Atomic Structure Flashcards
Relative sub-atomic particle values
Relative mass - proton = 1, neutron = 1, electron = 1/1840
Relative charge - proton = +1, neutron = 0, electron = -1.
Structure of an atom
Most mass is concentrated in the centre where the nucleus is (small area compared to the whole atom).
Protons
Protons are fixed in an element and identify which one it is.
Neutrons
They change in each atom of an element to create isotopes.
Electrons
They orbit the nucleus in electron shells.
Same number of protons and electrons (in a neutral atom).
Isotope abundance equation
(isotope mass 1 x isotope abundance 1) + (isotope mass 2 x isotope abundance 2) /
total abundance
Mass Spectrometry -
Electron Impact
The sample is vaporized and then an electron gun (a hot wire filament with a current that emits electrons) fires electrons at it. The high energy electrons knock off one electron when they collide with the particles. This forms +1 ions.
Electron Impact equation
X(g) + e- —-> X+(g) + 2e-
Mass Spectrometry -
Electrospray Ionisation
The sample is dissolved in a volatile (evaporates quickly) solvent (water or methane) and injected through a fine needle to create a fine mist. The tip of the needle is attached to the positive terminal of a high voltage power supply. The particles are ionised and gain a proton from the solvent as they leave the needle.
Electrospray Ionisation equation
X(g) + H+ —–> XH+(g)
Mass Spectrometry -
Acceleration
The positive ions are accelerated using an electric field so that they all have the same kinetic energy. Since all the particles have the same kinetic energy, the velocity depends on the mass of each particle. Lighter particles have a faster velocity, heavier particles have a slower velocity.
Mass Spectrometry -
Ion Drift
The ions move through a region with no electric field. They drift through with the same speed as the acceleration so they will drift at different speeds according to their masses. The lighter ions travel faster and reach the detector quicker than the heavier ions.
Mass Spectrometry -
Ion Detection
The positive ions hit the negatively charged plate and are discharged by gaining electrons from the plate. This generates a movement of electrons and a current is measured. The size of the current gives a measure of the number of ions hitting the plate.
Mass Spectra
When using electron impact, some peaks may be lower m/z values due to fragments caused by the break up of molecular ions.
First Ionisation Energy
The energy required to remove one electron from each atom of one mole of gaseous atoms to form one mole of gaseous 1+ ions.
Successive Ionisation Energies
A measure of the energy required to remove each electron in turn.
Li(g) –> Li+(g) + e- (first)
Li+(g) –> Li2+(g) + e- (second)
Li2+(g) –> Li3+(g) + e- (third)
Jumps in ionisation energies
The big jumps occur when the shells become empty and the jump to start emptying the next one.
Ionisation Energy
As each electron is removed there is less repulsion between the remaining electrons so they are drawn closer to the nucleus.
As the distance decreases to the nucleus, the electrons are held more strongly so more energy is required to remove them.
Factors impacting ionisation energies
Atomic Radius
Shielding
Nuclear Charge
Ionisation energy down the group
Atoms get bigger, shielding increases, therefore the attraction between the nucleus and the outer electron is weaker.
Ionisation energy across the period
Increased nuclear charge (more protons), so atoms get smaller, therefore a stronger attraction between the nucleus and the outer electron.
How do electrons fill orbitals?
The 2 electrons per subshell have tot have opposite spins (one clockwise and one anticlockwise).
Kinetic energy equation
KE = 1/2mv^2
v = d/t
Therefore, t = d square root m/2KE
What is a photon?
If an electron is in an excited state, it can return to a lower energy level and it loses energy. The amount of energy lost will be equal to the difference in the energy levels it moves between. The energy is released as a photon.
The filling order of electrons
Orbitals are not filled in numerical order because the principal energy levels get closer together as you get further from the nucleus.
Anomalies to the filling order
Cu - 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10.
Cr - 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5.
