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Atomic structure (Structures (Atoms :star: :star: (O, H) Smallest amount…
Atomic structure
Structures
Atoms
:star: :star: (O, H)
Smallest amount
of an
element
that still retains all the
features
of that
element
Element
:star: :star: (O)
One type of
substances
that
can't
be
chemically
broke down into
simpler
substances
Molecule
:star: :star: (O2)
+2 atoms
chemically
bonded
together through
intramolecular forces
Compound
:star: :star: (H2O)
+2 atoms
of
different elements
chemically
bonded
together through
intramolecular forces
Mixture
:star: :star: (air)
+2 atoms
or
molecules
mixed together, but
not
chemically
bonded
mixture
:
compound
/////////////////////////////////
no fixed composition
fixed composition
separated physically by properties
separated chemically by element
no chemical bonds between atoms
chemical bonds between atoms
Separating mixtures
Filtration
(sand, water)
Separate insoluble substances
use filter paper, dry solute after
Crystallisation
(salt water)
Separate soluble substance
Evaporate solvent (dish)
Preferably in water bath (gentle)
Crystal round edge of solution
Rest of solvent evaporate (room temp)
Distillation
(salt water)
To separate solution solute and solvent
Vapour goes in condenser, cool-down
(glass tube, water flow cooling jacket)
Collected in receiving vessel (purified)
Solute left in heating flask
Fractional distillation
(Ethanol, water)
Separate miscible (dissolved) liquids
Liquids have different boiling point
Difficult to distil similar boil points (vapour)
Fractionating column - Glass beads
Higher boil points condense back to flask
Ethanol burns blue flame - biofuel, alcohol
Chromatography
(pen dye, ink)
Some solvents dissolve better than others
Dab solution on pencil line (capillary tube)
Put paper in, pencil line above solvent
Relative solubility - distance up paper
History of the atom
Dalton
(early 1800s)
Atoms are tiny hard spheres
Elements had different masses
Atoms can't be split; chem rearrange
Helps visualise atomic structure
JJ Thomson
(late 1800s)
Discovers electrons (plum pudding)
Tiny -ve, 2000th of lightest atom
electrons embedded in cloud +ve charge
Gieger & Marsden
Experiment, shoot alpha particles
(+ve particles) at thin piece of gold
Should have passed through (cloud)
Particles scattered instead
Rutherford
Positive charge concentrate, dense centre
Electrons orbit round nucleus (centre)
Niels Bohr
(1914)
Electrons orbit in energy levels, set distances
Energy release when e- fall an energy level
(from high to low energy level)
Scientists, James Chadwick
(1932)
Nucleus had neutrons (missing mass)
Neutrons must have no charge J
James proves existence with experiment
Atoms
Symbols
Universal communication
Oxygen = O; Sodium = Na
Columns = Group; Rows = Shell
Staircase = non-metal / metal border
Metalloids = Ge, Si (semi-metals, border)
All substances are made of them
Nucleus = Protons + Neutrons = +ve
Electrons = Orbiters of the nucleus = -ve
Subscript - below
Superscript - above
Coefficient - to the left
Chemical equations
Reactant + Products
(Hydrogen + Oxygen = water)
Reactions - atoms are
rearranged
Balanced -
same amount
of atoms
each side
Symbols - help see substance
amounts/states
(CaCO3 = CaO + CO2)
Law of conservation of mass
Total
mass
of the
products
in a
reaction
is
equal
to the total
mass
of the
reactants
State symbols
s = solid; l = liquid
g = gas; aq = aqueous
(dissolved in water)
Structure of the atom
Protons
Positive charge(+1); 1 relative mass
Neutrons
No charge/neutral(0); 1 relative mass
Electrons
Negative charge(-1); 2000th relative mass
Normal atom
No. of protons = No. of electrons
No overall charge; 1 - 1 + 0 = 0
Element = no. of protons
Atomic number
No. of protons; order of periodic table
Relative atomic mass
No. of protons + no. of neutrons
electron mass to small to count
Number of neutrons
Mass number - atomic number
Ions, atoms, isotopes
Ions
A charged atom
(e.g. metal reacts w/ non-metal)
Gain electrons = anion = -ve charge
Lose electrons = cation = +ve charge
Atoms (lose/gain) electron (non-metal/metal)
O ion = (+8) + (-10) = (-2) charge
Body has 7 x 10^27 atoms
Atom size - 5 x 10^-10 m
Isotopes
(diff no. of electrons)
Same element, different relative mass
carbon-12 = 12 neutrons; carbon-13 = 13 neutrons
Sometimes extra neutrons = radioactive (unstable)
Different physical properties (density, radioactivity)
Same chemical properties
(react depends on e.structures)
Electronic
structures
Electron shell diagram
Shell = energy levels
Further = higher energy level
Order is
2,8,8
(11 e- = 2,8,1
Fourth goes to 2 then gets complex
Properties
New row = new energy level
Period No. = amount of e- in outer shell
Chemical properties depend on e-
Period elements react similarly
Group 0 - noble gases - very unreactive
Noble gas - 8 outer e- (He has 2 outer e-)
Physical
:
Chemical
Colour, shape, size, density, volume
Flammability, Rust, corrosion, reactivity
Without changing matter's chemical composition
Changing chemical identity of a substance