Group 1 (AQA GCSE Chemistry): Revision Notes
Group 1
What are Group 1 elements?
Group 1 elements are known as the alkali metals. These are the elements found in the first column of the periodic table. The main alkali metals you need to know are:
- Lithium (Li)
- Sodium (Na)
- Potassium (K)
- Rubidium (Rb)
- Caesium (Cs)
- Francium (Fr)
The term "alkali" comes from the Arabic word "al qali" meaning "from ashes" because early chemists obtained these metals from plant ashes. They're located in Group 1 because they all have the same number of outer electrons.
Properties of Group 1 elements
All alkali metals share similar properties because they have the same electronic structure in their outer shell. Here's what makes them special:
Physical properties
- They are all metals with a shiny appearance when freshly cut
- They have low density - the first three (lithium, sodium, potassium) actually float on water because they're less dense than water
- Melting and boiling points decrease as you go down the group (lithium has the highest, francium has the lowest)
Chemical properties
- They all form ions with a +1 charge when they react
- They react vigorously with water to make hydrogen gas and metal hydroxides
- They react with oxygen to form solid, white, ionic oxides
- They react with chlorine to form solid, white, ionic chlorides
All these similar properties occur because every Group 1 element has exactly one electron in its outer shell. This single outer electron determines how these metals behave in chemical reactions.
Reactivity patterns
Understanding why Group 1 elements react the way they do comes down to their electronic structure.
Electronic structure
Each Group 1 element has just one electron in its outer shell (highest energy level).
Electronic configurations for Group 1 elements:
- Lithium: 2,1
- Sodium: 2,8,1
- Potassium: 2,8,8,1
Notice how they all end in 1 - this represents the single outer electron that makes them so reactive.
Why reactivity increases down the group
When Group 1 elements react, they lose their outer electron to form a positive ion with a +1 charge. As you move down the group:
- The atoms get bigger
- The outer electron is further from the nucleus
- The outer electron is easier to remove
- Therefore, the element becomes more reactive
This means lithium is the least reactive and francium is the most reactive in Group 1.
Chemical reactions
Reactions with water
All Group 1 metals react with water to produce hydrogen gas and a metal hydroxide. The general pattern is:
General reaction pattern:
Worked Example: Sodium reacting with water
Word equation: sodium + water → sodium hydroxide + hydrogen
Chemical equation:
You can see hydrogen gas bubbling off and the solution becomes alkaline due to the sodium hydroxide formed.
Reactions with chlorine
Group 1 metals react with chlorine gas to form white, ionic compounds called chlorides:
For example: (sodium chloride)
Reactions with oxygen
These metals react with oxygen to form white, solid, ionic oxides. The more reactive metals lower down the group react more vigorously.
Safety Warning: Group 1 metals must be stored under oil to prevent them from reacting with oxygen and moisture in the air. The more reactive ones (like potassium) can even ignite spontaneously in air!
Key patterns to remember
- Reactivity increases as you go down Group 1
- All reactions follow predictable patterns because all Group 1 elements have one outer electron
- The products of reactions are always ionic compounds
- Reactions with water always produce hydrogen gas
Key Points to Remember:
- Group 1 elements are called alkali metals
- They all have one outer electron and form +1 ions
- Reactivity increases down the group because outer electrons become easier to lose
- They react with water to make hydrogen gas and hydroxides
- The first three alkali metals (Li, Na, K) float on water due to low density