chemistry

• at the centre of every atom is a nucleus.
• a nucleus contains protons and neutrons.
• atons contain equal numbers of positive protons and negative evectrons. (+1) (-1)
• neutrons have no charge.

• the atomic number is the number of protons in the nucleus.
• the mass number is the total number of protons and neutrons in the nucleus.
• the elements are arranged in order of increasing atomic number.
• a row = a period
• a clolumn = a group
• similar properties are found in the same group.
• relative atomic mass is used instead of atomic mass.

• the first shell can hold 2 electrons
• 2nd and 3rd shells can hold 8 electrons.
• the arrangement of electrons is called electronic configuration.
• the number of electrons in the outter shell of an atom is the same at he number of the group in the periodic table. (e.g. elements in group 4 will have 4 outer electrons)

ionic bonds

• an ion is an atom or a group of atoms with a positive or negative electric charge.
• Mg2+ are positively charged ions (if it has a positive power sige then it is positive)
• CL- are negatively charged )is it has a negative power sign then it is a negative charged ions
• ionic bonds share their shells. they will join together instead of giving up their outter most electrons

ionic compounds

• ions want to have a full outter most shell so they will share or give away their outter electrons. for example if the two atoms had the outter shells of 2.8.7 and 2.8.1 then the 2nd atom would give the first atom its last outer most shell so that they both have a full outer most shell.

• contain charged ions but do not conduct electricity unless they are molten or dissolve in water.
• have high melting and boiling points. (this is why they are solid at room temperature.
• ions in an ionic solid strongly attract eachother. the majority of the heat energy is used to sepperate the two ions.
• when melted ionic compound can conduct because the ions can move around freely.

• dissolves in water = soluble
• doesnt dissolve in water = insoluble
• rules -all nitrates are soluble
• precipitation reaction = when two solutions are mixed and a solid is formed.

• liquids that do not mix together are immiscible - e.g. oil and water
• mixtures of immiscible liquids can be separated with a separating funnel because of the separate layers
• liquids that do mix together are miscible - e.g. watre and ethanol
• mixtures of miscible liquids can be separated by fractional distillation - the liquid with the lowest boiling point will evaporate first. and can be condensed on its own,

• group 1 on periodic table (first coloumn) alkali metals - all solids at room temperature and have low melting points. they are sot enough to cut easily with a knife.
• they react with water and form alkaline solution of a metal hydroxide and hygrogen gas.
• the least reactive alkali metal is lithium
• pottasium reacts violently with water and the hydrogen catches fire and produces a lilac flame.
• the further down the group you go the more reactive they get.
• they react by losing one electron from outter shell
• the further the electrons are from the nucleus (more shells) this is why the reactivity increases as you go further down the group.

• they are in group 0 of the periodic table
• they already have full outter most shell
• non-flammable as they donot react easily (why they are used in fire extinguishing systems)