Atomic Structure Flashcards
What is the maximum number of electrons an orbital can contain?
2
What happens to the energy level of a 3d shell as soon as an electron enters it?
Before, 3d has higher energy levels than 4s. However as soon as an electron enters 3d, the energy level drops below 4s
Why does 4s get filled before 3d?
Because 4s is lower in energy than 3d (until 3d gains an electron and its energy level drops)
Why do the orbitals have negative values of energy?
Because that is the amount of energy you must give the electron in order to get rid of an electron from an atom in its gaseous state
Define ionisation energy
The energy required to remove 1 mole of electrons from 1 mole of atoms in their gaseous state
What are the factors affecting the size of the 1st ionisation energy?
Size of nuclear charge
Distance from the nucleus
Shielding (inner shells block attractive force of nucleus)
Pair repulsion
Describe the difference in 1st ionisation energies between Hydrogen and Helium
Helium has a much higher 1st ionisation energy because the nuclear charge has doubled, but the distance from the nucleus and the shielding is the same
Describe the difference in 1st ionisation energies between Helium and Lithium
Lithium has a much lower 1st ionisation energy because the electron is coming from a new quantum shell, meaning there is greater shielding and distance from the nucleus
Describe the difference in 1st ionisation energies between Lithium and Beryllium
Beryllium has a higher 1st ionisation energy because there is a greater nuclear charge but the shielding and distance from the nucleus is roughly the same
Describe the difference in 1st ionisation energies between Beryllium and Boron
Boron has a lower 1st ionisation energy because the electron is coming from a new sub-shell, meaning there is greater shielding and distance from the nucleus
Describe the difference in 1st ionisation energies between Boron and Carbon
Carbon has a higher 1st ionisation energy because the nuclear charge is greater but the shielding and distance from the nucleus is roughly the same
Describe the difference in 1st ionisation energies between Carbon Nitrogen
Nitrogen has a higher 1st ionisation energy because the nuclear charge is greater but the shielding and distance from the nucleus is roughly the same
Describe the difference in 1st ionisation energies between Nitrogen and Oxygen
Oxygen has a lower nuclear charge because there is pair repulsion but the shielding and distance from the nucleus is roughly the same
Why do alkali metals appear at the troughs in an atomic number vs ionisation energy graph?
Because they have the minimum nuclear charge for the quantum shell
Why do noble gases appear at the peaks in an atomic number vs ionisation energy graph?
Because they have the highest ionisation energy for their quantum shell
Why does Helium have the highest 1st ionisation energy?
Because it has the greatest nuclear charge in its quantum shell, and it is the closest to the nucleus
Why does 1st ionisation energy decrease as you go down each group?
Because shielding and distance from the nucleus increases
What do successive ionisation energies provide evidence for?
Quantum shells
What do successive ionisation energies NOT provide evidence for?
Sub-shells
What happens to atomic radius as you go across a period and why?
As you go across a period the atomic radius decreases because, as the charge of the nucleus increases, the electrons are more strongly attracted to the nucleus and so they are drawn inwards
Why is the 2nd ionisation energy always higher than the 1st?
Because it takes more energy to remove an electron from a positively charged ion than from a neutral atom (because the electrons are attracted to the positively charged nucleus)
What is the equation for kinetic energy?
KE = 1/2 mv^2
What is the equation for time of flight? (d = length of tube in metres)
t = d/v
What is the equation for the mass of an ion?
1000 x 6.022x10^23
What is the expression for time of flight using Ar, d, L and E?
Square root of Ar x d^2
—————-
2000 L E
What is an expression for time of flight using Ar?
t1^2 Ar1
——– = ——–
t2^2 Ar2
In order to obtain a mass spectrum of a gaseous sample of chromium, the sample must first be ionised. Give two reasons why it is necessary to ionise the chromium atoms in the sample
To allow particles to be accelerated
To generate a current in the detector
In a mass spectrometer, what is the difference in velocity between heavy ions and light ions?
The velocity of heavy ions is less than the velocity of light ions (because kE = 1/2 mv^2 and kE is equal for all ions)
Define Relative Atomic Mass
The mass of an average atom of an element divided by the mass of one 12C atom, multiplied by 12
State how the relative molecular mass of a covalent compound is obtained from its mass spectrum
The Mr is equal to the highest m/z value
Describe briefly how positive ions are formed from gaseous atoms in a mass spectrometer
High speed electrons or electrons from an electron gun knock out an (outer-shell) electron
What is used in a mass spectrometer to accelerate the positive ions?
A plate of negative voltage
Why can’t a mass spectrometer distinguish between a 14N^+ ion and a 14N2^2+ ion?
Because they have the same m/z
Why wouldn’t an F- ion reach the detector in a mass spectrometer?
Because it wouldn’t be accelerated (because it is a negative ion)
