Group 1 elements-lithium, sodium and potassium

Update: I've included the trends, physical and chemical properties of Group 1 elements as requested by someone. Some information taken from Edexcel Chem textbooks. :) 

Section 2: Chemistry of the elements

part b) Group 1 elements-lithium, sodium and potassium

2.6 describe the reactions of these elements with water and understand that the reactions provide a basis for their recognition as a family of elements

2.7 recall the relative reactivities of the elements in Group 1

Alkali metal	Hydroxide solution produced	Gas produced	Rate of gas produced
Lithium	Lithium hydroxide	Hydrogen	Fairly vigorous
Sodium	Sodium hydroxide	Hydrogen	Vigorous
Potassium	Potassium hydroxide	Hydrogen	Very vigorous
Rubidium	Rubidium hydroxide	Hydrogen	Explosive
Caesium	Caesium hydroxide	Hydrogen	Extremely explosive

As you can see, the reactions get more violent as you go down the group, telling you that the metals are more reactive down the group. 

Describe what happens when sodium is added to water:

When sodium is added to water, it reacts very quickly and vigorously. The reaction is exothermic and the heat produced melts the sodium. The molten sodium darts around the water surface and a yellow flame is seen. You may see a bit of fizzing/bubbling (effervescence) as hydrogen is evolved. 

Remember MM-FF. Melts, moves, floats, fizzes 
Li, Na and K are all less dense than water, hence they float on water. 

Write word equations to show the reactions of lithium, sodium and potassium with water:

Lithium + water à lithium hydroxide + hydrogen

Sodium + water à sodium hydroxide + hydrogen

Potassium + water à potassium hydroxide + hydrogen

So you see they all form hydroxides, and since all group 1 metal compounds are soluble it dissolves to form an alkali. (All alkalis are just soluble bases, but not all bases are alkalis, for example metal oxides are bases but not all of them are soluble to form alkalis.. e.g. Copper (II) oxide.)

If they ask you about what colour the solution will turn if universal indicator is added, it will turn blue or purple. This is because the solution is alkaline, and if they ask you to state what ion causes this, it’s the OH^- ion (hydroxide ion). They are called alkali metals for a reason!

2.8 explain the relative reactivities of the elements in Group 1 in terms of distance between the outer electrons and the nucleus. (single science)

As you go down the group the metals become more and more reactive. This is because their atoms get bigger, so the outer shell electrons are further away from the nucleus. So the electrostatic force between the nucleus and the outer shell electron (OSE) is weaker, hence it is easier to lose the OSE (alkali metals have only 1 OSE). The atoms want to lose the OSE to form full outer shells so they are more stable and unreactive after that. 

Also, you can think of how as the atoms get bigger, there are more electron shells in between the OSE and the nucleus. You can think of them as 'shields', so the force of the nucleus on the OSE is weaker the bigger the atom. 

The following is extra information someone has requested. 

Physical Properties

	Melting Point (°C)	Boiling Point (°C)	Density (g/cm3)
Lithium - Li	181	1342	0.53
Sodium - Na	98	883	0.97
Potassium - K	63	760	0.86
Rubidium - Rb	39	686	1.53
Caesium - Cs	29	669	1.88

• You will notice that the melting and boiling points of the elements are very low for metals, and decrease as you go down the group.
• Their densities tend to increase, but potassium has a lower density than sodium, so the densities don't increase that tidily. Lithium, sodium and potassium are all less dense than water, hence will float on it. 
• The metals are very soft and can be easily cut with a knife. They get softer as you go down the Group. They are shiny and silver when freshly cut, but tarnish within seconds on exposure to air. 

Storage and handling

All these metals are extremely reactive, and get more reactive as you go down the Group. They all react quickly with air to form oxides, and react between rapidly and violently with water to form strongly alkaline solutions of the metal hydroxides.

To prevent them from reacting with oxygen/water vapour in the air, lithium, sodium and potassium are stored under oil. Rubidium and caesium are so reactive that they have to be stored in sealed glass tubes to stop any possibility of oxygen getting to them. 

Great care must be taken not to touch any of these metals with bare fingers. There could be enough sweat on your skin to give a reaction producing lots of heat and a very corrosive metal hydroxide. 

Compounds of the alkali metals

All Group 1 metal ions are colourless. That means that their compounds will be colourless or white unless they are combined with a coloured negative ion. For instance,  Potassium dichromate (VI) is orange, because the dichromate (VI) ion is orange. Group 1 compounds are typical ionic solids and are mostly soluble in water.

Summary of the main features of the Group 1 elements:

Group 1 elements:

• are metals
• are soft with melting points and densities very low for metals
• have to be stored out of contact with air or water
• react rapidly with air to form coatings of the metal oxide
• react with water to produce an alkaline solution of the metal hydroxide and hydrogen gas
• increase in reactivity as you go down the Group
• form compounds in which the metal has a 1+ ion
• have mainly white compounds which dissolve to produce colourless solutions