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principles of chemistry - Coggle Diagram
principles of chemistry
calculations
Percentage yield = (Amount of product produced x 100)/ Maximum amount of product possible
reacting masses
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Masses of reactants & products can be calculated from balanced symbol
equations. If you are given the reacting mass of one reactant and asked to find the mass of one product formed:
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amount of substance, volume and concentration
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equations
(g) means gas, (s) means solid, (l) means liquid, (aq) means aqueous
Example of word equation: hydrochloric acid + sodium hydroxide -> sodium chloride + water
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to balance an equation: you need to make sure there are the same number of
each element on each side of the equation and if there isn’t use big numbers at the front of a compound to balance it e.g. 3H2 O
relative formula mass
Relative formula mass (Mr) of a compound: sum of the relative atomic masses of the atoms in the numbers shown in the formula
the mole
Chemical amounts are measured in moles (therefore it is the amount of substance). The symbol for the unit mole is mol.
The mass of one mole of a substance in grams is numerically equal to its relative formula mass.
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(Mr) from relative atomic masses (Ar)
For example, the Ar of Iron is 56, so one mole of iron weighs 56g.
The Mr of nitrogen gas (N2) is 28 (2x14), so one mole is 28g.
One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance
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periodic table
arrangement
Elements are arranged in order of atomic (proton) number (bottom number) and so that elements with similar properties are in columns, known as groups.
Elements in the same periodic group have the same amount of electrons in their outer shell, which gives them similar chemical properties.
elements with the same number of shells of electrons are arranged in rows called periods
electron configuration
the electronic configuration of an element tells you how many electrons are in each shell around an electron’s nucleus
for example, sodium has 11 electrons: 2 in its most inner shell, then 8, then 1 in its outermost shell.
remember- electrons fill the shells closer to the nucleus before filling any further out. 1st shell holds 2 electrons, 2nd and 3rd hold 8
metals or non-metals
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If an element is conductive and its oxide is basic then the element is a metal
If an element is not conductive and its oxide is acidic then it’s a non metal
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group vs period
group number: gives number of electrons in outer shell e.g. group 3 has 3 electrons in outer shell
period number: gives number of electron shells e.g. period 1 has 1 shell of electrons
noble gases
They have 8 electrons in their outer shell (except helium, which has 2).
They are unreactive and do not easily form molecules, because they have a stable arrangement of electrons.
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ionic bonding
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compounds have no overall charge, therefore charges of ions must cancel out
dot and cross diagrams
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Ionic bonds are formed by the transfer of electrons from the outer shell of the metal to the outer shell of the non-metal
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conductivity
As a solid, the ions are in fixed positions so can’t conduct electricity
when molten or in aqueous solution the ions are free to move carrying charge
and conducting electricity
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metallic bonding
structure
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The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure
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properties of metals
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layers of atoms in metals are able to slide over each other, so metals, can be bent and shaped.
electrolysis
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experiments
During electrolysis, positively charged ions move to the negative electrode (cathode), and negatively charged ions move to the positive electrode (anode) where they gain/ lose electrons and are reduced or oxidised
aqueous solutions
lower temperature means that it is more cost effective but using aqueous solutions can make it more difficult to predict the products as there are ions present in water as well
e.g NaCl
the sodium and chloride ions split up, giving Na+ and Cl- ions
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molten compounds
mocvement of ions
when the ions reach the electrodes they either gain or lose electrons and are discharged (they lose their charge)
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electrodes are typically made of an inert substance such as graphite or platinum so the electrodes do not react with the electrolyte or the products made in electrolysis
states of matter
three states of matter
solids
strong forces of attraction between particles, so particles are held in a fixed position, forming a regular lattice arrangement
the particles don't move, they vibrate around a fixed position
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liquids
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weak force of attraction, so are randomly arranged and are free to move around each other, while still touching
they have a definate volume but not a definate shape, so will fill the bottom of a container
the particles are constantly moving with random movement, with the speed increasing as heat increase.
gas
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they are constantly moving with random motion, with the hotter the gas gets, the faster they move
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interconversions
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when a solid is heated, its particles gain more energy. this makes the particles vibrate more, which weakens the forces that hold the solid together. at certain temperatures, the particles have enough energy to break free from their positions. this is melting
when a liquid is heated, the particles get even more energy. this energy makes the particles move faster, weakening the bonds and breaking them. at certain temperatures, the particles have enough energy to break their bonds. (evaporation)
dilution
when water is added to a solution, the colour becomes less intense and the solution becomes more dilute
diffusion
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bromine and air
fill half a gas jar with bromine gas, and the other half full of air. separate the 2 with a glass plate. when you remove the glass plate, the brown bromine gas diffuses through the air, and eventually it will diffuse right through the air
solubility
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as pressure of gases increases, solubility increases
as temperature of gases increases, solubility decreases
solubility curves
To plot a solubility curve, the maximum mass of solvent that can be dissolved in 100 g of water before a saturated solution is formed, is determined at a series of different temperatures
practical
Prepare a two beakers, one as a hot water bath and one as an ice bath
Using a small measuring cylinder, measure out 4 cm3 of distilled water into a boiling tube.
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definitions
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saturated solution
a solution where the maximum amount of solute has been dissolved, so no more will dissolve in the solution
elements, compounds and mixtures
separation techniques
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filtration
if you have produced e.g. a precipitate (which is an insoluble salt), you
would want to separate the salt/precipitate from the salt solution.
crystallisation
If you were to have produced a soluble salt and you wanted to separate this salt from the solution that it was dissolved in
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pure vs impure
a pure substance is a single element or compound, not mixed with any other substance
pure substances melt and boil at specific temperatures so melting and boiling data can be used to distinguish pure substances from mixtures which melt over a range of temperatures
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chromatogram
Compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents
chromatography practical
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Use a different capillary tube to put a tiny spot of each colouring A, B, C and D on the line
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Pour water into the beaker to a depth of no more than 1 cm and clip the top of the chromatography paper to the wooden spill. The top end is the furthest from the spots
Carefully rest the wooden spill on the top edge of the beaker. The bottom edge of the paper should dip into the solvent
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Remove the paper and draw another pencil line on the dry part of the paper as close to the wet edge as possible. This is called the solvent front line
Measure the distance in mm between the two pencil lines. This is the distance travelled by the water solvent
For each of food colour A, B, C and D measure the distance in mm from the start line to the middle of the spot
Rf values
Rf value = distance moved by substance / distance moved by solvent ( / represents a dividing sign)
atomic structure
atoms and molecules
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A molecule = formed when atoms join together by chemical bonds (can be made
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definitions
Atomic (proton) Number = number of protons (= number of electrons if it’s an atom, because atoms are neutral)
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Isotopes = different atoms of the same element containing the same number of protons but different numbers of neutrons in their nuclei
Relative atomic mass (of an element) = an average value that takes account of the abundance of the isotopes of the element
covalent bonding
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why do the melting and boiling points of substances with simple molecular structures increase with increasing relative molecular mass
the intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points
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Strong bonds between atoms that are covalently bonded are the result of electrostatic attraction between the positive nuclei of the atoms and the pairs of negative electrons that are shared between them
covalent bonds
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When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong.
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carbon allotropes
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graphite
each carbon atom is covalently bonded to 3 other carbons, forming layers of hexagonal rings, which have no covalent bonds between layers
the layers can slide over each other due to having weak intermolecular forces between them, rather than covalent bonds
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fullerenes
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based on hexagonal rings of carbon atoms, but may also contain rings of five or seven carbon atoms
carbon nanotubes
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their properties make them useful for nanotechnology, electronics and materials