AQA Additional Science C2.1 Structures & Bonding

In a nucleus of an atom:

- Electron (-1)

- Proton (+1)

- Neutron (0)

Number of protons in an atom is the atomic number

number of electrons = number of protons (hence atom's overall neutral charge)

Atoms arranged in the periodic table in order of atomic number

Electrons arranged around nucleus in shells (and energy levels)

Electrons in shells further away from nucleus have more energy than those closer

Energy levels can only hold a certain number of electrons (1st holds only 2)

Electronic structure is number of electrons written differently

i.e 2.6 is oxygen

Atoms with same number of electrons in outer shell belong to same group

Outer shell electrons determine the behaviour of the atom in a reaction

Atoms of 2 or more elements react = compound

Atom has full outer shell = unreactive (stable), like Noble gases

When they react, try and get a stable arrangement

 ---- achieved by : sharing electrons (covalent bonding)

                               transferring electrons (ionic bonding)

Atoms involved lose or gain electrons for stable structure

i.e sodium 2.8.1 loses electron, forms neon 2.8

This means more protons than electrons

------ means positive charge on atom, so sodium ion, Na+, with structure [2.8]+

dot and cross diagrams in square brackets to show ionic bonding

Ionic compounds formed when metals react with non-metals

ions held together by strong forces between oppositely charge ions = ionic bond

Regular structure of ions in giant structures - like tightly packed in a box

Non-metals react together = covalent bonding

Simple molecules formed when non-metals can't give away electrons in a reaction, so they share instead; held together by these sharing electrons (very strong)

Sometimes only the same amount of electrons are needed, but otherwise more atoms are involved in the reaction.

Covalent bonding represented like "Venn Diagrams"

Giant covalent structures have large numbers of atoms held together by networks of covalent bonds ( see Giant Covalent Substances)

Metal = giant lattice of metal atoms (or positive ions)

Outer electrons in each atom can move from one to the next

=====> forms a "sea" of delocalised electrons

Strong electrostatic attraction between electrons and positive ions, bonding them together.