What is an atom?
A tiny particle
What is an element?
A substance that contains all the same atoms
What is a compound?
A substance that contains 2 or more different elements, chemically joined together
What is a mixture?
A substance that contains 2 or more elements, not chemically joined together
What is a molecule ?
A group of atoms
Whats inside an atom?
- the middle of the atom is called the nucleas this is positively charged. its is small and heavy and make up of protons ans nutrons
- Tiny electrons orbit the nucleaus, they are negatively charged
Mendeleévs periodic table
- mendeleev first put the elements in order of mass number, today they are in order of atomic number
- he created rows so that elements that were alike could line up together
Reasons why his table still exists today
1. He left gas for elements that had not yet been dissovered
2. He changed the order round when similar elements did not line up
Groups and Periods
- a Group is a vertical colum of elements, elements in the same group have similar properties
- Periods are horizontal rows across the periodic table
The Alkali Metals ( Group 1 )
- Very low meting points
- As you go down the colum the metals become softer and easier to cut
- They also become more reactive as you go down
The Halogens ( Group 7 )
- Go round in pairs ( diatomic molecules )
- As you go down they turn from a gas to a solid and turn from a pale colour to a darker colour
The Noble Gases ( Group 8 )
- Very unreactive