bonding and structure (2) Flashcards
one way in which diamond differs from graphene and graphite
poor electrical conductivity
what is the trend in boiling temperatures of hydrogen halides
hydrogen chloride-> hydrogen iodide increases as size of halogen atoms increases (more electrons) which increases the strength of the London forces
hydrogen fluoride has a permanent dipole
what happens when ammonia gas reacts with hydrogen chloride gas
acid base
what is a metallic bond
electrostatic force of attraction between positive metal ions and delocalised sea of electrons
what is an ionic bond
electrostatic force of attraction between oppositely charged ions
what is a covalent bond
electrostatic attraction between two nuclei and the shared pair of electrons
which has higher melting temperatures, group 1 or 2
group 2:
-higher charge so electrostatic forces harder to overcome as electrons more attracted to nucleus
-smaller ionic radius due to added electron increasing attraction to nucleus, harder to overcome forces
which has higher melting temperatures, period 1 or 2
period 1: smaller ionic radius
what do metals and acid make
hydrogen gas and salt
what do metals and water make
metal hydroxide and hydrogen gas
why do ionic compounds have high melting temperatures
because each ion is surrounded by multiple other ions so there are a large number of forces to be overcome, ionic bonds require more energy to break
why do ionic compounds conduct in solution/when molten
when solid there are no free ions so unable to carry charge
when dissolved in solution ions are free to move and carry charge
properties of ionic compounds
-hard solids
-soluble in water
-brittle
what is ionic bond strength affected by
1) higher charge on cation/anion = stronger forces
2) closer packed ions = stronger forces
3) geometry
evidence that ions exist
electrolysis, migration of ions
physical properties: high melting temp + solubility in water required
what are valence electrons
electrons in the outer shell of an atom/ion
what is a lone pair
pair of electrons not used in bonding
what is a dative covalent bond
a covalent bond with both electrons in the shared pair provided by one atom
how does bond length affect bond strength
shorter bonds are stronger as the atoms are held closer together so forces of attraction are greater, requiring more energy to overcome
what are the 3 intermolecular forces
London forces
permanent dipole - permanent dipole interactions
hydrogen bonds
describe a London force
instantaneous dipole in one atom due to the uneven distribution of electrons causes an induced dipole on another atom
what is bond length
average distance between 2 nuclei in a covalent bond
what is bond angle
angle between two covalent bonds from the same atom
2 bond pairs no lone pairs
linear 180
3 bond pairs no lone pairs
trigonal planar 120
4 bond pairs no lone pairs
tetrahedral 109.5
5 bond pairs no lone pairs
trigonal bipyramidal 90 120
6 bond pairs no lone pairs
octahedral 90
2 bond pairs 2 lone pairs
v shaped 104.5
3 bond pairs 1 lone pair
trigonal pyramidal 107
define electronegativity
the power of an atom to attract the electron pair in a covalent bond towards itself
what makes a polar bond
electronegativity difference between 0.4 and 1.7
why might a molecule with polar bonds not be a polar molecule
carbon dioxide is linear so the dipoles cancel out on the C and O
what affects the strength of London forces
greater Mr - stronger London forces
straight chain - stronger London forces (less points of contact and reducing distance over which the force acts)
what elements can hydrogen bond
oxygen, nitrogen and fluorine (3 most electronegative elements)
why does ice have a lower density than water
hydrogen bonds hold the molecules in a rigid structure with lots of air gaps whereas in water the bonds constantly break and reform so molecules are closer together
describe trend in hydrogen halide boiling points
HF - hydrogen bonds so highest
increases as you go down group as ionic radius of halide increases so it has more electrons so stronger London forces
factors affecting strength of metallic bonds
-greater charge on positive ion- stronger attraction as more electrons released into sea
-larger ionic radius- weaker attraction
bonding and physical properties of ionic crystal lattice
high melting and boiling point
when molten or in solution they can conduct electricity as ions can carry charge and are free to move
brittle
bonding and physical properties of metallic compounds
good conductors as delocalised electrons can carry charge
malleable as positive ions slide over eachother
high melting point
solid at room temp
bonding and physical properties of simple molecular compounds
low melting and boiling points
very poor conductors
bonding and physical properties of giant covalent structures
high melting point = multiple covalent bonds
diamond properties
each atom bonded to 4 other carbon atoms
rigid tetrahedral structure
hardest material - why it is used on drills
graphite properties
each atom bonded to 3 other carbon atoms in flat hexagonal sheets
one delocalised electron per carbon atom - conducts electricity
layers slide over eachother due to weak intermolecular forces - lubricant
graphene properties
1 layer of graphite - one atom thick
hexagonal carbon rings
lightweight material
why are ionic compounds brittle
when struck with a hammer the layers slide and therefore the positive ions align with positive ions so they repel each other and the compound breaks.
what are isoelectric ions
different ions with the same number of electrons
carbon monoxide dot and cross
double bond and dative bond from oxygen to carbon
how to draw a dative covalent bond
draw an arrow towards whichever atom is gaining both electrons
if a bond is shorter does it have a higher/lower bond enthalpy
higher as if there is a greater electron density then the atoms are pulled further towards each other so there is stronger attraction of positive nuclei and negative shared pair of electrons
why are some molecules that have a difference in electronegativity not polar
symmetrical so has no overall charge
how to answer a shape of molecule question
how many bond pairs + lone pairs it has
shape name and bond angles
maximum seperation minimum repulsion of electrons
