Ch4 Relative Tomic Mass, Isotopes, Mass Spectrometry Flashcards
Isotopes
Atoms of the same element (same atomic number) but different mass number due to the different number of neutrons in the nucleus.
Who built the mass spectrometer and what does it do
Francis William Aston
Measure masses of atoms
What did Aston find with neon
Neon gas had two types of atoms one with mass 20, one with mass 22
Concluded that neon gas consisted of atoms with different numbers of neutrons in the nucleus
What did Aston also determine
Determined the percentages of the isotopes in a typical sample of these elements
How to find avg mass of cl
1.Multiple percentage by mass number for both isotopes
- Add answers together (100atoms mass)
- Divide by 100
Relative atomic mass
The average of the mass numbers of the isotopes of the element,
As they occur naturally
Taking their abundance into account
And expressed in a scale in which the atoms of the carbon 12 isotope have a mass of exactly 12 units
What units does realtive atomic mass have
lol none
Positive ion
Cation
Negative ion
Anion
How many electrons does 17 cl- have
18
How many electrons does 12 mg 2+ have
10
Uses of a mass spectrometer
-Identify presence of isotopes
-measure relative abundance
-measure relative atomic mass of an element
Name the 5 stages of mass spectrometry
- Vaporisation
- Ionisation
- Acceleration
- Serparation unit in a magnetic field/ deflection
- Detection
Vaporistation
A small amount of gas or liquid is injected in the sample inlet
A vacuum is inside so liquid turns to gas
If a liquid is injected into the sample inlet, it will be vaporised into a gas using the vacuum.
Ionisation
atoms or molecules are turned into ions using electric gun (in the ionisation chamber)
-a heated filament that gives off electrons-
These electrons are fired at a sample and knock out electrons from the sample’s particles to produce Positive ions.
Why is a vacuum needed inside the spectrometer
So the particles can move along without colliding with any air molecules
Accelerator
Positive ions produces pass between series of negatively charged plates.
-positive ions in the ionisation chamber are attracted to the negative plates and are accelerated
A fine beam of ions then passes into the analyser
Separation unit - magnetic field
In the analyser, the particles are mad to move in a curved path using a magne tic field.
- lighter particles are easier to deflect than heavier ones
- lighter ones are pushed further off course than heavier
Ions are separated according to their masses
Detector
Responds to the number of ions hitting it
-by changing strength of magnetic field, the operator brings ions of diff masses to focus on the detector
- signal is amplified into an electric current and viewed on a computer screen and sent to a recorder.
Mass of one atom of an element
1/12 mass of one atom of carbon -12
How many electrons can s, p , d sub levels hold
S - 2 ē
P - 6 ē
d - 10 ē
Aufbau principle
States that when building up the electronic configuration of an atom in its ground state, the electrons occupy the lowest available energy level.
Pauli exclusion principle
No more than 2 electrons may occupy an orbital and they must have opposite spin.
Hands rule of maximum multiplicity
When 2 or more orbitals of equal energy are available, electrons will electrons occuoy them singly before filling them in pairs
Two exceptions and give their electronic configurations.
Cu 29 copper 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10,
Cr 24 chromium 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5
