Atomic Structure Flashcards
Stage one - electron impact
Electron impact - electrons are fired at the sample using a high energy electron gun. This causes the ejection of the electron from the sample forming an ion of 1+ charge.
Eg Mg —> Mg+ + e-
The electron gun is a hot wire filament that acts the source of electrons. The ions are always positively charged.
Stage 1 - electrospray ionisation
Electrospray ionisation - methord used for high mr compounds such as protiens and other macro molecules.
The sample X is dissolved in a volatile solvent (eg water or methanol) and injected through a fine hypodermic needle to give a fine mist (aerosol).
The tip of the needle is attached to the positive terminal of a high-voltage power supply.
The particles are ionised by gaining a proton (ie an H+ ion which is simply one proton) from the solvent as they leave the needle producing XH+ ions (ions with a single positive charge and a mass of Mr + 1).
X(g) + H+ —> XH+(g)
The solvent evaporates away while the XH+ ions are attracted towards a negative plate where they are accelerated.
Stage 2 acceleration
Acceleration, once the sample has been ionised, the ions pass into the next compartment - they are attracted to the electric field.
The next stage involves an electric field. The ions accelerate so they all have the same kinetic energy.
Kinetic energy = 0.5mv(squared)
Lighter ions will accelerate faster than the heavier ions.
Stage 3 flight tube
The flight tube is a fixed distance so that the ions travel through. No electric field means the ions drift through at constant velocity. Lighter ions are faster so reach the detector first - this allows the ions to separate.
Stage 4 detection
Detection - the ions hit a detector and gain an electron. This generates an electrical current. The size of the current is related to the abundance of a particular ion if more ions of a particular type hit the generator, then a greater current is produced
The peak with the larger m/z value (furthest to the right) is molecular ion peak m+ and its value is the mr of the sample.
The other peaks are caused by fragmentation of the molecular ion, producing smaller ions.
The peak with the largest abundance is the parent ion or the base peak rarely the molecular ion peak is caused by the most stable fragmentation.
When do subshell energy increase?
As we move away from the nucleus
Rules for writing electron configurations
• Electrons enter the lowest energy orbital first.
• Electrons enter the orbitals singularly, they only pair when no empty orbitals are available.
• Pair of electros in orbitals must have opposite spin - this minimises the repulsion between two electrons in the same orbital.
Why does the electron configuration not show individual orbitals in the 2p shell
The eelctron configuration only shows the subshells and not the individual orbitals
The energy of the 3d shell
The energy of the 4s subshell is less than the energy in the 3d subshell. This means we fill the 4s subshell before we fill the 3d subshell
What elements are exeptions to writing the elctron configuration
Chromium and copper
Why is chromium an exception of the electron configuration
The 3d subshell is more stable when it is either half full or completely full.
So in the case of chromium, by having only one electron in the 4s subshell, it can have a half full 3d subshell making it more stable.
Why is chromium an exception of the electron configuration
The 3d subshell is more stable when it is either half full or completely full.
And in the case of copper, by having only one electron in the 4s subshell, it can have a full 3d subshell.
Why is chromium an exception of the electron configuration
The 3d subshell is more stable when it is either half full or completely full.
And in the case of copper, by having only one electron in the 4s subshell, it can have a full 3d subshell.
Easiest way to find the electon configuration
Easiest way to figure out the electron configuration, count the periods downwards, this determines amount of energy levels for example: 3 periods down means that the outer electron is in the third energy level. Next count how many across the their subshell group laterally. This tells us how many electrons are in the subshell of the highest energy level.
Electron configuration of ions
When ions form the subshell with the highest energy gains or loses an electron. In this case the 3s subshell has the highest energy so two electrons are lost from there.
Once the 4s subshell contains electrons, it has now higher energy than the 3d subshell. So when forming ions, the electrons are always lost from the 4s subshell before the 3d subshell. There are no exceptions to this rule.
Electrons absorbing energy
Electrons can absorb energy from heat, electricity or electromagnetic radiation. When it does this, it moves up an energy level.The energy absorbed is then transferred back to the electron once it has fallen to ground state.
Evidence for the energy levels
• Neil Bohr proposed the idea of electrons being found in fixed energy
levels.
• The emission spectrum for the hydrogen atom shows discrete bands-spectral lines.
• These lines have a characteristic frequency and therefore energy value, corresponding to the energy levels of the H atom.
• The discrete energy levels are sometimes referred to as “quanta”-packets.
• The spacing between energy levels is not equal- the energy levels converge as they get further from the nucleus.
