Structure and Bonding

- partciles in a solid are packed closely together, vibrate around fixed positions

- particles in a liquid are also close toegher but they can slip and slide over each other

- particles in a gas have lots of space between them and move around randomly

- in melting and boiling, energy is transferred from surroundings to substance

- in freezing and condensing, enrgy is transferred from the substance to the surroundings

- elements can react together to form compounds by gaining or losing electrons or by sharing electrons

- the elements in gorup 1 react with group 7, as they react atoms of group 1 elements can each lose one electron to gain stable electronic structure of noble gas

- this electron can be given to an atom from group 7, which then also achieves the stable electronic structure of a noble gas

- ionic compounds are held together by strong forces of attraction between their oppositely charged ions

- besides the elements in group 1 and 7, other elements that can form ionic compounds include:

   those from group 2 (forming 2+ ions)

   and group 6 (forming 2- ions)

- takes alot of energy to break the many strong ionic bonds, operating in all directions, that hold a giant ionic lattice together

- ionic compounds have high melting points, they are all solids at room temperature

- ionic compounds will conduct electricity when molten or dissolved in wter, this is because their ions can then become mobiole and can carry charge through the liquid

- covalent bonds are formed when atoms of non-metals share pairs of electrons with each other 

- each shared pair of electrons is a covalent bond

- many substances containing covalent bonds consist of simple molecules but some have giant covalent structures

- substances made up of simple molecules have low melting and boiling points

- the forces between simple molecules are weak, these weak intermolecular forces explain why substances made up of simple molecules have low melting and boiling points

- simple molecules have no overall charge, so they can't carry electrical charge, therefore, substances made of simple molecules do not conduct electricity

- molecules are used to help understand bonding but each model has its limitations in representing reality

- some covalently-bonded substances have giant structures, these substances have very high melting and boiling points

- graphite contains giant layers of covalently bonded carbon atoms, however, there are no covalent bonds between the layers, meaning they can slide over each other, making graphite soft and slippery

- the carbon atoms in diamond have a rigid giant covalent structure, making it a very hard substance

- graphite can conduct electricity and thermal energy because of the delocalised electrons that can move along it's layers

- as well as diamond and graphite, carbon also exists as fullerenes, which can form alrge cage-like structures and tubes, based on hexagonal rings of carbon atoms

- the fullerenes are finding uses as a transport mechanism for drugs to specific sites in the body, as catalysts, and as reinforcement for composite materials

- graphene is a single layer of graphite and so is just one atom thick.

- its properties, such as excellent eletrical conductivity, will help create new developments in the electronics industry in the future

- the atoms in metals are closely packed together and arranged in regular layers

- you can think of metallic bonding as positively charged metal ions, which are held together by electrons from the outermost shell of each metal atom

- delocalised electrons are free to move throughout the giant metallic lattice

- metals can be bent and shaped because the layers of atoms (or positivley charges ions) in a giant metallic structure can slide over each other

- alloys are harder than pure metals because the regular layers in a pure metal are distorted by atoms of different sizes in an alloy

- delocalised electrons in metals enable electricity and thermal energy to be transferred through a metal easily

- nanoscience is the study of small particles that are between 1 and 100 nanometres in size

- nanoparticles may have properties different from those for the same materials in bulk, this arises because nanoparticles have a high surface area to volume ration with a high percentage of their atoms exposed at their surface

- nanoparticles may result in smaller quantities of materials, such as catalysts, being needed for industrial processes

- new developments in nannoparticulate materials are very exciting and could improve many aspects of modern life

- the increased use of nanoparticles needs more research into possible issues that might arise in terms of health and the environment