Chemistry C1

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

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