igcse - free- chemistry notes Atoms, Bonding and the Periodic Table

The group number is related to the number of electrons in the outer shell. e.g. (Mg) Magnesium, in group 'II', has two electrons in the outer shell
electrons are arranged in shells surrounding the nucleus, with the first shell containing 2 electrons and subsequently 8.

All atoms want a full outer shell of 8 electrons (like noble gasses)


Ionic Bonding:


Ions are formed by gaining or loosing electrons
is the transfer of electrons from one atom to another, giving the atom a positive of negative charge

The two atoms together have a neutral charge
It occurs mainly when metals bond with non-metals

Examples

Magnesium + Oxygen
Electron Configuration
Mg: 2 --> transfer two electrons from Mg to give both atoms a stable


electron configuration
O: 2,6

Properties of Ionic Compounds
solids at room temperature (strong bonds, opposite charges)
high melting and boiling point (lots of energy required to overcome strong bonds)
don't conduct electrivity in the solid state, since electrons can't move (can in the molten state)
form crystaline solids because of ionic lattice
dissolve readily in water, but not in molecular solvents
Covalent Bonding
occurs when non-metals bond.
They share electrons to get a noble gas structure
Example: Hydrochloric Acid (HCl)
both H and Cl need one electron.
They form a single covalent bond to get a full outer shell
Properties of Covalent Compounds
molecules have no charge
low melting and boiling points. (little attraction between molecules,)
dont attract electricity (don't have charged particles)
liquids of gasses at room temperature
dissolve readily in molecular solvents, but not in polar solvents like water
Isotopes
are atoms of the sama element with:
same number of protons
same number of electrons
different number of neutrons
Examples
126C (6 electrons, 6 protons, 6 neutrons[12-6])
and

146C (6 electrons, 6 protons, 8 neutrons [14-6])

note: top number is the atomic mass

Relative Atomic Mass

average mass of atombased on various isotopes present

Noble Gasses

unreative (inert)because of full outer shell of electrons