Revision C4

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Chemistry C4 Revision

The Nucleus

  • Protons have a positive charge (+1)
  • Neutrons have no charge (0)
  • Overall the nucleus has a positive charge because of the protons

The Electrons

  • Electrons have a negative charge (-1)
  • Have no mass (0.0005)
  • Arranged in shells around the nucleus

Particles

  • Protons are heavy and positivley charged
  • Neutrons are heavy and nuetral
  • Electrons are tiny and negatively charged
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Chemistry C4 Revision

Proton number equals the number of Electrons

Each element has a different number of protons

  • Its the number of protons that decides what element it is
  • Atoms of the same element all have the same number of protons - and atoms of different elements will have different number of protons

Atoms are not lost or made in chemical reactions

  • You still have the same atoms at the end of the chemical reaction as you had at the start
  • They are just arranged in different ways
  • Balanced symbol equations show the atoms at the start (reactant atoms) and the atoms at the end (the product atoms) and how they are arranged
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Chemistry C4 Revision

State symbols show the physical state the chemical is in

  • (s) - Solid 
  • (l) - Liquid
  • (g) - Gas
  • (aq) - Dissolved in water

When balancing equations

  • Must have the same number of atoms on both sides 
  • Balance the equation by putting numbers in front of the formulas where needed
  • You can not change formulas you can only put numbers in front of them
  • This is done by sorting out unbalanced compounds or elements
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Chemistry C4 Revision

Some elements emit distinctive colours when heated

  • Lithium (Li) produces a red flame
  • Sodium (Na) produces a yellow/orange flame
  • Potassium (K) produces a lilac flame
  • These colours have helps chemists to identify a metal in a compound 

Each element gives a characteristic line spectrum

  • When electrons in an atom are heated they become excited, and release energy as light
  • The wave lengths emitted can be recorded as a line spectrum
  • Different elements emit different wavelengths of light, this is because each element has a different electron arrangement 
  • So this means each element has a different pattern of wavelength and a different line spectrum
  • Line spectrums can be used to identify elements
  • The practical technique used to produce line spectrums is called spectroscopy
  • By chemists doing this they have identified new elements e.g. Caesium and Rubidium
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Chemistry C4 Revision

The Periodic Table puts element with similar properties together

  • Groups go down and tell you the amount of electrons on the last shell
  • Rows (periods) go across and tell you the amount of shells the atoms has

Each element tells you information about it 

  • At the top is The Relative atomic mass
  • Next there is The Symbol e.g. N
  • Then The name e.g. Nitrogen
  • At the bottom is The proton number 

The relative atomic mass

  •  The relative atomic mass of each element tells you the total number of protons and neutrons there are in the nucleus, you can calculate the number of neutrons by subtracting the number of protons from the relative atomic mass
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Chemistry C4 Revision

Shells and Electrons

  • Electrons are always based around the nucleus in the shells (sometimes known as energy levels)
  • Only a certain number of electrons are allowed in each shell:

1st Shell: 2    

2nd Shell: 8    

3rd Shell: 8

  • Atoms are much more stable when they have full electron shells
  • In most atoms the outer shell is not full and this makes the atom want to react
  •  An elements electron arrangement determines its chemical properties


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Chemistry C4 Revision

Ionic Bonding

  • An ion is a charged particle
  • It is formed when atoms gain or lose electrons
  • ions can be made from single atoms or groups of atoms

A shell with just one electron

  • All atoms in group 1, e.g. Lithium, Sodium, Potassium etc have just one electron in their outer shell 
  • Because they are more stable with full shells, they lose the 1 electron so that they have full shells left
  • Because they lose they become + positive ions
  • Where as Group 7 would gain a electron to make a full shell would become - negative ions
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Chemistry C4 Revision

Ionic bonding

  • This is Transferring Electrons
  • Oppositely charged ions are strongly attracted to each other, as opposites attract
  • So ions with opposite charges come together to form an ionic bond
  • An example of this is the reaction of sodium and chlorine 

The sodium atom gives up its outer electron and becomes and Na+ ion, and then the chlorine atom gains the spare electron and becomes a Cl- ion

Compounds formed between Group 1 and Group 7 elements are held together by ionic bonds - they are ionic compounds

Ionic compounds

  • Ionic compounds form a regular lattice
  • solid ionic compounds like sodium chloride are made up of a giant lattice of ions, Each lattice forms a single crystal
  • When ionic compounds become molten or are dissolved in water they can conduct electricity because the ions are able to move
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Chemistry C4 Revision

Group 1 - The Alkali Metals

  • Metals in Group 1 are known as the alkali metals
  • These metals include Lithium, Sodium, Potassium etc they are all positive +
  • Because they are in Group one it means they have one electron on the last shell
  • Because they have 1 electron on the last shell they react in order to get rid of it and become positive ions
  • The alkali metals are shiny when freshly cut, but quickly react with the oxygen in the moist air and tarnish 
  • As you go down Group 1, the alkali metals:
  • More reactive
  • Have a higher density 
  • And lower melting and boiling points
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Chemistry C4 Revision

Reaction with cold water produces Hydrogen Gas

  • When group 1 metals Lithium, Sodium, Potassium are put in water, they react vigorously
  • They move around the surface, fizzing furiously
  • When they react with the water they produce Hydrogen
  • To find out if Hydrogen is produce you can do the squeaky pop test, just light a splint and find out 
  • Potassium get hot enough to ignite the Hydrogen 
  • This reaction makes the alkaline solution - Group 1 Alkali metals
  • When the Group 1 metals come into contact with the water, a hydroxide of the metal forms because it has released hydrogen
  • For example Lithium -> Lithium hydroxide (LiOH), Sodium -> Sodium hydroxide (NaOH) and Potassium -> Potassium hydroxide (KOH)
  • The more violent the reaction, the more reactive the alkali metal is 
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Chemistry C4 Revision

Group 7 - Halogens

  • Group 7 elements are known as the Halogens
  • The Group 7 elements include Chlorine, Bromine and iodine
  • Because they are in Group 7 they have 7 electrons on the last shell
  • This means they are very reactive because they need to gain one more electron meaning they become negative ions
  • The halogens form diatomic molecules which are pairs of atoms

As you go down Group 7, the halogens:

  • They become less reactive
  • have a higher melting and boiling point
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Chemistry C4 Revision

The Halogens are all Non-metals with Coloured Vapours

  • Fluorine is a very reactive, poisonous yellow gas at room temperature and pressure
  • Chlorine is a fairly reactive, poisonous dense green gas at room temperature and pressure
  • Bromine is a dense, poisonous, orange volatile liquid at room temperature and pressure and forms a orange gas
  • Iodine is a dark grey crystalline solid at room temperature or a purple vapour

The halogens go from gases to solids as you go down the group, this shows the trend in melting and boiling points Halogens become less reactive down the group

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Chemistry C4 Revision

Halogens become less reactive as you go down the group

Reactions with alkali metals

  • The halogens (Group 7) react with the alkali metals (Group 1) like lithium, sodium and potassium to form salts called metal halides
  • For example sodium chloride (NaCl), potassium bromide (KBr) and lithium iodide (Lil)
  • The reactions become less vigorous as you go down the group

Reactions with Iron

  • Halogens (Group 7) react with iron to form coloured solids called iron halides
  • Again the reactions become less vigorous as you go down the group

Displacement reactions

  • A displacement reaction is where a more reactive element displaces (pushes out) a less reactive element from a compound 
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Chemistry C4 Revision

Alkali metas (Group 1)

  • The group  1 elements are really reactive and can combust spontaneously
  • If they come into contact with water vapour in the air there can be a violent reaction, depending on how much alkali metal is present - in order for that not to happen they get stored under oil to prevent this
  • Alkali metals should never be touched with bare hands - this is because the sweat on your skin is enough to cause a reaction that will produce lots of heat and a corrosive hydroxide
  • Because of this every piece of equipment needs to be kept completely dry
  • The Alkaline solutions form a corrosive and may cause blistering - thats why it should not touch the eyes or skin

Halogens (Group 7)

  • The Group 7 elements are also harmful, Chlorine and iodine are both toxic
  • Fluorine is the most reactive halogen - too dangerous to keep in the lab
  • Halogens have poisonous vapours that irritate the respiratory system and the eyes


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