C 2 STRUCTURE AND BONDING Atomic Structure Atoms

C 2 STRUCTURE AND BONDING

Atomic Structure Atoms are made of protons, neutrons and electrons. Protons and neutrons are found in the nucleus, and electrons in shells. Each one has a different charge: ■ Protons: + ■ Neutrons: 0 ■ Electrons: -

Using the Periodic Table ■ Each element on the periodic table will have two numbers on them. The on the bottom will be the atomic number. This tell you the number of protons the element has, which also tells you the amount of electrons in an element with no charge as the number of protons is equal to the number of electrons. ■ The top number is the mass number. The mass number is equal to the amount of protons + neutrons, so to get the amount of neutrons, take away the atomic number from the mass number. ■ For example, fluorine has a mass number of 19 and an atomic number of 9. ■ We can see the amount of electrons and protons from the atomic number. The amount of neutrons will be 19. So, it has 9 protons, 9 electrons, and 10 neutrons. ■ You can also see how many rings an element will have in it's electronic structure by looking at the row it is in, and how many electrons it will have on the outer shell by looking at the group it is in. (Fluorine will have 2 rings, and 7 electrons on the outer shell).

Ionic Bonding ■ Ionic bonding - the transfer of electrons from a metal to a nonmetal resulting in the formation of - and + ions (charged atoms). It is shown using dot and cross diagrams. An example of this is aluminium oxide. ■ Positive ions are formed when a metal loses electrons, and negative ions are formed when a non-metal gains electrons. This is because electrons have a negative charge.

Ionic Compounds Properties: ■ High melting and boiling point because it has an electrostatic force which is very strong throughout the lattice which means lots of energy is needed to break it. ■ Only conducts electricity in a solution or melted (molten) because the electrostatic force is then weakened and the ions are free to move.

Covalent Bonding - bonding between two non metals. Involves the sharing of at least one pair of electrons. An example of a covalent substance is water, H 2 O

Covalent Compounds Properties: ■ Low melting point because of intermolecular forces which are weak (this is NOT the covalent bond) so only a little bit of energy is needed to break it. ■ They can't conduct electricity as there are no ions in covalent bonding. This means there are no free electrons to carry electricity.

Metallic Bonding Properties: ■ High melting and boiling points because of strong electrostatic attraction between free delocalised electrons (-) and metal ions (+). Lots of energy is needed to break it. ■ Good conductors because of the free electrons. They can move around and carry heat and electricity. ■ Malleable (bendy) because the electrons get in the way. The layers slide over each other without getting too close to each other. No bonds are broken.

Alloys ■ Metals can be mixed with other metals (and sometimes non-metals) to form alloys e. g. pure iron + small amounts of C 02 and nickel = stainless steel. ■ Smart alloys are alloys that can return to their original shape because they have shape memory. ■ Alloys are stronger and more corrosion resistant. They are less malleable. This is because foreign atoms are different sizes so the layers of metal can't slip over each other.

Giant Covalent Structure - Diamond: ■ Strong covalent bonds. ■ Each C atom is covalently bonded with 4 bonds (4 other carbon atoms). ■ Chemically unreactive. ■ Hard, atoms can't slide over each other. ■ Can't conduct electricity as no free electrons.

Giant Covalent Structure - Graphite: ■ Contains layers of atoms which can slide (slippery). ■ Hexagonal shape ■ Each C has 3 covalent bonds which lead to delocalised electrons which carry a charge therefore can conduct electricity. ■ Weak intermolecular bonds between layers.

Giant Covalent Structure Fullerenes: ■ Lots of C atoms join to form odd shapes, each C has 3 bonds. ■ Discovered in 1985 ■ Used for drug delivery in the human body, engine lubricants, catalysts, nanotubes for strengthening tennis rackets.