Chapter 7 - Periodicity Flashcards
What is periodicity?
The repeating trend in properties across each period in the periodic table.
What factors affect ionisation energy?
Atomic radius
Nuclear charge
Electron shielding
What is first ionisation energy?
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
Why does the value of successive ionisation energy increase with the ion number (eg. 1+, 2+, 3+)?
As each electron is lost, there is the same number of protons attracting fewer electrons.
The electrons are drawn in slightly closer to the nucleus, increasing the attraction.
There is a large increase between the 7th and 8th ionisation energies of fluorine.
How does the change provide evidence for the existence of shells?
The 8th electron is being removed from a different shell, closer to the nucleus.
The 8th electron is attracted much more strongly by the nucleus than the 7th electron.
Explain the trend in first ionisation energies down a group.
First ionisation energy decreases down a group.
- Atomic radius increases as electrons are added to a different shell further from the nucleus.
- There are more inner shells, increasing electron shielding.
- There is less attraction between the nucleus and the outer electrons.
(Nuclear charge increase is outweighed by increasing atomic radius and electron shielding).
How does the fall in first ionisation energy between magnesium and aluminium provide evidence for the existence of sub-shells?
- In Al, the electron is lost from the 3p sub-shell which has a higher energy than the 3s sub-shell.
- The 3p electron in Al is lost more easily than a 3s electron in Mg.
Therefore, Al has a smaller first ionisation energy than Mg.
How does the fall in first ionisation energy between phosphorus and sulfur provide evidence for the existence of orbitals?
- In sulfur, the electron is lost from the 3p orbital that contains paired electrons.
- In phosphorus, all three 3p orbitals contain one unpaired electron.
- In sulfur, the paired electrons repel one another and one of the paired electrons is lost more easily than one of the unpaired electrons in P.
- Therefore, sulfur has a lower first ionisation energy than phosphorus.
What is a metallic bond?
The strong attraction between positive ions (cations) and delocalised electrons.
Explain why graphite and graphene conduct electricity but diamond and silicon do not.
In graphite and graphene, three outer-shell electrons are involved in covalent bonding within each layer, with one outer shell electron able to move and conduct electricity.
Diamond and silicon do not conduct electricity as all four outer-shell electrons are involved in covalent bonding.
What are the properties of giant metallic structures?
- High melting and boiling points
- Conduct electricity (delocalised electrons are free to move)
What factor affects the melting point of metals?
Metals with more electrons per atom will have a higher melting point.
What is a period?
A row of elements with their highest energy electron(s) in the same shell.
What is a group?
A column of elements with similar chemical and physical properties and with the same number of electrons in their outer shell.
Explain the trend in first ionisation energies across a period.
First ionisation energy generally increases across a period:
- Nuclear charge increases
- Electrons are added to the same shell
- More attraction between nucleus and outer electrons
- Decreasing atomic radius.
