MODULE 2: Shapes of Molecules and Intermolecular Forces Flashcards
How many degrees does the bond angle in a covalent bond decrease per lone pair of electrons?
2.5 degrees
What is the bond angle in a covalent bond with 4 bonded pairs?
109.5 degrees
What is the bond angle in a covalent bond with 3 bonded pairs and 1 lone pair?
107 degrees
What is the bond angle in a covalent bond with 2 bonded pairs and 2 lone pairs?
104.5 degrees
What is the bond angle in a covalent bond with just 3 bonded pairs and no lone pairs?
120 degrees
What is the bond angle in a covalent bond with 6 bonded pairs and no lone pairs?
90 degrees
What is the name of a covalent bond with 4 bonded pairs?
Tetrahedral
What is the name of a covalent bond with 3 bonded pairs and 1 lone pairs?
Trigonal pyramidal
What is the name of a covalent bond with 2 bonded pairs and 2 lone pairs?
Non-linear (because they’re bent!)
What is the name of a covalent bond with 3 bonded pairs and no lone pairs?
Trigonal planar
What is the name of a covalent bond with 6 bonded pairs and no lone pairs?
Octahedral
Why do lone pairs cause more repulsion?
Because they are not shared, therefore have a more concentrated negative charge
When drawing 3D molecules, what does a solid line represent?
A bond on the same plane as the paper
When drawing 3D molecules, what does a solid wedge represent?
A bond that comes forward from the plane of the paper (towards you)
When drawing 3D molecules, what does a dotted wedge represent?
A bond that goes away from the plane of the paper (away from you)
What is electronegativity?
The ability of an atom in a covalent bond to attract the bonded pair of electrons
How does electronegativity increase across the periodic table?
Up and to the right (towards fluorine)
How is electronegativity measured?
Pauling electronegativity scale (0.0-4.0)
What is a polar bond?
A bond where the shared pair of electrons is unequally distributed as the atoms sharing the bonds have different electronegativity values
What is a non-polar bond?
A bond where the shared pair of electrons is shared equally between atoms
What happens to the atoms with a polar bond?
They gain partial charges
What symbol is used to represent partial charges?
Delta (δ)
What are the partial charges in a polar bond called?
Permanent dipoles
What are the different types of intermolecular forces?
London forces, permanent dipole-dipole interactions, hydrogen bonding
What are London forces?
Weak intermolecular forces that exist between all molecules, occur due to movement of electrons around the nucleus (temporary)
How does the strength of London forces change?
Increases as number of electrons increases
What are simple molecular substances?
A substance made up of simple molecules (diatonic molecules) and only have London forces (H2, I2, etc)
What are the properties of simple molecular substances?
Low melting and boiling points, no conductive
What is the solubility of non-polar simple molecular substances?
Soluble in non-polar solvents, (tend to be) insoluble in polar solvents
What is the solubility of polar simple molecular substances?
May dissolve in polar solvents, solubility depends on strength of dipole (stronger dipole = more soluble)
What is a hydrogen bond?
A form of permanent dipole-dipole interaction that involves an electronegative atom with a lone pair of electrons (oxygen, nitrogen, fluorine) and a hydrogen attached to an electronegative atom with a lone pair of electrons
How are hydrogen bonds represented in diagrams?
Dashed lines
What are the anomalous properties of water?
Solid is less dense than liquid form, has a relatively high melting and boiling point
Why is water less dense as a solid (ice)?
Hydrogen bonds hold water molecules in a lattice structure, so therefore the water molecules are ‘pushed’ further apart and ice expands, increasing the volume but maintaining the same mass (density is mass/volume). This causes ice to float)
Why does water have a relatively high melting/boiling point?
Because of the stronger hydrogen bonds require more energy to break
