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A full outer shell of electrons
A ‘layer’ of electrons
An atom that has lost or gained electrons
Free to move around the system
Loss of electrons
Gain of electrons
The force between positive and negative charges
Free to move around the system
3D arrangement of atoms/ions
All atoms want a full outer shell of electrons. This is a stable state. They achieve this by forming chemical bonds with other atoms. (all need 8, except H & He that want 2).
You are only expected to be able to work with the first 20 atoms of the periodic table. An element’s group number tells you how many electrons are in its outer shell, and you can work out how many it needs to fill the shell.
Strong, electrostatic forces hold ions of opposing charges together.
The structure is described as an ionic lattice. The compounds have very high melting points because of this.
Oxidation is Loss, Reduction is Gain
Metals always form positive ions (oxidised/lose electrons).
A group 2 metal will form a 2+ ion (loses two electrons).
Non-metals form negative ions (reduced/gain electrons).
Non-metal atoms bond by sharing electrons to form a very strong covalent bond.
Both fluorine atoms originally have 7 electrons on their outer shell, so need one more each.
By sharing one electron each, they form a single covalent bond. Each atom now has a full outer shell (8 electrons).
Positive ions held together by a “sea of delocalised electrons” from the outer shells of the metal atoms.
The strong electrostatic forces between the ions and electrons mean metals have very high melting points.
The free electrons are able to move so metals are good conductors of electricity and heat.
Metals are malleable. This means the regular layers can slide over each other if they are hammered.
States of Matter
Ionic compounds have regular structures. They make giant ionic lattices of oppositely charged ions. These ions experience strong, electrostatic forces of attraction in all directions. This means they have high melting points, as high energy is needed to break the bonds.
Ionic compounds can conduct electricity when molten or dissolved in water, as the ions are free to move = charge can flow.
These have strong covalent bonds within the molecule, but weak intermolecular forces of attraction. This means they are either gas or liquid at room temperature.
They do not conduct electricity as there are no free electrons.
Metals & Alloys
Pure metals are too soft for many uses. An alloy is a mixture of a metal with another element(s), and these have more desirable properties. They have different properties to the metals that are in them.
Alloys are less malleable than pure metals as they have irregular layers, and so they cannot slide over each other as easily. The atoms are still held together by metallic bonding.
These compounds are solid at room temperature. All of the atoms in a giant covalent structure are held together by strong covalent bonds. These bonds have to be broken, by large amounts of energy, to melt or boil these substances.
Diamond is made up of carbon forming four covalent bonds.
Graphite is made of hexagonal rings of carbon, each atom forming three bonds. Each atom contributes an electron to the “sea of delocalised electrons”.
Polymers are large molecules, made of ‘repeating units’ called monomers. All atoms are bonded to other atoms, and they make a chain of strong covalent bonds.
The intermolecular forces are much weaker, and they chains can stretch and move over each other. There are many forces over the long chains, so polymers are solid at room temperature.
To increase the melting point, cross-links between chains can be added.
Weak forces hold the layers together, so they can slide over each other, thus making graphite a great lubricant.
Only 3 electrons from each carbon atom form strong covalent bonds, and one delocalised electron.
High melting point, and a good thermal/electrical conductor.
Graphene is just a single layer of graphite, and is one atom thick.
Fullerenes can be thought of as graphene sheets rolled into a ball, however graphene is made of 6 sided rings, and fullerenes are made of 5 and 6 sided rings.
Fullerenes can take the shapes of balls, or other shapes like tubes (nanotubes)
Every carbon atom is bonded to four others, and because of this it forms a 3D lattice, called a tetrahedron.
No free electrons exist in this structure, so it does not conduct electricity.
Diamonds are used as cutting tools.
They are not ‘shiny’, as they do not reflect light - they refract it.
Between 1 and 100 nm in size. Fullerenes and nanotubes are small enough to be nanoparticles.
· Silver - Clothes/deodorant as antibacterial
· Titanium dioxide - Sunscreens as anti-UV
· Medicine - Drugs designed to work on one type of cell only
Nanoparticles have a large surface area, because of how small their individual volumes are.
Last updated: 12/08/2017