PHYSICAL CHEM - ATOMIC STRUCTURE Flashcards
What is the diameter of the nucleus?
approx 10^-15 m
What is the diameter of an atom?
approx 10^-10 m (~100000x the diameter of the nucleus)
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/1840
Why do protons not repel each other in the nucleus?
protons and neutrons are held together by strong nuclear force which is strong enough to overcome the repulsion between protons in the nucleus
What are isotopes?
atoms of the same element with the same no. of protons but a diff no. of neutrons
How can we use isotopes for carbon dating?
- some isotopes are unstable and radioactive. they become stable by emitting radiation over time
- this means that we can use the amount of an isotope in an object to work out how old it is
What are the 4 types of sub-shell?
- s
- p
- d
- f
How many orbitals does each subshell contain?
- s: 1
- p: 3
- d: 5
- f: 7
How many electrons can each orbital hold?
2
What is the Aufbau principle?
orbitals with the lowest energy are filled up first
What is the Pauli exclusion principle?
each orbital can only hold 2 electrons and they must have opposite spins
What is Hund’s rule?
electrons fill orbitals separately before they start sharing
Which orbital is filled first: 3d or 4s? why?
4s - lower in energy than 3d
What 2 elements are exceptions to the rules when filling up orbitals and why?
- copper - only fills 1 electron in the 4s orbital allowing 10 to go into the 3d orbital in order to have a more stable configuration
- chromium - only fills 1 electron in 4s and 5 go into 3d because 5 single electrons in each d orbital is more stable
What is ionisation energy?
the energy required to remove 1 mole of electrons from a mole of atoms in the gaseous state (measured in KJ mol ^-1)
What is the trend in first ionisation energy down a group?
IE decreases
Explain why ionisation energies decrease when you go down a group?
- increase in shielding
- increase in distance of outer electron
- less attraction between outer electron and nucleus
What is the trend in first ionisation energy across a period?
IE increases
Explain why ionisation energies increase when you go across a period?
- increased nuclear charge
- greater force of attraction between nucleus and outer electron
- same amount of shielding
Why is it easier to remove an electron from Al than Mg?
- outer electron in Al is in 3p orbital, outer electron in Mg is in 3s orbital
- 3p orbital is slightly higher in energy than 3s orbital
Why is it easier to remove an electron from sulfur (S) than from phosphorus (P)?
- outer electron in S is paired with another electron
- it is easier for S to lose one electron due to repulsion between paired electrons
What is a mass spectrometer?
accurate scientific instrument used to determine relative isotopic mass and isotopic abundance (these values are then used to calculate RAM)
What are the uses of mass spectrometry?
- carbon-14 dating
- detecting illegal drugs
- forensic science
What are the 4 stages of mass spectrometry?
- ionisation
- acceleration
- ion drift in flight tube
- detection
Electrospray ionisation
- sample dissolved in volatile solvent and pushed through needle at high pressure
- high voltage applied causing each atom to gain a proton (H^+ ion)
- X (g) + H^+ –> XH^+ (g)
Electron impact ionisation
- sample is vaporised
- high energy electron fired at sample to knock one electron off of each particle
- X (g) –> X^+ + e^-
What happens during the 2nd step of mass spectrometry?
- acceleration
- +vely charged ions accelerated by electric field so they all have the same Ek
What happens during the 3rd step of mass spectrometry?
- ion drift in flight tube
- ions enter region with no electric field so they drift
- lighter ions drift faster than heavier ions therefore heavier ions take longer to reach the detector
What happens during the 4th step of mass spectrometry?
- detection
- ions reach detector (-ve plate) and generate a small current (produced by e^- transferring from -ve detector to +ve ions)
- current size is proportional to abundance of isotope
What is a mass spectrum?
plot of relative abundance against mass : charge ratio (m/z)
How do you calculate time of flight?
TOF (s) = length of flight tube (m) x √ ( mass (kg) / 2 x kinetic energy (J)) t = d√(m/2Ek)
