position, what can you predict about a Group 1 element?
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Group 1 elements are reactive metals with one outer electron, forming +1 ions.
Deduce from properties
- You can also work backwards — from properties to position.
- From an unknown element's physical and chemical clues, deduce its likely group, period and identity.
- Predict: an element in Group 2, Period 4 (calcium) → a reactive metal that forms a Ca²⁺ ion and reacts with water.
- Deduce: an unknown element is a pale-yellow gas that forms a −1 ion and displaces 置换 bromine from KBr → it must be fluorine (Group 17, above chlorine).
Periodicity also lets you:
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Working backwards from physical and chemical properties, you can place an unknown element in the table.
Periodicity 周期性 is a repeating pattern
- Properties such as atomic radius and ionisation energy 电离能 repeat in a pattern each period.
- Atomic radius decreases across a period; first ionisation energy broadly increases.
- This repeating periodicity is what gives the Periodic Table its structure.
You've got it
- the same periodic patterns apply to every group and period
- predict properties from position (Group 1 → reactive metal, +1 ion; Group 17 → reactive non-metal, −1 ion)
- deduce an unknown element's position/identity from its properties (e.g. yellow gas, −1 ion, displaces Br → fluorine)