Periodicity Flashcards
How does the periodic table arrange the known elements?
In order of increasing proton number
Does the number of shells in elements along a period vary?
No - all the elements along a period have the same number of shells
Does the number of outer electrons of each element in a group vary?
No - all elements down a group have the same number of outer electrons
Elements in the same group have similar…
Chemical properties
What do elements in the same block have the same of?
The have their outer electrons occupying the same orbital
What is periodicity?
The study of repeating trends in the properties of elements across each period of the periodic table
Is Calcium an anomaly for its electron configuration/ why?
Yes - it’s 4s shell is filled and it’s 3d shell is not
Is chromium an anomaly/ why?
Yes - it’s 3d and 4s subshells fill singularly and there are no paired electrons in either sub shell
How does atomic radius vary along a period?
It decreases
Why does atomic radius vary along a period?
Decrease since there is an increased nuclear charge for the same number of electron shells, so the outer electrons are pulled in closer to the nucleus as the increased charge produces a greater attraction
How does atomic radius vary down a group?
It increases
Why does atomic radius vary down a group?
With each element, a shell is added which increases the distance between the outer electrons and nucleus, reducing the power of attraction. More shells increased shielding so nuclear attraction is reduced.
What is shielding?
The repulsion between electrons in different inner shells
What is shielding’s effect on the net attractive force between the positive nucleus on the outer shell electrons?
It reduces it
What is the first ionisation energy?
(kJ/mol)
The minimum energy required to remove one mole of electrons from one mole of atoms in a gaseous state
Show sodium’s first ionisation energy in an equation:
Na (g) —> Na+ (g) + e-
When do successive ionisation energies occur?
When further electrons are removed.
Why do successive ionisation energies require more energy?
As the electrons are removed, the electrostatic force of attraction between the positive nucleus and negative outer electrons increases, so more energy is needed to overcome the attraction
Why does first ionisation energy across a period overrall increase?
There is decreasing atomic radius and greater electrostatic forces of attraction across a period
Why does the first ionisation energy decrease down a group?
There is an increasing atomic radius and an increase in electron shielding which reduces the effect of the electrostatic forces of attraction across a period
What is a successive ionisation energy?
The process of removing one mole of electrons from one mole of gaseous ions.
What does a large jump in successive ionisation energies indicate?
(E.G large jump between 3rd and 4th)
Which group an element is in (indicated there are 3 outer electrons so in group 3)
What are two exceptions from the trend of ionisation energies increasing across period 2?
- boron
- oxygen
Why is boron an exception?
Has a lower 1st ionisation energy than expected by the general trend as there is an energy difference between the 2s and 2p subshells - removed from a higher energy level that is further from the nucleus so is held less strongly.
Why is oxygen an exception?
Has a lower 1st ionisation energy than expected due to repulsion within the 2p orbital as there are 2 Electrons in it - repulsion is destabilising in comparison to nitrogen and allows Oxygen’s electron to be more easily removed.
What are the two exceptions for increasing ionisation energies across period 2?
-aluminium
- sulfur
Why is aluminium’s 1st ionisation energy lower than expected by the general trend?
There is an energy difference between the 3s and 3p sub shell - electron is being removed from a higher energy level that is further from the nucleus so is held less strongly
Why is sulfur’s 1st ionisation energy lower than otherwise expected?
Repulsion within the 3p orbital as there are 2 electrons in the same one - repulsion is destabilising in comparison to the configuration of phosphorus and allows the electron to be removed more easily.
