✅3.3: Chemistry Of The P Block Flashcards
What makes an element a p block element?
An element is a p block element if their outer electrons are located in p sub shells
What does every p block element have?
A full s sub-shell in their outer shell with between 1-6 further electrons in their p sub shell
Give an example of the electronic configuration of group 3,4,5 and 6 p block elements
Group 3= s2p1
Group 4= s2p2
Group 5= s2p3
Group 6= s2p4
What is the maximum oxidation states a p-block element can have?
The oxidation state that is equal to their group number e.g C has a maximum oxidation state of 4
What is the other common oxidation state of a p block element
Two less than the group number e.g C has an oxidation state of +2 and +4
What is the trend in oxidation states of p block elements as you descend the group
As you descend a group, the most stable oxidation state of an element decreases:
E.g in group 4 most stable oxidation state of Sn = 4 whereas oxidation state of Pb=2
Define the inert pair effect
The tendency of the s2 pair of electrons in an atom to stay paired leading to a Lower oxidation state
Define octet expansion
The ability of some atoms to use d-orbitals to have more than 8 electrons in their valence shell
What does the phrase “when a group 4 element has an oxidation state of 4, it involves all 4 electrons” mean?
It means that one electron from the S sub-shell has been promoted to the p sub-shell, allowing a maximum of 4 covalent bonds to form
What does the phrase “when a group 4 element has the oxidation state of +2, the inner two electrons do not become involved” mean?
The energy required to unpair the S orbitals > the energy released by making 2 extra bonds and :: not energetically favourable, making the lower oxidation state more stable
What is the inert pair?
The inner two electrons (s2) that do NOT become involved (not unpaired and then promoted) allowing a more stable lower oxidation state
Where does the trend of ns2 electrons to become an inert pair occur in the periodic table?
Group 3,4 and 5
What is the maximum number of outer shell electrons that can surround the atoms in the elements in the first members of each group (2nd period and above?)
8 -four pairs of electrons
Describe basic bonding in B, C, N, O2
Boron: 3 covalent bonds and is electron deficient (explaining why it makes co-ordinate bonds)
Carbon: 4 covalent bonds
Nitrogen: 3 covalent cons and 1 lone pair
Oxygen: 2 covalent bonds and 2 lone pairs
Why can elements in the p block period 3 and below expand their octet?
They have access to d-orbitals that are not present in the second shell :: every electron in the outer shell can be used to form a covalent bond as there’s no longer a limit of 8 electrons in the outer shell.
What groups are affected by the possibility of expanding the octet?
Groups 5.6 and 7
E.g: phosphorus can form 5 covalent bonds (PCl5)
Sulfur can for 6 covalent bonds (SF6)
Chlorine can form up to 7 covalent bonds (ClO4-)
Why does the effect of the inert pair effect become stronger down the group?
1) The unpairing energy must come from the energy released when bonds are formed
2) As you go down the group the bonds get weaker, so less energy is released as they form.
3) For The lowest members of the group the energy released by making extra bonds is not enough to balance the energy needed to move an electron from the s to p sub shell
Describe the p-block elements at the top and bottom.
Top= non metals such as B, C or N Bottom= metals such as Tl, Pb or Bi
Describe why there’s a change in non metallic to metallic properties as you decrease down the p block
1) Ionisation energy decreased on going down a group so it’s easier for the atoms to form positive ions.
2) This allows some atoms to contribute to form ionic bonds with non metals
3) This also helps elements form metallic bonds as the atoms form positive ions and a sea of delocalised electrons easily
Define the term Amphoteric
Amphoteric materials react with both acids and bases
Define an acid
a molecule which can donate a proton or accept an electron pair in reactions
Define a base
A molecule that can accept a hydrogen ion (H+) from another substance
What do amphoteric oxides show?
They show both acidic and basic properties (normally close to the line separating metals and non metals)
How would you show that a substance (metal oxide) is amphoteric?
Show it reacting with an acid e.g HCL and a base e.g NaCl