Paper 1- IMFs & electronegativity

Question 1

what is the electron-pair repulsion theory?

Answer 1

A model used in chemistry for explaining and predicting the shapes of molecules and polyatomic ions.

Question 2

what repels more, a bonded pair/bonded pair, bonded pair/ lone pair or lone pair/lone pair?

Answer 2

lone pair/lone pair.

Question 3

how does one lone pair change the bonding angle?

Answer 3

each lone pair reduces the bonding angle by 2.5 degrees.

Question 4

how many lone pairs and bonded pairs does a tetrahedral have? state the bond angle.

Answer 4

0 lone pairs
4 bonded pairs
bond angle is 109.5 degrees

Question 5

How many lone pairs and bonding pairs does a pyramidal shape have? State the bond angle.

Answer 5

1 lone pair
3 bonded pairs
bond angle is 107 degrees

Question 6

how many lone pairs and bonded pairs does a non-linear shape have? state bond angle.

Answer 6

2 lone pairs
2 bonded pairs
bond angle of 104.5 degrees

Question 7

What are the principles of the electron-pair repulsion theory?

Answer 7

• Electron pairs around the central atom repel each other as far apart as possible
• the greater the number of electron pairs, the smaller the bond angle.
• lone pairs of electrons repel more strongly compared to bonded pairs of electrons.

Question 8

how many electron pairs does a trigonal planar have and what is the bond angle?

Answer 8

3 electron pairs
bond angle is 120 degrees

Question 9

How many electron pairs/regions does an octahedral have? state the bond angle

Answer 9

6 electron pairs
90 degrees

Question 10

what is electronegativity?

Answer 10

Electronegativity is the attraction of a bonded atom for a pair of electrons in a covalent bond.

Question 11

what is the most electronegative element in the periodic table?

Answer 11

Fluorine (value of 4.0)

Question 12

How is electronegativity measured?

Answer 12

The Pauling scale; each element has a Pauling electronegative value depending on its position in the periodic table.

Question 13

what happens to electronegativity as you go across the periodic table and why?

Answer 13

Electronegativity increases as you go across the periodic table because the nuclear charge increases and the atomic radius decreases

Question 14

What happens in a non-polar bond?

Answer 14

The bonded electron pair is shared equally between the bonded atoms. A bond will be non-polar the bonded atoms are the same or they have the same/similar electronegativity.

Question 15

what happens in a polar bond?

Answer 15

• the bonded electron pair is shared unequally between the bonded atoms.
• a bond will be polar when the bonded atoms are different and have different electronegativity values which will result in a polar covalent bond.

Question 16

what is a dipole?

Answer 16

separation of opposite charges (delta negative and delta positive)

Question 17

explain how HCL (H—CL) is a polar molecule

Answer 17

• Hydrogen has a smaller electronegative value (2.1) and chlorine has a greater electronegative value (3.0)
• This means that chlorine is more electronegative than hydrogen
• therefore the chlorine atom has a greater attraction for the bonded pair of electrons than the hydrogen atom which results in a polar covalent bond.
• HCL bond is polarised with a small partial charge on either atom.

Question 18

Does a dipole in a polar covalent bond change?

Answer 18

no, it is a permanent dipole.

Question 19

What are intermolecular forces?

Answer 19

Weak interactions between dipoles of different molecules. There are three main categories:
- induced dipole-dipole interactions (London forces) (weakest)
- permanent dipole-dipole interactions
- hydrogen bonding (strongest)

Question 20

what are intermolecular forces largely responsible for?

Answer 20

physical properties such as boiling and melting point

Question 21

how do London forces (induced dipole-dipole) occur?

Answer 21

• movement of electrons produces a changing dipole in a molecule
• An instantaneous dipole will exist at any instant but its position will constantly shift.
• the instantaneous dipole induces a dipole on a neighbouring molecule
• the induced dipole induces further dipoles on neighbouring molecules which then attract another one.

Question 22

How would more electrons in each molecule change the strength of induced dipole-dipole interactions (London forces)

Answer 22

• the larger the instantaneous and induced dipoles are.
• the greater the induced dipole-dipole interactions
• the stronger the attractive forces between molecules.

Question 23

What is a simple molecular lattice?

Answer 23

contains simple molecules from a simple molecular substance in a solid state which forms a regular structure.
- molecules are held in place by weak intermolecular forces.
- the atoms within each molecule are bonded together strongly by covalent bonds.

Question 24

What are the properties of simple molecular substances?

Answer 24

• low melting point
• low boiling point

Question 25

why are non-polar simple molecular substances soluble in non-polar solvents?

Answer 25

• when a simple molecular compound is added to a non-polar solvent (like hexane) the intermolecular forces form between the molecules and solvent.
• the interactions weaken the intermolecular forces in the simple molecular lattice. The IMFs break and the compound dissolves.

Question 26

why are simple molecular substances insoluble in polar solvents?

Answer 26

• when a simple molecular substance is added to a polar solvent, there is little interaction between the molecules in the lattice and solvent molecules.
• the intermolecular bonding within the polar solvent is too strong too be broken