3.1-3.7

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Johann Dobereiner. when elements are put into groups of three (with similar chemical properties) it states that the atomic mass of the second element falls halfway between the first and third.

calcium, strontium, barium and chlorine, bromine, iodine

he arranged the 62 elements known at his time by atomic mass. he noticed a repeating pattern every 8 elements called the law of octaves. this pattern broke when he reached the transition metals.

he ordered the elements by atomic mass. when certain elements were put in columns a pattern of properties emerged. he left gaps and predicted properties of unknown elements. he switched the positions of some elements to better group them by properties

he noticed that when ordered by increasing atomic number the errors in Mendeleev’s table were corrected.

a repeating trend in the properties of the elements across each periods in the periodic table

• atomic radii • 1st ionisation energy • electronegativity • conductivity • M.P and B.P

it decreases. shielding stays the same but nuclear charge increases. the attraction is stronger so outer electrons are pulled closer.

increases. shielding stays the same but nuclear charge increases and atomic radius decreases. stronger attraction between the nucleus and outer electron

it increases. shielding stays the same. atomic radius decreases, nuclear charge increases. causes stronger attraction between nucleus and bonding pair

first three elements: increases. the electron cloud gets denser, others: non-conductive cause there’s no free charge.

first three elements: increases, electron cloud gets denser, atomic radius decreases, charge increases. group 4: larger M.P than metals. strong covalent bonds in the giant covalent lattice group 5-8: much lower M.P’s. intermolecular forces are weak so low energy requirement.

the gain of oxygen or the loss of electrons

the loss of oxygen or the gain of electrons

when oxidation and reduction take place

oxidising agent: the species that accepts the electrons reducing agent: the species that transfers the electrons

the hypothetical charge on an element in an ion or molecule if the bonding is considered 100% ionic.

• always 0 in elements or diatomic molecules • the most electronegative element has a negative ON • in simple ions the ON is the same as the charge 4, ON’s add to zero in neutral molecules • ON’s add to equal the charge of molecular ions

Fluorine: always -1 but 0 in the diatomic molecule (F2) oxygen: -2 but 0 in O2. -1 in H2O2. +2 in F2O Hydrogen: +1 but 0 in the diatomic molecule (H2) chlorine: -1 but O in Cl2. +1 to +7 with oxygen and fluorine

put the ON in roman numerals in brackets next to its name. ie, Lead(II) oxide. or sulphate(VI)

assign ON’s to each element. any changes to the ON’s of the reactants indicate the loss or gain of electrons. this shows you what was oxidised and reduced.

when the same species is oxidised and reduced in a reaction.

makes the number of electrons equal by multiplying everything in the reaction. combine the reactants and products to write a full equation. cancel out any electrons, hydrogens and waters if there on both sides.