Chemistry Unit 1

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Atoms and Elements

All substances are made of atoms, which are very small particles. A small central nucleas is inside each atom, and they are made up of protons and neutrons. Orbiting electrons surround the nucleas. 

An element is a substance that only contains one type of atom, and there are about 100 different ones. The atoms of each element are represented by a different chemical symbol. 

For Example: 

  • sodium = Na                                                 
  • carbon = C 
  • iron = Fe 


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The Periodic Table

The Periodic Table is where all the elements are arranged. Elements that have similar properties are what makes the groups in the table. 

For Example, all group 1 elements are the alkali metals, which react vigourously with water to produce an alkaline solution or hydrogen gas. They form metal oxides when they react with oxygen.

The Noble Gases are group 0, which are all unreactive due to the fact that they have full outer shells of electrons, which means that they are stable.  Atoms of noble gases have eight electrons on their outer shell, except for Helium which only has two. 


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Atomic Structure

Protons, neutrons and electrons each have an electrical charge:

  • Protons are positive
  • Neutrons are neutral
  • Electrons are negative

As a whole, Atoms have no overall charge because they contain an equal number of protons and electrons.

All atoms of a particular element have the same number of protons, which is the opposite for atoms that have different elements. The Atomic Number is what you call the amount of protons in an atom. The Mass Number is the sum of the protons and neutrons in an atom. The order of atomic number is how elements are arranged in the periodic table. 

The mass number is the number on top of the element symbol, while the atomic number is the number under the element symbol.  The number of neutrons in an atom is calculated by Mass number - Atomic number.

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Electron Configuration and Structure

Electrons in an atom occupy the lowest available energy shell, so basically the innermost shell. For the first 20 elements:

  • Only a maximum of two electron can be contained in the first shell.
  • The energy levels after this can each hold a maximum of eight electrons.

Electron Configuration tells us how the electrons are arranged around the nucleus in energy levels/shells. It is written as a series of numbers, for example:

  • oxygen is 2,6
  • aluminium is 2,8,3

Elements are grouped in the periodic table according to its electronic structure. Elements in the same group have the same number of electrons in their out most energy shell which gives them similar chemical properties. Particular energy levels are gradually filled from left to right with electrons across each period. 

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Compounds

Compounds are formed when elements react and their atoms join with other atoms. This involves the giving or taking of electrons to form ions or the sharing of electrons to form molecules.

Positive ions are formed when metal atoms lose electrons, while non-metal atoms gain electrons to form negative ions. Compounds formed between metals and non-metals consist of ions, which compounds formed between just non-metals form molecules; the atoms are held together by covalent  bonds

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Chemical Formulae

Compounds are represented by a combination of numbers and chemical symbols called a chemical formula

They are used to show:

  • different elements in a compound.
  • how many atoms are in each element in a compound.

The position of the numbers tells you what is multiplied:

  • a small number that sits below the line multiplies only the symbol that comes immediately before it.
  • a number that is the same size as the letters multiplies all the symbols that come after it.

For example:

  • H2O - (2 x H) + (1 x 0)
  • 2NaOH - 2 x (Na + O + H)
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Chemical Reactions

Chemical reactions shows what is happening during a reaction by writing a word or symbol equation.

Reactants are the substances that react, and they are on one side of the equation while the Products, which is the newly formed substance, are on the other side. 

Total mass of the products of a chemical reaction is always equal to that of the total mass of reactants, which is due to the fact that no atoms are lost or made. The atoms of the reactants and product are exactly the same. 

Chemical symbol equations must always be balanced, as there must be the same number of atoms of each element on the reactant side of the equation as there is on the product side. 

Number of atoms of each element on reactants side = Number of atoms of each element on products side.

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Limestone CaCO3

Limestone is a sedimentary rock that consists mainly of calcium carbonate. It is cheap, easy to obtain and has various uses including:

  • as a building material
  • for making cement, mortar and concrete

Some metal carbonates may not decompose at the temperatures reached by a Bunsen burner. The calcium oxide can then be reacted with water to produce calcium hydroxide, which can be used to neutralise soils and lakes, preventing crop failure. 

Carbonates of other metals decompose in a similar way when they are heated. 

Dilute acids react with carbonates to form carbon dioxide gas as well as a salt and water. This turns limewater, which is a solution of calcium hydroxide in water, cloudy. 

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Ores

The Earth's crust contains many naturally occurring elements and compounds called minerals.

A metal ore is a mineral that contains enough metal to make it economically viable to extract it. Over time it may become more or less economic to extract a metal from an ore as technology develops.

Ores are mined and impurities may be removed before the metal is extracted and purified.

This mining involves the digging up and processing of large amounts of rock.


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Extracting Metals from their Ores

The method of metal extraction depends on how reactive the metal is. 

Unreactive metals, such as gold, exist naturally in the earth and can be obtained through panning. But most

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Comments

Beth

thanks

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