Person Edexcel Chemistry O level

Unit 2chapter 11

Alkali metals

1.Lithium’(Li)

2.Sodium(Na)

3.Potassium(K)

4.Rubidium(Rb)

5.Caesium(Cs)

6.Francium(Fr)

Reactivity of alkali metals

increase down the group

Melting and boiling points of alkali meals

decrease down the group

Density of alkali metals

increase down the group

physical properties of alkali metals

1.melting and boiling point are decreased down the group

2.density increase down the group

3.reactivity increase down the group

4.Become softer as you move down the group , easily cut with a knife

5.shiny and silver when they are freshly cut or tarnish very quickly on exposure to air

6. Li , Na , K are less dense than water

7. there could be enough to react with sweat on your skin to give a reaction , producing lot of heat and a very corrosive metal hydroxide

Storage of alkali metals

1.Li, Na and K are stored under oil to stop react with oxygen and water

2.Rubidium and Caesium are very reactive so they have to be store in the sealed glass tube

How to handle to alkali metals

• touch these metals with bare fingers

Why do alkali metal have same chemical properties

Because they have the same electrons in their outer shells. Chemical properties depend on the number of electrons in their outer shell.

What substance formed when alkali metals react with water.

Form metal hydroxide with the formula MOH

What happened when they react with oxygen

Meta oxide will be formed with the formula M₂ O.

what happen when they react with halogens

formed compounds with the formula MX

Reaction of sodium with water

2Na_(s) +2H₂ O_(l) »»2NaOH_(aq) +H_2(g)

• sodium floats because is less dense than water

• sodium melts into a ball because its melting point is low and a lot of heat is produced by the reaction

• there is fizzing because hydrogen gas is produced

• sodium move around the surface of the water .Because the hydrogen is not given off symmetrically around the ball , the sodium is pushed around the surface of the water like a hovercraft

• the piece of sodium get smaller and eventually disappears ..The sodium is used up in the reaction

• if you test the solution that is formed with the universal indicator solution, the universal indicator goes blue. since the alkaline solution has been formed.(the metal hydroxide is alkaline)

Lithium with water

2Li(s)+2H2O(l)—→2LiOH(aq)+H2(l)

• reaction is very similar with sodium

• reaction is slower since lithium’s melting point is higher than sodium

• lithium doesn’t melt since heat is not produce so quickly

potassium with water

2K(s)+2H2O(l)—→2KOH(aq)+H2(g)

• reaction faster than sodium’s

• enough heat is produced to ignite the hydrogen which burn with a lilac flame

• end with potassium spitting around and exploding

reaction of rubidium and caesium

react even more violently than potassium and can be explosive. Rubidium hydroxide and caesium hydroxide will be formed.

reactivity of alkali meals

1. reactivity depend on how easily the outer electron of the metal is lost in each case

2. depend on how strongly it is attracted to the nucleus in the original atom(as we move down the group , the atoms have more shells of electrons and get bigger . As the atom get bigger , the outer electrons , which is the one lost in the reaction , is further from the nucleus .

Reaction of alkali metals with air

1. lithium burns with a red flame to form lithium oxide

2. sodium burns with a yellow flame to form sodium oxide

3. potassium burns with a lilac flame to form potassium hydroxide

4. 4M(s)+O2(g)—>2M2O(s)

Compound of the alkali metals

• Group 1 metal ions are colorless(means that they are white ions when are not combine with negative ions)

• Potassium dichromate(VI)is orange, since dichromate(VI) ion is orange and potassium manganate(VII)is purple because the manganate (VII)ion is purple.

Features of group 1 metals

1. are metals

2. are soft with melting points and density which are very low for metals

3. have to be stored out of contact with air or water

4. react rapidly with air to form coatings of the metal oxide

5. react with water to produce an alkaline solution of the metal hydroxide and hydrogen gas

6. increase in reactivity as you goes down the group

7. form compounds in which the metal has a 1+ ion

8. have mainly white/colorless compounds which dissolve to produce colorless solution

Properties of Francium

1. is very soft

2. will have a melting point around the room temperature

3. has density which is probably just over 2g/cm³

4. will be a silvery metal, but will tarnish almost instantly in air

5. will react violently with water to give francium hydroxide and hydrogen

6. will react violently with water to give francium hydroxide, with the formula FrOH ,which will be soluble in water and form strongly alkaline solution

7. will form compounds that are white/colorless and dissolves in water to give colorless solution