chemistry aqa additional - key terms

atom

• very tiny
• made of protons, neutrons and electrons
• makes up everything in the universe
• not charged (if it is its called an ion)
• number of protons = number of electrons
• number of protons + number of neutrons = mass number
• most of the atom is empty space
• protons and neutrons are in the middle of the atom in the nucleus
• electrons are in shells around the nucleus

ion

• just a charged atom
• this usually happens when the atom is trying to bond to another atom
• the loss or gain of electrons makes it charged
• if it looses one electron it is +1 charged
• if it gains two electrons it is -2 charged
• because electrons are -1 charged

element

• elements consist of one type of atom only
• quite a lot of everyday substances are elements:
• copper
• aluminium
• iron
• oxygen
• nitrogen 

compound

• compounds are chemically bonded
• compounds are formed when two or more elements chemically react together
• its difficult to separate the two elements out again
• the properties of a compound are totally different from the properties of the original elements
• carbon + oxygen -> carbon dioxide
• hydrogen + oxygen -> hydrogen oxide (water)

isotope

• isotopes are the same element but with a different number of neutrons, thats it
• unfortunatly you have to learn the posh way of saying the same thing, which is:
• isotopes are different atomic forms of the same element, which have the same number of protons but a different number of neutrons
• if they have a different proton number they're a different element

will this be in your exam - isotope so...

carbon dating

• an isoptope of carbon is used for carbon dating
• carbon 12 has 6 protons, 6 electrons, 6 neutrons
• carbon 14 has 6 protons, 6 electrons, 8 neutrons
• when things die, c-14 is trapped inside the daed material, and it gradually decays into nitrogen
• so by mesuring the proportion of c-14 found in some old axe handle you can calculate how long ago it was living wood
• so you know how long ago it was cut down and made into the axe

mole

• the mole is simply the name given to a certain number
• just like a million is: 1 000 000
• a mole is: 602 300 000 000 000 000 000 000
• when you get precicly that number of atoms of carbon 12 it weighs exactly 12g
• iron has an Ar (mass number) of 56, so one mole of iron = 56g
• oxygen has an Ar of 16, so one mole of oxygen = 16g
• this means that 12g of carbon, or 56g of iron , or 16g of oxygen, all contain the same number of particles, namely one mole or 602 300 000 000 000 000 000 000 atoms
• number of moles=mass in g/Mr (or Ar)