Atomic Structure Flashcards
Relative mass and charge
Proton M= 1 C= +1
Neutron M= 1 C= 0
Electron M= 1/1835 C= -1
atomic number definition
The atomic number is equal to the number of protons.
mass number definition
The mass number is equal to the number of protons and neutrons combined.
Atomic Radius size
determined by number of protons and electrons
Cations & Anions
Positive Ions (cations) ā lost electrons
Negative Ions (anions) ā gained electrons
Isotopes
Isotopes are atoms with the same number of protons but a different number of neutrons
Isotopes of the same element have the same chemical properties because they have the same electron configuration
Ionisation energy definition
Ionisation energy is the amount of energy needed to remove a mole of electrons from a mole of atoms, in the gaseous state.
(K(g) -> K+(g) + e-)
units are kJmol-1
Successive ionisation energies
1st IE Na(g) -> Na+(g) + e-
2nd IE Na+ (g) -> Na2+(g) + e-
3rd IE Na2+ (g) -> Na3+(g) + e-
Why is the second ionisation energy of S higher than the first?
The second electron is removed from an ion that already has a positive charge.
Factors influencing IE
-more protons, stronger attraction, more energy needed to remove outer e-
-closer e- is to nucleus, stronger attraction, more energy needed to remove outer e-
-more shells, more shielding, less energy for ionisation
Using successive IE data to identify element
- The biggest jump is between the 4th and 5th ionisation energies
- the 5th electron is on the shell closer to the nucleus
- The element must have 4 electrons on its outer shell
- in period 3 this must be Silicon.
Shells
Cr = 1s2 2s2 3s2 3p6 4s1 3d5
Cu = 1s2 2s2 2p6 3s2 3p6 4s1 3d10
Ca2+ = 1s2 2s2 2p6 3s2 3p6
Trends across period
- greater nuclear charge
- greater attraction between e- and nucleus
- shielding stays same
Trends down group
- more shells
- more shielding
- weaker attraction between e- and nucleus
- IE decreases down group
Explain why Aluminium has a lower 1st IE than Magnesium
- The first e- removed from Mg is from a 3s sub level.
- The first e- removed from Al is from a 3p sub level.
- The 3s sub level is lower in energy than 3p.
- Therefore less energy is needed to remove the electron from Al.
Applies to any element in group 3
Explain why Sulfur has a lower 1st IE than Phosphorous
- The first e- removed from P is from a 3p sub level and is unpaired.
- The first e- removed from S is also from a 3p sub level, but is from a paired orbital.
- This means Sulfur has a lower ionisation energy due to electron pair repulsion.
- Therefore less energy is needed to remove the electron from S.
Applies to any element in group 6
time of flight mass spectrometer
(1) Vacuum
(2) Ionisation
(3) Acceleration
(4) Ion Drift
(5) Detection
(6) Data Analysis
Why are the sample particles ionised?
- So they can be accelerated towards the negatively charged plate
- So they generate a current when they hit the detector
How is the ion accelerated?
- Positive ions attracted to the negatively charged plate
- All ions have the same kinetic energy
How are ions separated in the flight tube?
- Ions travelling at higher speeds (small m/z) move ahead of those travelling more slowly (large m/z)
How are the ions detected?
- Each ions hits the detector
- Ion gains an electron
- Generates a current
- Size of the current is proportional to the abundance of the ion
How is a current generated?
e- transferred from detector to positive ion
Electron impact
(also known as electron ionisation)
sample vaporised and high energy e- fired at it by an electron gun. e- knocked off to form 1+ ions
X(g) -> X+(g) + e-
Electrospray ionisation
dissolve sample in volatile solvent and inject through hypodermic needle attached to positive terminal of high voltage power supply. particles gain proton as leave needle
X(g) + H+ -> XH+(g)
Calculating relative atomic mass (Ar)
(Mass 1 x % 1) + (Mass 2 x % 2) + (Mass n x % n) / 100
Mass of one atom in KG
mass / 6.022 x10^23 / 1000
time of flight equations
KE = 0.5 x mass x velocity^2
v = d / t
t = time of flight (s)
d = length of flight tube (m)
š£ = velocity of the particle (m sā1)
m = mass of the particle (kg)
KE = kinetic energy of particle (J)
Relative abundance
