AS - Atomic structure Flashcards
What is the atomic number?
Number of protons found in the nucleus of an atom
What is the relative charge of a proton?
+1
What is the relative mass of a proton?
1
What is the relative charge of a neutron?
0
What is the relative mass of a neutron?
1
What is the relative charge of an electron?
-1
What is the relative mass of an electron?
1/1840
What does an atom consist of?
A nucleus containing protons and neutrons surrounded by electrons.
What is the mass number?
The total number of protons and neutrons in the nucleus of an atom.
What is the atomic number?
The number of protons in the nucleus.
What can be said about the number of protons and electrons for neutral atoms?
They have the same number of protons and electrons.
How to atoms form ions?
By losing or gaining electrons.
What is an isotope?
Atoms of the same element with the same number of protons but different numbers of neutrons.
What determines the chemical properties of an element?
The number and arrangement of electrons.
What determines the physical properties of an element?
Tends to depend on the mass of the atom.
What can mass spectrometry be used to identify?
Can be used to identify elements, determine relative molecular mass, relative isotopic mass and the relative abundance of isotopes.
What are the four stages of mass spectrometry?
- Vaporisation and ionisation
- Acceleration
- Ion drift
- Detection/data analysis
Describe what happens during vaporisation/ionisation.
The sample is dissolved and pushed through a small nozzle at high pressure.
A high voltage is applied to it, causing the particles to lose an electron and turning the sample into a gas made up of positive ions.
What happens during acceleration?
The positive ions are accelerated by an electric field (the particles need to be positively charged to be accelerated by the field).
Ions with a lower mass/charge ratio experience a greater acceleration.
What happens during ion drift?
When ions leave the electric field they have a constant speed and kinetic energy. They entera region with no electric field and so they drift.
Ions with lower mass/charge ratios drift at higher speeds.
What happens during detection?
The detector detects charged particles and an electrical current is produced. This produces a mass spectrum.
What is plotted on a mass spectrum?
The y-axis shows the abundance of ions.
The x-axis shows the mass/charge ratio. Since the charge on the ions is mostly +1, you can usually assume the x-axis is simply the relative isotopic mass.
If the sample is an element, what does each line on the mass spectrum represent? What does the height of each peak represent?
A different isotope of the element. The height of each peak gives the relative isotopic abundance.
How do the electron configurations of chromium and copper differ from the accepted rules? Why?
They donate one of their 4s electrons do the 3d sub-shell. This makes them more stable.
What happens to transition metals that is unique, in terms of their electron configurations, when they become positive ions?
They lose 4s electrons before 3d electrons.
What is 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.
Why is ionisation an endothermic process?
Because you have to put energy in to ionise an atom or molecule.
What is the general equation for first ionisation energy?
X(g) —> X+(g) + e-
What is the general equation for second ionisation energy?
X+(g) —> X2+(g) + e-
What are the three factors affecting ionisation energy?
- Nuclear charge
- Distance from nucleus
- Shielding
What is the general trend in ionisation energies down a group of the periodic table?
They decrease.
What is the general trend in ionisation energies across a period of the periodic table?
They increase.
Explain the trend in first ionisation energies down group 2.
They decrease.
This is because each element down group 2 has an extra shell compared to the one above, so the extra inner shells will shield the outer electrons from the attraction of the nucleus.
Also, the extra shells mean that the outer electrons are further from the nucleus, so the nucleus’ attraction is greatly reduced.
Both these factors make it easier to remove outer electrons, meaning lower ionisation energy.
Explain the general trend in first ionisation energies across period 3, not including the anomalies.
Generally increases.
This is because the number of protons is increasing, meaning stronger nuclear attraction.
Also, all the extra electrons are at roughly the same energy levels meaning there’s little extra shielding effect or extra distance to lessen the attraction from the nucleus.
Where do the anomalies occur in the first ionisation energies across period 3?
Between groups 2 and 3 and groups 5 and 6.
Explain the drop in first ionisation energy across period 3 between groups 2 and 3.
What does this provide evidence for?
This is between Mg and Al where Al’s first ionisation energy is lower.
Al’s outer electron is in a 3p sub-shell, whereas Mg’s is in a 3s. The 3p orbitals has a slightly higher energy than the 3s orbital so the electron is on average, further from the nucleus. The 3p orbital has additional shielding from the 3s^2 electrons too.
Both these factors override the trend and provide evidence for the theory of electron sub-shells.
Explain the drop in first ionisation energy across period 3 between groups 5 and 6.
What does this provide evidence for?
Between P and S where S has a lower first ionisation energy.
The shielding is identical in both atoms and the electron is being removed from an identical orbital.
In P’s case, the electron is being removed from a singly occupied orbital but in S, the electron is being removed from an orbital containing two electrons. The repulsión between the two electrons means that electrons are easier to remove from shared orbitals.
Provided evidence for the electronic structure model.
