Periodicity Flashcards
How are elements ordered in the modern periodic table?
They are ordered by atomic number.
What is ionisation energy?
This is the minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in gaseous state.
Define the secondary ionisation.
The secondary ionisation is the minimum energy required to remove 1 mole of electrons from 1 mole of +1 ions in the gaseous state.
Write down the equation for the second ionisation of sodium.
Na+ (g) > Na2+ (g) + e-
What can affect the ionisation of atoms and ions?
Shielding_ More electron shells between the outer electron and nucleus means there is a weaker electrostatic force, so less energy is required to remove the outer electron.
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Nuclear charge- More protons in the nucleus give a stronger electrostatic charge to the outer electrons.
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Atomic radius- The bigger the distance between the outer electrons and nucleus, gives a weaker electrostatic attraction.
Describe the general ionisation trends down a group.
Going down a group, the number of electron shells increases. Hence, this also means that shielding and atomic radius increases. As a result of the both, there is a weaker electrostatic attraction between the outer electron and nucleus, which means less energy is required to remove this electron. This gives a decreasing ionisation energy.
Describe the general ionisation trends across a period.
Going across a period, there is an increasing nuclear charge (due to increase in protons), which increases the electrostatic attraction. (The shielding is similar across a period.) The atomic radius generally decreases, which gives a stronger electrostatic attraction. Thus, more energy is required to remove an outer electron, giving an increasing ionisation energy.
There is a drop in ionisation energy between groups 2 and 3 (Between Mg and Al). Why is this?
Group 3 elements lie in the p-orbital, rather than the s-orbital. The p-orbital has a slightly higher energy than the s-orbital, so the electron is to be found further from the nucleus. P-orbital also has a shielding provided by s electrons. This gives a lower ionisation energy.
There is also a drop in ionisation energy between group 5 and 6 (Between phosphorus and sulphur). Why is this?
In group 5 elements, the outer electron is being removed from a singly occupied orbital. For group 6 elements, the outer electrons is being removed from an orbital containing two electrons. Due to the repulsion between the two electrons, it means the outer electron can be more easily removed.
Describe the successive ionisation trend of magnesium.
There is a general increase in energy as removing an electron from an increasingly positive ion. After the second ionisation energy, there is a jump in I.E. This is because after the 2nd I.E, Mg loses an electron shell, so its outer electrons are now closer to the nucleus; shielding and atomic radius decreases. This gives a stronger electrostatic attraction, so more energy is required to remove an outer electron.
