The nucleus contains protons and neutrons and has a positive charge.
The electrons move around the nucleus and are negatively charged.
Elements have different properties due to differences in Atomic structure.
Protons have a mass of 1 and have a positive charge.
Neutrons have a mass of 1 and have a neutral charge.
Electrons have no mass and have a positive charge.
Number of protons = electrons.
Each element has a different number of protons.
Different element = different number of protons
Atoms arent lost or made in a chemical reaction.
State symbols tell you what physical state its in.
(aq) dissolved in water
There has to be an equal number of each element on either side of the equations.
2Na (s) + 2H2O (l) = 2NaOH (aq) + H2 (g)
Some elements emit distinctive colours when heated.
Lithium- Red flame Sodium- Yellow/Orange flame Potassium- Lilac flame
Each element gives off a characteristic line spectrum. These colours and and line spectrum's help chemists identify a metal in a compound.
When heated, the electrons in an atom are excited and release energy as light. The wavelengths emitted can be recorded as a line spectrum.
Different elements emit different wavelengths of light due to each element having different electron arrangements.
Line spectrum's are used to identify elements and have identified new elements. Helium discovered by line spectrum of the sun and caesium and rubidium were discovered by line spectrum.
The Periodic Table
The periodic table puts elements with similar properties together.
Laid out in order of increasing proton number.
Metals- left Non-metals- right
Elements with similar properties form groups. If you know the properties of one element, you can predict the properties of the other elements in that group.
Rows are called periods which represents another full shell of electrons.
Relative atomic mass- total number of protons and neutrons in the nucleus.
Proton number- how many protons there are in the nucleus (so there is the same amount of electrons).
Electrons always occupy shells (energy levels) from the inside out. 1st shell- 2 2nd shell- 8 3rd shell- 8
Electrons are much happier when they have full electron shells.
If the outer shell of the atom is not full, the atom wants to react to make it full.
Electron configuration- the way the electrons are laid out in an atom.
E.g. Nitrogen has 7 protons...so must have 7 electrons
1st shell takes 2...
2nd shell takes up to 8...
Therefore the electron configuration for nitrogen must be 2.5.
Group 1- Alkali metals
All have ONE electron in their outer shell which makes them very reactive and gives them all similar properties.
They are all shiny when freshly cut, but all tarnish in moist air.
As you go down group 1:
- The atoms get more reactive as the outer electron is lost more easily as its further away from nucleus
- Higher density
- Lower melting and boiling points
A reaction with cold water produces hydrogen gas.
Li, Na and K react vigorously with water, moving around the water, fizzing which produces hydrogen gas. Potassium gets hot enough to ignite or a lit splint will indicate the presence of hydrogen with a squeaky pop. The reaction makes an alkaline solution- hydroxide of the metal forms.
Reactions with chlorine produces colourless crystalline salts.
Group 7- Halogens
Chlorine (kills bacteria used in bleach and swimming pools), Bromine and Iodine.They all have SEVEN electrons in their outer shell which makes them very reactive and gives them similar properties.
As you go down group 7:
- The atoms become less reactive as the extra electron is further from the nucleus and therefore gained less strongly.
- Higher melting and boiling points (least reactive has higher melting and boiling points).
Fluorine is a very reactive, poisonous yellow gas at room temp.
Chlorine is a fairly reactive, poisonous dense green gas at room temp.
Bromine is red-brown liquid at room temp.
Iodine is a dark grey crystalline solid at room temp or a purple vapour.
A displacement reaction is where a more reactive element pushes out a less reactive element from a compound. (Read page 17).
Hazard symbols (read page 18):
- Oxidising- produces oxygen which allows metals to burn more fiercely eg Liquid oxygen.
- Highly flamable eg Petrol.
- Toxic- can cause death by breathing in or swallowing eg Chlorine and Iodine.
- Harmful- not quite as dangerous eg copper sulfate and both of group 1 and 7.
- Irritant- can cause reddening or blistering to skin eg bleach.
- Corrosive- attacts and destroys living tissue eg concentrated sulfuric acid and liquid bromine.
Halogens are poisonous vapours
Group 1- very reactive- combust whenever, so are stored in oil.
Ionic bonding is transferring electrons. Atoms lose or gain electrons to from charged particles called ions which are strongly attracted to eachother due to + and - charges.
Groups 1 and 2 have just 1 or 2 electrons in their outer shell and are keen to get rid, groups 6 and 7 have a nearly full shell which makes them keen to gain an extra electon.
Group 1 (form positive ions) is most likely to react with group 7 (form negative ions).
Ions are charged particles that can be made from single atoms (eg Cl-) or groups of atoms (NO3-)
Solid ionic compounds form crystals which are made up of charged particles (ions).
Ions with opposite charges are strongly attracted to one another which form a regular lattice.
Very strong chemical bonds called ionic bonds which takes lots of energy to over come these forces so they have high melting and boiling points.
Ionic compounds conduct electricity when dissolved or molten.
When an ionic compound dissolves, the ions separate and are free to move in the solution. this means they are able to carry and electric current. The same thing happens when ionic compounds melt.
When ionic compounds are solids, the ions are not free to move, so an electric current cant pass through.
Ions and Formulas
The charges in an ionic compound add up to zero.
Positive ions Negative ions
Sodium Na+ Chloride Cl-
Potassium K+ Fluoride Fl-
Calcium Ca2+ Bromide Br-
Iron(II) Fe2+ Carbonate CO32-
Iron(III) Fe3+ Sulfate SO42-