Section 1 - Atomic Structure Flashcards
Define Isotope
Atoms of the same element with different numbers of neutrons.
Define Relative Atomic Mass
The average mass of an atom of an element on a scale where an atom of carbon-12 is 12.
Define 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.
Define Relative Molecular Mass
The average mass of a molecule on a scale where an atom of carbon-12 is 12.
What are the 4 stages of Mass Spectrometry?
1) Ionisation
2) Acceleration
3) Ion Drift
4) Detection
What happens during Ionisation in Mass Spectrometry? (Two types)
Electrospray Ionisation - Sample is dissolved and pushed through a nozzle at a high pressure. High voltage applied causing each particle to gain a H+ ion. The sample is turned into a gas made up of positive ions.
Electron Impact Ionisation - Sample is vaporised and an electron gun is used to fire high energy particles at it. This knocks an electron off each particle so they become +1 ions.
What happens during Acceleration in Mass Spectrometry?
The positively charged ions are accelerated by an electric field so that they all have the same kinetic energy.
What happens during Ion Drift in Mass Spectrometry?
The ions enter a region with no electric field so they drift through it. They move at different speeds depending on their weights.
What happens during Detection in Mass Spectrometry?
The detector detects charged particles and a mass spectrum is produced.
Define Ionisation
The removal of one or more electrons.
Define First Ionisation Energy
The energy needed to remove one electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
Is ionisation exothermic or endothermic?
Endothermic
What’s the general equation for first ionisation?
X(g) —> X+(g) + e-
What’s the general equation for second ionisation?
X+(g) —> X2+(g) + e-
What are the factors affecting Ionisation Energy?
1) Nuclear Charge
2) Distance from Nucleus
3) Shielding
How does nuclear charge affect ionisation energy?
More protons = stronger attraction for electrons
How does distance from nucleus affect ionisation energy?
Electrons closer to the nucleus will be much more strongly attracted than one further away
How does shielding affect ionisation energy?
As number of electrons between outer electrons and nucleus increases, the attraction weakens.
What does it mean if something has a high ionisation energy?
There’s a high attraction between the electron and the nucleus so more energy is needed to remove the electron.
Define 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.
What is the trend in successive ionisation energies?
- Within each shell, it increases - electrons are being removed from an increasingly positive ion and there’s less repulsion among remaining ions so they’re held more strongly.
- Big jumps mean a new shell is being broken into - an electron is being removed from a shell closer to the nucleus
How can you tell which group an element belongs to from its successive ionisation energies graph?
Number of electrons removed before first big jump = group number.
When do you use Electron Impact?
During Ionisation in Mass Spectrometry for elements and low Mr compounds.
When do you use Electrospray Ionisation?
During Ionisation in Mass Spectrometry for high Mr compounds.
What’s the formula for Kinetic Energy?
1/2mv^2
What’s the equation used to calculate time taken to reach the detector in Mass Spectrometry?
time = distance x square root(mass / 2 x kinetic energy)
What happens when ions hit the detector in Mass Spectrometry?
A current is produced.
Why are ions attracted to the detector in Mass Spectrometry?
The detector is negatively charged and the ions are positively charged - there is an attraction.
How do you calculate Relative Atom Mass (Ar) using the mass spectrum?
Average mass of atoms = Total mass of all atoms/Total number of atoms
How do you find the Mr of a compound from a Mass Spectrum?
The peak in the spectrum is equal to the relative molecular mass.
What is the trend in First Ionisation Energies down a group?
It decreases.
Because:
-The extra inner shells shield the outer electrons from the attraction of the nucleus.
- The outer electrons are further from the nucleus.
What is the trend in First Ionisation Energies across a period?
It increases.
Because:
- There are more protons, therefore a stronger attraction.
- All the extra electrons are at roughly the same energy level therefore there’s little shielding.
Why is there a drop in First Ionisation Energy between group 2 and 3?
The element’s outer electron is in the 3p shell which has a slightly higher energy than the 3s so it is slightly further from the nucleus and has more shielding.
Why is there a drop in First Ionisation Energy between group 5 and 6?
The shielding in the elements is equal but the Group 6 element loses its outer electron from an orbital containing two electrons and the repulsion between these electrons means they’re easier to remove.
