Unit 2: The Alkali Metals

What properties do the compounds of alkali metals share?

1. All group 1 metal ions are colorless so they are either colorless or white unless combined with a colored negative ion: a) Potassium dichromate (VI) is orange because the dichromate (VI) ion is orange b) The potassium magnate (VII) ion is purple 2. They are typically ionic solids (composed of positively and negatively charged ions) 3. They are mostly soluble in water

How does sodium react with water?

1. The sodium floats because it is less dense than water 2. The sodium melts into a ball because its melting point is low and a lot of heat is produced by the reaction 3. There is a fizzing because hydrogen gas is produced 4. The sodium moves around on the surface of the water Because the hydrogen isn't given off symmetrically around the ball, the sodium is pushed in the direction where less hydrogen evolved 5. The piece of sodium gets smaller and eventually disappears. The sodium is used up in the reaction 6. A white trail is formed of sodium hydroxide which dissolves in the water If you test the solution that is formed with a universal indicator solution, you will see that the universal indicator goes blue, indicating an alkaline solution has been formed

Why are the Group 1 elements grouped together?

1. They all have one electron in their outer shell: a) Lithium - 2, 1 b) Sodium - 2, 8, 1 c) Potassium - 2, 8, 8, 1 2. They have similar chemical properties due to the fact that they have the same number of electrons in their outer shell a) They all react with water to form a hydroxide with the formula MOH (e.g. LiOH, NaOH) and hydrogen b) They all react with oxygen to form an oxide with the formula M2O (e.g. Na2O, K2O) c) They react with halogens to form compounds with the formula MX (e.g. LiCl, KBr) d) They form ionic compounds which contain an M+ ion

How are the alkali metals stored and handled?

All of the alkali metals are extremely reactive and reactive and get more reactive as you go down the group They react quickly with oxygen to form oxides and react rapidly with water to form strongly alkaline solutions of metal hydroxides (which is why group 1 metals are known as the alkali metals) 1. Storing To stop them reacting with oxygen or water vapor in the air, lithium, sodium and potassium are stored under oil Rubidium and cesium are so reactive that they have to be stored in sealed glass tubes to stop any possible oxygen reaching them 2. Handling These metals should never be handled with direct contact to skin because there could be enough sweat on your skin to cause a reaction This would produce lots of heat and highly corrosive metal hydroxide

How to the alkali metals react with water? (general formula)

All the alkali metals react in the same way with water to produce a metal hydroxide and hydrogen: alkali metal + water -> alkali metal hydroxide +hydrogen 2M + 2H2O -> 2MOH + H2 The formula for the alkali metal hydroxide is MOH because the metal ion is positive and the hydroxide ion is negative (the metals lose electrons which are then gained by the water molecules producing hydroxide ions and hydrogen gas) The main difference in reactions with water as you go down the group is the metals become more reactive and the reactions occur more rapidly

Why does reactivity increase as you go down the Group 1 elements?

As you go down the group, the metals become more reactive In all these reactions, the metal atoms are losing elections and forming metal ions in a solution The differences between the reactions depend on how easily the outer electron of the metal is lost in each case: 1. The nucleus contains protons so it's positively charged and therefore attracts negative electrons 2. As we move down the group the atoms have more shells of electrons and get bigger: A sodium atom is bigger than a lithium atom 3. As atoms get bigger, the outer electron, which is the one lost in the reaction, is further from the nucleus 4. Since it is further from the nucleus, there is weaker electrostatic attraction between the outer electron and the protons so it is more easily lost

What are the main properties of group one elements?

As you go down the group: 1. They get softer, lower melting points and greater densities 2. React more rapidly with air to form coatings of the metal oxide 3. React more rapidly with water to produce and alkaline solution of the metal hydroxide and hydrogen gas 4. Increase in reactivity as you go down the group 5. Form compounds in which the metal has a 1+ ion 6. Have mainly white/colourless compounds which dissolve to produce colourless solutions

What is Francium

Francium is radioactive and one of its isotopes is produced during the radioactive decay of uranium-235 It is an extremely short lived isotope so scientist predict that there is only ever 20-30g of it present in the Earth's crust at a time and no one has ever seen a piece of it

What happens when you heat the alkali metals with a Bunsen burner?

If we heat each of the metals in the air using a Bunsen burner, we get a much more rapid and vigorous reaction so it is more difficult to see which metal is most reactive: 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 oxide The equation for these reactions is: 4M(s) + O2 (g) -> 2M2O (s) In each case the product formed is a white powder - the alkali metal oxide

How does lithium react in water?

Lithium has a similar reaction to sodium The differences are: 1. Lithium reacts more slowly than sodium since it is less reactive 2. It takes longer to disappear, fizzes and moves more slowly 2. Lithium's melting point is higher and the heat isn't produced so quickly so the lithium doesn't melt

How do the alkali metals react with air?

Lithium, sodium and potassium are all stored in oil because they react with air to form an oxide with the formula: M2O If we take a piece of sodium out of the oil, there will be a crust on the outside When the piece of sodium is cut, the fresh surface is shiny but it tarnished rapidly as it reacts with oxygen in the air If we do the same with a piece of lithium it tarnishes more slowly because lithium reacts more slowly than sodium A freshly cut piece of potassium tarnishes extremely rapidly, more quickly than sodium Metal peroxides (M2O2) and super peroxides (MO2) can also be formed Lithium can form a nitride (Li3N)

How does potassium react with water?

Potassium's reaction is similar to sodium's except: 1. It's more reactive so the reaction is faster: a) It moves around more quickly b) Fizzes more vigorously c) Disappears more quickly 2. Enough heat is produced to ignite the hydrogen which burns with a lilac flame The reaction often ends with the potassium spitting around and exploding

How can we predict the properties of Francium?

Since we know the properties of the other alkali metals we can predict Francium's properties We can predict that Francium: 1. Is very soft 2. Will have a melting point of room temperature (predicted using a graph of melting point plotting against atomic number for the different alkali metals) 3. Will have a density just over 2 g/cm3 4. Will be a silvery metal but tarnish almost instantly to form francium oxide 5. Will react violently with water to give francium hydroxide and hydrogen 6. The francium hydroxide will dissolve in water to give a strongly alkaline solution 7. Will form compounds that are white/colourless and will dissolve in water to form colourless solutions

What are the alkali metals?

The alkali metals are elements in group 1 of the periodic table: 1. Lithium 2. Sodium 3. Potassium 4. Rubidium 5. Caesium 6. Francium Special Properties: 1. Low melting point The melting and boiling points of the elements are very low for the alkali metals and get lower as you move down the group 2. Varying densities Their densities increase irregularly down the group. Lithium, sodium and potassium are all less dense than water, so will float on it 3. Soft to cut The metals are very soft and easily cut with a knife, becoming softer as you move down the group 4. Tarnish in air They are shiny and silver when freshly cut, but tarnish very quickly on exposure to air

How do rubidium and caesium react with water?

They react similarly to sodium except: 1. They react even more violently than potassium: a) Disappear and move more quickly b) Fizz more vigorously 2. The reaction can be explosive