Lesson focus: An element’s position in the periodic tableA chart of all the elements in order of proton number, with elements that have similar properties in the same column (group). connects its atomic structure to patternSomething that happens again and again in results, such as "the hotter the water, the faster the sugar dissolves". in its properties.
Use atomic numberThe number of protons in an atom; each element has its own atomic number., groupA vertical column of the periodic table; elements in a group have the same number of outer-shell electrons, so they react in similar ways. and periodA horizontal row of the periodic table; elements in the same period have the same number of occupied electron shells. to locate elements and make cautious predictions about their properties.
Build on earlier learning
Metals and non-metalsThe previous lesson used physical evidence to classify metals and non-metals. This lesson adds periodic position and atomic structure as stronger organising evidence.
You will be successful when you can…
- Define atomic number, group and period.
- Locate an element from its symbol or atomic number.
- Link period number to occupied electron shells for the first three periods.
- Use group membership to make a justified prediction.
Words that carry the science
- periodic table
- A table of elements arranged by increasing atomic number so that repeating property patterns are visible.
- atomic number
- The number of protons in the nucleus of an atom.
- group
- A vertical column in the periodic table; main-group elements in one group have the same number of outer-shell electrons.
- period
- A horizontal row in the periodic table.
- outer shell
- The highest occupied electron shell in an atom.
- pattern
- A repeated relationship in observations or data that can support a prediction.
Read the periodic table as a map of atomic patterns
01Atomic number fixes the order
Every element has a unique atomic numberThe number of protons in an atom; each element has its own atomic number., equal to its number of protons. The modern periodic tableA chart of all the elements in order of proton number, with elements that have similar properties in the same column (group). places elements in increasing atomic-number order, reading from left to right and then continuing on the next row.
An element symbol is a precise shorthand: the first letter is uppercase and any second letter is lowercase. Co means cobalt; CO represents a compound containing carbon and oxygen.
02Groups reveal chemical families
A vertical column is a groupA vertical column of the periodic table; elements in a group have the same number of outer-shell electrons, so they react in similar ways.. Main-group elements in the same groupA vertical column of the periodic table; elements in a group have the same number of outer-shell electrons, so they react in similar ways. have the same number of electrons in their outer shellThe outermost layer of electrons in an atom., which helps explain why they undergo similar types of reaction.
Similarity does not mean identity. Properties such as reaction rate, melting point and density can change systematically down a group, so a prediction should state both the shared patternSomething that happens again and again in results, such as "the hotter the water, the faster the sugar dissolves". and any trend.
03Periods track occupied shells
A horizontal row is a periodA horizontal row of the periodic table; elements in the same period have the same number of occupied electron shells.. For the first 20 elements, period 1 atoms have one occupied electron shell, period 2 atoms have two and period 3 atoms have three.
Moving across a period increases atomic number one proton at a time. The outer-electron pattern changes, so properties gradually shift from metals on the left towards non-metals on the right.
The periodic table: groups and periods
Elements are arranged in order of atomic number. Columns are groups: elements in a group have similar properties. Rows are periods. Metals are on the left, non-metals on the right of the staircase line.
Blue: metals. Yellow: non-metals. Green: metalloids (in between). Tap an element to read about it.
Controls
The group number tells you the number of electrons in the outer shell (group 0: a full outer shell). The period number tells you the number of shells.
Locate an unfamiliar element
Element X has atomic number 12 and electron arrangement 2,8,2. Identify its period and group, then predict whether it is likely to be a metal.
- Atomic number 12 identifies the element as magnesium; atomic number is the proton number.
- Three occupied shells place magnesium in period 3.
- Two electrons in the outer shell place it in group 2 under the KS3 main-group numbering used here.
- Its position on the left of the table and membership of Group 2 support predicting metallic properties.
How to make the reasoning visible: X is magnesium, a period 3, Group 2 metal. Its position supports the prediction; the classification is not based on appearance alone.
Decode periodic-table evidence
Use the data for the first three periods. Electron arrangements are simplified shell totals suitable for these elements.
| Element | Atomic number | Electron arrangement | Position clue |
|---|---|---|---|
| Lithium (Li) | 3 | 2,1 | Period 2; Group 1 |
| Carbon (C) | 6 | 2,4 | Period 2; Group 4 |
| Neon (Ne) | 10 | 2,8 | Period 2; Group 0 |
| Sodium (Na) | 11 | 2,8,1 | Period 3; Group 1 |
| Chlorine (Cl) | 17 | 2,8,7 | Period 3; Group 7 |
Explain why lithium and sodium are expected to have similar chemical behaviour.
Compare carbon and chlorine using their positions. Include one similarity and two differences.
Check your understanding
Answer from memory, then check against the suggested answer.
What does atomic number tell us?
What is a group in the periodic table?
What is a period in the periodic table?
An element is in period 3 and Group 1. State its number of occupied shells and outer-shell electrons, then predict one broad property.
Calcium is below magnesium in Group 2. Explain what you can predict confidently and what would still need evidence.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Element A has electron arrangement 2,8,1. Element B has electron arrangement 2,1.
Give the period of each element and explain how you know.
(1)Which group are both elements in? Give the reason.
(1)What does this tell you about how A and B react? Will they react in exactly the same way?
(2)Total for this question: 4 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., translate each part of the electron arrangement into a position, then connect that position to a justified prediction.