Please enable JavaScript.
Coggle requires JavaScript to display documents.
Atomic structure and the periodic table (Size and mass of atoms (Atoms:…
Atomic structure and the periodic table
Atoms, elements & compounds
Atom
: the smallest part of an element that can exist
Compound
: two or more elements chemically combined in fixed proportions
Chemical reaction
: always involve the formation of one or more new substances, and often involve a detectable energy change
can only be separated into elements by chemical reactions
Element
:consist of atoms with the same atomic number
Mixture
: consists of two or more elements or compounds not chemically combined together
the chemical properties of each substance in the mixture are unchanged
can be separated by physical processes
Filtration
: separates insoluble solids from liquids
pour solution through filter paper
Crystallisation
Steps
1) pour the solution into an evaporating dish and gently heat until some of the solvent has evaporated
2) when crystals start to form remove dish from heat and leave to cool
3) the salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
4) filter the crystal out of the solution, and leave in a warm place to dry
Simple Distillation
: used to separate out a liquid from a solution
Steps
1) solution is heated - the part of the solution with the lowest boiling point evaporates first
2) the vapour is then cooled, condenses and is collected
3) the rest of the solution is left behind in the flask
can be used to get pure water from salt water - salt is left behind
problem is it can only be used to separate things with very different boiling points
Fractional Distillation
: used to separate a mixture of liquids
Steps
1) put your mixture in a flask and stick a fractionating column on top, then heat it
2) the different liquids will all have different boiling points - so they will evaporate at different temperatures
3) the liquid with the lowest boiling point evaporates first, reaches the top and is collected
4) the temperature is increased and the liquid with the next boiling point is collected
Chromatography
Steps
1) draw pencil line near bottom of filter paper
2) adda spot of ink to the line and place the bottom edge in solvent, make sure solvent doesn't touch ink
3) solvent seeps up the paper carrying ink with it - the point it reaches is the solvent front
4) each different dye will have different attraction to the stationary phase- creates a chromatogram
The development of the model of the atom
atoms were thought to be tiny spheres that could not be divided
the discovery of electrons led to the plum pudding model - suggested that the atom is a ball of positive charge with negative electrons embedded in it
the result from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre and the nucleus was charged
Niels Bohr adapted the nuclear model - electrons orbit nucleus at specific distances - theoretical calculations of Bohr agreed
positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge - proton
James Chadwick provided the evidence to show the existence of neutrons within the nucleus. About 20 years after the nucleus became an accepted idea
Charges of subatomic particles
Proton
: +1
Neutron
: 0
Electron
: -1
number of protons is atomic number
Size and mass of atoms
Atoms
: radius = 0.1nm
Nucleus
: radius = 1/10 000 of an atom
almost all of the mass is in the nucleus
Proton
: mass 1
Neutron
: mass 1
Electron
: mass very small
sum of protons and neutrons is mass number
Atoms of the same element can have different numbers of neutrons; these atoms are called
isotopes
of that element
the relative atomic mass = average value that takes account of the abundance of the isotopes of the element
Periodic table
Groups
: same group = same number of electrons in the outer shell - similar chemical properties
Period
: same period = same number of shells
Development of the periodic table
before the discovery of neutrons, protons and electrons, - elements were arranged in order of their weight
early tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed
Mendeleev left gaps for elements that hadn't been discovered, and in some places changed the order based on atomic weights
elements with properties predicted by Mendeleev were discovered and filled the gaps
Knowledge of isotopes made it possible to explain why the order based on atomic weights wasn't always correct
Metals and non-metals
elements that react to form
positive ions
are
metals
most elements are metals
found to the left and towards the bottom of the periodic table
elements that
do not
form positive ions are
non-metals
Group 0
: Nobel gases
unreactive
do not easily form molecules
their atoms have stable arrangements
8 electrons in their outer shell except helium that has 2
the boiling point increase going down the group
Group 1
: alkali metals
have characteristic properties because of the single electron
reactions with water
react vigorously
Lithium, Sodium and Potassium float and move around the surface, fizzing furiously
they produce hydrogen - for potassium and below in the group, there's enough energy to ignite hydrogen
also form hydroxides that dissolve in water to give alkaline solutions
reactivity increases going down the group
reactions with chlorine
react vigorously when heated in chlorine gusto form white salts Calle metal chlorides
as you go down the reaction gets more vigorous
reactions with oxygen
react with oxygen to form metal oxides
metal reacts with oxygen in the air to form a dull metal oxide layer
Group 7
: halogens
non-metals and consist of molecules made of pairs of atoms
as you go down the group the higher the relative molecular mass, melting point and boiling point
the reactivity of the element decreases going down the group
more reactive halogens will replace less reactive halogen from an aqueous solution of its salt
reaction with metals
form ionic bonds - form 1- ions called halides
reaction with non-metals
form simple molecular structure with covalent bonds