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C2 Topic 1: Atomic Structure and the Periodic
Table
The Periodic Table: Mendeleev
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In 1869, Dmitri Mendeleev arranged the elements (known at the time) in order
of increasing atomic structure
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Mendeleev left gaps in the table for elements that had not yet been
discovered and he was often able to accurately predict the properties of these
elements
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The Modern Periodic Table
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The modern periodic table is arranged in order of increasing atomic number,
instead of atomic mass
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This is because they have the same number of electrons in their outermost
shell
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Non-metal elements are in the top right
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Atomic Structure
Atoms are made up of three subatomic particles; protons, neutrons and electrons
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The electrons “orbit” this nucleus in energy levels called electron shells
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A proton has a charge of positive 1
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The relative mass of a proton or neutron is 1
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All atoms of an element have the same number of protons
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All atoms (not ions obviously) have a neutral charge and for this reason the number
of protons = the number of electrons
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The mass number of an element is the number of protons and neutrons
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Because of isotopes this number is not always a whole number
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They have the same properties and charge, but a different mass
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The shells are configured 2,8,8, meaning that the
first shell can hold two electrons, the second eight and so on
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This is why periodicity exists- “characteristics of repeating patterns of properties in
the periodic table”
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For example, if an element in group two
(X) is reacted with oxygen, it produces the compound XO
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This is why elements in Group 0 are unreactivethey’ve got full outer shells- and why elements in Group 1 are very reactive
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This results in them having charge; being ions
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This is what metals do
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This is what non-metals do
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Those are a thing that exist
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If it
ends –ate this negatively charged ion is in a
compound with oxygen
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There are
strong intermolecular forces of attraction between the
positive and negative ions in these lattices which makes
them very strong
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Also, ionic compounds only conduct electricity when
they’re molten or dissolved in water
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They can’t when they’re solid
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Also, if two soluble compounds combine and
any combination of them will make an insoluble salt, that insoluble salt is a
precipitate
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Using salts in X-Rays
When somebody’s going to have an X-Ray of their gut, they drink a suspension of
barium sulphate, called a barium meal
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Barium sulphate is toxic, but because it’s
insoluble it isn’t absorbed into the bloodstream and therefore is safe to ingest
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We dip a nichrome wire in acid, dip the wire in the
compound and then put the wire in a flame
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Potassium
Sodium
Calcium
Copper

Lilac
Orange-yellow
Brick red
Blue-green

Assorted other tests (not involving fire for the most part)
This is how we test for anions
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If you get a gas, collect it and add it to
limewater
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Chloride = add silver nitrate
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Sulphate= add hydrochloric acid and barium sulphate
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Spectroscopy
Different elements, when you heat them, emit light of different frequencies
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It’s led to the discovery
of elements like caesium and rubidium
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They usually share a
pair of electrons, but sometimes it’s two or three pairs
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Note: you draw covalent bonds with dots and crosses – you represent the electrons
of one element with a dot, the other
with a cross, and you overlap their
electron shells like you were drawing
a venn diagram and put the shared
electrons within it
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Covalent bonds come in two
varieties: simple and giant molecular
covalent
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They generally aren’t soluble and don’t conduct
electricity
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Giant molecular covalent substances have very high melting and boiling points,
because there are many strong covalent bonds present
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They’re never soluble and don’t conduct electricity
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The layers rub off very easily, which is why pencils work as a thing
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Ionic

High melting and Often soluble
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Conducts electricity
when molten or in a
solution
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Doesn’t conduct
electricity
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boiling point
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Doesn’t conduct
electricity (except
graphite)
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You
turn the tap on, wait for the bottom liquid to run out, and then turn the tap off
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As liquids have different boiling points, fractional distillation involves heating liquids
until they evaporate and then collecting them, leaving other liquids with different
boiling points behind
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This is much more easily explained with a diagram
but damn if I can find one
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You remove assorted shit from the air, like dust, carbon dioxide and water
vapour
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You cool the air down to -200 degrees Celsius, so that all gases condense
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You gradually heat the air again
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At about -196 degrees Celsius, nitrogen evaporates
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This leaves oxygen by itself
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It’s used by the food and forensic
science industries
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You then put spots of the
substances you’re testing on the line
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Then you
fill the container with a solvent so the solvent is between
the bottom of the paper and the line
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Different colours makes spots at different points up the paper
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If you want to work out the distance travelled of a substance relative to the solvent
you do it by distance travelled by substance / distance travelled by solvent
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Breaking bonds takes in thermal energy
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If there are more bonds made than bonds broken, energy is given out and the
reaction is exothermic

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