C2 notes

Isotopes

• isotopes are different atomic forms of the same element, which have the same number of protons but a different number of neutrons

Ionic Bonding

• atoms lose or gain electrons to form charged particles which are then strongly attracted to one another
• all the atoms on the left hand side of the periodic table have just one or two electrons in their outer shell
• they like to lose them in order to have a full outer shell
• on the other side of the periodic table, the elements in group 6 and group 7 have outer shells which are nearly full
• they like to gain electrons to have a full outer shell
• they become ions if this happens and become attached to the atom that gave the electrons (because of the opposite charges)
• ionic compunds always have giant ionic lattices
• the ions form a closely packed regular lattice arrangement
• there are very strong electrostatic forces of attraction between oppositely charged ions, in all directions
• they all have high melting points and high boiling points due to the strong attraction between the ions
• it takes a large amount of energy to overcome this attraction
• when ionic compunds melt, the ions are free to move and they'll carry electric current
• they dissolve easily in water
• the ions separate and are all free to move in the solution, so they'll carry electric current

Ions

• ions have the electronic structure of a noble gas
• the elements that most readily form ions are those in groups 1,2,6 and 7
• group 1 and 2 elements are metals and they lose electrons to form positive ions
• group 6 and 7 elements are non-metals and gain electrons to form negative ions
• the charge on the positive ions is the same as the group number of the element
• only elements at oppostie sides of the periodic table will form ionic compounds, where one of them becomes a positive ion and one becomes a negative ion

Formulas of Ionic Compounds

• the overall charge of any compound is zero
• all the negative charges in the compound must balance all the positive charges

Electronic Structure of Ions

• use a big square bracket and a + or - to show the charge

Covalent bonding

• sharing electrons with other atoms
• only share electrons in their outer shells
• this way both atoms feel that they have a full outer shell
• each covalent bond provides one extra shared electron for each atom
• a covalent bond is a shared pair of electrons
• each atom involved has to make enough covalent bonds to fill up its outer shell

Covalent substances: Simple Molecular

• the atoms form very strong covalent bonds to form small molecules of several atoms
• the forces of attraction between these molecules are very weak
• this means that the melting and boliing points are very low because the molecules are easily parted from each other
• its the intermolecular forces that get broken not the much stronger covalent bonds
• most molecular substances are gases or liquids at room…