Atomic Structure Flashcards
What is the relative mass and relative charge of a proton?
Relative mass:1
Relative Charge: +1
What is the relative mass and relative charge of a neutron?
Relative mass: 1
Relative charge: 0
What is the relative mass and relative charge of an electron?
Relative mass: 1/1840
Relative charge: -1
What are isotopes?
Atoms with the same number of protons but different number of neutrons
Why do isotopes have similar chemical properties?
They have the same electronic structure
What can mass spectrometer be used for?
To determine all the isotopes present in a sample of an element and to therefore identify elements.
What’s a condition for mass spectrometer?
Need to be under a vacuum otherwise air particles would ionise and register on the detector
Explain ionisation? Electron impact
Vaporised sample is injected at low pressure
An electron gun fires high energy electrons at the sample
This knocks out an outer electron
Forms a positive ions with different charge
Explain ionisation? Electro spray Ionisation
Sample dissolved in a volatile polar solvent
Injected through a fine needle giving a fine mist or aerosol
Tip of needle has high voltage
At tip of needles the sample molecule gains a proton from solvent forming
Solvent evaporates away while MH+ ions move towards negative plate
What is electron impact used for?
Elements and substances with low formula mass, can cause larger organic molecules to fragment
What can electro spray ionisation be used for?
Larger organic molecules, the softer conditions of this technique mean fragmentation does not occur
Explain acceleration in mass spectrometer?
Positive ions are accelerated by electric field
To a constant kinetic energy
KE= 1/2 n v squared
KE= kinetic energy of particles
M= mass of particle
V= velocity of the particle
What does the velocity of the particle depend on?
It’s mass, lighter particles have a faster velocity and heavy particles have a slower velocity
Explain the flight tube in mass spectrometer?
Positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster
Heavier particles take longer to move through drift air
Ions are distinguished by different flight times
( t= d/v)
T= time of flight
D= length of flight tube
V= velocity of the particle
Explain detection in mass spectrometer?
Ions reach the detector and generate a small current, which is fed into a computer of analysis. Current is produced by electrons transferring from the detector to the positive ions. Size of current is proportional to abundance of species
How do you work out time of flight?
1.) find mass of one ion: mass of one mole (small number next to element) divided by avogadros constant
2.) convert into kg from grams (divide by 1000)
3.) do the length times the square root of mass of one ion divided by 2 times the kinetic energy
You then get your answer
How do you calculate relative atomic mass?
Isotopic mass x % abundance divided by 100
Number above bar times small number next to element divided by 100
How do you calculate Relative Atomic mass using relative abundance?
Isotopic mass x relative abundance divided by total relative abundance
Why have mass spectrometers been included in planetary space probes?
So elements on other planets can be identified
What is the peak with the largest m/z due to?
The complete molecule and will be equal to the molecular mass MR of the molecule, this is called the parent ion or molecular ion
What happens to the peaks in a mass spectrometer done with electron impact ionisation?
The molecule will often break up and give a series of peaks caused by fragments
What happens to the molecule if its put through a mass spectrometer with electron pray ionisation?
Fragmentation will not occur and there will be one peak equal to the mass of the mH ion, you subtract 1 from the Mr of the molecule.
What are electrons arrangement into?
Principle energy levels 1,2,3,4… 1 is closest to nucleus
What are principle energy levels split into?
Sub energy levels
S holds 2 electrons
P holds up to 6
D holds up to 10
F holds up to 14
Principle level related to its sub-level 1,2,3,4
1: sub level: 1s
2: sub level: 2s, 2p
3: sub level: 3s, 3p, 3d
4: sub level: 4s,4p,4d,4f
How do you write electronic structure using letters and numbers?
Number of main energy level name of type of sub level number of electrons in sub level
What happens when a positive ion is formed?
Electrons are lost from the outermost shell
What block on the periodic table loses ions in there 4s before their 3d?
Block d
What is the first ionisation energy? Equation?
The enthalpy change when one mole of gaseous atoms forms one mole of gaseous ion with a single positive charge.
H—-> H+ + E-
What is second ionisation energy? Equation?
Enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge
Ti+ ——-> Ti2+ + e-
What are factors that affect ionisation energy?
1.) attraction of the nucleus (more protons in the nucleus the greater the attraction)
2.) the distance of the electrons from nucleus (the bigger the atom the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus)
3.) shielding of the attraction of the nucleus (an electron in an outer shell is repelled by electrons in complete inner shells, weakening the attraction of the nucleus)
Why are successive ionisation energies always larger?
Second ionisation energy of an element is always bigger than the first.
When first electron is removed a positive ion is formed
Ion increases attraction on remaining electrons so energy required to remove next electron is larger
What is periodicity?
Repeating pattern across a period
Why do first ionisation energies decrease down a group?
The outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller
Why is there a small drop from P to S?
When the second electron is added to the 3P orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove
Define ionisation energies?
Energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous ions
Ionisation energy equation?
O (g) ——> O+(g) + e-
Mg (g) ——-> MG+ (g) + e-
What changes between the 1st ionisation energy and the 2nd?
It turns from turning 1 mol of gases out atoms to 1 ion of gases out atoms to form 2+ of gaseous ions
What happens when you increase the charge of the nucleus?
The ionisation energy increases
What happens when you increase distance from nucleus?
Ionisation energy decreases
What happens when you increase shielding?
Ionisation energy decreases
