Atomic Structure Flashcards
What is the first ionisation energy?
The energy required to remove one electron from each atom in a mole of gaseous atom to form 1+ ions.
Total ionisation energy is total of all electrons taken.
How does ionisation energy vary through each energy level/shell?
Ionisation energy will increase from i1 to i3 due to getting loser to the nucleus. So increasing positive charge attracts the remaining electrons more strongly.
Experiements found:
Increase when 1st electron is removed
Increase when next electron from the next shell is removed
Huge increase in last 2 electrons
How do we know the electron configurations of atoms?
We can knock the electrons off the atoms one by one and measure how much energy was needed at each stage. We interpret variations in ionisation energies.
Factors affecting Ionisation energies
Ionisation energy increases if:
Distance decreases
number of inner shielding shells decreases
If positive charge on nucleus increases
THE STRENGHEN ELECTROSTATIC FORCE ON OUTER ELECTRON
Ionisation energy decrease if :
Distance increases
number of shielding shells increases
positive charge on the nucleus decreases
THEY WEAKEN ELECTROSTATIC FORCE ON OUTER ELECTRON
What are the shapes of an s and p orbital ?
S is a spherical shape
P is a pair of lobes. The 3p orbitals in a sub level are perpendicular to each other and are shown on different axes.
How are electrons filled?
They are filled via the amount of energy is needed. So differences between shielding from the nucleus means different sub levels have different energies. The electrons will always fill the sub level with the lowest energy first.
Example: 4s is always filled before 3D as it requires less energy. Removing electrons IT DOES NOT MATTER
What is Hunds rule of maximum multiplicity
1)Every orbital in a sublevel is singly occupied before any orbital is doubly occupied.
2) All of the electrons in singly occupied orbitals have the same spin (to maximize total spin).
When assigning electrons to orbitals, an electron first seeks to fill all the orbitals with similar energy and the same spin before pairing with another electron in a half-filled orbital. So they occupy the max number of orbitals.
What does time of flight mass spectrometry do?
-finds the abundance and mass of each isotope
- find relative mass of a substance made of molecules
Stage 1 (time of flight spectrometry)
Ionisation
-either electron impact or electrospray
What is electron impact ionisation?
Sample is vapouriest and electrons are fired at it. The high energy electrons come from an electron gun which is made up of hit wire filament. This knocks of 1 electron from each particle forming a 1+ ion. Ions are then attracted towards a negative plate where they are accelerated
What is electrospraying
Sample dissolved in a volatile solvent and injected through a fine hypodermic needle to give a fine mist. The tip of the needle is attached to the positive terminal of a high voltage supply where the particles are ionised by gaining a proton from the solvent as they leave the needle producing ions with the mr + 1 mass.
When are each technique used?
-electron impact is used for elements and substances with low formula mass and forms molecular ions
Molecular ions often fragment
- electrospray is used for substances with higher molecular mass.
Stage 2
Acceleration
-positive ions are accelerated using an electric field so that they all have the same kinetic energy
-so given they all have the same kinetic energy the velocity of the particle depends on its mass, and heavier particles have a slower velocity
Stage 3
Flight tube
-positive ions travel through a hole in a negatively charged plate towards the detector the velocity at which this happens depends on their mass.
-time of flight is proportional to the square root of the mass of the ions.
Stage 4
Detection
-positive ions hit a negatively charged plate and are discharged via gaining electrons on the plate, this generates movement of electrons therefore a current which is measured. Size of current gives a measure of number of ions hitting the plate
The mass spectrum
-Shows mass to charge ratio and abundance of each ion that reaches the detector.
-Relative atomic mass of the element can be found by calculating the mean mass of the isotopes shown on the graph
-for molecules which where ionised via electron impact the greatest m/z value is from the molecular ion and this will tell the relative molecule mass. Other peaks will be due to isotopes
May also be peaks at lower m/z values due to the fragmentation of the molecular ion
Why is mass spectrometry done in a vacuum?
If not air molecules causes collisions with the beam of ions obstructing their path
Why is mass spectrometry done in a vacuum?
If not air molecules causes collisions with the beam of ions obstructing their path
What can change the path of an ion?
The m/z value (lightest will be deflected the most)
The strength of the magnetic field
Why is your calculated relative atomic mass different to the periodic table?
Periodic table accounts for other isotopes
Different isotopes are detected
Why is the melting point of sodium lower than magnesium?
Fewer protons and delocalised electrons.
Na is a bigger atom
