Bonding and structure- shape of molecules Flashcards
What shape occurs when there are 2 bonding pairs and no lone pairs?
Linear
What is the bond angle in linear molecules?
180
Give an example of a substance with a linear shape
BeF2
What shape occurs when there are 3 bonding pairs and no lone pairs?
Trigonal planar
What shape occurs when there are 4 bonding pairs and no lone pairs?
Tetrahedral
What shape occurs when there are 3 bonding pairs and 1 lone pair?
Trigonal pyramid
What shape occurs when there are 2 bonding pairs and 2 lone pairs?
Bent/v-shape
What shape occurs when there are 5 bonding pairs and no lone pairs?
Trigonal bipyramid
What shape occurs when there are 6 bonding pairs and no lone pairs?
Octahedral
What is the bond angle in trigonal planar?
120
What is the bond angle in tetrahedral?
109.5
What is the bond angle in bent/v-shaped?
104.5
What is the bond angle in trigonal pyramid?
107
What is the bond angle in octahedral?
90
What is the bond angle in trigonal bipyramid?
90 and 120
Give an example of a molecule which has as octahedral shape?
SF6
Give an example of a molecule which has a trigonal bipyramidal shape
PF5
Give an example of a molecule which has a trigonal pyramid shape
NH3
Give an example of a molecule which has a trigonal planar shape
BH3
Relative to single bonds, how much do double bonds repel?
Equally
What shape of bonding is present in Carbon dioxide?
Linear
When representing an ion in 3D what must you remember to draw?
Square brackets around the structure and the charge in the top right corner outside the brackets
Explain why NH3 has a different shape to BH3
- BH3 does not have any lone pairs so has a bond angle of 120
- NH3 has one lone pair
- Lone pairs repel more the bonding pairs so the atoms are pushed into a trigonal pyramid shape
What conditions are needed for a bond to be non-polar?
- the bonding atoms to be the same
- the bonded atoms have the same or similar electronegativity
What happens to the electron pair in a non-polar bond?
The bonded pair is shared equally between the bonded atoms
What kind of dipole is present in a polar covalent bond?
A PERMANENT dipole
What would you look for in a molecule to tell if it has a polar bond?
A delta charge
a difference in electronegativity values
the presence of N, O, F, or Cl
In addition to having polar bonds, molecules with a dipole must have what other property?
Asymmetry in the arrangement of the atoms
What are the 3 types of intermolecular forces?
- London forces (temporary dipole-dipole interactions)
- Permanent dipole-dipole interactions
- Hydrogen bonds
What is the order of relative strength of intermolecular forces from weakest to strongest?
- London forces
- Permanent dipole-dipole interactions
- Hydrogen bonding
What does hydrogen bonding occur between?
The lone pair of an electronegative element and a hydrogen atom attached to an electronegative atom
What is the shape around the hydrogen atom involved in the hydrogen bond?
linear
What are the 3 anomalous properties of water?
1) High melting and boiling point compared to similar molecules
2) Expansion on freezing (The solid is less dense than the liquid)
3) High surface tension
How many hydrogen bonds can a water molecule form?
4
Why can a water molecule form 4 hydrogen bonds?
- it has 2 lone pairs on the oxygen
- it has 2 hydrogen atoms
Why does ice float on water?
- Hydrogen bonds in ice hold water molecules apart in an open lattice structure
- Water molecules in ice are further apart than in water
- Solid ice is less dense than liquid water and floats
