Shapes of simple molecules and ions

what is the shape of a molecule determined by?

the number of pairs of electrons in the outer shell of the central atom

what are bonding pairs?

shared electrons taking part in the bond

what are lone pairs?

unbonded/ unshared electrons

what do electron pairs exist as?

charge clouds

what is a charge cloud?

an area where you have a big probability of finding an electron. electrons whizz around in their charge clouds

where are clouds formed?

in bonding pairs

describe electron pair repulsion:

charge clouds will repel one another as far apart as possible

What affects how far lone pair charge clouds can repel?

lone pair charge clouds differ in shape to bonding pair chair clouds

which pair repels more and why?

lone-pairs repel more as they are closer to the central atom- more squat and spread out

what is the order of size of bond angle created from the repulsion? (Valence shell electron pair repulsion theory (VSEPR) )

• lone-lone pairs= biggest angle

• lone-bonding= second biggest angle

• bonding- bonding = smallest angle

what determines the shape of molecules?

the number of electron pairs around the central atom

what does molecular shape depend on?

electron pairs around the central atom

why do electron pairs repel each other?

they are negatively charged

what does VESPR explain?

the electron pairs around a central atom arrange themselves as far apart from each other as possible in order to minimise repulsion

how do you draw a bond going into the page?

dashed lines

how do you draw a bond coming out of the page?

a shaded in wedge / triangle

what shape would be found in a molecule with 2 bonding charge clouds? what is the angle?

linear. 180

what shape would be found in a molecule with 3 bonding charge clouds? what is the angle?

trigonal planar. 120

what shape would be found in a molecule with 4 bonding charge clouds? what is the angle?

tetrahedral. 109.5

what shape would be found in a molecule with 5 bonding charge clouds? what is the angle?

trigonal bipyramidal. 120 and 90

what shape would be found in a molecule with 6 bonding charge clouds? what is the angle?

octahedral. 90 and 180

describe the charge clouds and bonding/lone pairs of methane? bond angle? molecular shape?

• 4 charge clouds

• 0 lone pairs and 4 bonding pairs

• tetrahedral            

• 109.5

describe the charge clouds and bonding/lone pairs of ammonia? bond angle? molecular shape?

• 4 charge clouds

• 3 bonding pairs and 1 lone pair

• Trigonal pyramidal

• 107

how do you calculate the bond angel when there are lone pairs?

decreases by 2.5 for each lone pair from 109.5

describe the charge clouds and pairs in water? what is the bond angle?

• 4 charge clouds

• 2 bonding pairs and 2 lone pairs

• 109.5

• v-shaped / bent shape

what are the 5 fundamental shapes of molecules?

• linear (180)

• trigonal planar (120)

• tetrahedral (109.5)

• trigonal bipyramidal (90 and 120)

• octahedral (90)

which shape would be found in a molecule with 2bp 0lp? what angle?

linear 180

what shape and angle would be found in a molecule with 3bp 0lp?

trigonal planar 120

what shape and angle would be found in a molecule with 2bp 1lp?

bent. slightly less than 120

what shape and angle would be found in a molecule with 4bp 0lp?

tetrahedral 109.5

what shape and angle would be found in a molecule with 3bp 1lp

tetrahedral/trigonal pyramidal 107

what shape and angle would be found in a molecule with 2bp 2lp

bent 104.5

what shape and angle would be found in a molecule with 5bp 0lp?

trigonal bypramidal 120 and 90

what shape would be found in a molecule with 4bp 1lp?

seesaw

what shape and angle would be found in a molecule with 3bp 2lp?

trigonal bipyramidal 90

what shape and angle would be found in a molecule with 2bp 3lp?

trigonal bipyramid 180

what shape and angle would be found in a molecule with 6bp 0lp?

octahedral 90

what shape and angle would be found in a molecule with 5bp 1lp?

octahedral 90

what shape and angle would be found in a molecule with 4bp 2lp?

square planar 90