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