1 - Atomic structure Flashcards
What particles do atoms consist of
Protons, Neutrons and Electrons
What is the atomic number Z
The number of protons
What is the mass number A
The number of Nucleons and therefore the mass of the atom in relation to a twelfth of the mass of a carbon 12 atom
What are Isotopes
Atoms with the same number of protons, therefore the same atomic number but differing numbers of neutrons, so they are chemically identical as they have identical electron structure, just differing stabilities and masses
In 1913, what was Niels Bohr’s theory for the structure of the atoms
Much like the solar system, a small positive charge at the center and tiny negative charges orbiting it
who discovered the neutron and when
James Chadwick in 1932
What are the two methods of Ionization in mass spectroscopy
Electron spray ionization - where the sample is sprayed through a positively charged needle which leads it to pick up a proton and a +1 charge which is needed to be taken off if reading from the mass to charge ratio graph.
Electron impact ionization - where an electron gun is fired perpendicular to the flight path of the particles, causing an electron to be knocked of the molecule giving it a +1 charge.
What are the six steps in Mass spectroscopy
Evacuation - The whole chamber has to be a vacuum to prevent impact with air molecules
Ionization - giving each of the molecules a +1 charge to allow it to be detected, also occasionally doubly charging causing a peak at half the mass to charge as the original peak
Acceleration - the positive ions are attracted towards a negatively charged plate and accelerate towards it, each attaining the same energy, therefore having lighter particles travel faster.
Ion drift - The ions pass through a hole in the negatively charged plate, allowing a beam to ‘drift towards the detector’ maintaining constant speed.
Detection - Due to lighter particles traveling faster, the times will be shorter, and the there will be a flow of charge which is detected
Data analysis - this data is passed through a computer which produces a mass / charge ratio graph
what is Ionization energy, or IE
The energy required to remove a mole of electrons from a mole of atoms in the gaseous state and is measured kJ/mol
What is the trend in ionization energy across a period and why
There is a general increase along the period apart from when a sub-shell is either half full or completely full, which gives it relative stability, so the next element along the period will have a FIE lower than the half full. this general trend is due to the atomic radius decreasing due to a greater positive attraction of the nucleus
What is the trend in ionization energy down a group and why
As you go down a group, the FIE massively decreases due to increased shielding and increased atomic radius, causing the electrostatic attraction to be less for the outer shell electrons
