7 - Periodicity Flashcards
What did Mendeleev do
- in order of increasing atomic mass
- left gaps and predicted their chemical properties
- grouped elements with similar chemical properties
- swapped Iodine
Periodic table now
- in order of increasing atomic number
- similar chemical properties
- groups and periods
What is periodicity and what does that entail
The general trend along a period from metal to non metals
- electron configuration
- ionisation energy
- structure
- melting and boiling point
Electron configuration?
Each period starts with an electron in a new highest energy shell
Trend across a period
Across period 2, the 2S subshell fills with two electrons, followed by 2p subshell with 6
Across period 3, it’s repeated with 3S then 3P
Trend down the group
The group number indicates how many electrons are in its outer most shell. This means that they also have atoms with the same number of electrons in each sub-shell. The similarity in electron configuration gives the elements of the group similar chemical properties.
What is ionisation energy?
The energy required to remove one electron from each atom in one mole of gaseous atom of an element to form one mole of gaseous +1 ion
Factors affecting ionisation energy
- atomic radius: the greater the distance between the nucleus an outer electron, the less efoa and so easy to remove
- nuclear charge: the more protons in the nucleus, the greater the efoa on the outer electron, making it harder to remove
- Electron shielding: the more electrons between the nucleus, and outer electron, the less efoa experience on the outer electron, making it easier to remove
Successive ionisation energy definition
The energy required to remove an electron from each ion in one mole of a gaseous +1 ion of an element to form one mole of a gaseous +2 ion
Ionisation energy graph of an atom
- as the ionisation number increases, it becomes increasingly difficult to remove an electron answer requires more energy
- If a large difference in ionisation energy is seen, this shows how a new shower has started. This will be much closer to the nucleus, with the greater efoa and so harder to remove
What can be seen from graph of ionisation energy of an atom
- The number of electrons in the outer shell
- The group of the element
- The identity of the element
Ionisation energy graph down a group
visualise the graph:
- overall trend is an increase, as the atomic number increases, the proton number increases and atomic radius decreases (due to the slight pull from nucleus) and stronger forces of attraction, so more energy required to remove
- Peak of every period (the noble gases) have a decrease in trend, as you go down, the group, less energy is required to remove due to electron shielding and atomic radius
- same for beginning of every period (alkali metal). As you go down, large atomic radius, more electron, shielding, so easy to remove. But for each period has the least number of protons, so easier to remove.
Why small blips
- between beryllium (1s2, 2s2 ) and boron (1s2, 2s2, 2p1) - would expect boron with the greater IE, however, it is much easier to remove one electron from people that electron from 2s2, which is not only stronger, but closer to new place, so boron has lower ionisation energy
- Between nitrogen (1s2, 2s2, 2p3 ) and oxygen (1s2, 2s2, 2p4 ) - would expect oxygen to be greater.
However, due to the P orbital arrangement of oxygen (with a pair), the electron pair oppose each other and repel, making it easier to remove than oxygen with a lower IE
Metallic
- what: metallic bonding
- bonding: efoa between lattice positive metal ions and sea of delocalised electrons
- structure: giant metallic lattice
- mpbp: high due to strong metallic bonds and efoa between in lattice
- conducts? Delocalised e allow to conduct, solid or molten
- soluble: cannot dissolve and only result in reactions with water (explosive)
- can it be increased? Metallic bonds are increased, depending on the strength of the metallic bonds, holding the atoms together (ie. If the charge increases)
Covalent (giant)
- what: giant covalent
- bonding: efoa between shared pair of electrons and nucleus of bonding atoms
- structure: giant covalent structure
- mpbp: high due to many and very strong bonds
- conducts: no delocalised so no, however allotropes like graphite, graphene and nanotube (not Bucky) are able to conduct
- how increased: simple mols have weak intermolecular and so change state easy
- soluble: insoluble as cov bonds are too strong to be broken by interactions with solvent
Periodic trend in melting point
- general increase through metals as charge increases an metallic bond increase
- peak at giant covalent structure (C or Si)
- sharp decrease after as all are rest simple molecules
- P4 compared to S8 as S has more LF and requires more energy to break so higher mpbp
