Chapter 7 - Periodicity Flashcards
How were the elements ordered by Mendeleev?
By increasing atomic mass
What is ionisation?
The removal of one or more electrons from an atom
Define first ionisation energy.
The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
How does atomic radius affect first ionisation energy?
Greater distance between the nucleus and outer electrons, so less attraction.
Increasing atomic radius decreases first ionisation energy.
How does nuclear charge affect first ionisation energy?
More protons creates greater attraction between nucleus and outer electrons.
Increasing nuclear charge increases first ionisation energy.
How does electron shielding affect ionisation energy?
Shielding is the repulsion of outer shell electrons by inner shell electrons. This reduces attraction between the nucleus and outer electrons.
Increasing shielding decreases the first ionisation energy.
Why does ionisation energy decrease going down a group?
Because atomic radius increases, and there is more shielding. This reduces attraction between electrons and nucleus so first ionisation energy decreases.
Why does ionisation energy increase across a period?
The nuclear charge increases, causing atomic radius to decrease. Shielding stays the same so there is overall increase in attraction between electrons and nucleus across a period, so first ionisation energy increases.
Why do successive ionisation energies increase?
Because there are less electrons so nuclear attraction on remaining electrons increases.
Define second ionisation energy.
The energy required to remove one electron from each ion in one mole of gaseous +1 ions of an element to form one mole of 2+ gaseous ions.
What causes large jumps in successive ionisation energies and why?
Moving down to a different shell that is closer to the nucleus.
Because it has less shielding and a smaller atomic radius, so attraction increases.
What predictions can be made from a graph of successive ionisation energies?
Number of electrons in outer shell.
The group of the element.
Both of these combined to identify the element.
In period 2, explain the fall from beryllium to boron of first ionisation energy.
The new electron enters the 2p sub-shell in Boron which is higher energy than the 2s sub-shell in Beryllium.
Boron loses a 2p electron and Beryllium loses a 2s electron.
In period 2, explain the fall from nitrogen to oxygen of first ionisation energy.
Nitrogen’s electrons in the 2p sub-shell are unpaired and oxygen’s 8th electron is paired, causing repulsion and lower ionisation energy.
What happens in metallic bonding?
Each atom donates an outer shell electron, which becomes delocalised, forming cations.
