PHYSICAL - ATOMIC STRUCTURE Flashcards
first ionisation energy
energy required when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge
H –> H+ + e-
second ionisation energy
energy required when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a positive charge
Ti+ –> Ti 2+ + e-
factors affecting ionisation energies
- ATTRACTION OF THE NUCLEUS
= More protons in nucleus means more attraction - DISTANCE OF E- FROM NUCLEUS
= larger atom means weaker attraction - SHIELDING OF ATTRACTION FROM THE NUCLEUS
= e- in outer shell is repelled by e- in complete inner shell = weaker attraction
what is successive ionisation energy
the energy required to remove one electron after the other. An element can have as many successive ionisation energies as it has electrons
importance of jumps
Jumps are evidence for the arrangement of electrons in energy levels
NUMBER OF E- BEFORE A JUMP IS THE GRP NUMBER THAT THE ELEMENT BELONGS TOO.
- therefore group 1 jump to remove 2e-
The jump is to remove an electron from the next shell inwards which requires more energy as its closer to the nucleus so had stronger electrostatic attraction to overcome
evidence for energy levels - reference graph on notes
-Helium has largest 1st IE as its 1st e- is in the first shield closest to nucleus so has no shielding
- Nobles gases at peak but there is a decrease in IE down the group (applies to all groups)
-Groups 2 and 3 have similar repeating patterns refer to this as periodicity
explain the drop from group 0 to 1
large drop from group 0 to group 1. As group 1 has its outer electron in a a new shell further from the nucleus and is more shielded. Easier to remove so lower ionisation energy
evidence for the electron sub energy levels (period 3)
general increase in ionisation energies across a period - because as you go across a period the number of protons increases making nucleus attraction greater
2 EXCEPTIONS :
- Ionisation energy decreases from Mg to Al = outer e- in Al 3p orbital is of slightly higher energy than 3s orbital. More shielding so weaker attraction and less energy required to remove it.
- Ionisation energy decrease from P to S = In P each of the 3p orbitals contain one electron while in S one the 3p orbitals contain 2e-. Repulsion between these paired electrons makes it easier to remove despite the increase in nuclear charge.
what is TOF mass spec
mass spectrometer can be used to determine all the isotopes present in a sample of an element and to therefore identify elements
- needs to be in a vacuum otherwise air particles would ionise and register on the detector
stage 1 : ionisation
sample can be ionised using electro spray or electron impacts
ELECTRON IMPACT:
- used for low formula mass as causes larger molecules to fragment
1. Vaporised sample is injected at low pressure
2. Electron gun fires high energy e- at the sample
3. Knocks out an outer electron
4. Forms positive ions with diff charge
ELECTRO SPRAY IONISATION
- used for larger molecules
1. Sample is dissolved in a volatile, poor solvent
2. Injected through a fire hypodermic needle giving a mist
3. . The tip of the needle is attached to the positive terminal of a high-voltage power supply.
4.The particles are ionised by gaining a proton from the solvent as they leave the needle producing
XH+ ions
5. Solvent evaporates away while the MH+ ions move towards the negative plate.
stage 2 : accelaration
Positive ions are accelerated by an electric field to a constant kinetic energy
Velocity depends on mass
EK = 1/2mv2
stage 3 : flight time
Positive ions with small m/z values have same kinetic energy as those with larger m/z and will move faster
Heavier particles take longer to move through the drift area
Ions distinguished the different flight times
t = d (square root) m/2KE
stage 4 : detection
the ions reach the detector and generate a small current which is fed to a computer for analysis
current is produced by e- transferring from the detector to the positive ions. size of current is proportional to abundance of the species
For each isotope the mass spectrometer can measure a m/z (mass/charge ratio) and an abundance
periodicity melting and boiling points
sodium, magnesium, potassium = metallic bonding , mp increase due to greater +ve charged ions
silicon = macromolecualr so strong covalent bonds
phosphorus, chlorine, sulfur = simple covlent weak VdW forces
argon = noble gas so stable and weak VdW.
ionisation in periods
increases due to incresing nuclear charge and decreasing atmoic radius
outer e- held more strongly so stronger attraction
