All revsion notes for c4

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C4 ­ Chemical Patterns
Atoms
The Nucleus
The nucleus is the middle of an atom. It contains protons and neutrons. The
protons make the atom have a positive charge. Almost the whole mass of
the atom is concentrated in the nucleus , but it is tiny compared to the rest of
the atom.
The Electrons
The electrons move aorund the nucleus. They are negetivly chraged and are
tiny, but cover a lot of space. The voulme of their orbits determine how big an atom is. They have
virtually no mass and are arranged in shells around the nucleus.
Particle Relative Mass Charge
Proton 1 +1
Neutron 1 0
Electron 0.0005 -1
Neutral Atoms
Neutral atoms have no charge overall. The number of protons equals the number of electrons. The
charge on the electrons is the same size as the charge on the protons ­ but opposite. This means that
the number of protons always equals the number of electrons in a neutral atom. If some electrons are
added or removed, the atom becomes charged and is then an ion. The number of neutrons isn't fixed
but it is usually about the same as the number of protons.
Line Spectrums
When heated, some elements produce flames with a distinctive colour. These colours help identify a
metal in a compound.
Lithium, Li, produces a red flame
Sodium, Na, produces a yellow/orange flame
Potassium, K, produces a lilac flame
When heated, the electrons in an atom are excited, and release energy as light. The wavelengths
emitted can be recorded as a line spectrum. Different elements emit different wavelengths of light.
This is due to each element having a different electron arrangement. So each element has a different
pattern of wavelengths, and a different line spectrum. This means that line spectrums can be used to
identify elements. The practical technique used to produce line spectrums is called spectroscopy.

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History of the Periodic Table
In the 1800's the only thing they could measure was relative atomic mass, and so the known
elements were arranged in order of atomic mass.
Doberiner
In 1828 a man called Doberiner started to put this list of elements into groups based on their
chemical properties. He put the elements into groups of three, which he called the triads. The middle
element of each triad had a relative atomic mass that was the average of the other two.…read more

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Elements with similar properties form columns. These vertical columns are called groups. The group
number tells you how many electrons there are in the outer shell. For example: group 1 elements all
have one electron in their outer shell and group 7 all have seven electrons in their outer shell. The
rows are called periods. Each new period represents another full shell of electrons.…read more

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Ionic Bonding
When atoms lose or gain electrons they form charged particles called ions. Ions can be made from
single atoms or groups of atoms. When atoms lose or gain electrons, all they are trying to do is get a
full outer shell.
All the atoms in group 1 of the periodic table have one electron in their outer shell and they are
pretty keen to get rid of it as they'll only have full shells left.…read more

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Group 1 ­ The Alkali Metals
Group 1 metals include lithium, sodium, potassium, rubidium, caesium and francium. They all have one
outer shell electron, making them very reactive and give them all similar properties. When alkali
metals react they form similar compounds. The alkali metals are shiny when freshly cut, but quickly
react with the oxygen in moist air and tarnish.
As you go down group 1, the alkali metals:
1.…read more

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Group 7 ­ The Halogens
Group 7 elements include fluorine, chlorine, bromine, iodine and astatine. They all have seven outer
electrons. This makes them very reactive, gives them similar properties and means they form similar
compounds to each other. The halogens form diatomic molecules which are pair of atoms.
As you go down group 7, the halogens:
1. Become less reactive because the outer electrons are further from the nucleus and so
additional electrons are attracted less strongly.
2. Have higher melting point
3.…read more

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