Atomic Structure Flashcards
What does an atom consist of?
An atom consists of a nucleus containing protons and neutrons surrounded by electrons
What is the relative charge and mass of a proton ?
Relative mass is 1
Relative charge is +1
What is the relative mass and charge of a neutron?
Relative mass is 1
Relative charge is 0
What is the relative mass and charge of an electron ?
Relative mass is 1/1840
Relative charge -1
What are isotopes?
Isotopes are atoms with the same number of protons and different number of neutrons
Why do isotopes have similar chemical properties ?
Isotopes have similar chemical properties because they have the same electronic structure. They may have slightly varying physical properties because they have different masses.
What can the mass spectrometer be used to determine ?
The mass spectrometer can be used to determine all the isotopes present in a sample of an element and to therefore identify elements
Why does the mass spectrometer have to be under a vacuum?
It needs to be under a vacuum otherwise air particles would ionise and register in the detector
What are the four steps of a mass spectrometer?
1.ionisation
2.acceleration
3.flight tube/ion drift
4.detection
What are the two ways a sample can be ionised?
Electron impact
Electro spray ionisation
Describe electron impact
A vaporised sample is injected at low pressure
An electron gun fires high energy electrons at the sample
This knocks out an outer electron
Forming positive ions with different charges e.g TI(g)->Ti+(g)+e-
Describe electro spray ionisation
Sample is dissolved in a volatile polar solvent
Injected through a fine needle giving a fine mist or aerosol
The tip of needle has high voltage
At the tip of the needle the sample molecule M gains a proton H+ from the solvent forming MH+
M(g)+H+->MH+(g)
The solvent evaporates towards a negative plate
What is electron impact used for?
Electron impact is used for elements and substances with low formula mass . Electron impact can cause larger organic molecules to fragment
What is electro spray ionisation used for?
Electro spray ionisation is used preferably for larger organic molecules.The softer conditions of this technique mean fragmentation doesn’t occur
Describe acceleration in a mass spectrometer
Positive ions are accelerated by an electric field to a constant kinetic energy
KE=1/2mv^2
What does the velocity of each particle depend on ?
Given that all the particles have the same kinetic energy the velocity of each particle depends on its mass.lighter particles have a faster velocity and heavier particles have a slower velocity
Describe the flight tube
Positive ions with smaller M/z values will have the same kinetic energy as those with larger M/z and will move faster. The heavier particles take longer to move through the drift area
The ions are distinguished by different flight times
t=d/v
Describe detection
The ions reach the detector and generate a small current which is fed to a computer for analysis.The current is produced by electrons transferring from the detector to the positive ions .The size of the current is proportional to the abundance of the species
What can the mass spectrometer measure for each isotope?
For each isotope the mass spectrometer can measure a M/z (mass /charge ratio) and an abundance
How do you give the species for a peak in a mass spectrum?
If asked to give the species for a peak in a mass spectrum then give charge and mass number eg 24Mg+
Equation for R.A.M
R.A.M=
How are electrons arranged ?
Electrons are arranged around the nucleus in principal energy levels or principal quantum shells
What are principal quantum number used for?
Principal quantum numbers are used to number the energy levels or quantum shells
What does it mean if there’s a lower principal quantum number ?
Lower the principal quantum number the closer the shell is to the nucleus (first shell closest to nucleus is n=1)
What does a higher principal quantum mean in terms of distance?
Higher principal quantum number greater energy of the shell and the further away from the nucleus
How many electrons can each principal quantum level hold
N=1 up to 2
N=2 up to 8
N=3 up to 18
N=4 up to 32
What are subshells?
S p d f
What is the order of sub shells?
1s 2s 2p 3s 3p 4s 3d 4p 4d 4fp
How many electrons in s p d f
S=2
P=6
D=10
F=14
Which elements have an f shell?
Elements with more than 57 electrons also have an f shell
What do subshells contain ?
Subshells contain one or more atomic orbitals
How do orbitals exist ?
Orbitals exist at specific energy levels and electrons can only be found at specific levels not in between them
What can each atomic orbital be occupied with maximum?
Each atomic orbital can be occupied by a max of two electrons
Describe s orbital shape
Spherical
Size of orbital increases with increasing shell number
Can only accept 2 electrons with opposite spins
Describe p orbital
Dumbbell shape
Each shell has three p orbitals except for the first one
Contains a max of 8 electrons in 2 different sub levels
The lobes of the p orbitals become larger and longer with increasing shell number
Describe ground state
Most stable electronic configuration of an atom which has the lowest amount of energy
Achieved by filling the sub shells of energy with the lowest energy first
What electrons are filled first for transition metals?
The transition metals fill the 4s sub shell before the 3d subshells but lose electrons from the 4s first and not the 3d subshells(4s is the lowest in energy)
Define ionisation energy
For an atom to form a positive ion an electron must be given enough energy to be completely removed beyond the outer shell of the atom
What is the energy for one more of an atom in in terms of ionisation energy?
The energy for one atom is so small that the energies are quoted for one more of atoms in kilojoules mole^_1 at 298k (25degrees)
What is the first ionisation energy of an element?
The first ionisation energy of an element is the energy requires to remove one electron from one mole of gaseous atoms to form one mole of gaseous one plus ions
Ionisation energy equation
X(g )—>X+(g) + e-
What is the trend for the first ionisation energies for group 2 elements?
Ionisation energy decreases down the group
As you go down group to the number of energy levels increases, therefore the outermost electrons are further from the nucleus
Number of inner energy levels increases
Why is a 3P sublevel easiest to remove the 3S sub level?
3 P sub level is higher in energy than the 3S sublevel thought it’s easiest to remove the outermost electron from aluminium than it is for magnesium
Describe the second ionisation energy
Energy required to remove one electron from each ion in one mole of gaseous one plus ions to form one mole of gas is 2+ ion
What is the equation for the second ionisation energy?
X+(g)->X2+(g) + e-
Describe the third ionisation energy
Energy required to remove one electron from each ion in one mole of gaseous 2+ ions to form one mole of gassiest 3+ ion
What is the equation for the third ionisation energy?
X2+ (g) -> X3+ (g) + e-
How does the energy require to removing electron from the outermost energy level change for the successive ionisation energy?
The energy required to remove an electron from the atom energy level increases for successive ionisation energy because magnesium for example needs less amount of energy because the electron is being removed from neutral atom
What happens if an electron is being removed from a 2+ ion on the 2P is lower in energy than the 3S?
If an electron is being removed from a 2+ ion and the 2p is lowering energy than the 3S (electrons closer to nucleus so harder to remove as well as different in shielding needs more energy than others)
