C1- Fundamental Ideas

Atoms have a small NUCLEUS surrounded by ELECTRONS

THE NUCLEUS

1. It's in the middle of the atom.
2. It contains protons and neutrons.
3. Protons are positively charged.
4. Neutrons have no charge.
5. So the nucleus has a positive charge overall because of the protons.
6. It's tiny compared to the rest of the atom.

THE ELECTRONS

1. Move around the nucleus.
2. They're negatively charged.
3. They're tiny, but they cover a lot of space.
4. They occupy shells around the nucleus.

-Atoms have different numbers of protons, neutrons and electrons. It's the number of protons in the nucleus that decides what type of element it is.

-If a substance only contains one type of atom it is called an element.

-All the elements in the groups have the same number of electrons in their outer shell. 

-This is why elements in the same group have the same properties.

-All the elements in the periods have the same number of energy levels. 

-The elements in the final column (group 0) are the noble gase. They all have 8 electrons in their outer shell (apart from helium).This means that they're stable and unreactive.

RULES-

1. Electrons always occupy shells (sometimes called energy levels)
2. The lowest energy levels are always filled first-these are the ones closest to the nucleus.
3. Only a certain number of electrons are allowed in each shell: 2,8,8 
4. Atoms are much happier when they have full electron shells-like the noble gases in Group 0.
5. In the atoms the outer shell is not full and this makes the atom want to react to fill it.

When different elements react, atoms form chemical bonds with other atoms to form compunds.

-Making bonds involves atoms going away, taking or sharing electrons. (Only the elctrons are involved)

-The properties of a compound are totally different from the original elements.

-Compounds can be small molecules of water, or lattices like sodium chloride. 

MIXTURE -----heat----> COMPOUND

-A compound which is formed from a metal and a non-metal consists of ions. The metal atoms lose electrons to form positive ions and the non-metal atoms gain electrons to form negative ions. The opposite charges (postive and negative) of the ions mean they're strongly attracted to each other.

-A compound formed by non-metals consists of molecules. Each atom shares an electron with another atom - This is called a covalent bond. Each atom has to make enough covalent bonds to fill up its outer shell. 

Atoms are not lost or made in Chemical Reactions

MG+ 2HCL--->MGCL2+H2

2H2+O2--->2H20