Atoms

Ionic Bonding

Ionic Bonding

Ionic bonding occurs between a metal and a non-metal. Metals lose electrons to become positively charged.

Ionic compounds form structures called giant lattices.

E.G. Sodium Chloride

Na has 1 electron in its outer shell Cl has 7 electrons in its outer shell. When an atom loses/gains an electron it becomes an ion (charged atom)

Na loses one electron , Cl gains one electron

Na forms an Na + ion

Cl forms a Cl- ion

NaCl

Properties

Ionic compounds are solid at room temperature because they are arranged in a giant lattice structure which is held together with strong electrostatic attraction. It takes a lot of energy to break the bonds so they have high melting point ( are solids)

Ionic compounds are brittle (they shatter break when they are hit)

Solid ionic compounds cannot conduct electricity unless they are molten or dissolved in water

Covalent Bonding

Covalent bonding occurs between non-metals only, the atoms share a pair of electrons so they can both have a full outer shell. Simple covalent molecules have a low boiling point this is because weak intermolecular forces hold together the molecules and they don’t require much energy to break. The covalent bonds that hold the atoms together is strong. They do not conduct electricity because they do not have any delocalised electrons.

Dot and cross diagrams are useful to show the bonding in simple molecules. However it only shows the electrons on the outer shell

Stick diagrams are easy to draw however they don’t show any electrons or the shape of the atoms

3D diagrams are difficult to draw and don’t show electrons however they do show the shape well

Giant covalent structures

Diamond

Each carbon atom is bonded to four other carbon atoms making diamond very hard. Large amounts of energy are needed to break the strong covalent bonds therefore it has a high melting point

Silicon dioxide

Silicon dioxide has a similar structure to diamond - there are four bonds for each silicon atom and 2 bonds for each oxygen has a high melting and boiling point

Graphite

Graphite is made up of layers of carbon arranged in hexagons. Each carbon is bonded to three other carbons and has a delocalised electron that is able to move around and carry charge. The layers of carbon can slide over each other easily as they are held together by weak intermolecular forces, this gives it a slippery texture

Metallic Bonding

Metallic bonding occurs between metals only. Metals are held together by strong electrostatic attraction between positive metal ions and negative delocalised electrons that came from the outer shell.

Metals can conduct electricity because they have delocalised electrons that can carry charge. They have a high melting point as it takes a lot of energy to break the strong bonds.

Alloys

An alloy is a mixture of metals, however steel contains iron with amounts of carbon (a non metal)

Alloys are stronger than pure metals because they contain different sized particles that distort the layers so they cannot easily slide over each other

Polymers

Polymers can be made in nature or manmade (synthetic)

Each polymer molecule is made from a repeating unit : a monomer

Monomers are small molecules (not single atoms)

Catalysts speed up the reaction

Monomers in a polymer are joined by covalent bonds

Fullerenes

Fullerenes are spherical hollow shaped molecules of carbon. The structure is based on hexagonal rings of carbon atoms.

They can be used for drug delivery into the body.

Nanoscience

Nano means one billionth of a metre

1 nanometer (1nm) = 1*10^-9 m

They contain only a few hundred atoms

Nano particles are very small

Suncream contains nanoparticles of zinc oxide and titanium oxide, which absorb and reflect harmful UV rays from the sun

Plasters and bandages can contain nanocrystals of silver because it is toxic to bacteria. It can be woven into socks to kill the bacteria that makes socks smell.