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properties of metals
strong but malleable, great at conducting heat and electricity, high boiling and melting points, form positive ions, high density, hard, shiny
properties of non-metals
if solid, they are dull, low density, poor conductors of heat and electricity, if solid, they are brittle, low melting and boiling points
atomic weight
the average mass of an atom of an element, taking into account the different isotopes and their abundance
compounds
two or more elements chemically combined in fixed proportions
atoms
the smallest part of an element that can exist
transition metal properites
have the properties of a typical metal and can have more than one ion, often coloured and make good catalysts
mixtures
two or more elements or compounds not chemically combined together
methods for separating mixtures
filtration, crystallisation, simple distillation, fractional distillation, chromatography
examples of mixtures
salt solution, air, sandy water
filtration
separates an insoluble solid from a liquid
crystallisation
separates a soluble solid from a solvent
simple distillation
heat with electric heater to the first boiling point, the vapour passes through the condenser for the pure liquid
chromatography
separates inks/pigments from a mixture
trends as you go down group 1
increasing reactivity, lower melting and boiling points, higher relative atomic mass
trends as you go down group 7
less reactive, higher melting and boiling points due to the stronger forces of attraction between bigger molecules, higher relative molecular mass
halogens exist as
molecules made of pairs of atoms (eg F2)
trends as you go down group 0
increasing boiling points due to the atoms becoming larger and the forces of attraction between the atoms getting stronger (gases have the high boiling point - not the atoms)
properties of alkali metals
soft, low density
alkali metal reaction with oxygen
all react with oxygen to make the metal oxide (a white solid)
alkali metal reaction with chlorine
all react to make the metal chloride
eg container with chlorine gas inside it covered by a lid, a scoop of sodium heated up using a bunsen burner placed into the jar of chlorine gas, a vigorous reaction with yellow flames and a white solid as finished product
alkali metal reaction with water
all react to make the metal hydroxide (alkali) and hydrogen gas
lithium - fizzes/bubbles (hydrogen gas produced) floats and moves around
sodium - fizzes/bubbles more vigorously, floats and moves around more
potassium - fizzes vigorously and ignites to produce a lilac flame, floats and moves around
displacement reaction in group 7
a more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt
properties of noble gases
unreactive, stable arrangement of electrons
more reactive halogens
displace less reactive ones
jj thompson plum pudding model
a ball of positive charge with negative electrons stuck in it
alpha particle scattering experiment
positively charged alpha particles fired at a thin sheet of gold. most particles were expected to pass through because of the thought spread out positive charge, however more particles were deflected than thought and a small number were deflected directly backwards proving the existence of a positively charged nucleus where most of the mass is concentrated
niels bohr
bohr realised a ‘cloud’ of electrons would be attracted to the nucleus, which would collapse the atom so he proposed electrons orbit the atom in fixed shells
how was the periodic table arranged in the early 1800s
placed in order of atomic weight as protons neutrons or electrons had not been discovered. properties were not taken into account
mendeleev’s changes to the periodic table
arranged elements mostly by atomic weight however the order was switched if the properties of the element meant it should be. left gaps in the table to ensure elements with similar properties stayed in the same groups, which meant properties of undiscovered elements could be predicted.
radius of the atom
0.1 nm (1 × 10^-10 m)
radius of the nucleus
10,000x smaller than the radius of the atom (1 × 10^-14)
isotopes
atoms of the same element that have the same number of protons but different number of neutrons. have same chemical properties but different physical properties
calculating relative atomic mass with given abundance of isotopes
(% abundance x RAM) + (% abundance x RAM) / 100
why was the order based on atomic weight not always correct
knowledge of isotopes
properties of transition metals
high melting boiling points (group 1 metals have low ones), high density, strong/hard, not very reactive, form coloured compounds, form ions with different positive charges, can be used as catalysts