Science Revision cards

Electrons are not spread evenly around an atom but exist in layers called energy levels or shells. The arrangement of these electrons is called electron configuration.

An ion is an atom or group of atoms that have an electrical charge which can be either positive or negative. Atoms with incomplete outer shells are unstable. By either gaining or losing electrons, atoms can obtain full outer electron shells and become stable.

Metals form giant structures in which electrons can move freely in the outer shells of the metal atoms. The metallic bond is the force of attraction between these free electrons and metal ions. Metallic bonds are so strong, so metals can resist high temeperatures.

An ionic compound is a chemical compound in which ions are held together in a lattice structure by ionic bonds. Ionic compounds usually have a high melting point because of the force of electrical attraction between the ions requires a large amount of of energy to break the bonds apart. They can't  conduct electricity because there are no mobile ions or electrons in the lattice but they will conduct electricity if they are melted. They often have a high solubility in water. Depending on structure, they are either strong or brittle when they are hit, depending on which ions are in the lattice.

Nanoparticles are 1-100 nanometres across, which is how they get their name. They contain roughly a few hundred atoms, and also contain fullerenes. These are molecules of carbon, shaped like ahollow balls or closed tubes,which are arranged in hexagonal shapes/rings. different fullerenes also contain diferent numbers of carbon atoms. Nanoparticles are different from their 'bulk' chemical (their properties differ) it's made from. Fullerenes can be joined together to form nanotubes, tiny hollow carbon tubes, a few nanometres across. All the covalent bonds make carbon nanotubes very strong, so they require a large amount of energy to break apart. The hardest of which is the diamond.

Using nanoparticles is called nanoscience, and they are being used for all sorts of purposes:

• Because of their large surface area, they can help make new industrial catalysts.
• They can be used to make sensors to detect one type of molecule and nothing else. These are being used to test water purity.
• Nanotubes can be used to make stronger, lighter building materials.
• New cosmetics such as suncream aand deodorant have been made which don't leave white marks on the screen.