Atomic Structure Flashcards
What is the plum pudding model?
An initial idea is that the atom consists of a sphere of small positive charge with a small negative charge distributed within it.
What is the electron shell model?
A model that which the atom consists of a small dense, central nucleus surrounded by orbiting electrons in shells.
What is the relative mass and charge of protons, electrons and neutrons respectively?
Proton - 1, +1
Electron - 1/1840, -1
Neutron - 1, 0
What is represented by the number A.
Mass number/ sum of protons and neutrons in an atom.
What is represented by the number Z.
Atomic Number/ equal number of protons
Define Isotopes
Isotopes
? Atoms of the same element with the same atomic number but different number of neutrons.
Define orbitals
Orbitals
? Regions of space that electrons are most likely to be in which can hold up to two electrons.
How are ions formed?
When an atom loses or gains electrons meaning it is no longer neutral and have an overall charge.
What is Mass Spectrometry
It is an analytical technique used to identify the different isotopes and find the overall atomic mass of an element.
What are the 4 steps in mass spectrometry?
Ionisation, Acceleration, Ion Drift, Detection.
Describe electron impact ionisation.
- The sample is vapourised and injected into the mass spectrometer where a high voltage is passed through.
- This causes electrons to be removed from the atoms leaving with a +1 charge.
Better for species of small molecules
Describe the acceleration step.
The positively charged ions are accelerated towards a negative charged detection plate.
Describe Ion drift.
The ions are deflected by a magnetic field into a curved path. The radius of the path is dependent on the charge and mass of the ion.
Describe the detection step.
When the positive ions hit the negatively charged detection plate, they gain an electron producing a flow of charge.
The greater the abundance the greater the current produced.
Calculating Ar from mass spectrometry
=m/z * abundance divided by total abundance
What is an electron spin?
Within an orbital, electron pair up with opposite spin, so that the atom is as stable as possible. Electron in the same orbit must have the opposite spin (represented by arrows).
What are the 3 rules for writing out electronic configurations?
- The lowest energy orbital is filled first
- Electron with the same spin fill up an orbital first before pairing begins
- No single orbital holds more than 2 electrons.
Define ionisation energy
? The minimum energy required to remove one mole of electrons from one mole of atoms in gaseous state.
When do successive energies happen?
When further electrons are removed. This requires more energy as the electrostatic attraction increases.
Trends in ionisation energy, along a period and down a group.
Along a period - increases, due to decreasing atomic radius and greater electrostatic forces of attraction
Down a group - decreases, due to an increasing atomic radius and shielding which reduces the effect of the electrostatic forces of attraction.
Describe electrospray ionisation
Good for high Mr compounds
- Sample molecules are dissolved in a volatile solvent
- Sample is injected through a hypodermic needle to give fine aerosol
- The tip of the needle is attached to the (+) terminal of a high voltage power supply
- The sample is ionised by gaining a proton from the solvent as they leave the needle
X + H+ –> XH+
What are the advantages and disadvantages of electron impact ionisation
Sometimes part of the molecules are knocked off by high energy electrons - fragmentation
Parts of methyl groups or side chains are removed.
Detects the exact Mr
What are the advantages and disadvantages of electrospray ionsiation
Soft ionisation technique - limited fragmentaion
Data would be given in Mr+1 You need to remember to subtract the mass of the proton to find the correct Mr
Why are there multiple peaks?
Different isotpoes
