Chemistry

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Particles in atoms

Protons, neutrons and electrons are called SUBATOMIC PARTICLES. You can work out how many of each type of subatomic particle an atom has from its atomic number and mass number.

Atomic number

The number of protons in an atom of an element is called its ATOMIC NUMBER.

The atoms of different elements have different numbers of protons - no two elements can have the same atomic number.

Number of electrons

Atoms have no overall charge. This is because the number of electrons in an atom is the same as the number of protons.

Mass number

The total number of protons and neutrons in an atom is called its MASS NUMBER.

The number of protons is goven by the atomic number, which is 11 for sodium, for exxample

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Electronic structure

You should be able to represent the electronic structure of the first 20 elements.

Energy levels

The electrons in an atom occupy different ENERGY LEVELS around the nucleus. Each electron in an atom is at particular energy level. Electrons occupy the lowest available energy levels.

Shells

Energy leveks are also called SHELLS:

  • The innermost shell is the lowest energy level.
  • The outer shell is the highest occupied energy level.

(http://f.tqn.com/y/chemistry/1/S/2/9/1/sodiumatom.jpg)

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Electronic structure and groups

Atoms of the elements in a group in the periodic table have the same number of electrons in their highest energy level (outer shell). This gives the elements similar chemical properties.

Group 1 (alkali metals)

The elements in Group 1 include lithium, sodium and potassium. Their atoms all have just one electron in their highest occupied energy level (outer shell).

(http://www.bbc.co.uk/staticarchive/eb117f97d74b8901936cbd3472e8b03fbf077b7d.jpg)

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Making compounds

When elements react with each other, their atoms join together to form COMPOUNDS.

Forming ions

Metals and non-metals react together to form compounds. The compounds are made of IONS.

An ion is a charged particle formed when an atom, or group of atoms, loses or gains electrons.

Giving and taking electrons

 

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Chemical equations

We use word equations and balanced symbol equations to represent chemical reactions.

Word equations

In a chemical reaction:

  • REACTANTS are the substances that react together
  • PRODUCTS are the substances made.

In a WORD EQUATION, two or more reactants or products are seperated by a + sign.

(http://study.com/cimages/multimages/16/propane.jpg)

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Limestone

LIMESTONE is a type of rock. It is mostly calcium carbonate, CaCO3.

Uses of limestone

(http://upload.wikimedia.org/wikipedia/commons/thumb/c/c3/Limestone_house.jpg/1280px-Limestone_house.jpg)

  • As raw material for making cement, mortar and concrete.
  • As blocks and slabs for walls and pavements.
  • As AGGREGATE (small lumps) for the base of roads and railways.
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Calcium carbonate chemistry

Thermal decomposition

Many metal carbonates break down when they are heated. The reaction is called THERMAL DECOMPOSITION.

metal carbonate -------> metal oxide + carbon dioxide

When calcium carbonate is heated, it decomposes  to form calcium oxide and carbon dioxide:

(http://image.tutorvista.com/content/p-block-elements/calcium-carbonate-thermal-decomposition.gif)

Other carbonates

These carbonates decompose in a similar way to calcium carbonate when heated:

  • magnesium carbonate
  • zinc carbonate
  • copper carbonate

Not all carbonates of metals in Group 1 decompose when heated with a Bunsen flame.

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Extracting metals

Unreactive metals such as gold are found in the Earth's crust as the metal element itself. However, most metals are found as compounds. These need chemical reactions to extract them from their ores.

Ores

Rocks contain metals or their compounds. An ORE is a rock that contains enough of a metal to make its extraction economical.

Rocks may contain too little metal to make extraction worthwhile (if the cost of extracting the metal is greater than the value of the metal itself). Over time, metal prices may rise and these LOW-GRADE ORES may become useful.

Reduction

Iron is extracted from iron oxide in a blast furnace by reaction with carbon:(http://www.chemguide.co.uk/inorganic/redox/redoxeqtn1.gif)

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Extracting copper

High-grade copper ores contain a high proportion of copper compounds.

Smelting

Copper is extracted from these ores by SMELTING. This involves heating copper ores in a furnace. For example, copper sulphide is heated in air to produce copper:

(http://resources.schoolscience.co.uk/CDA/14-16/cumining/images/eq3.gif)

Electrolysis

Copper is purified by ELECTROLYSIS.

(http://scienceaid.co.uk/chemistry/applied/images/copper.png)

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Recycling metals

Recycling metals instead of extracting them from ores has many benefits.

Extracting metals

Extracting metals from their ores:

  • uses up limited resources
  • uses a lot of energy
  • damages the environment

Recycling metals reduces these disadvantages. Used metal items are collected. Rather than throwing them away, these are taken apart. The metal is melted down to make new items.

Recycling

Recycling metals means:

  • metal ores will last longer
  • less energy needed to recycle metals than to mine ores and extract metals
  • fewer quarries and mines needed
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