Where are the alkali metals? The elements in group 1, on the left of the periodic table, are called the alkali metals. Fr Cs Rb K Na Li lithium sodium potassium rubidium caesium francium These metals are all very reactive which makes them different from other metals

THE UNUSUAL PROPERTIES OF THE ALKALIS METALS 1. HOW ARE GROUP 1 METALS STORED? The alkali metals are so reactive that, as elements, they have to be stored in oil. This stops them reacting with oxygen in the air. Photo credit: Dr John Mileham

2. GROUP 1 METALS ARE ALL SOFT? Alkali metals are soft enough to be cut with a knife. They become softer as we go down the

3. SOME GROUP 1 METALS HAVE LOW DENSITY AND FLOAT ON WATER? Most common alkali metals, lithium, sodium and potassium, all float on water as they have low densities compared to other metals of the Periodic Table. What is the trend in density? The alkali metals generally become more dense going down the group, but the trend is not perfect because potassium is less dense than sodium. Element Density (g/dm3) 0.53 lithium sodium 0.97 potassium 0.86 rubidium 1.53 caesium 1.87 Water has a density of 1 g/dm3. Which elements in group 1 will float on water?

What is the trend in melting and boiling points? 4. GROUP 1 METALS HAVE LOW MELTING AND BOILING POINTS The melting and boiling points of group 1 metals are much lower than other metals What is the trend in melting and boiling points? The melting points and boiling points of alkali metals decrease going down the group. The melting and boiling points decreases as we go down the group.

Electron structure All alkali metals have 1 electron in their outer shell. This means that: lithium 2,1 They can easily obtain a full outer shell by losing 1 electron. sodium 2,8,1 They all lose their outer shell electron in reactions to form positive ions with a +1 charge. They have similar physical and chemical properties. potassium 2,8,8,1

The metal loses electrons from its outer shell to form a positive +1 ion i.e. Na Sodium ion (Na+) Sodium atom (Na)

REACTION OF GROUP 1 METALS WITH WATER All the alkali metals react vigorously with water. It is an exothermic reaction as it releases a lot of heat. The reaction produces hydrogen gas that ignites a lighted splint with a squeaky pop. When green universal indicator is added to the reaction mixture, it turns purple. This shows that the reaction produces a substance which is an alkalis Hence this is why they are know as alkalis metals

Lithium with water VIDEO

How does lithium react with water? From this video we can see that when lithium is added to water:- it fizzes It floats it moves around slowly across the surface of the water. It DOES NOT produce a flame NOTE: Lithium is the least reactive of the alkali metals.

The equation for this reaction is shown below: lithium + water  lithium + hydrogen hydroxide 2Li (s) + 2H2O (l)  2LiOH (aq) + H2 (g) REMEMBER/ Alkalis solutions contain OH- ions, hence it is the Lithium hydroxide which turns the indicator blue

Watch the video below to show how sodium reacts with water https://www.youtube.com/watch?v=ODf_sPexS2Q From this video we can see that when sodium is added to water:- it fizzes It floats it moves across the surface of the water quickly And it burns with a yellow/orange flame

The equation for this reaction is shown below: 2Na (s) + 2H2O (l)  2NaOH (aq) + H2 (g) sodium + water  sodium + hydrogen hydroxide Again it is the Sodium hydroxide which turns the indicator blue

Potassium with water VIDEO

From this video we can see that when potassium is added to water:- it fizzes It floats it moves across the surface of the water very quickly And it burns with a lilac flame

The equation for this reaction is shown below: 2K (s) + 2H2O (l)  2KOH (aq) + H2 (g) potassium + water  potassium + hydrogen hydroxide Again it is the Potassium hydroxide which turns the indicator blue

EXPLANING THE REACTIVITY OF GROUP 1 The reactivity of alkali metals increases down the group. As we go down the group the reactivity increases because: There are more electron shells therefore the radius of the atom is bigger So there will be less attraction between the outer shell electrons and the nucleus as the outer electron will be further away There is increased shielding of inner shells So it is because of this that the outer electron is more easily lost as you go down the group increase in reactivity lithium 2,1 Li + Na K sodium 2,8,1 increase in reactivity + increase in reactivity Rb Cs potassium 2,8,8,1 +

Electron structure and reactivity The reactivity of alkali metals increases down the group. What is the reason for this? The size of the element’s atoms, and the number of full electron shells, increases down the group. increase in reactivity Li Na This means that, down the group, the electron in the outer shell gets further away from the nucleus and is shielded by more electron shells. K Rb The further away an electron is from the positive attraction of the nucleus, the easier it can be lost in reactions. Cs This means that reactivity increases with the size of the atom.

FANTASTIC VIDEO ON THE REACTIONS OF ALL ALKALIS METALS INCLUDING RUBIDIUM AND CAESIUM https://www.youtube.com/watch?v=HvVUtpdK7xw