2 bond pairs, 0 lone pairs
Linear 180° e.g. BeCl2
3 bond pairs, 0 lone pairs
Trigonal Planar 120° e.g. BF3
2 bond pairs, 1 lone pair
Bent 118° e.g. NO2
4 bond pairs, 0 lone pairs
Tetrahedral 109.5° e.g. CH4
3 bond pairs, 1 lone pair
Pyramid 107° e.g. NH4
2 bond pairs, 2 lone pairs
Bent 104.5° e.g. H2O
5 bond pairs, 0 lone pairs
Trigonal Bipyramid 120°,90° e.g. PCl5
6 bond pairs, 0 lone pairs
Octahedral 90° e.g. SF6
In 1803 John Dalton said...
That all atoms are SPHERES and all elements are made from different spheres
Plum pudding model
In 1897 J.J Thompson discovered the electron and said there were negative electrons "plums" in a positive "pudding"
Gold Leaf Experiment
1909, Ernest Rutherford. Fired positive alpha particles at gold leaf. Most went through to other side, some deflected back. Very few deflected directly back. He concluded that the atom had a very small positively charged nucleus and a negative cloud of empty space.
Electron shell discovery
1913, Niels Bohr. Found a problem with previous model (electrons would collapse into positive nucleus). He fired heat energy at atoms. The energy is absorbed by electrons and they move up an energy level and emit Em radiation when they drop back down. The photon given out is directly proportional to the frequency. E=hv. energy levels are quantised.
Nuclear fusion
-2 nuclei fuse together to make a heavier molecule -happens in the sun and other stars -needs VERY HIGH TEMPERATURES AND PRESSURES to overcome repulsive forces. E.g. H+H -> He
s subshell
1 orbital, can hold 2 electrons
p subshell
3 orbitals, can hold 6 electrons
d subshell
5 orbitals, can hold 10 electrons
f subshell
7 orbitals, can hold 14 electrons
Spin pairing
When 2 electrons occupy 1 orbital they 'spin' in opposite directions
S orbital shape
Spherical
P orbital shape
Px, Py and Pz
What does 1s2 mean?
1 is the energy level (period) s is the orbital type 2 is the number of electrons in orbital
Find the electron configuration of iron (Fe)
1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2
Electron blocks
What is ionic bonding?
Oppositely charged ions held together by electrostatic attractions
Hydroxide ion
OH -
Ammonium ion
NH4 +
Carbonate ion
CO3 2-
Nitrate ion
NO3 -
Sulfate ion
SO4 2-
Giant ionic structure
Regular structure, cubic shape and giant repeating pattern. e.g. sodium chloride
Ionic compounds properties
-high melting and boiling point ( because strong electrostatic attractions between ions) -most are soluble in water (because water molecules are polar and can attract ions to break up the structure) -hard and brittle e.g. Lithium hydroxide
What is covalent bonding?
Shared pair(s) of electrons
Covalent compounds properties
-low melting and boiling points ( because strong forces between atoms but weak forces between molecules) -soft and flexible (normally) -don't conduct electricity when dissolved in water e.g. ethanol, CO2, methane (CH4)
Diamon properties
-giant covalent structure -each carbon is bonded to four other carbon atoms -high melting point -doesn't conduct electricity -insoluble -very hard
Graphite
-giant covalent structure -each carbon is bonded to three other carbon atoms, in layers -high melting point -soft, slippery, used in locks and pencils -conducts electricity ( has delocalised electrons) -insoluble -used in pencils and as a lubricant
Silicon dioxide
-giant covalent structure -same as diamond but one oxygen between each silicon bond -high melting point -hard -doesn't conduct electricity -insoluble
What is metallic bonding?
Giant lattice structure of positive ions in a sea of delocalised electrons
Metallic structures
-high melting and boiling points (except for group 1 metals because they have large atoms and don't form as many bonds) -conduct electricity (because delocalised electrons can carry a charge) -conduct heat -malleable and ductile -insoluble
Bohr's theory
When an atom becomes excited (absorbs energy) it moves up to a higher energy level and when it eventually comes back down it emits extra energy as EM and gives off an emission spectrum
Emission spectra
Shows the frequency of light given out when an electron moves down energy levels. Appear as coloured lines on a black background.
Absorption spectra
-EM radiation passed through an element in a gaseous state. -Appear as black lines on a colourful background. -Shows the missing frequencies from an otherwise continuous spectrum. -Can be used to detect the presence of hydrogen and helium in stars.
Ground state
The shell closest to the nucleus
When electrons fall to the ground state...
... they produce a series of lines in the ultra violet part of the spectrum
When electrons fall to the second energy level...
... they produce a series of lines in the visible part of the spectrum
When electrons fall to the third energy level...
... they produce lines in the infrared part of the spectrum
Frequency =
Speed of light (3x10^8) / wavelength (m)
Energy difference between shells (J) =
Planck's constant (6.63x 10^-34 JHz^-1) x frequency (Hz)
How to do flame test
Dip nichrome wire into hydrochloric acid
Dip into solid sample
Place in blue Bunsen flame and observe colour (Alternatively, can use liquid samples)
Flame test for Li+
crimson red
Flame test for Na +
Yellow/orange
Flame test for K+
Lilac
Flame test for Ca 2+
Brick red
Flame test for Ba 2+
Apple green
Flame test for Cu 2+
Blue green
Mass spectrometer steps
Vaporisation 2.Ionisation 3.Acceleration 4.Ion drift 5.Detection
Isotopes
have the same number of protons but a different number of neutrons
How many atoms/ molecules are in one mole of substance?
6.02 x 10^23 Avogadro's constant (given exam)
number of particles=
Avogadro's number x number of moles
moles=
mass/ Mr or concentration (mol dm^3) x volume (dm^3)
mass=
Mr x moles
How to write ionic equations
Write out equation
Make into ions
Cancel out ions that appear on both sides 3.Write out ionic equation
What are spectator ions?
ions that don't get involved in the reaction
What is empirical formula?
the smallest whole number ratio of elements in a compound
how do you find empirical formula?
Write out elements involved
Write out masses or the percentages as masses (e.g. 77.5% = 77.5g)
Divide these by relative atomic mass to find the number of moles
Divide all numbers by the smallest number of moles
Write out the compound e.g. C4H8
How to find water of crystallisation
Write out two molecules involved
Write out the masses of each molecule
Divide these b the relative molecular mass to get moles
Divide all numbers by the smallest number of moles
percentage yield=
actual yield/ theoretical yield x 100
How to make standard solutions
Weigh out solid precisely
Transfer it to a beaker and wash out any solid left behind
Stir the solid to dissolve 4.Use a funnel to transfer it to a volumetric flask, rinse to make sure all solid is transferrred 5.Use a pipette to fill up with water up to graduation line
Invert a few times to mix it
When using a more concentrated solution to make a standard solution, volume to use=
final concentration/ initial concentration x volume required
Titrations method
-used to find concentration -put acid or alkali in burette with known concentration -use pipette to measure acid or alkali and out in conical flask -add drop by drop until colour changes (the endpoint) -read from burette the amount of acid / alkali used. read at eye level from bottom of miniscus. record to two decimal places -repeat until concordant results (0.1cm^3 away from each other
phenolphthalein indicator
Turns: acid- colourless alkali- pink
methyl orange indicator
Turns: acid- yellow alkali- red
How to do titration calculations
Write out BALANCED equation ratio conc vol moles ^put in all values and find moles (moles= conc x volume) multiply using the ratio to find the moles of the other
how to convert from cm^3 to dm^3
divide by 1000
groups in periodic table
-columns -have similar properties -same number of electrons on outer shell
periods in periodic table
-rows -have the same number of electron shells
melting points of elements in periods 2 and 3
-generally increase as metal ions have increasing positive charge, increasing number of delocalised electrons and smaller ionic radius so have a stronger metallic bond -silicon has very high because giant covalent structure -phosphorus has a lower melting point because it has a simple molecular structure -sulphur has a larger simple molecular structure than phosphorous so higher melting point -chlorine is even lower because it has a simple molecular structure -Argon has very low melting point because only exists as individual atoms
what is ionisation energy?
the minimum amount of energy required to remove 1 mole of electrons form one mole of atoms in a gaseous state
is ionisation always an exothermic or endothermic process?
endothermic, requires energy, has a positive value
What happens to ionisation energy down a group?
it decreases, because shielding increases
What happens to ionisation energy as you go across a period?
it increases, because increasing number of protons means there's increasing nuclear attraction and more energy is needed to remove the outer electron
metal+ water→
= metal hydroxide+ hydrogen
metal+ oxygen →
=metal oxide
what colour are group 2 metal oxides?
When they burn in oxygen white solids are formed
are group 2 oxides &hydroxide acids pr bases?
Bases, group 2 oxide + water → metal hydroxide, the hydroxide ions devolve and ionise in the water, producing strongly alkaline solution
EXCEPTION : MgO only reacts slowly with water and the hydroxide isn't very soluble
what's the trend of reactivity of group 2 with water?
reactivity increases down the group because the hydroxide gets more soluble
what's the trend for the thermal stability off group 2 carbonates?
thermal stability increases down group
What happens to the solubility of group 2 carbonates down the group?
solubility DECREASES down the group
What happens to the solubility of group 2 hydroxides down the group?
solubility INCREASES down the group
are cations positive or negative?
positive think: cats are pawsitive :)
are anions positive or negative?
negative think: onions are bad :(
solubility of nitrates
all: Potassium Lithium Ammonium Nitrates Sodium are soluble. think: PLANS
solubility of halides
most are soluble except: silver halides, copper iodide (white), lead chloride, lead bromide(white) and lead iodide (yellow)
solubility of hydroxides
only: Sodium Calcium Ammonium Lithium Potassium Strontium and barium hydroxides are soluble think: SCALPS
solubility of carbonates
Potassium Ammonium Lithium Sodium are soluble, think: PALS
Most carbonates aren't soluble -copper carbonate is blue/green -silver carbonate is yellow -most other carbonates are white
What reactions make soluble salts?
precipitation reactions 2 soluble salts -> insoluble salt + soluble salt
how to make soluble salt ?
acid + metal(or insoluble base e.g. metal oxide/hydroxide)
acid + alkali
steps of making a soluble salt with acid + metal or insoluble base
add metal/metal oxide/metal hydroxide to acid
How do you get a pure dry sample of a salt?
Filter
Rinse with deionised water
Dry