Unit 1: Section 1- Atomic Structure Flashcards
What is the relative mass and charge of an electron?
1/1840 and -1
What is the difference between mass number and atomic number?
Atomic number= number of protons
Mass number= total number of protons and neutrons
How do you work out the number of neutrons in an element?
subtract the atomic number from the mass number
Define isotope
an isotope of an element is an atom with the same number of protons but a different number of neutrons
Explain the differences and similarities of different isotopes and their chemical and physical properties
Isotopes of an element have the same electronic configuration, and therefore have similar chemical properties. However, their physical properties may vary due to the difference in mass.
How are electrons arranged?
principle energy levels (1,2,3,4) , sub- energy levels (s,p,d,f) and orbitals
What is the trend in principle energy levels as you move away from the nucleus?
Principle energy levels increase in energy as you move away from the nucleus.
What block are group 1 and 2 elements found in?
s
What block are group 3 elements found in?
p
What elements are found in block d?
transition metals
Where can the f-block be found?
below the periodic table
What shape is the s-orbital?
spherical
How many orbitals does the s subshell have?
1
How many orbitals does the p subshell have?
3
How many orbitals does the d subshell have?
5
How many orbitals does the f subshell have?
7
Why does the 4s subshell fill before the 3d subshell?
The 4s subshell fills before the 3d subshell because the 4s subshell is lower in energy than the 3d subshell.
What happens when elements in the d-block form positive ions?
the electrons are removed from the 4s subshell before the 3d subshell.
What is noble gas configuration used for?
to avoid long configurations, find the noble gas from the previous period, then write out the rest of the configuration
Why do electrons favour half or fully filled d subshells?
because of the symmetrical distribution of electrons
Name and explain two examples of elements with electron arrangements that favour the half or fully filled d subshell
Chromium, Copper
For chromium, the 3d subshell is made to be half full leaving the 4s subshell with only one electron. Similarly, for copper, the 4s subshell is left with only one electron to allow for the 3d subshell to be completely full.
How do you fill subshells when drawing spin diagrams?
When filling up subshells, fill in each orbital with one electron before beginning to pair them up. This is because electrons first enter the orbitals that are empty before filling singularly occupied orbitals.
Define ionisation energy
the enthalpy change when one mole gaseous atoms form gaseous ions with positive charges
Define first ionisation energy
the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge.
Define second ionisation energy
the enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge
Name three factors that effect ionisation energy
- nuclear charge
- size of the atom
- shielding
Why does nuclear charge effect ionisation energy?
the more protons in the nucleus the greater the nuclear charge and the greater the attraction of the electrons to the nucleus.
Why does the size of the atom effect ionisation energy?
the outer shell of bigger atoms will be further from the nucleus so there would be a weaker attraction between the nucleus and the electrons
Why does shielding effect ionisation energy?
the more shells there are the weaker the attraction of the outer shell to the nucleus.
What can a jump in a line of a graph showing successive ionisation energies mean?
The electron must be in a different shell to the prior electrons, as it experiences a greater attraction to the positive nucleus
Why is first ionisation energy always lower than the second?
because each time an electron is removed, the attraction between the outer electrons and nucleus becomes stronger, making it harder to remove the next electron so more energy is required.
What element has the highest first ionisation energy?
helium
Why does helium have the highest first ionisation energy?
The first electron removed in helium has no shielding effect and is very close to the nucleus so it requires a lot of energy to remove. The ionisation energy is higher than hydrogen because it has more protons.
What is the trend of ionisation energy going down a group?
it decreases
Why does first ionisation energy decrease down a group?
As you go down a group, there is an additional shell for each element so the outer electrons are further from the nucleus and have a weaker attraction to it. This means that less energy is required to remove the first electron.
Why are electrons more easily removed from orbitals containing two electrons?
Electrons are removed more easily from orbitals containing two electrons due to electron-electron repulsion
What happens to first ionisation energy moving across a period?
It increases, so more energy is needed to remove the valence electron from the element to form an ion
Explain why first ionisation energy increases along a period
Increasing nuclear charge and attraction leads to an increase in first ionisation energy
As shielding remains similar, there is no significant increase in repulsion of this outer electron and so ionisation energy increases
Name four exceptions to the trend of increasing first ionisation energy
Magnesium and Aluminium
Phosphorus and Sulfur
What happens to the trend in first ionisation energy between magnesium and aluminium?
Between magnesium and aluminium, there is a drop in the 1st ionisation energy.
Why is there a drop in first ionisation energy between magnesium and aluminium?
- the outer electron of Mg is in the 3s subshell while the outer electron of Al is in the 3p subshell.
- so, when removing an electron from the Al outer shell, the electron is being removed from a 3p subshell which has a higher energy than the 3s subshell
- the higher energy level makes it easier for an electron to be removed, decreasing the energy required to remove the electron
What happens to the trend in first ionisation energy between phosphorous and sulfur?
Between phosphorous and sulfur, there is a drop in the 1st ionisation energy.
Why is there a drop in first ionisation energy between phosphorous and sulfur?
- the outer electron of sulfur is paired up, however the outer electron of phosphorous is not, even though they are both in the 3p orbital
- this causes a small repulsion between the two electrons (S) making it easier for an electron to be removed
- It is also more energetically favourable for the atom to have an exactly half full subshell. Sulfur can lose its outer electron to gain an exactly half filled subshell.
What is TOF mass spectroscopy?
a form of mass spectroscopy that is used to determine which elements or molecules are present within a given sample
What are the four stages of TOF mass spectroscopy?
- ionisation- this can be due to electron impact or electrospray ionisation
- acceleration- all ions in the sample are accelerated to the same kinetic energy
- ion drift/ flight- the region of the spectrometer where the ions are separated
- detection- the ions are detected and recorded
Why are samples vapourised in mass spectroscopy?
Samples are typically vaporised before being fed into the mass spectrometer. This allows for easier ionisation, and for the resulting ions to drift through the drift region.
What equal charge are the samples all ionised to in TOF mass spectroscopy?
+1
What are the two ways that a sample can be ionised in TOF mass spectroscopy?
electron impact (electron ionisation)
electrospray ionisation
Describe electron impact in TOF mass spectroscopy
- An ‘electron gun’ is used to fire high-energy electrons at the sample Y.
- The high-energy electrons remove one electron from each particle in the sample Y.
- The loss of an electron gives the particle a +1 charge.
Y (g) → Y+ (g) + e−
Describe electrospray ionisation in TOF mass spectroscopy
- Using a volatile solvent, such as ethanol, the sample Y is dissolved.
- It is then injected through a fine, hypodermic needle which turns the sample into a mist.
- At the tip of the needle, a very high voltage is applied, which causes the sample to become protonated (gaining an H+ ion).
Y(g) + H+ → YH+ (g)
What substances would you use electron impact for compared to electrospray ionisation energy in TOF mass spectroscopy
Electron Impact is primarily used for smaller substances with low formula masses while electrospray ionisation is used for substances with a higher mass.
Describe what happens in acceleration
Once the particles are ionised, the 1+ ions are attracted towards the negative electric plate that generates an electric field to accelerate the ions. The electric field gives all of the particles in the sample the same kinetic energy.
In the acceleration stage of TOF mass spectroscopy, what does the velocity of the particle depend upon?
the velocity will depend on how heavy the particle is. Particles that are lighter, will travel faster, while those that are heavier will travel more slowly.
Recall the kinetic energy equation
KE= 1/2 x m x v²
KE= J
m = kg
v= ms⁻¹
What happens after the electrons move through an electric field in TOF mass spectroscopy?
After moving through the electric field, the positive ions enter the flight tube.
What does the velocity that an ion moves at determine in TOF mass spectroscopy?
The velocity at which an ion moves will determine its ‘time of flight’. That is, the time it takes for the particle to move through the tube.
How can time of flight be calculated?
By combining the two equations:
KE= 1/2 x m x v²
t = d/v
Why does TOF mass spectroscopy have to be done inside of a vacuum?
Time of flight mass spectrometry has to be done inside of a vacuum because if it isn’t, the air particles would become ionised instead, which would be registered on the detector.
In TOF mass spectroscopy, what is at the end of the flight tube?
a negatively charged plate which ionised particles collide with at different times depending on their time of flight
Describe what happens at the negatively charged plate in detection
When the positively charged ions collide with the detector, the detector donates electrons to the positively charged sample.
The donation of an electron causes a movement of other electrons within the plate.
This movement of electrons causes an electric current to be generated.
The current is then measured and the size of the current used to calculate the number of ions hitting the plate and therefore, the abundance of a given species.
What happens to the data collected from the time of flight mass spectrometer?
The data collected is fed into a computer to produce a mass spectrum.
What does the mass spectrometer do?
creates a mass spectrum
can be used to find the relative atomic mass of an element
Define relative atomic mass
the weighted average mass of an atom of an element, relative to one twelfth of the mass of an atom of carbon-12.
What two equations can be used to help to calculate relative atomic mass?
relative atomic mass = (isotopic mass x %abundance) / 100
relative atomic mass = (isotopic mass x relative abundance) / total relative abundance
How are mass spectra created and what are they?
Mass spectra are created from data collected by the mass spectrometer.
It shows the relative abundance against m/z, the mass charge ratio.
How many isotopes do chlorine and bromine have?
2
What can happen if electron impact ionisation is used in TOF mass spectroscopy?
If electron impact ionisation is used, a molecule may break up into fragments which will cause multiple peaks.
Define relative molecular mass
the average mass of a molecule of an element or a compound compared to one twelfth the mass of an atom of carbon.
How do you find the Mr of a molecule using a mass spectra?
find the peak with the biggest m/z value
What will a mass spectra look like if electrospray ionisation is used?
there will be no fragmentation and so there will be only one peak caused by the intact molecule
How do you determine the Mr of a substance when electrospray ionisation is used?
because the molecule will have a H+ ion added to it, to determine the Mr, 1 will need to be subtracted to account for the H+ ion
