Periodic Trends (Cambridge (CIE) IGCSE Chemistry)
Revision Note
Written by: Alexandra Brennan
Reviewed by: Stewart Hird
The metallic character of elements
The metallic character of the elements decreases as you move across a period on the Periodic Table, from left to right, and it increases as you move down a Group
This trend occurs due to atoms more readily accepting electrons to fill their outer shells rather than losing them to have the previous, already full, electron shell as their outer shell
Metals occur on the left-hand side of the Periodic Table and non-metals on the right-hand side
Between the metals and the non-metals lie the elements which display some properties of both
These elements are referred to as metalloids or semi-metals
Properties of metals and non-metals
Property | Metal | Non-metal |
|---|---|---|
Electron arrangement | 1-3 outer shell electrons | 4-7 electrons in the outer shell |
Bonding | metallic | covalent |
Electrical conductivity | good conductors | poor conductors |
Type of oxide | basic oxide | acidic oxides |
Reaction with acids | many react with acids | do not react with acids |
Physical characteristics | malleable | brittle |
A zig-zag line in this diagram separates the metals on the left, from the non-metals on the right
Periodic trends & electronic Configuration
The electronic configuration is the arrangement of electrons into shells for an atom
E.g. the electronic configuration of carbon is 2,4
There is a link between the electronic configuration of the elements and their position on the Periodic Table
The number of notations in the electronic configuration will show the number of occupied shells of electrons the atom has, showing the period
The last notation shows the number of outer electrons the atom has, showing the group number
Example: Electronic configuration of chlorine:
The electronic configuration of chlorine as it should be written
Period: The red numbers at the bottom show the number of notations which is 3, showing that a chlorine atom has 3 shells of electrons.
Group: The final notation, which is 7 in the example, shows that a chlorine atom has 7 outer electrons and is in Group VII
The position of chlorine on the Periodic Table
Elements in the same group in the Periodic Table have similar chemical properties
When atoms collide and react, it is the outermost electrons that interact
The similarity in their chemical properties stems from having the same number of electrons in their outer shell
For example, both lithium and sodium are in Group 1 and can react with elements in Group 7 to form an ionic compound by reacting in a similar manner
As you look down a group, a full shell of electrons is added to each subsequent element
Lithium's electronic configuration: 2,1
Sodium's electronic configuration: 2,8,1
Potassium's electronic configuration: 2,8,8,1
Examiner Tips and Tricks
Electronic configurations can be shown with the numbers separated by commas or by full stops. In this course commas are used, but you will often see full stops used elsewhere. Both are accepted.
Predicting properties
Because there are patterns in the way the elements are arranged on the Periodic Table, there are also patterns and trends in the chemical behaviour of the elements and their physical properties
These trends in properties occur down groups and across the periods of the Periodic Table
As a result, we can use the Periodic Table to predict properties such as:
boiling point
melting point
density
reactivity
Some common properties / trends in properties include:
Group 1 elements react very quickly with water
Noble gases are unreactive
Transition elements are denser than Group 1 elements
Reactivity decreases going down Group 7
Melting point decreases going down Group 1
In this way the Periodic Table can be used to predict how a particular element will behave
Identifying Trends
Extended tier only
Using given information about elements, we can identify trends in properties
An example of when this might be used is to determine the trend in reactivity of Group 1 metals
The table below shows the reactions of the first three elements in Group 1 with water
Observations of lithium, sodium, and potassium with water
Element | Reaction | Observations |
|---|---|---|
Li | lithium + water → lithium hydroxide + hydrogen 2Li (s) + 2H2O (l) → 2LiOH (aq) + H2 (g) |
|
Na | sodium + water → sodium hydroxide + hydrogen 2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g) |
|
K | potassium + water → potassium hydroxide + hydrogen 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g) |
|
The observations show that reactivity of the Group 1 metals increases as you go down the group
Using this information we can predict the trend going further down Group 1 for the elements rubidium, caesium and francium
As the reactivity of alkali metals increases down the group, rubidium, caesium and francium will react more vigorously with air and water than lithium, sodium and potassium
Lithium will be the least reactive metal in the group at the top, and francium will be the most reactive at the bottom
Francium is rare and radioactive so is difficult to confirm predictions
Element | Observations |
|---|---|
Rb |
|
Cs |
|
Fr |
|
Examiner Tips and Tricks
For the extended course you may be asked to identify other trends in chemical or physical properties of Group 1 metals, given appropriate data.
Firstly, ensure that the metals and associated data are written in either descending or ascending order according the their position in the Group. Then look for general patterns in the data.
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