• Created by: wader
  • Created on: 27-03-15 20:23

Atoms And Elements

The Nucleus:

  • Its in the middle of the atom.
  • It contains protons and neutrons.
  • Protons and positively charged.
  • Neutrons have no charge (they're neutral)
  • So the nucleus has a positive charge overall because of the protons

The Electrons:

  • Move around the nucleus
  • They're negatively charged.
  • They're tiny, but they cover a lot of space.
  • They occupy shells around around the nucleus.
  • These shells explain the whole of chemistry
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Atoms And Elements Card 2

Number of protons equals number of electrons:

  • Atoms have no charge overall, they are neutral.
  • The charge on the electrons is the same size as the charge on the protons- but opposite.
  • This means the number of protons always equals the number of electrons in an atom.
  • If some electrons are added or removed the atom becomes charged and is then an ion

Elements consist of one type of atom only:

  • Atoms can have diffrent numbers of protons, neutrons and electrons its 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
  • If a substance only contains one type of atom its called an element.
  • There are about 100 diffrent elements- quite a lot of everyday substances are elements

Copper, Aliminium, Iron, Oxygen and Nitrogen.

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The Periodic Table.

Atoms can be represented by symbols.

Atoms can be represented by a one or two letter symbol- its a type of shorthand.

E.G.  C=carbon  Li=lithium  Mg=magnesium

The top number is the MASS NUMBER.

The bottom number is the ATOMIC NUMBER.

Group 1 and 2- Reactive Metals.

Group 3- Non Metals.

Group 0- noble gases.

All of the between are the TRANSITION METALS

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Electron Shells.

Electrons always occupy shells - Energy Levels.

The lowest energy levels are always filled first - these are the ones closest to the muscles.

Only a certain number of electrons are allowed in each shell-

1st Shell - 2

2nd Shell - 8

3rd Shell - 8

Atoms are happier when they have a full electron shells - like the noble gases in Group 0.

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Electron Shells 2

The periodic table tells us nitrogen has seven protons so it must have seven electrons.

The first shell can only take 2 electrons and the second shell can take a maximum of 8 electrons.

The periodic table has a big gap where the transition metals fit in on row four.

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When diffrent elements react, atoms form chemical bonds with other atoms to form compounds its useally difficult to separate the two origianal elements out again.

Making bonds involves atoms giving away, taking or sharing electrons. Only the electrons are involved- its nothing to do with the nuclei of the atoms at all.

A compound which is formed from a metal and a non-metal consists of ions. The metal atoms lose electrons to form positive ions and the non-metal atoms gain electrons to form negative ions. The opposite charges (positive and negative) of the ions mean that they're strongly attracted to each other. This is called IONIC bonding.

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Compounds 2

A compound formed from non-metals consists of molecules.  Each atom shares an electron with another atom- this is called a covalent bond. Each atom has to make enough convalent bonds to fill up its outer shell.

E.G. HCI- Hydrogen atom bonds with a Chlorine atom by sharing an electron with it.

The properties of a compund are totally diffrent from the properties of the elements, if iron and sufler react, the compound formed (iron sulfide).

Compounds can be small moleclues like water, or great whopping lattices like sodium chloride.

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Formulas And Reaction.

Carbon dioxide CO2, is a compound formed from a chemical reaction between carbon and oxygen. It contains 1 carbon atom and 2 oxygen atoms.

You still have the same atoms at the end of the chemical reaction as you had at the start.

Word Equations-

Magnesium + Oxygen ---- Magnesium Oxide.

2Mg             + O2        ---- 2MgO

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Balanced Equations.

2Cu + O2    →    2CuO(

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Balanced Equations 2

  • Mg + Cl2    →    MgCl2
  • 2Na + Cl2    →    2NaCl
  • 4Fe + 3O2    →    2Fe2O3
  • 4Na + O2    →    2Na2O
  • 2Na + 2H2O    →    2NaOH + H2

Some other exapmles

Balanced equations give the symbols and formulas of the substances involved in a reaction.

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