Chemistry - topic 4

Chemistry - topic 4

1. Properties of metals

   • Metals: conducts electricity well. This makes them great fro making electrical wires. They're malleable so they can be bent or hammered into different shapes. This makes them handy for making into things like bridges.
     • Transition metals have similar properties: High melting points. Form very colourful compounds, they're responsible for e.g. hair dyes.
       • It's the structure of metals tht gives them their properties: Metals consist of a regular arrangement of atoms held together with metallic bonds. The metallic bonds give the metal a giant structure consisting of positive ions and free electrons. This is because metallic bonds allow outer electrons of each atom to become delocalised. This creates a sea of delocalised electrons e.g. the ability of electrons to move freely through the structure makes metals good conductors of electricty. Metals have high melting and bpiling points and are insoluble due to the giant metallic structure and strong bonds. They also allow the layers of atoms to slide over each other, allowing metals to be bent and shaped which makes metals malleable.

2. Group 1 - the Alkali metals

   • They're soft and can be cut with a knife. They have low melting points compared with other metals.
     • Group 1 elements react vigorously in water: When lithium, sodium and potassium are put in water, they react vigorously to form hydroxides. The reaction makes an alkaline solution. As you go down group 1, the lone electron is in a shell that's further from the nucleus. As they're further apart, the attraction between + charged and - charged electron decreases. This means the electron is easier to get rid of. That makes the elements further down group 1 more reactive. Lithium is least reactive while potassium is the most reactive.The elements in group 1 get more reactive as the atomic number increases.
       • Reactions with water: lithium = The lump of lithium moves slowly around the surface, fizzing until it disappears. The water ahs become alkaline so the indicator solution turns purple. Sodium = Sodium fizzes rapily and moves quickly around the surface and may ignite. Potassium = Potassium reacts vigorously, burns with a lilac flame and sometimes explodes.
   • The reaction of an alkali metal with ewater produces hydrogen which is what you can see fizzing. A lighted splint will indicate the hydrogen by making the notorious 'squeaky pop' as the H2 ignites. e.g. sodium = 2Na + 2H2O -> 2NaOH + H2

3. Group 7 - the Halogens

   • At room temperatire: Chlorine = fairly reactive, poisonous, dense green gas. Bromine = dense, poisonous, orange liquid. Iodine = dark grey crystalline solid.
     • The halogens react with metals to form metal halides e.g. 2Al + 3Cl2 -> 2AlCl3 (Aluminium chloride)
     • Halogens react with hydrogen to form hydrogen halides. Hydrogen halides are soluble and they dissolve in water to form acidic solutions. e.g. Cl2 + H2 -> 2HCl
   • More reactive halogens will displace less reactive ones: The higher up group 7 an element is, the more reactive it is. This is because the outer shell is nearer to the nucleus, so the pull from the positive nucleus is greater which attracts extra electrons more strongly. When halides dissolve in water, the halide ions are free to react. If a more reactive halogen reacts with a solution containing halide ions it will displace the less reactive halogen. This is called a displacement reaction. e.g. Cl2 + 2Kl -> I2 + 2KCl

4. Group 0 - the Noble gases

   • All elements in group 0 are colourless gases at room temperature. They're inert which means they don't react. They're non-flammable. These properties make the gases ahrd to observe so it took a long time for them to be discovered. e.g. Argon is used to provide an inert atmosphere in filament lamps. It is also used to protect metals that are being welded. The inert atmosphere stops the hot metal reacting with oxygen. e.g. Helium is used in airships and parry balloons. Helium has a lower density than air so it makes balloons float. The boiling points and densities of the noble gases increase as you move down the group.