topic 2 Flashcards
what are isoelectronic ions
atoms, ions or molecules that have the same electronic configuration/structure
what is the trend in ionic radii of a set of isoelectronic ions across a period
if the number of protons increase electrons are more attracted to the nucleus
so ionic radii falls
what provides evidence for the existence of ions
1- physical properties such as electrical conductivity, ionic substances are brittle
2- electron density maps
3- migration of ions using copper (III) dichromate
how does the migration of ions prove the existence of ions
copper ions are blue and positive -> attracted to cathode
dichromate ions are orange and negative -> attracted to the anode
what is a covalent bond
strong electrostatic attraction between two nuclei an the shared pair of electrons between them
recall the names of shapes of molecules
linear
trigonal planar
bent
tetrahedral
trigonal pyramidal
trigonal bipyramidal
octahedral
square planar
T shape
seesaw
square pyramid
how many bonding/lone pairs does a linear molecule have- draw the shape and label the bond angle
2 bond pairs
180 degrees
how many bonding and/lone pairs does a trigonal planar molecule have- draw the shape and label the bond angle
3 bond pairs
120 degrees
how many bonding and/lone pairs does a bent molecule have- draw the shape and label the bond angle
1 lone pair
2 bond pairs
<120 degrees
or
2 bond pairs
2 lone pairs
<109 degrees
refer to VESPR table for shape
how many bonding and/lone pairs does a tetrahedral molecule have- draw the shape and label the bond angle
4 bond pairs
109 degrees
how many bonding and/lone pairs does a trigonal pyramidal molecule have- draw the shape and label the bond angle
3 bond pairs
1 lone pair
<109 degrees
how many bonding and/lone pairs does a trigonal bipyramidal molecule have- draw the shape and label the bond angle
5 bond pairs
90 and 120 degrees
how many bonding and/lone pairs does a seesaw molecule have- draw the shape and label the bond angle
1 lone pair
4 bond pairs
<120 degrees and <90 degrees
how many bonding and/lone pairs does a T shape molecule have- draw the shape and label the bond angle
2 lone pairs
3 bond pairs
<90 degrees
or
3 bond pairs
3 lone pairs
<90 degrees refer to VESPR table for shape
how many bonding and/lone pairs does an octahedral molecule have- draw the shape and label the bond angle
6 bond pairs
90 degrees
how many bonding and/lone pairs does a square pyramidal molecule have- draw the shape and label the bond angle
1 lone pair
5 bond pairs
<90 degrees x2
how many bonding and/lone pairs does a square planar molecule have- draw the shape and label the bond angle
2 lone pairs
4 bond pairs
90 degrees
what causes bonds to be polar
electronegativity differences as electrons in the bond arent shared equally
how can you predict whether a molecule is polar
whether the molecule is symmetrical
whether the molecule has polar bonds
how do london forces form
caused by an uneven distributions of electrons within an atom
this results in a slight negative and slight positive charge on either side of the atom -> temporary dipole
this temporary dipole can induce a temporary dipole on a neighbouring molecule
how does a permanent dipole force arise
the forces are between the slightly positive end of one polar molecule and the slightly negative end of another polar molecule
the slight charges are due to permanent dipoles which arise when theres an electronegative atom or a halogen
how do hydrogen bonds arise
they result from the attractive force between a hydrogen atom, which is covalently bonded to a very electronegative atom, and another very electronegative atom
how does hydrogen bonding arise in water
hydrogen bonds form between neighbouring hydrogen atoms and oxygen atoms of adjacent water molecules
how does hydrogen bonding arise between ammonia (NH3) molecules
electronegativity difference between hydrogen and nitrogen which means that a partial charge develops on them
why does water have a relatively high bpt
due to hydrogen bonding
requires more energy to overcome as its the strongest I force
why is ice less dense than water
this is because when hydrogen bonds form it pushes water molecules further apart which decreases the density
what is the trend in boiling temperatures of alkanes with increasing chain length
stronger/increased number of london forces as theres more electrons in longer chained alkanes
what is the effect of branching in the carbon chain on boiling temperatures of alkanes
as branching increases, the surface area of the molecule decreases
smaller area of contact
london forces decrease therefore bpt decreases
why are alcohols less volatile compared to alkanes with a similar number of electrons
this is because alcohols can form hydrogen bonds between molecules whereas alkanes only form london forces which are weaker
what does volatile mean
a substance that is readily changing from a solid or liquid to a gas
why is water a good solvent for some ionic compounds
ions attracted to the water molecules
ions hydrated
why is water used to dissolve simple alcohols
water can form hydrogen bonds with them
why is water a poor solvent for polar molecules and halogenoalkanes
this is because they cant form hydrogen bonds with water
when are non aqueous solvents used
used for compounds that have similar intermolecular forces to those in the solvent
why are non polar substances soluble in hexane and not water
- insoluble in water as it cant hydrogen bond to water
- this is because none of the hydrogen atoms in the non polar substance have a slight positive charge
- its soluble in hexane because the london forces in the substance and hexane are similar in strength
why are ionic/ polar substances soluble in water and not hexane
ionic substances ions are hydrated
the enthalpy of hydration is greater than the energy needed to break apart the lattice
its insoluble in hexane because any london forces that form between the ionic substance and hexane will be smaller in size than the forces between the ions in the ionic/polar substance
