- Created by: elle cooper
- Created on: 13-05-09 20:59
Sometimes atoms make up covalent bonds. These are strong bonds where electrons are shared. Covalent bonds form when the outer shells are lack electrons. A full outer shell has 8 electrons. Instaed of borrowing or losing electrons like ionic compounds the electrons are shared because the two atoms can need the same number of electrons for a full shell.
Eg. Hydogen need just one more elctron for a full shell. So two hydogen toms share their outer electron so that they each have a full shell. The outer shell only needs 1 more electron because Hydrogen has a a relative atomic mas of 1 and the first shell only needs two electrons to be full.
Crabon dioxide is a nother good example carbon has a relative atomic mass of 16 and oxygen has a relative atomic mass of 12. Carbon needs four more electrons to fill its outershell. Oxygen needs four. So two double covalent bonds are formed Carbon is in the cnter with an Oxygen atom on either side,
Chemicals in the Hydosphere
The hydrosphere is the oceans, seas, lakes, rivers, puddles and so on. You can guess that, because hydro means water.
It contains compounds that have dissolved in the water.Many of these compounds are ionic compounds called alts - that is why sea water is salty. Examples of salts are Sodium Chloride, Magnesium Chloride and Potassium Bromide.
Ionic compounds are made of charged particles called ions. Ions with opposite charges attract to each other very strongly, which make a giant lattice. a single crystal of salt is one giant ionic lattice which is why salt crystals tend to be a cuboid shape.
Ionic compounds have high melting and boiling points because the forces of attraction between the atoms are very strong. It takes a lot of energy to overcome the forces hence their high boiling and melting points.
They can conduct electricity when dissolved or molten because the ions separate which makes them able to carry an electric current.
Chemicals in the Atmosphere
The atmosphere is mostly made up of which element? No it is not oxygen , which it is mostly mistaken as. It is Nitrogen, Nitrogen makes up 78% of the Earth's atmosphere Oxygen come second with 21% and in third place it is Argon with 0.9%. Carbon is a mere 0.03%, water vapour is present but that can very from time to time.
Molecular Substances such as Carbon Dioxide and Water have low melting and boiling points because of their intermolecular bonds, which are weak. Intermolecular bonds are bonds in between each molecule not between atoms. Don't get the two mixed up! The bonds between these atoms in the molecule are very strong. A molecule with these properties is a COVALENT bond.
You need a little energy to overcome the weak intermolecular bonds, hence the low melting and boiling points.
This means they are usually gases or liquids at room temperature.
Pure molecular substances don't conduct electricity because their molecules aren't charged like ions in an IONIC bond.
Chemicals in The Lithosphere
The lithosphere is the Earth's rigid outer layer - the crust and part of the mantle.
It is made up of minerals often containing Silicon, Oxygen and Aluminium.
Most of the Silicon and Oxygen in the Earth's crust exists as the compound Silicon Dioxide aka silica. Different types of rock i. e limestone ;contains a lot of Calcium, whereas sandstone contains a lot of Silicon.
Giant covalent structures like Silicon Dioxide contain no charged ions. All the atoms are bonded to each other with strong covalent bonds giving them a rigid structure , which makes the substance hard. They have a high melting and boiling point contrary to most covalent bonds and they are solids.
Chemicals in the Biosphere
the biosphere is everything that lives.
All living things are formed from compounds made up of basic elements. The main elements are Carbon, Hydrogen, Oxygen and Nitrogen along with small amounts of Phosphorous and Sulfur. These make up molecule vital for life such as DNA, proteins, carbohydrates.
DNA - contains Phosphorous and Nitrogen
Proteins - contain Nitrogen and sometimes Sulfur
Carbohydartes - contain Carbon and Hydrogen
Elements constantly move from one sphere to the next. Carbon in the atmosphere (Carbon Dioxide) can be captured in plants (biosphere). An animal eats the plant and when it dies it can dies the plant will become part of the the lithosphere in rocks. Then the rock can be burnt as a fossil fuel releasing the Carbon back into the atmosphere.
Metals from Minerals Part 1
Rocks are made of minerals. Minerals are are made up of solid elements and compounds.
Metal ores are rocks that contain varying amounts of minerals from which metals can be extracted. In many cases the ore is an Oxide.
Iron ore is an example of a metal oxide it is called haematite.
For some metals a lot of ore must be mined to extract a small percentage. In the exam you may be asked to calculate the mass of a metal that can be extracted to obtain a small percentage follow these steps:
Example: How much copper can be extracted from 800g of Copper Oxide?
Step 1 Calculate Calculate the proportion of copper in the Copper Oxide = the relative atomic mass x no. of atoms / relative formula mass*
Step 2 Multiply answer by the mass of Copper Oxide
*relative formula mass is the sum of the relative atomic mass of each element
Metals from Minerals Part 2
The more reactive the metal the harder it is to extract (e.g Sodium that is why it took longer to discover.)
Metals can be exacted in different ways depending on how reactive they are.
Some metals are extracted by reduction with Carbon or Carbon Monoxide. Metals like Zinc Iron, Tin and Copper can be extracted with Carbon because they are less reactive than Carbon. When the Carbon takes the Oxygen the metal oxide is REDUCED. The Carbon gains Oxygen, so it is OXIDOSED. The following equation shows what happens when Carbon is added to an Iron ore: Iron Oxide + Carbon Monoxide => Iron + Carbon Dioxide.
However when the metal ore is more reactive than Carbon a more expensive method is used to extract the metal: Electrolysis. The word electrolysis actually means 'Splitting up with electricity'. A liquid is needed to conduct the electricity - called the electrolyte. Electrolyte are free ions dissolved in water (e.g dissolved salts) or molten ionic compounds. In electrolysis electrons are taken away from the ions at the positive electrode and given to the negative electrode. As the ions gain or lose electrons they become atoms or molecules.
Metals from Minerals Part 3
Lets take bauxite, the main ore of Aluminium. The Al^3+ ions are attracted to the negative electrode where they pick 3 extra electrons and then they become neutral atoms. These are now no longer free flowing electrons and sink to the bottom of a container. The O^2- ions are attracted to the positive electrode where they lose two electrons and became a neutral Oxygen atoms, the atoms rise out of the electrolyte and become part of the air.
At the Negative electrode: At the Poitive electrode:
(Al^3+) + (3 negative electons) => Al (2O^2-) => O2 + 4 negative electrons
Reduction - a gain of electrons Oxidation - a loss of electrons