structure, bonding and physical properties Flashcards
What structure does a metallic substance have?
giant metallic lattic
What structure does an ionic substance have?
giant ionic lattice structures
What structures does a covalent substance have?
giant covalent lattice structure
simple covalent lattice structure
What is a giant metallic lattic structure?
metal atoms form a lattice held together by metallic bonding
Describe metallic bonding in terms of electrons and orbitals.
the outer orbitals of the metal atoms overlap to some extent, so the metal can be thought of a lattice of positive ions surrounded by a ‘sea’ of delocalised electrons
What is metallic bonding?
the attraction between a lattice of positive metal ions and a sea of delocalised electrons
Why are metals good conductors of electricity?
the delocalised electrons are mobile
the more delocalised electrons there is the higher the conductivity
Why do metals have a relatively high melting point?
a lot of energy is needed to break the strong metallic bonding
more delocalised electrons = the stronger the bond
What are the key physical properties of metals?
conduction of heat, malleable, ductile, shiny, sonorous
How is the structure maintained in a giant metallic lattice?
the positive charges repel each other which keeps the cations fixed in position
What affects the BP and MP in giant metallic lattices?
the charge of the cations and the size of the cations
the larger the atomic radius = lower MP
Why are metallic lattices insoluble in water?
the polar H2O and the charges in the metallic structure would lead to a reaction rather than dissolving
How can you strengthen metals?
increase delocalised e-
increase positive charge of metal atoms
decrease the size of metal ions = tigher lattice
What is a giant ionic lattice?
alternating arrangement of positive and negative ions
What is the bond in a giant ionic lattice?
electrostatic attraction between oppositely charged particles
Why do giant ionic substances have a high MP and BP?
lots of energy needed to break string ionic bonds
if the charge increases then the bond strength also increases
Why are giant ionic lattices soluble in water?
the water can form ion-dipole forces with dissolved ions to compensate for the loss of ionic bonds
Why can giant ionic lattices conduct electricity when molten or aqueous?
the ions are mobile
What are covalent substances?
mainly non-metallic elements and compounds involing only non-metals
Which type of covalent structure is more common?
simple molecular
What are simple molecular structures?
each molecule is made up of a defined no. of atoms, covalently bonded together. the molecules are attracted together by intermolecular forces
Why do simple molecular substances have a low MP and BP?
only the intermolecular forces have to be broken which are relatively weak
the covalent bonds are strong but they remain intact - has no affect
Why do simple molecular substances have a low electrical conductivity?
they have no mobile electrons or ions
Usually simple molecular structures have low solubility in water, what 2 conditions make them more soluble in water?
- they react with water to form ions eg: hydrogen chloride —> H+ and CL-
- they can form hydrogen bonds with water
What allows simple molecular substances to form h bonds with water?
some of the hydrogen bonds between water molecules need to be broken
the energy needed for this endothermic process comes from the exothermic process of forming H bonds at the same time
What simple molecular compounds have high solubility in water?
compounds with OH or NH groups
What is a giant covalent structure?
the covalent bonds extend throughout the whole crystal, usually in three dimensions
Why do giant covalent lattices have high MP and BP?
due to covalent bonds acting in all directions and they need to be broken
Describe diamond’s structure
each carbon atom is covalently bonded to 4 other carbon atoms
tetrahedral - 109.5
What are diamond’s properties?
very high MP = C-C bonds need to be broken
very hard = giant lattice holding atoms together
non-conductor = no mobile electrons or ions
What are diamond’s uses?
drill bits
saw blades
jewellery
Describe Graphite’s structure?
the covalent bonding only extends in two dimensions, giving layers which are held together by induced dipole- dipole forces
each c atom is bonded to 3 other c atoms - arranged in a hexagon
trigonal planar
What are the properties of graphite?
layers can slide - weak d-d forces
high MP = covalent bonds need to be broken
delocalised electrons move freely within a layer = conducts electricity
What are graphite’s uses?
lubricants
pencils
Describe the structure of graphene?
iduvidual layers of hexagonal rings of 6 c atoms
each c atom is bonded to 3 other c atoms
trigonal planar
What are the properties of graphene?
high tensile strength
very high electrical conductivity
high MP
What are the uses of graphene?
biomedicene - drug delivery
electronics
membranes for cleaning water
What bonding type is found in groups 1-3?
giant metallic
What bonding types are found in groups 4-7?
giant covalent
What bonding type is found in group 8?
simple molecular
Why is the melting point of Be higher than Li?
Be has more outer shell electrons therefore more delocalised electrons per atom = metallic bonding is stronger
Why does carbon have a higher Mp than Boron?
C has 4 covalent bonds per atom
B only has 3 covalent bonds per atom
more energy needed in C
Why do N,O,F and Ne have low MP?
they are simple molecular
only london forces need to be broken
Why does neon have a lower MP and BP than N,O and F?
the other simple molecular elements are diatomic
neon exists as induvidual atoms - fewer electrons and smaller SA for contact with other atoms
fewer and weaker london forces
