GCSE Chemistry C1 - Atomic Structure and The Periodic Table

compounds

- formed from elements by chemical reactions.

- Chemical reactions always involve the formation of one or more new substances, often involve an energy change

- contain two or more elements combined in fixed proportions

- can only be seperate into elements by chemical reactions

mixtures

- consists of two or more elements or compounds not chemically combined together

- chemical properties of each substance in the mixture are unchanged

how can be mixtures be seperated?

- filtration

- crystallisation

- simple distilation

- fractional distillation

- chromotography

these are physical properties so no new substances are created

Filtration

- used to seperate a insoluble solid and a liquid

- use a filter funnel and filter paper and a conical flask

- the filtrate passes through the small holes in the filter paper and the solid is trapped inside the filter paper

Crystallisation

- used to seperate a soluble solid and a liquid

- if you leave the solution for a few days, the liquid will evaporate and leave crystals of the solid. you can make this process faster by heating the solution however the

simple distilation

- to seperate the dissolved solid from the liquid but you want to keep the liquid

- evaporate the liquid by heating which turns the liquid into vapour

- condense the liquid by cooling

- the vapour goes through the condensor filled with cold water and turns into a liquid

fractional distillation

- seperate a mixture of different liquids with different boiling points

- in flask, mixture of several liquids with different boiling points

- diff from simple distillation is that the flask is connected to a fractionating column filled with beads

- this helps to seperate the mxiture by allowing the vapours to cool, condense and vapourize again.

- not useful for seperating large volumes of liquid or solutions with similar boiling points

chromotography

- seperate substances based on their different solubilities

- take chromotography paper and draw pencil line at the bottom. put the dots on the line

- place bottom of paper in a solvent

- the solvent moves up the paper and dissolves the ink and the ink now moves up the paper

- the paper is stationary phase as it doesn't move and the solvent mobile phase

- a pure compound will produce a single spot, a mixture can produce multiple spots

-rf value = distance the ink has traveled/ distance the solvent has travelled

monatomic molecule

- full outer shell so they are stable

- low boiling points, as you go down the boiling point increases because the atomic radius increases

History of the atom

Dalton

Thompson

Rutherford

Bohr

discovery of protons

Chadwick

Dalton

first: atoms were thought to be tiny invisible spheres that could not be divided (dalton)

Thompson

discovery of the electron - plum pudding model (positively charged sphere with negative electrons embedded in it) (thompson)

Rutherford

- conducted the gold foil experiment - discovered the nucleus

- discovered that the atom is mostly empty space with nearly all of the mass concentrated in the tiny nucleus

Bohr

- electrons orbit the nucleus in shells

- the plannetry model. electrons orbit the nucleus of the atom in specific allowable paths called orbits at specific distances

discovery of protons

positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge

Chadwick

discovered the neutron and explained the existance of isotopes

Rutherford's experiment

- a beam of alpha particles was aimed at very thin gold foil and their passage through was detected

- most of the alpha particles passed straight through the foil (atoms are mostly empty space)

- a small number were deflected by large angles as they passed through the foil (nucleus of the atom has a strong positive charge)

- a very small number came straight back off the foil (the atoms contain a small heavy nucleus as the positive alpha particles were being repelled by the positive nucleus)

difference between the plum pudding model and the nuclear model

- plum pudding has no empty space

- nuclear model has shells

- nuclear model has a nucleus

relative mass of proton

1

relative mass of neutron

1

radius of an atom

0.1 nm

radius of an nucleus

1/10,000 of an atom

isotopes

atoms of the same element with the same number of protons but different number of neutrons. atoms of the same element with the same atomic number but different mass number

relative atomic mass

average value that takes account of the abundance of the isotopes of the element

how to calculate relative atomic mass

(mass number 1 x its abundance) + (mass number 2 x its abundance) ÷ abudance 1 + abundance 2

john newland's periodic table

- ordered his table in order of atomic weight

- similar properties occured every 8th element (law of octaves) but broken down after calcium

Dmitri Mendeleev's periodic table

- ordered his table in order of atomic mass but always strictly

- left gaps for elements that he though had not been discovered yet

- similar properties occur at regular intervals

modern periodic table

- knowledge of isotopes made it possible to explain why the order based on atomic weight was not always correct

metals and non-metals

metals forms postive ions

non metals form negative ions

Group 0

- noble gases

- do not easily form molecules because they have a stable arrangement of molecules

- boiling points increase with increasing atomic mass

Group 1

- alkali metals

- the reactivity of elements increases going down the group

Group 1 reaction with water

Li - fizzes steadily, eventually disappears.

Na - melts to form a ball, It fizzes rapidly before it disappears quickly

K - It moves around very quickly on the surface of the water. metal self-ignites, which also ignites the hydrogen gas. This results in sparks and a lilac flame.

Group 1 reaction with chlorine

- white smoke and powder produced for all metals

Li - bright orange flame

K - bright lilac flame, same as sodium but more vigorous

Na - bright yellow flame, clouds of white powder

Group 1 reaction with oxygen

forms metal oxide, all produce a white solid

Li - burned with red tinged flame

Na - strong orange flame

K - large pieces profuce lilac flame and small pieces make a solid immediately

Group 7

- halogens

- more reactive as you go up - as you go down metling/ boiling point increases,

- theyre diotomic molecules

- a more reactive halogen can displace a less reactive one in an aqueous solution of its salt

halogen (F2) halide (F-)

comparing group 1 and transition metals

- harder, stronger,

- higher density and melting point

- less reactive and dont react as vigorously with oxygen or water

- ions ith different charges

- form coloured compounds

- useful as catalysts

examples of transition metals and their properties

copper - mealleable and soft

cobalt - high melting point

nickel - hard