Atomic structure, Amount of substance, Shapes of molecules, Halogens, Alkaline Earth Metals and Craking Flashcards
Mass number, A
Number of protons+number of neutrons
Atomic number, Z (bottom)
Number of protons
A mass spectrometer determines…
The mass of separate atoms
In a mass spectrometer there is a high vacuum. Why?
So that the ions do not collide with air molecules which might stop them reaching the detector.
In a mass spectrometer the sample is investigated in its gaseous state. If a sample is a solid what is done to it?
It is vaporised first by heating it.
What are the four stages of the mass spectrometer?
Ionisation
Acceleration
Deflection
Detection
What happens in ionisation in a mass spectrometer?
A beam of electrons from an electron gun knocks out electrons from atoms or molecules of the sample so that they form positive ions, usually with a 1+ charge but a small number loose 2 electrons and gain a 2+ charge.
What happens in acceleration in a mass spectrometer?
Positive ions are attracted to negatively charged plates and they are accelerated. The speed they reach depends on their mass.
Some ions pass through slits in the plates. This forms the ions into a beam.
In a mass spectrometer what happens in deflection?
The beam of ions moves into a magnetic field at right angles to its direction of travel. The beam of ions is deflected into an arc. Heavier ions deflected less than lighter ones, 2+ are deflected twice as much as 1+. The stronger the field the greater the deflection.
In a mass spectrometer what happens in detection?
The magnetic field is gradually increased so that ions of increasing mass enter the detector one after another. Ions strike the detector, accept electrons, lose their charge and create a current which is proportional to the abundance of each ion.
In a mass spectrometer the computer works out…
The mass/charge ratio of the particular ion which hits the detector (not the same as the specific charge). A mass spectrum read out is produced.
Doubly charged ions behave like ions with…
Half the mass of a singly charged ion
If a molecules is diatomic you can get…
Peaks caused by ionised Cl2 molecules. These ions are molecular ions.
Mass spectrometry can be used to…
Find out the identity of an element or calculate the relative molecular mass.
Define ionisation energy
The energy required to remove a mole of electrons from a mole of isolated gaseous atoms or ions.
What is the trend going across a period in the periodic table?
Ionisation energy increases as nuclear charge increases.
What are the exceptions for the increased ionisation energies across period three and what are they evidence for?
Aluminium is lower than magnesium because the outer electron in aluminium is in a 3p orbital which is of a slightly higher energy than the 3s orbital. It therefore needs less energy to remove it.
Sulfur is lower than phosphorous, the repulsion between the paired electrons make it easier to remove, despite the increase in nuclear charge.
These are evidence for the existence of sub-levels.
What is the trend in ionisation energies down a group?
There is a decrease in first ionisation energies. The outer electron gets further away from the positive nucleus so the ionisation energy goes down, despite the nuclear charge increasing - there is also shielding by inner shell electrons.
What ionisation energy is it when electrons are removed one by one from the same atom?
Successive ionisation energies of sodium
If you are drawing the trend in first ionisation energies across period three how many kJ mol^-1 do Na, Al, P and Ar respectively?
500, 550, 1000, 1500
Define relative atomic mass
The relative atomic mass Ar, is the weighted average mass of an atom of an element, taking into account it’s naturally occuring isotopes, relative to 1/12th the relative atomic mass of an atom of carbon-12.
Or
Ar = average mass of one atom of an element/ 1/12th mass of an atom of 12C
Define relative molecular mass.
The relative molecular mass, Mr, of a molecule is the mass of that molecule compared to 1/12th the relative mass of an atom of carbon-12.
Or
Mr=average mass of one molecule/ 1/12th mass of an atom of 12 C
Define the Avogadro constant.
The number of atoms in 12g or carbon-12
How many entities are there in a mole?
6.022 x 10^23
What is electronegativity?
The power of the atom to attract the electrons in a covalent bond
What structure do you get when bonds + lone pairs = 2?
Linear and the bond angle is 180 degrees
What structure do you get when bonds + lone pairs = 3?
Trigonal planar and the bond angle is 120 degrees
What structure do you get when bonds + lone pairs = 4?
Tetrahedral and the bond angle is 109.5 degrees
What structure do you get when bonds + lone pairs = 5
Trigonal bipyramid and the bond angles are 90 and 120 degrees
What structure do you get when bonds + lone pairs = 6?
Octahedral and the bond angle is 90 degrees
At room temperature what state is fluorine in and what colour is it?
Pale yellow gas
At room temperature what state is chlorine in and what colour is it?
A greenish gas
At room temperature what state is bromine in and what colour is it?
A red-brown liquid
At room temperature what state is iodine in and what colour is it?
A black solid
What are the conditions for thermal cracking?
High temperature - 700-1200K
High pressure - 7000 kPa
What does the thermal cracking of alkanes produce?
Alkanes and alkenes
Typically an alkane and an alkene
What are the conditions for catalytic cracking?
Temperature - 720K
Low pressure
Zeolite catalyst (silicon oxide and aluminium oxide)
What is catalytic cracking mainly used to produce?
Motor fuels
What are the products of catalytic cracking?
Branched alkenes, cycloalkanes and aromatic compounds.
What lab experiment shows catalytic cracking?
Mineral wool soaked in paraffin and an aluminium oxide catalyst
What is the test for a carbon to carbon double bond?
It decolourises bromine solution
Where do the untypical properties of fluorine stem from?
F to F bond is weaker than expected. It is small and so there is repulsion between the non-bonding electrons. (In diatomic molecule)
What is the trend in bond energies for the halogens?
Decreases down the group (except fluorine which is the lowest because one smallness and electrons repelling).
What is trend for the size of atoms down the halogens?
Hey increase down the group- one extra main level down a group compared to the one above it.
What is the trend in electronegativity down the halogen group?
Decreases down the group
- shared electrons get further away from the nucleus
- (therefore) increased shielding by inner shell electrons
Despite the increasing nuclear charge.
What is the trend in melting and boiling points down the halogens?
They increase as we go down the group. The larger atoms have more electrons and this makes the van der Waals forces between the molecules stronger.
What is the trend in oxidising ability in the halogens?
The oxidising ability increases as we go up the group.
Fluorine is one of the most powerful oxidising agents known
What is one of the most powerful oxidising agents known?
Fluorine
Halogens …………………. Metal halides in a ……………….. ……………….
Halogens displace metal halides in a displacement reaction
More oxidising halogens will displace
Less oxidising halides
What is the most reducing halide ion?
IODIDE
The reducing power of the HALIDE IONS down the group?
Increases down the group(of IONS)
Solid sodium halides all react with…
Sulfuric acid
NaCl (s) + H2SO4 (l) —>……. + ………
NaCl (s) + H2SO4 (l) —> NaHSO4 (s) + HCl (g)
Steamy fumes of hydrogen chloride are seen
There is no redox reaction (no oxidation takes place)
It is just an acid base reaction
Sodium fluoride + H2SO4 produces same reaction
Which halide salts only produce acid-base reactions?
The chloride salt (e.g sodium chloride) and the fluoride salt
NaBr (s) + H2SO4 (l) —> …….. + ……..
Acid-base reaction
NaBr (s) + H2SO4 (l) —> NaHSO4 (s) + HBr (g)
Redox reaction
2Br^- —-> Br2 + 2e^- and H2SO4—-> SO2
Metal Halides react with silver ions in aqueous solution (e.g silver nitrate) to form….
A precipitate of insoluble silver halide
Silver fluoride is soluble in water and does not form a precipitate
Why is dilute nitric acid first added to the halide solution?
To get rid of any soluble carbonate or hydroxide impurities which would form insoluble silver carbonate or insoluble silver hydroxide.
(See reactions of HNO3 with OH^- (forms H2O + NO3^-) and CO3^2- (forms CO2 + H2O + NO3^-))
Silver fluoride
No precipitate
Silver chloride
White precipitate
Dissolves in dilute ammonia
Silver bromide
Cream precipitate
Dissolves in concentrated ammonia
Silver iodide
Pale yellow precipitate
Insoluble in concentrated ammonia
What is the redox reaction called where some atoms of the same element increase and other decrease?
Disproportionation
Cl2 (g) + H2O (l) ……. + ……..
Cl2 (g) + H2O (l) HClO (aq) (chloric I acid) + HCl (aq) (Hydrochloric acid)
Chloric I acid is a….
Oxidising agent and kills bacteria by oxidation. It is also a bleach.
Apart from chlorine what else is added to swimming pools instead?
Sodium/calcium chlorate
NaClO(s) + H2O Na^+ (aq) + OH^- (aq) + HClO (aq)
(In alkaline solution the equilibrium moves to the left and the HClO is removed as ClO^- ions. To prevent this swimming pools are kept slightly acidic)
……. Is lost rapidly from …… In ……
Chlorine is lost rapidly from pool water in sunlight.
Chlorine reacts with cold, dilute sodium hydroxide (alkali) to form…
NaClO which is a bleach (other halogens behave similarly)
Why are the alkaline earth metals named so?
Their oxides and hydroxides are alkaline
How many outer electrons do the alkaline earth metals have?
2
What is the trend in melting points in the alkaline earth metals?
Decreases as we go down the group. The sea of delocalised electrons are further away from the positive nuclei.
(Magnesium goes against this trend because it’s lattice arrangement is different which makes the atoms easier to separate)
Alkaline earth metals form ions of…
2+ charges
What is the trend in reactivity of the alkaline metals?
They get more reactive as they go down the group.
The alkaline metals are always…
Oxidised - they loose two electrons.
What is the trend in reactivity of alkaline earth metals with water?
They react more going down the group.
What is the standard reaction of an alkali earth metal and water?
M (s) + 2H2O (l) —-> M(OH)2 (aq) + H2 (g)
What is the standard reaction of an alkali earth metal and steam?
M (s) + H2O (l) —-> MO(aq) + H2 (g)
What is the trend in solubility for the hydroxides?
Solubility increases down the group
What is the most soluble hydroxide?
Barium hydroxide
How soluble is magnesium hydroxide?
Almost insoluble
How soluble is calcium hydroxide?
Sparingly soluble
How soluble is strontium hydroxide?
More soluble
How soluble is barium hydroxide?
Completely dissolves
What is the solubility trend in the sulfates?
They are more less going down
How soluble is barium sulfate?
Insoluble (barium meal)
Test for sulfates?
Solution is acidified with nitric acid. Barium chloride is added - if sulfate is present a barium sulfate precipitate is formed
