Chemistry c4

All elements give off light when heated although sometimes this light is not visible to the human eye.

When elements are heated they emit coloured flames.Some elements emit distinctive flame colours e.g lithium salts produce a red flame.

A prism or diffractionn grating can be used to split this light to form a line spectrum,which is unique to each element.This technique is known as spectroscopy and has been used to discover elements such as Helium.

Scientists used the spectra as evidence that electrons in atoms are arranged in a definite way at partiular energy levels.

Atoms:

• have a tiny nucleus which contains Protons and Neutrons ( also known as nucleons)
• have electrons which orbit around the outside of the nucleus arranged in shells ( energy levels)

The closer the electron shell is to the nucleus the lower the energy level.

The first shell arranged around the nucleus can only hold two electrons the other shells after that can hold 8 electrons.

The nucleus is the centre of mass of an atom and has a positive charge.

The overall charge of the atom is neutral as the proton ( + ) and electron ( - ) cancel eachother out.

The metals are located on the left hand side all the others are non-metals.

Ther periodic table is split into groups along the top from 1-8(0) and into periods going down from 1-7.

The Group number tells you how many electrons there are in the outer shell

The Period number tells you how many shells the element has

When looking at the individual elements : 

• top number = relative atomic mass ( which is the total number of protons and neutrons in the nucleus)
• Bottom number = atomic (proton) number ( which determines the number of protons and electrons).

Number of Protons + number of neutrons = relative atomic mass

Number of protons = number of protons

relative atomic mass - proton number = number of neutrons

Properties e.g melting points, change across a period.these changes are called  trends.

Elements in group 0 have full electron shells and are inert ( they are very unreactive)

Group 1 - The alkali metals

Group 2 - The alkaline earth metals

Group between 2 and 3 - The transition metals

Group 7 - Halogens

Group 0 - The noble gases ( Helium)

All elements in group 1 :

• are metals
• have one electron in their outer shell of their atoms
• soft ( easily cut with a knife)
• react with water ( the reaction gets more violent as you move down group 1)
• flammable
• their hydroxides are harmful and corrosive

The physical properties of Group 1 e.g melting point, boiling point and density show trends down the group.

Therefore when handling group 1 metals keep them away from water and naked flames.

During the reaction with water hydrogen gas is formed (which pops when lit) and makes a metal hydroxide which is an alkali ( turning the pH indicator blue ).

Metal + water ---> metal hydroxide + hydrogen

Sodium reacts vigorously with chlorine to give a yellow flame ; it makes a white solid ( sodium chloride).

the other group 1 metals react in a similar way , and the reactions are faster down the group.

Sodium + chlorine ---> sodium chloride

The state of Sodium is solid (s) at room temperature wheras chlorine is a gas (g).

group 7 element patterns :

• contain diatomic molecules ( meaning they have 2 atoms joined together in each molecule)e.g

  F₂ , Cl₂, Br₂ , I₂ , At₂ - elements going down order

• corrosive and toxic elements (so are kept in a fume cupboard)
• group 7 elemnts react with alkali metala and  with other metals such as iron to form metal halides.
• melting and boiling points increase down the group whilst reactivity decreases.
• All have 7 electorns in the outer shellwhen a more reactive halogen takes the place of a less reactive halogen in a compound it is called a displacement reaction.e.g. when chlorine water solution is added to bromide solution the chlorine displaces the orange-coloured bromine.For non-metals the smaller the atom (the fewer the electron shells) the more reactive the element is.

Ionic bonding is the complete transfer of electrons. Unstable atoms (atom's without a full outer shell) lose or gain electrons to complete their outer shell so they are stable.

• Ionic bonds form when a metal reacts with a non-metal.
• Metals form positive ions whilst non-metals form negative ions.
• Ionic binds are the electrostatic forces of attraction between oppisitely charged ions.
• They form Ionic compounds with charged ions which are arranged in a regular pattern called a giant ionic crystal lattice.

Properties

Solid ionic substances can't conduct electricity. However when dissolved in water or molten the ions seperate and are free to move.

If you place electrodes in the solution the negative ions are attracted to the positive electrode and the positive ions are attracted to the negative electode;conducting electricity.

Not all ionic substances are soluble ( but salt is !) therefore you can melt the substance so the ions are free to move ; conducting electricity.

Compounds of a group 1 element and a group 7 element e.g sodium chloride are solids with high melting points.