Atoms and Elements !
Everything is made of atoms !
Atoms have a nucleus surrounded by electrons.
- it is in the middle of the atom
- it contains protons and neutrons
- protons are positively charged
- neutrons have no chjarge (they are neutral)
- so the nucleus has a positive charge overall because of the protons
- it is very samall compared to the rest of the atom.
- move around the nucleus
- they are negatively charged they are tiny but cove a lot of sapce
- they are found on the shells which are around the nueclues
- these shells explain the whole of chemistry !!!
Number of protons equals number of electrons:
- atoms have no charge overall
- the number of protons will always equal the number of electrons in an atom
- if some electrons are added or removed the atom becomes charged and is then an ion
Elements consists of one type of atom only :
- atoms can have different numbers of protons ,neutrons and electrons
- the number of protons decided what type of atom it is eg an atom with one proton will be hydrogen and a atom with 2 protons will be helium
- if a substance only contains one type of atom it is called an element
- there are 100 different elements
So all the atoms of a particular element (nitrogen) have the same number of protons
And differenet elements have differnt atoms with different numbers of protons.
Electron Shells !
Electron shell rules:
- electron are always found on the shells ( sometimes called energy levels )
- The lowest energy levels are always filled first- thses are the ones closets to the nucleus
- only a certain number of electrons are allowed on each shell 1st shell:2 2nd shell:8 3rd shell:8
- atoms are much happier when they have a full shell - like the noble gases
- in most atoms the outer shell is not full (so the atom is not happy ) and so the atom will want to react top fill it up
Atoms join togther to make compounds.
When different elements react atoms form chemical bonds with other atoms to form compounds.
Making bonds involves atoms giving away, taking or sharing electrons.
- happens between a metal and a non metal
- the metal atoms losse electrons to form positive ions and the the non metal atoms gain electrons to form negative ions.
- the opposite charges of ions means that they are strongly attracted to each other.
- happens between a non metal and a metal
- each atom shares an electron with another atom. each atom has to to make enough covalent bounds to fill up its outer shell.
The properties of a compound are very different from the properties of the original elements. eg if iron ( a lustrous magnmetic metal ) and sulfur ( a nice yellow powder ) react the compund formed ,iron sulfade, is a dull grey solid lump ,and doesnt behave anything like iron ot sulfuer.