1.1ATOMIC STRUCTURE, MASS, MASS SPECTROMETRY & ELECTRONIC CONFIGURATION: Flashcards
Atomic Structure
three types of subatomic particles –
protons, neutrons, and
electrons
Atomic Structure
what does an atom contain
An atom consists of a nucleus containing protons and neutrons surrounded by electrons.
Describe the Plum Pudding Model
After the discovery of electrons, the theory of atoms by which electrons are located in a sea of dispersed positive charge
Relative Masses
Define Relative Isotopic Mass
Relative isotopic mass is the mass of an atom of an isotope
compared with 1/12th of the mass of an atom of carbon-12. For
an isotope, the relative isotopic mass = its mass number.
Relative Masses
Define Relative Atomic Mass
Relative atomic mass is the ratio of the average mass of
an atom of an element to 1/12th of the mass of an atom of
carbon-12.
Relative Masses
Define Relative Molecular Mass
Relative molecular mass is the ratio of the average mass of a
molecule of an element or compound to 1/12th of the mass of
an atom of carbon-12.
Relative Masses
Define Relative Formula Mass
Relative formula mass is similar to relative molecular mass but
applies to ionic compounds.
Mass Number & Isotopes
Define Mass number
total number of protons
and neutrons in the nucleus
Mass Number & Isotopes
Define Atomic Number
the number of protons.
Mass Number & Isotopes
What is mass number
Mass number = number of protons + number of neutrons
Mass Number & Isotopes
What is Atomic Number
- Atomic number = number of protons = number of electrons
Mass Number & Isotopes
What is an Isotope and its features
same number of protons
different numbers of neutrons.
different mass numbers
same atomic number.
same electronic configuration
different physical properties
Mass Spectrometry
What is Mass Spectrometry
molecular chemical analysis
that allows us to:
- find the abundance and mass of each isotope in an element allowing us to determine its relative atomic mass
- find the relative molecular mass of substances made of molecules
Mass Spectrometry
What is the steps of Mass Spectrometry
- Ionisation
- Acceleration
- Ion Drift
- Detection
- Data Analysis
Mass Spectrometry
What are the two main techniques of ionisation?
Electrospray ionisation.
Electron impact ionisation
Mass Spectrometry
What are the 3 key points about electrospray ionisation?
- a gentler technique and prevents fragmentation.
- Adds a H⁺, so Mr +1
-it’s typically used for polymers and biological materials like DNA.
Mass Spectrometry
What is electron impact ionisation used for?
is used for elements and substances with low formula mass (that can be inorganic or organic molecules).
When molecules are ionised in this way, the 1+ ion formed is known as a molecular ion.
Mass Spectrometry
How does electrospray ionisation happen? (4 marks)
- the sample X is dissolved in a volatile solvent (eg water or methanol)
- it is injected through a fine hypodermic needle to give a fine mist (aerosol).
- the tip of the needle is attached to the positive terminal of a high-voltage power supply.
- the particles are ionised by gaining a proton (ie an H⁺ ion which is simply one proton) from the solvent as they leave the needle producing XH⁺ ions (ions with a single positive charge and a mass of Mr + 1).
Mass Spectrometry
What’s an equation for electronspray ionisation if the sample is X?
X(g) + H+ → X(g) + XH+
Mass Spectrometry
How does electron impact ionisation work? (4 marks)
- the sample is first vaporised and then hit with electrons from an electron gun.
- The electrons knock off electrons from the molecule
- The molecules are now positively charged ions.
- This method often causes the sample to fragment.
Mass Spectrometry
What’s an equation for electron impact ionisation if the sample is X?
X(g) + e- → X(g)+
Mass Spectrometry
What happens during Acceleration in the mass spectrometer? (2 marks)
- Molecules are accelerated to all have the same kinetic energy,so the speed is dependent on the mass of the molecule.
- Lighter particles move faster and are detected before heavier particles
Mass Spectrometry
Given the equation for kinetic energy, the velocity of each particle is given by?
(2KE/m)= v^2
Mass Spectrometry
What happens during the ion drift stage of the Mass Spectrometer? (2 marks)
- the positive ions travel through a hole in the negatively charged plate into a tube.
- the time of flight of each particle through this flight tube depends on its velocity which in turn depends on its mass.
Mass Spectrometry
During the ion drift stage what equation can be used to determine the time of flight?
Time of flight = Distance / Velocity
t = time of flight (s)
d = length of flight tube (m)
𝑣 = velocity of the particle (m s⁻¹)
Mass Spectrometry
Which ions of the three isotopes reach the detector first?
The one with the lowest mass number
Mass Spectrometry
What is the Detection stage of Mass Spectrometry? (3 marks)
- the ions hit a negatively charged electric plate.
- when they hit the detector plate, the positive ions are discharged by gaining electrons from the plate. This generates a movement of electrons and hence an electric current that is measured.
- the size of the current gives a measure of the number of ions hitting the plate.
Mass Spectrometry
A computer uses the data to produce a mass spectrum. What does this show? (3 marks)
- the mass to charge (m/z) ratio
- and abundance of each ion that reaches the detector.
- given that all ions produced by electrospray ionisation and most of the ions by electron ionisation have a 1+ charge, the m/z is effectively the mass of each ion.
Mass Spectrometry
On the spectrum what is the x-axis, and what is the y-axis?
The x-axis is mass/charge ratio.
The y-axis is % abundance.
Mass Spectrometry
What does the main peak on the spectrum indicate?
- Molecular ion peak.
- This is the peak of the greatest mass/charge ratio.
- This represents the mass/charge value of the molecule we are analyzing.
Mass Spectrometry
What are the smaller peaks that cluster around the molecular ion peak?
- These are from the same molecules but with different isotopes in them.
- The isotopic molecules have different masses and so different mass/charge ratio values.
Mass Spectrometry
Why do smaller and significantly lighter peaks in the spectrum occur?
- Because of fragmentation.
- The molecule can fragment in the spectrometer
- Does not usually happen during electrospray ionisation.
Mass Spectrometry
In a mass spectrum of a sample of elemental boron. The spectrum shows that approximately 20% of the boron is ¹⁰B and 80% is ¹¹B.
Calculate the relative atomic mass
(80 × 11) + (20 × 10) = 10.8
100
Mass Spectrometry
For molecules that are ionised by electron impact how can the molecular ion be identified?
the signal with the greatest m/z value is from the molecular ion and its m/z value gives the relative molecular mass.
Mass Spectrometry
What other small peaks may be present around the molecular ion, if electron impact ionisation has been used?
due to molecular ions that contain different isotopes.
Electron Configuration
How many main energy levels do atoms contain?
Four
Electron Configuration
What sub-level does a first main energy level contain?
The s sub-level (1s2)
Electron Configuration
What sub-levels does a second main energy level contain?
s and p sub-levels
1s2, 2s2, 2p6
Electron Configuration
What sub-levels does a third main energy level contain?
s, p and d sub-levels
1s2, 2s2, 2p6, 3s2 3d10
Electron Configuration
What sub-levels does a fourth main energy level contain?
s p d and f sub-levels
Electron Configuration
What do sub-levels contain?
Orbitals
Electron Configuration
How is electronic structure written?
1sⁿ2sⁿ2pⁿ3sⁿ3pⁿ4sⁿ3dⁿ
Electron Configuration
Why is copper and chromium is an exception to the order in which sub-levels are filled?
- One of the 4s electrons fills the 3d orbital instead
- This is because a half-filled 3d orbital is more stable than a partially filled 3d orbital
Electron Configuration
What is the electronic structure of chromium?
1s²2s²2p⁶3s²3p⁶4s¹3d⁵
Electron Configuration
What is the electronic structure of copper?
1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰
Electron Configuration
What order are the shells of ions filled?
1sⁿ2sⁿ2pⁿ3sⁿ3pⁿ4sⁿ3dⁿ
Electron Configuration
Why are electrons are removed from the 4s sub-level before the 3d sub-level?
The electron is always removed from the lowest energy sub-level
Ionisation Energy
What is ionisation energy?
The energy required to remove one mole of electrons from one mole of gaseous atoms or ions
Ionisation Energy
What units is ionisation energy measured in?
kJmol⁻¹
Ionisation Energy
What is first ionisation energy?
The energy required to remove one mole of electrons from one mole of a gaseous neutral atom.
Ionisation Energy
What is the general equation for the first ionisation energy of an atom?
M(g) → Mⁿ(g) + e⁻
Ionisation Energy
What are successive ionisation energies?
The ionisation energies required to remove each electron from an atom or ion one after another
Ionisation Energy
What is the general trend of the first ionisation energy down group 2?
A decreasing trend
Ionisation Energy
How does the general trend of first ionisation energy down group 2 show the existence of shells?
- The atomic radius of the elements and size of the atom increases
- The attraction between the nucleus and outer electron decreases
- Shells exist as all electrons in an energy level would be the same distance from the nucleus
Ionisation Energy
Why do the third successive ionisation energies of group 2 elements show that all elements in a group have the same number of electrons in their highest energy level?
- The third successive ionisation energy of any group 2 element shows a big increase* This is because all electrons have been removed from an s orbital.
What is the general trend of first ionisation energies across period 3?
An increasing trend
Why is the general trend of first ionisation energies across period 3 an increasing trend?
- The number of protons in the nucleus and the nuclear charge of the elements increases
- The attraction between the outer electron and the nucleus increases
How does the deviation of the first ionisation energy of aluminium show that orbitals exist within sub-levels?
- Aluminium has a lower ionisation energy than expected
- This is because the outer electron is being removed from a 3p orbital
- The 3p orbital is further away from the nucleus than the 3s orbital
Why does the deviation of sulfur show that electrons occupy empty orbitals before pairing up?
- Sulfur has a lower ionisation energy than expected
- This is because sulfur has a 3p orbital containing two electrons
- The spin repulsion between them decreases the energy required to remove one of them
