p-block - elemental structure Flashcards
(22 cards)
what are the 4 main types of structures of p-block elements?
monatomics
discrete molecules
covalent polymeric structures
metallic lattices
monatomic definition
individual atoms with no bonds between them
what p-block elements exist as monatomics?
this is exclusive to group 18 elements as they already have 8 valence electrons and do not need to form any bonds to fulfil the octet rule
what physical properties do group 18 elements have as a result of their monatomic structure?
they are all gases with only weak dispersion forces between atoms, these forces increase with Mr therefore b.p of group 18 elements increases down the group
discrete molecule definition
a known number of 2 or more atoms linked together by covalent bonds
what p-block elements exist as discrete molecules?
this is favoured by non-metals that don’t need to form many bonds to reach an octet, e.g. halogen diatomics, O2, N2, P4, S8, etc
what state do discrete molecules normally exist in at room temperature and pressure?
can be gases, liquids or solids as shown by halogen diatomics
what affects the boiling point of discrete molecules?
boiling point is proportional to strength of dispersion forces, which is proportional to Mr
covalent polymeric structure definition
very large, non-specific number of atoms covalently bonded to one another to form extended solid structures
what p-block elements form covalent polymeric structures?
this structure is favoured by elements that prefer to form single bonds and need to form more than 1 bond to obtain an octet - this makes them difficult to terminate, as all atoms want to achieve an octet
- common in metalloids/ elements close to metalloids
give 3 examples of forms of covalent polymeric structures
chains, sheets/layers, 3D networks
give 3 examples of a covalent polymeric structure
Si = giant covalent structure
C/diamond = giant covalent structure
C/graphite = layers
is a buckminster fullerene a covalent polymeric structure?
no, it has molecular formula C60, which is a specific number of atoms, making it a discrete molecule
what p-block elements form metallic lattices?
metal p-block elements
what is a metallic lattice?
held together by metallic bonds, a network of many metal cations fixed in place forming a 3D lattice, surrounded by many delocalised electrons - able to form a kind of sea/cloud as metals have very low electronegativities, so valence electrons are loosely held + free to move
what is metallic bonding?
electrostatic attraction between sea of valence electrons and metal cations
what structures are formed by group 13 elements?
B is the only metalloid, 3 valence electrons which isn’t enough to get an octet, so uses delocalised multicentred bonding via hydride bridges
Al = fcc metallic lattice
Ga = bct metallic lattice, structure has different Ga-Ga distances, resulting in a low m.p ~30C
In = hcp metallic lattice
what structures are formed by group 14 elements?
C can form many allotropes
Si + Ge favour diamond structure at room temp and pressure
Ge can form bct metallic structure at very high pressures
Sn also forms a diamond structure <13C and metallic lattice >13C
Pb forms fcc metallic lattice
what structures are formed by group 15 elements?
N = N2 triple bond
P = P4/white phosphorus discrete molecule, can also form allotropes, P2 at high temp or covalent polymeric structures red + black phosphorus which are less favourable
As forms As4 which is quite unstable, and forms the same CPS as black phosphorus, same for Sb
Bi forms a metallic lattice
what structures are formed by group 16 elements?
O forms O2, O3
S forms S8 or S2 at very high temps, can also form other allotropes, differently sized rings or packing structures
Se can form Se8 rings, but prefers more stable helical covalent polymeric structure
Te forms the same helical covalent polymeric structure
Po forms primitive cubic metallic lattice
what structures are formed by group 17 elements?
all diatomics
what structures are formed by group 18 elements?
all monatomic
