C2.1/2.2 Structure and Bonding

Atoms gain or lose E- to gain a full outer shell. Ions have the electronic structure of a noble gas. They are now called ions. This occurs between a metal and a non-metal. They are held together by an electrostatic attraction. These forces act in a giant ionic lattice. If the ionic solid is dissolved in water then the ions separate and are free to carry a current.

Example: Sodium Chloride

Properties

• does not conduct electricity - ions held closely together and have no free electrons so can't carry a current
• high mpt. and bpt. - strong electrostatic attraction, takes a lot of energy to overcome

A molecule is when a group of atoms is joined together by sharing electrons called covalent bonds. This occurs between 2 non-metals. The covalent bonds have weak intermolecular forces.

Example: Water

Properties

• low mpt. and bpt. - weak intermolecular forces, not a lot of energy needed to overcome
• does not conduct electricity - no free electrons or ions to carry a current

The atoms in a giant covalent structure share electrons. It can also be called a macromolecular. The covalent bonds are very strong. This occurs between 2 non-metals.

Example: Diamond

Properties

• extremely high mpt. and bpt. - each carbon atom forms 4 strong covalent bonds, so it's difficult for the structure to move or slide, takes a lot of energy to overcome
• hardest substance known to man - forms 4 strong covalent bonds so structure is very hard to move/slide

This occurs just in metals. Metals lose their outer shell electrons into a sea of delocalised ions. This leaves positive metal ions and a sea delocalised. This creates a strong attraction between them.

Example: Sodium

Properties

• high mpt. and bpt. - strong bond which takes a lot of energy to overcome
• conducts electricity - contains free elctrons and free ions to carry a current

Pure Water (deionised) will not conduct electricity as there are only H2O molecules present. There are no free ions or free electrons to carry a current. Tap water contains dissolved ions such as calcium fluoride etc. It is these ions that carry a current not the water.

An ionic formula tells us the ratio of ions of metal to non-metal in a giant ionic lattice.

Ionic Compounds have no overall charge which means the total number of the +ve must equal the total number of -ve.

Example:

Na+ O2-

+ - - (not balanced)

Na+ Na+ O2-

+ + - - (balanced)

Diamond

• made up of carbon atoms
• carbon is in group 4
• 4e- in outer shell
• each carbon atom forms 4 strong covalent bonds to 4 different carbon atoms
• called a giant covalent structure or macromolecule

Graphite

• conducts electricity
• has layers
• one free electron per atom
• 3 covalent bonds
• held together by weak intermolecular forces
• soft

Silicon Dioxide

• 2 oxygen atoms for 1 silicon atom
• every silicon atom covalently bonded to 2 oxygens
• high mpt.

Fullerene

Uses

• for appliances such as catalytic methane activation to higher hydrocarbons (catalysts)
• drug delivery systems in the body
• lubricants

Properties

• 60 carbon atoms
• molecules are spherical
• made of balls, 'cages' or tubes of carbon atoms

Fullerenes are made from carbon atoms joined together to make balls, 'cages' or tubes of carbon atoms.

• Easy to Shape (Malleable) - same size atoms, layers side over each other, layers of metal ions, arranged in layers
• Good Thermal Conductor - has free electrons, unfilled outer shells, transfer energy, close arrangement, when heated electrons start to vibrate
• High Melting Point - strong electrostatic attraction between ions, takes a lot of energy to overcome, in giant metallic lattice
• Good Electrical Conductor - has free electrons to carry a current
• Shiny - when light shines on free electrons they vibrate and instead of energy springing from atom to atom it is reflected as visible light

Metals lose their outer shell electron into a sea of delocalised electrons.

An alloy is a metal mixed with another element.

Pure Iron - Strong(ish), Somewhat soft, Easily shaped, Ions same shape/size, So layers can slide.

Metal Alloy - Add different sized atoms, Disrupt layers, Don't slide easily, Now harder and stronger.

Shape memory alloys can be deformed/reshaped when below their transition temperature. If they are heated above their transition temperature they will return to their original shape. To change the transition temperature we change the composition of the alloy.

Thermosoftening Polymer

• Chains held together by weak IM forces
• As you heat the plastic, the IM forces break, chains now free to slide over each other
• Plastic can be reshaped

Thermosetting Plastic

• Covalent bonds are strong to plastic keeps its shape even when heated
• Microwavable plates, baby bottles and hospital equipment

Many ethene monomers have their double bonds broken and join together to form a long chain called a polymer.

LDPE (low density polyethene)
High Pressure and High Temperature needed to form it. Fast and Random polymerisation. Branched chains. Don't pack closely together. Weak IM Forces. Low Density. Uses include plastic bags.

HDPE (high density polyethene) 
50 degrees Celsius Catalyst and Only slightly raised pressure needed to form. More ordered polymerisation. Leads to straighter chains. Can pack closely together. High Density. Strong IM Forces. Stronger and Higher mpt. Uses include stronger packaging.

Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms.

Nanoparticles have a unique structure to the precise way the particles are arranged. They have a high surface area to volume ratio. Scientists have found that material behave very differently on a small scale, for example, gold on a nanoscale is red in colour.

Scientists are discovering that nanoparticles can make valuable contributions to real world applications such as computers, catalysts, sensors and constructive materials.