Chapter 6 - Shapes of molecules and intermolecular forces Flashcards
How is the shape of a molecule or ion determined?
- The number of electron pairs around the central atom
- The repulsion between electron pairs
What is the name of the shape of a molecule with:
1) 2 bonding pairs
2) 0 lone pairs
3) The bond angle
Linear
180
What is the name of the shape of a molecule with:
1) 2 bonding pairs
2) 2 lone pairs
3) The bond angle
Non-Linear or Bent
104.5
What is the name of the shape of a molecule with:
1) 3 bonding pairs
2) 0 lone pairs
3) The bond angle
Trigonal planar
120
What is the name of the shape of a molecule with:
1) 3 bonding pairs
2) 1 lone pair
3) The bond angle
Trigonal pyramidal
107
What is the name of the shape of a molecule with:
1) 4 bonding pairs
2) 0 lone pairs
3) The bond angle
Tetrahedral
109.5
What is the name of the shape of a molecule with:
1) 5 Bonding pairs
2) 0 lone pairs
3) The bond angle
Trigonal bypyramidal
180 and 120
What is the name of the shape of a molecule with:
1) 6 bonding pairs
2) 0 lone pairs
3) The bond angle
Octahedral
90
Define ‘Electronegativity’
The ability of an atom to attract the bonding electrons in a covalent bond towards itself
What electronegativity difference determines a bond type as covalent?
0
What electronegativity difference determines a bond type as polar covalent?
0 to 1.8
What electronegativity difference determines a bond type as polar covalent?
Values greater than 1.8
What happens in a non-polar bond?
The bonded electron pair is shared equally between the bonded atoms
What makes a bond non-polar?
- The bonded atoms are the same
- The bonded atoms have the same or similar electronegativity
What happens in a polar bond?
The bonded electron pair is shared unequally between the bonded atoms
What makes a bond polar?
When the bonded atoms are different and have different electronegativity values
What are the 3 types of intermolecular forces?
- Induced dipole-dipole interactions (London forces)
- Permanent dipole-dipole interactions
Hydrogen bonding
State the weakest to strongest type of bond?
- London Forces (weakest)
- Permanent dipole-dipole interactions
- Hydrogen bonds
- Single covalent bonds
What is the origin of induced dipoles?
- Movement of electrons produces a changing dipole in a molecule
- An instantaneous dipole will exist, but its position is constantly shifting
- The instantaneous dipole induces a dipole on a neighbouring molecule
- The induced dipole induces further dipoles on neighbouring molecules which then attract another
Why do polar molecules have a higher boiling point than simple molecular substances?
- Polar molecules have London forces and permanent dipole-dipole interactions between molecules
- Simple molecular substances require extra energy to break the additional permanent dipole-dipole interactions between polar molecules that are stronger than London forces
Why are symmetrical molecules non-polar?
- They contain identical bonds and have no lone pairs
- This causes each individual dipole on the bonds to cancel each other out due to it being symmetrical
Define a ‘hydrogen bond’
A special type of permanent dipole-dipole interaction found between molecules containing an electronegative atom with a lone pair of electrons or a hydrogen atom attached to an electronegative atom
Why is ice less dense than water?
- The hydrogen bonds extend outwards, holding the water molecules slightly apart and forms an open lattice structure which contains holes
Why does water have a high melting and boiling point?
1) Hydrogen bonds require large amounts of energy to break the hydrogen bonds in water
