1.4.1Principles of Chemistry: Part 1
Periodic Table: Basics — Edexcel International GCSE Science Double Award (Modular) - Chemistry Unit 1 Revision Notes & Topical Questions
10 min read 7 parts Lesson 12 of 23
Part 1 of 7Key ideas
1
Elements are arranged in order of increasing atomic number.
2
Group number = number of outer electrons (Group 0 has a full shell).
3
Period number = number of occupied shells.
4
Shell capacities for the first 20 elements
2, 8, 8, 2.
5
Metal oxides are basic; non-metal oxides are acidic.
6
Group 0 elements are unreactive because their outer shells are full.
7
Elements in the same group have similar chemical properties because they have the same number of outer electrons.
Part 2 of 7Learning objectives
1
Describe how the Periodic Table is arranged into groups and periods.
2
Deduce electronic configurations of the first 20 elements.
3
Classify elements as metals or non-metals using position, conductivity and oxides.
4
Explain how electronic configuration relates to chemical reactivity.
Part 3 of 7Essential knowledge
Essential knowledge
Periodic Table basics
Periodic Table basics elements are arranged in order of increasing atomic number. Vertical columns are groups (1–7 and 0) and horizontal rows are periods. The table shows repeating patterns of properties.
Electronic configurations
Electronic configurations electrons occupy shells around the nucleus. For the first 20 elements the shells hold 2, 8, 8 then 2. Sodium (11 electrons) is 2.8.1; chlorine (17) is 2.8.7; calcium (20) is 2.8.8.2.
The number of outer-shell electrons equals the group number, and the number of occupied shells equals the period number. For example, 2.8.6 is sulfur in Group 6, Period 3.
Classify metals and non-metals
Classify metals and non-metals metals are on the left and centre; non-metals are on the right. Metals conduct electricity, form positive ions and have basic oxides. Non-metals are usually poor conductors, form negative ions or covalent bonds, and have acidic oxides.
Electronic configuration and reactivity
Electronic configuration and reactivity elements in the same group have the same number of outer electrons and therefore react in similar ways. Group 1 metals lose one electron easily; Group 7 non-metals gain one electron.
Noble gases (Group 0) have full outer shells so they do not easily gain, lose or share electrons; they are inert and exist as single atoms.
Atoms react to achieve a stable, full outer shell
Atoms react to achieve a stable, full outer shell metals lose electrons, non-metals gain or share electrons. This link between structure and reactivity is why the Periodic Table can be used to predict properties of elements.
Configurations of ions
Write an ion's configuration from its new electron count. Na (2,8,1) loses one electron to give Na+ 2,8; Cl (2,8,7) gains one to give Cl− 2,8,8. The number of protons does not change.
Helium is an exception
Helium is in Group 0 but has only 2 outer electrons, because its single shell is full with 2. All other noble gases have 8 electrons in their outer shell.
Trends down a group
Elements in a group react similarly, but reactivity changes steadily. Group 1 metals become more reactive down the group, while Group 7 elements become less reactive down the group.
Metalloids
A zig-zag line separates metals (left) from non-metals (right). Elements next to the line, such as silicon, have some properties of each and are called metalloids or semi-metals.
Physical properties of metals and non-metals
Metals usually have high melting and boiling points and are solids at room temperature (mercury is liquid). Non-metals usually have low melting and boiling points and can be solid, liquid (bromine) or gas at room temperature.
Part 4 of 7Process & sequence
1
Find the atomic number: this equals the number of electrons in a neutral atom.
2
Fill the first shell with up to 2 electrons.
3
Fill the second shell with up to 8 electrons.
4
Fill the third shell with up to 8 electrons (for the first 20 elements).
5
Place any remaining electrons in the fourth shell.
6
Read the group from the outer-shell electrons and the period from the number of shells.
Working out an element's positionwrite these steps in this order; each step is a marking point.
1
Atomic number gives electrons
2
Fill shells 2, 8, 8, 2
3
Outer electrons give group
4
Shell count gives period
5
Predict metal or non-metal
Part 5 of 7Worked examples
12.8.3
Element X has atomic number 13. Give its electronic configuration, group, period and whether it is a metal.
- 13 electrons: 2.8.3.
- Three outer electrons, so Group 3; three shells, so Period 3.
- It is on the left of the dividing line, so it is a metal (aluminium).
2Explain why neon is unreactive but fluorine is very reactive.
- Neon is 2.8, a full outer shell, so it has no tendency to gain, lose or share electrons.
- Fluorine is 2.7;
- it needs only one more electron to fill its outer shell, so it readily gains an electron and reacts vigorously.
- Fluorine is 2.7;
Part 6 of 7Summary
1
The table is ordered by atomic number.
2
Group = outer electrons; period = number of shells.
3
Metals form positive ions and basic oxides.
4
Same outer electrons means similar reactions.
Part 7 of 7Compare: Compare
| Property | Metals | Non-metals |
|---|---|---|
| Position | Left and centre | Right (and hydrogen) |
| Electrical conductivity | Good conductors | Poor conductors (except graphite) |
| Ions formed | Positive (lose electrons) | Negative (gain electrons) |
| Oxides | Basic | Acidic |
| Appearance | Shiny, malleable, ductile | Dull, brittle when solid |
| Element | Atomic number | Configuration | Group / Period |
|---|---|---|---|
| Lithium | 3 | 2.1 | 1 / 2 |
| Oxygen | 8 | 2.6 | 6 / 2 |
| Sodium | 11 | 2.8.1 | 1 / 3 |
| Chlorine | 17 | 2.8.7 | 7 / 3 |
| Argon | 18 | 2.8.8 | 0 / 3 |
| Calcium | 20 | 2.8.8.2 | 2 / 4 |
Key terms
Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Periodic Table · Atomic number · Group · Period · Electronic configuration · Metal · Non-metal · Noble gas · Valence electrons
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.
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