Periodic Properties Flashcards
What is periodicity
A repeating pattern- this is periodic
How does first ionisation energy change from left to right across a period
First ionisation energy increases
Three factors that determine ionisation energy of an element
-size of positive nuclear charge(attraction to outermost electrons increases as positive nuclear charge increases= increase IE)
-distance of outermost electron from nucleus(as distance increases the attraction of positive nucleus for negative electron decreases= reduce IE)
-shielding effect of electrons(electrons in inner shells exert repelling effect on outer electrons= reduces pull of nucleus on electrons in outer shell, effect increases as number of inner shells increases)
Why does first ionisation energy increase across period
-nuclear charge increases as electrons are added to same outer shell=pulls outer electrons closer to nucleus= increases attraction, also more protons
-shielding effect of full inner shell constant and extra electrons in same outer shell do not shield each other well=shielding hardly changes across period
-increased nuclear charge and decreased distance= more difficult to remove outer electrons
Why does melting temperature rise from group 1 to 2 to 3
As these involve metallic bonding, the more electrons each atom contributes from its outermost shell to the shared delocalised electrons the stronger the bonding and positive metal cations have greater charge and smaller ionic radii=requires more energy to break these bonds
Why is group 4 the peak of the melting graph (carbon and silicon)
They have giant covalent structures in which there are a large number of strong bonds= require a lot of energy to overcome and melt
Why do elements in groups 5,6,7 and 0 have low melting temperatures
They form simple molecules with weak London forces between molecules which require little energy to overcome and break
Given that first ionisation energy increases across a period, why does oxygen have a lower ionisation energy than nitrogen
During ionisation the paired 2p electron in oxygen is removed while in nitrogen one of its unpaired 2p electrons is removed. The repulsion between the negatively charged electrons in the same orbital of an oxygen atom is greater than between the unpaired electrons in a nitrogen atom. This means it is easier to remove the oxygen electron despite the increase in nuclear charge
How does first ionisation energy change down a group
It decreases going down a group
Why does first ionisation energy decrease going down a group
Despite the increase in nuclear charge due to increase in number of protons, the outermost electron is more strongly shielded down group as number of inner shells increases= decreased strength of attraction between outermost electron and nucleus. In addition the outermost electron is in a higher principle energy level so takes less energy to remove and is also further from nucleus
Why does aluminium have a lower ionisation energy than magnesium despite it being further along period 3
Aluminium has its outer electron in 3p sub shell while magnesium has its outer electron in 3s sub shell, 3p sub shell is higher in energy so less energy needed to remove it and it is also shielded by the 3s electrons and further from nucleus
Why does atomic radii decrease across period
As number of protons increases but shielding does not change significantly since electrons are added to the same shell. Means outer shells are pulled in more as greater positive charge in nucleus attracts electrons by greater amount
Why does sulfur have a higher melting point than phosphorus
Sulfur forms S8 molecules while phosphorus forms P4 molecules, S8 has greater number of stronger bonds due to greater number of electrons and stronger London forces meaning more energy is required to overcome these bonds
Why do noble gases have the lowest melting and boiling points
They are single atoms so London forces between atoms are very weak and require little energy to overcome
