Groups and Metals

They share chemical properties as they have 1 outer electron

• Low melting and boiling points
• Low density
• Very soft

They form ionic compounds, and you can test for them using flame tests

• They are very reactive and increase in reactivity as you go down the group - the outer electron is further away from the nucleus so can easily be lost

They react vigorously in water and form hydrogen gas and a metal hydroxide

The halogens are diatomic molecules as they exist by sharing one pair of electrons in a covalent bond

• As you go down group 7 the melting and boiling points increase

As you go down group 7 the reactivity decreases as it gets harder to attract electrons- the electron is further away from the nucleus

At room temperature:

• Chlorine is a poisonous green gas
• Bromine is a poisonous red-brown liquid that gives off an orange vapour
• Iodine is a dark grey crystal solid that gives off a purple vapour

Halogens react with alkali metals to form salts called metal halides

A more reactive halogen will displace a less reactive one

They are inert(unreactive) colourless, monatomic gases 

They are inert because they have no outer electrons, they can't give up or gain electrons

They are also non-flammable

Because they are colourless the gases are hard to observe

As you go down the group the boiling point, melting point, density all increase

They have typical metallic properties ao high melting points and density

Their metals and compounds make good catalysts for example iron

They also often have more than one ion like 2+ and 3+

The compounds are often very colourful

They are relatively unreactive but can from metal salts

You can test the reactivity of a metal by placing it in hydrochloric acid - the more reactive the more vigorous

metal + water --> metal hydroxide + hydrogen

Very reactive metals react vigorously - copper doesn't react at all

Reactivity series:

Potassium , sodium , calcium , magnesium , aluminium , zinc , iron , copper , silver

More reactive metals displace a less reactive metal

Carbon dioxide - 

Bubbling limewater through it and if there is carbon dioxide present the limewater will turn cloudy

Hydrogen - 

Hydrogen will make a squeaky pop with a lighted splint as it burns with oxygen

Oxygen - 

It will relight a glowing splint

Chlorine - 

If chlorine is present it will turn damp blue litmus paper white and possibly red for a moment

To test for metal ions you can use flame tests

Lithium - crimson red

Sodium - yellow

Potassium - lilac

Calcium - brick red

Copper - blue/green

Some form a coloured precipitate with sodium hydroxide

Calcium - white

Copper - Blue

Iron(ii) - green

Iron (iii) - brown

Zinc - White at first - redissolves and is colourless

To test for halide ions you can use silver nitrate solution -

Chloride - white precipitate

Bromide - cream precipitate

Iodide - yellow precipitate

To test for carbonate ions use barium chloride and hydrochloric acid - 

Add barium chloride and carbonates will produce a white precipitate 

Add HCL and if there are carbonates it will fizz and produce CO2

Test for sulfate ions using barium chloride solution - 

Add barium chloride and sulfate ions  will produce a white precipitate 

Add HCL and if t us sulfate it will not react

It means that you use machines instead of humans

They are sensitive, fast and accurate

Infrared spectroscopy - produces frequencies of infrared radiation that a molecule will transmit

Gas Chromatography - used to separate out mixtures and produces a chromatogram for each chemical

Mass Spectrometry - a technique that can be used to find the rfm of a mystery compound