C1 Fundamentals of Chemistry

The nuclear model of the atom has a nucleus, which contains protons (positive) and neutrons (neutral), surrounded by shells of electrons (negative).  

Atoms have no overall charge as the number of protons and electrons are equal; however when electrons are gained or lost the atom becomes charged - thus an ion.

An element consists of only one type of atom.  In an atom the number of protons determine what type of atom it is. 

The Periodic Table is laid out in columns which are called groups.  Every group has the same amount of electrons in their outer shells; so they have similar properties - thus react similarly to each other.

Group 0 contain all of the noble gases which are all stable due to full outer shells: so they're very unreactive.  

The top number (on an element) is the mass number - the sum of the protons and neutrons

The bottom number is the atomic number - the number of protons (equal to the number of electrons

When atoms form chemical bonds with other atoms (of different elements) they from compounds.

IONIC BONDING

A compound from a metal and non-metal has ions.  Metal atoms lose electrons: with this loss they have more protons than electrons so they become positively charged.  The non-metal atoms gain electrons (becoming negatively charged) so that they can become more stable and less reactive.  The oppisite charges between the metal and non-metal mean that they're strongly attracted to each other.  For instance NaCl 

COVALENT BONDING

A compound formed by two non-metals sharing electrons to fill up their outer shells. Since the two non-metals gain electrons they both become negatively charged.  For instance HCl