groups in the periodic table

the alkali metals

reactivity increases down the group due to shielding (the number of shells increases therefore the electrons get further away from the nucleus. this makes them easier to discharge.)

in order to gain a full outer shell, they loose an electron.

lithium + water : bubbles on the surface (effervesence)

sodium + water : turns into a molten ball and wizzes around on the surface

postassium + water : bursts into a lilac flame.

equation : alkali metal + water ---> metal hydroxide + hydrogen

stores in oil to prevent it from reacting with oxygen

the halogens

they are all diatomic molecules and are covalently bonded together.

melting/boiling point and density increase as you go down the group.

halogens react with metals to form salts

sodium chloride : (table salt)

sodium floride : (toothpaste)

sodium bromide : (disinfectant in pools)

sodium iodide : (prevents iron deficiency)

halogens react with hydrogen to form hydrogen halides, which dissolve in water to form acidic solutions.

reactivity decreases down the group.

the reactivity of the halogens decreases down the group.

the haolgens need to gain an electron, so this is when the reaction occurs. a bigger period number means more shells. when there are more shells,there is a weaker force of attraction so it is harder to gain an electron. this is known as shielding.

when a metal reacts with oxygen , you get a metal oxide.

oxidation is the loss of electrons

reduction is the gain of electrons.

properties:

inert (dont react)

colourless

low melting/boiling points

poor conductors of heat and electricity

helium : has a low density, so it can be used for airships, balloons and hot air balloons.

neon: when electricity is passed through it,it emits light. can be used for lighting.

argon: denser than air.used inbetween windows and in wine storage.prevents it from going off.

krypton: produces a very bright white light. can be used for camera flashes.

the noble gases all exist as single atoms as they dont need to bond to complete the outer shell.

melting/boiling point and density increase down the group.

the density increases down the group as there are more occupied shells,which means that there are more protons/neutrons..

the melting/boiling point increases down the group,because as you go down,the size of the element increases e.g helium is smaller than krypton,so you need to transfer less energy to make them change state.

the noble gases can radiate different colours, as shown by the absorbtion spectrum and emission spectrum.when the electrons move from shell to shell,they emit a certain colour.