8.1The Periodic Table

Arrangement of elements — Combined Science 0653 - Chemistry Revision Notes & Topical Questions

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📚 Combined Science 0653 - Chemistry Hub / Topical Revision

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8.1 Arrangement of elements — COMBINED SCIENCE (CHEMISTRY) notes: Describe the Periodic Table as periods and groups in order of atomic number and the trends from metallic to non-metallic character.Order — elements are arranged in order of increasing atomic number, each having one…

Hydrogen and helium
Period number
Group number
Group 0 / VIII
Ion charge
Same group

Section 1 of 10Layout of the Periodic Table

Layout of the Periodic Table

Order

Order elements are arranged in order of increasing atomic number, each having one proton more than the one before.

Groups

Groups vertical columns of elements with similar properties.

Periods

Periods horizontal rows.

Hydrogen and helium

Hydrogen and helium are in Period 1.

Section 2 of 10Periods

Period number

= number of occupied electron shells.
Period 2 elements have two shells and Period 3 elements have three.

Numbering

Numbering periods are numbered from 1 to 7 and the period number is not labelled on the table.

Section 3 of 10Groups

Groups

Group number

= number of outer-shell electrons for Groups I to VII.
Group IV atoms have four outer electrons and Group VI atoms have six.

Group 0 / VIII

Group 0 / VIII the noble gases have full outer shells.

Ion charge

Ion charge metals in Groups I and II lose 1 and 2 electrons,
forming 1+ and 2+ ions; non-metals in Groups VII and VI gain 1 and 2 electrons,
forming 1− and 2− ions.

Section 4 of 10Electronic configuration and position

Electronic configuration and position

Link

Link the number of numbers in the electronic configuration gives the period and the last number gives the group.
Chlorine is 2,8,7: Period 3, Group VII.

Same group

Same group atoms have the same number of outer electrons and so similar chemical properties.
Lithium 2,1, sodium 2,8,1 and potassium 2,8,8,1 are all Group I.

Section 5 of 10Metals and non-metals

Property	Metal	Non-metal
Position	Left of the table	Right of the table
Outer electrons	1-3 (more in Periods 5 and 6)	4-7
Bonding	Metallic	Covalent
Electrical conductivity	Good	Poor
Oxide	Basic	Acidic
Reaction with acids	Many react	Do not react
Physical	Malleable, high melting point	Brittle, low melting point

Metalloids
- elements between the two display some properties of both.

Section 6 of 10Trends across and down

Trends across and down

Across a period

Across a period metallic character decreases from left to right.

Down a group

Down a group metallic character increases.

Reason

Reason atoms more readily gain electrons to fill the outer shell towards the right and lose them towards the left.

Section 7 of 10Predicting properties

Use

Use patterns across groups and periods predict boiling point, melting point, density and reactivity.

Examples

Group I elements react quickly with water, noble gases are unreactive, reactivity decreases down Group VII and melting point decreases down Group I.

Section 8 of 10More from the specification

Observation

What is seen, heard, smelt or measured

Francium

The most reactive Group I metal, rare and radioactive.

Section 9 of 10Key terms

Term	Meaning
Period	Horizontal row of the Periodic Table.
Group	Vertical column of elements with similar properties.
Atomic number	Number of protons in an atom.
Metalloid	Element with properties of both metals and non-metals.
Outer electrons	Electrons in the outermost shell.
Noble gas	Group VIII element with full outer shell.

Section 10 of 10Exam technique

Saying the group number equals the number of shells — that is the period number.

Forgetting hydrogen and helium are in Period 1.

Saying metallic character increases across a period — it decreases.

Mixing up the oxidesmetals form basic oxides.

Last updated: 14 October 2026