Unit 1: Section 1 - Atomic Structure Flashcards
Relative atomic mass definition
The average mass of an atom of an element on a scale where an atom of carbon-12 is 12 (an average, so not usually a whole number)
What is the mass number of an atom?
The number of protons and neutrons
What are the relative charges and masses of the subatomic particles?
Protons - +1 1
Neutrons - 0 1
Electrons - -1 1/2000
What letters represent mass number and atomic number?
Mass number - A
Atomic number - Z
What is the definition of Relative isotopic mass?
The mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is 12 (usually a whole number)
What is the relative molecular mass?
The average mass of a molecule on a scale where an atom of carbon-12 is 12
What can a mass spectrometer be used to find?
Relative atomic mass, relative molecular mass, relative isotopic abundance and to identify elements
What is the process when a sample is squirted into a TOF mass spectrometer?
- Ionisation
- Acceleration
- Ion drift
- Detection
What are the 2 ways of ionising the sample in TOF mass spectrometry?
- Electrospray ionisation
- Electron impact ionisation
What is electrospray ionisation
- The sample is dissolved and pushed through a small nozzle at high pressure
- A high voltage is applied to it, causing each particle to gain an H+ ion
What is electron impact ionisation?
- The sample is vaporised and an ‘electron gun’ is used to fire high energy electrons at it
- This knocks one electron off each particle, so they become +1 ions
What is acceleration in TOF spectrometry?
- Electric field accelerates positively charged ions
- All have the same kinetic energy
- Lighter ions travel faster than heavier ions
What is ion drift in TOF spectrometry
The ions enter a region with no electric field, so they just drift through it (lighter ions will drift through faster than heavier ions)
What is ion detection in TOF spectrometry?
- Because lighter ions travel at higher speeds in the drift region, they reach the detector in less time than heavier ions.
- The detector detects charged particles, an electrical current is produced in the detector when a charged particle hits it
- A mass spectrum is produced
What is a mass spectrum?
- mass/charge against abundance (often as a percentage)
- If the sample is an element, each line will represent a different isotope of that element
- If the spectrum was produced using electrospray ionisation, then you have to take away one from the m/z ratio to get the relative mass of each isotope
How to work out relative atomic mass from a mass spectrum
- For each peak read the % relative isotopic abundance from the y- axis and the relative isotopic mass from the x-axis, and multiply them together to get the total mass for each isotope
- Add up these totals
- Divide by 100 (percentages were used)
- If the relative abundance is not given as a percentage, divide by the sum of the relative abundances instead of 100
How do chromium and copper’s electron configuration differ?
They donate one of their 4s electrons to the 3d sub-shell, because they favour a more stable full or half filled d sub-shell
How do transition metals behave unusually when it comes to electronic configuration?
When they become ions, they lose their 4s electrons before their 3d electrons
What is the definition of the first ionisation energy?
The energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions - endothermic
What does an equation of the first ionisation energy look like?
X(g) → e− + X+(g)
What are the important things you have to remember about ionisation energies?
- You must use the gas state symbol because ionisation energies are measured for gaseous atoms
- Always refer to 1 mole of atoms rather than 1 singular atom
- The lower the ionisation energy, the easier it is to form an ion
What are the factors affecting ionisation energy?
- Nuclear charge - the more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons
- Distance from nucleus - weaker attraction the further away the electrons are
- Shielding - as the number of energy levels between the outer electrons and the nucleus increases, the outer electrons are less attraction towards the nucleus
What is the definition for the second ionisation energy?
The energy needed to remove 1 electron from each ion in 1 mole of gaseous 1+ions to form 1 mole of gaseous 2+ ions
How do successive ionisation energies change?
- Within each shell, successive ionisation energies increase, this is because electrons are being removed from an increasingly positive ion - there’s less repulsion amongst the remaining electrons, so they’re held more strongly by the nucleus
- The big jumps in ionisation energy happen when a new shell is broken into as an electron is being removed from a shell closer to the nucleus
What are the trends in 1st ionisation energies?
- Down a group they decrease
- Across a period they generally increase
How does ionisation energy decrease down group 2?
- Each element down group 2 has an extra electron shell compared to the one above, so the extra inner shells will shield the outer electrons from the attraction of the nucleus
- The extra shell means the outer electrons are further away from the nucleus, so the attraction to the nucleus will be greatly reduced
How does ionisation energy increase across period 3?
- The number of protons is increasing, which means a stronger nuclear attraction
- All the outer electrons are at roughly the same energy level even if they’re in different orbitals
- There’s generally little shielding effect or extra distance to lessen the attraction from the nucleus
Why is there a drop in 1st ionisation energy between groups 2 and 3?
- Aluminium’s outer electron is in a 3p orbital rather than a 3s, the 3p orbital has a slightly higher energy than the 3s orbital, so the electron on average is found to be further from the nucleus
- The 3p orbital has additional shielding provided by the 3s2 electrons
- Both of these factors override the effect of the increased nuclear charge
- This pattern provides evidence for the theory of electron sub-shells
Why is there a drop in 1st ionisation energy between groups 5 and 6?
- The shielding is identical in the phosphorus and sulfur atoms, and the electron is being removed from an identical orbit
- In phosphorus’ case, the electron is being removed from a singly-occupied orbital, but in sulfur’s case the electron is being removed from an orbital containing 2 electrons
- The repulsion between 2 electrons in an orbital means that electrons are easier to remove from shared orbitals
What is an orbital?
A region around the nucleus that can hold up to 2 electrons
What would the relationship between 2 electrons in the same orbital in terms of spin be?
Have opposite spin as repel each other as both negative
