8.1.2The Periodic Table
Periodic Trends — Combined Science 0653 - Chemistry Revision Notes & Topical Questions
5 min read 7 parts Lesson 3 of 8 Unit quiz
Part 1 of 5Metallic character in the Periodic Table
Across a period
- Across a period Metallic character decreases from left to right.
- Elements on the left are metals and those on the right are non-metals.
Down a group
- Down a group Metallic character increases as you go down, because outer electrons are further from the nucleus and are lost more easily.
Metalloids
- Metalloids Elements along the stepped dividing line,
- such as silicon, show some properties of both metals and non-metals and are called metalloids or semi-metals.
Part 2 of 5Metals and non-metals compared
| Property | Metals | Non-metals |
|---|---|---|
| Outer electrons | Usually 1 to 3 | Usually 4 to 7 |
| Bonding | Metallic | Covalent |
| Electrical conductivity | Good conductors | Poor conductors (graphite is an exception) |
| Oxides | Basic | Acidic |
| Reaction with dilute acids | Many react | Do not react |
| Physical form | Malleable; usually high melting and boiling points | Brittle solids or gases; usually low melting and boiling points |
Part 3 of 5Reading position from electronic configuration
1
Write the electronic configuration, showing how many electrons are in each shell, for example carbon is 2,4.
2
Count the numbers in the configuration. This is the number of occupied shells, and it equals the period.
3
Look at the last number. This is the number of outer-shell electrons, and it equals the group number for Groups I to VII.
4
A full outer shell (2 for helium, 8 for neon and argon) places the element in Group VIII or 0, the noble gases.
Part 4 of 5Worked examples
| Element | Configuration | Period | Group |
|---|---|---|---|
| Sodium | 2,8,1 | 3 | I |
| Carbon | 2,4 | 2 | IV |
| Chlorine | 2,8,7 | 3 | VII |
| Argon | 2,8,8 | 3 | VIII (0) |
Part 5 of 5Why groups share properties
1Same outer electrons
- Same outer electrons Elements in one group have the same number of electrons in their outer shell.
2Same reaction pattern
- Same reaction pattern Chemical reactions involve outer electrons, so these elements lose or gain them in similar ways.
3Similar properties
- Similar properties Group I metals all form 1+ ions and react with water; Group VII elements all form 1- ions.
4Gradual trends
- Gradual trends Properties change steadily down the group because the number of shells increases.
Key terms
| Term | Meaning |
|---|---|
| Period | A horizontal row of the Periodic Table; its number equals the number of occupied electron shells. |
| Group | A vertical column of the Periodic Table; for Groups I to VII it equals the number of outer electrons. |
| Metalloid | An element with some metal and some non-metal properties, found near the dividing line. |
| Electronic configuration | The arrangement of an atom's electrons in shells, for example 2,8,7. |
| Outer shell | The highest-energy occupied shell, which controls how an element reacts. |
Avoid these mistakes
1
Mixing up period and group
- the period is the number of shells (number of numbers in the configuration);
- the group is the outer electrons (last number).
2
Saying metallic character increases across a period. It decreases from left to right.
3
Claiming every non-metal is a poor conductor without noting graphite conducts electricity.
4
Writing the configuration as one number, such as 17 for chlorine, instead of 2,8,7.
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