Products and Rocks- Chemistry Core

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  • Created on: 19-12-15 13:13

Atoms and Elements

Atoms have a small nucleus containing protons (positively charged) and neutrons(no charge). So the nucleus has a postive charge overall because of the protons. The electrons (negatively charged) move around the nucleus and occupy shells around the nucleus. 

Atoms have no charge overall. They are neutral. This is due to the fact that the number of protons equals the number of electrons. If some electrons are added or removed, the atom becomes charged and is then an ion because there are more number of protons than electrons. 

It's the number of protons in the nucleus that decides what type of atom it is. For example, an atom with one proton in its nucleus is hydrogen and an atom with two protons is helium. 

Elements consist of one type of atom only. So all the atoms of a particular element have the same number of protons and different elements have atoms with different numbers of protons.

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The Periodic Table

The Periodic table puts elements with similar properties together. They form columns. The vertical columns are called groups. All of the elements in a group have the same number of electrons in their outer shell.The elements in the final column (Group 0) are the noble gases. They all have 8 electrons in their outer shell, apart from helium (which has 2). this means that they're stable and unreactive. 

    (http://4e7221.medialib.glogster.com/media/a083090a9f94bb30a7bd0e8fcc19013ac3aaaa35031dd0fa654f54b3588239a4/hydrogen-symol.jpg)

The top number is the mass number. this is the total number of protons and neutrons. The bottom number is the atomic number. this is the number of protons, which conveniently also tells you the number of electrons

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Electron Shells

Electron Shell Rules: Electrons always occupy shells (energy levels). The lowest energy levels are always filled first - these are the ones closest to the nucleus.

In the 1st shell: 2 electrons.

2nd shell: 8 electrons.

3rd shell: 8 electrons.

In most atoms the outer shell is not full and this makes the atom want to react to fill it. 

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Compounds

When different elements react, atoms form chemical bonds with other atoms to form compounds. it's usually difficult to separate the two original elements out again. Making bonds involes atoms giving away, taking or sharing electrons. Only the electrons are involved. 

Ionic Bonding- A compound which is formed from a metal and a non-metal consists of ions. the metal atoms lose electrons to form postive ions and the non-metal atoms gain electrons to form negative ions. The opposite charges of the ions mean that they're strongly attracted to each other. 

Covalent Bonding- A compound formed from non-metals consists of molecules. Each atom shares an electron with another form. Each atom has to make enough covalent bons to fill up its outer shell. 

The properties of a compound are totally different from the properties of the original elements. Compounds can be small molecules like water or great lattices like sodium chloride. 

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Balancing Equations

Atoms aren't lost or made in chemical reactions. You still have the same atoms at the end of a chemical reaction as you had at the start. They're are just arranged in different ways. Because atoms aren't gained or lost, the mass of the reactants equals the mass of the products. 

(http://www.mikeblaber.org/oldwine/chm1045/notes/Stoich/Equation/balance4.gif)

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Using Limestone

Limestone is often formed from sea shells.It is mainly Calcium Carbonate. Limestone's quarried out of the ground - it's great for making into blocks for building with. When limestone is heated it thermally decomposes (when one substance chemically changes into at least two new substances when it's heated) to make calcium oxide and carbon dioxide. Calcium carbonate also reacts with acid to make a calcium salt, carbon dioxide and water. This reaction means that limestone is damaged by acid rain.

Calcium Oxide reacts with water to produce Calcium Hydroxide. Calcium hydroxide is an alkali which can be used to neautralise acidic soil in fields. Powdered Limestone can be used for this too, but the advantage of calcium hydroxide is that it works much faster. If you make a solution of calcium hydroxide in water (limewater) and bubble gas through it, the solution will turn cloudy if there's carbon dioxide in the gas. The cloudiness is caused by the formation of calcium carbonate. 

Powdered limestone is heated in a kiln with powdered clay to make cement. cement can be mixed with sand and water to make mortar. Mortar is the stuff you stick bricks together with. Or you can mix cement with sand and aggregate(water and gravel) to make concrete.

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Using Limestone (2) Problems,

Quarrying limestone makes a right mess of the landscape. It makes huge ugly holes which permanently change the landscape. Quarrying processes makes a lot of noise and dust in quiet, scenic areas. Quarring destroys the habitats of animals and birds. The limestone needs to be transported away from the quarry usually in lorries, this causes more noise and pollution. Waste materials produce unsightly tips. 

Making stuff from Limestone causes pollution too, cement factories make a lot of dust, which can cause breathing problems for some people. Energy is needed to produce cement and quicklime. the energy is likely to come from burning fossil fuels, which causes pollution. 

But on the plus side, limestone provides things that people want - like houses and roads. Chemicals used in the making dyes, paints and medicines also come from limestone.Limestone products are used to neautralise acidic soil. Acidity in lakes and rivers caused by acid rain is also neautralised by limestone products. Limestone is also used in power station chimneys to neutralise sulfur dioxide, which is a cause of acid rain. The quarry and associated businesses provide jobs for people and bring more money into the local economy. this can lead to local improvements in transport, roads, recreation facilities and health. Once quarrying is complete, landscaping and restoration of the area is normally required as part of the planning permission

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Using Limestone (3) Advantages and Disadvantages

Limestone and concrete (made from cement) are used as building materials. Limestone is widely available and is cheaper than granite or marble. it's also fairly easy rock to cut. Some limestone is more hard-wearing than marble, but it still looks attractive. Concrete can be poured into moulds to make blocks or panels that can be joined together. it's a very quick and cheap way of constructing buildings -  and it shows concrete has got to be the most hideously unattractive building material ever-known.Limestone, concrete and cement don't rot when they get wet like wood does. they can't be gnawed away by insects of rodent either. And to top it off, they're fire-resistant too. Concrete doesn't corrode like lots of metals do. it does have a fairly low tensile strength though, and can crack. it it's reinforced with steel bars it'll be much stronger.

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Getting Metals from Rocks

Ores are rocks containing enough metal to make extraction economically worthwhile. Most metals need to be extracted from their ores using a chemical reaction. 

Metals are extracted from their ores chemically -  by reduction or by electrolysis. Some ores may have to be concentrated before the metal is extracted- this just involves getting rid of the unwanted rocky material. Electrolysis can also be used to purify the extracted metal. occasionally, some metals are extracted from their ores using displacement reactions. 

A metal can be extracted from its ore chemically by reduction using carbon. When an ore is reduced, oxygen is removed from it. The position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon. Metals higher than carbon in ther reactivity series have to be extraced using electrolysis which is expensive. metals below carbon can be extracted by reduction using carbon. This is because carbon can only take the oxygen away from the metals which are less reactive than carbon itself is. 

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Getting Metals from Rocks (2) Electrolysis

Metals that are more reactive than carbon have to extracted using electrolysis of molten compounds. However the process is much more expensive than reduction with carbon because it uses a lot of energy. 

Copper can be easily extracted by reduction with carbon, the ore is ehated in a furnace - this is called smelting. However, the copper produced this way is impure -  and impure copper doesn't conduct electricity very well. This isn't very useful because a lot of copper is used to make electrical wiring. So electrolysis is also used to purify it which pruduces very pure copper, which is a much better conductor. 

Electrolysis is the breaking down of a substance using electricty. It requires a liquid to conduct the electricity, called the electrolyte. Electrolytes are often metal salt soloutions made from the ore or molten metal oxides. The electrolyte has free irons - these conduct the electricity and allow the whole thing to work. Electrons are taken away by the positive anode and given away by the negative cathode. As ions gain or lose electrons they become atoms or molecules and are released. 

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