electronegativity + polarity

Question 1

What is a covalent bond?

Answer 1

A covalent bond is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 2

What is electronegativity?

Answer 2

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

Question 3

How can electronegativity be measured?

Answer 3

It’s measured on the Pauling scale

Pun: appauling
Scale made by Linus pauling

Question 4

What are the trends in electronegativity ?

Answer 4

Electronegativity increases across a period and up a group

In all directions towards fluorine

Question 5

Why does electronegativity increase across a period?

Answer 5

The charge on the nucleus increases across a period
The number of protons in the nucleus increases
Thus there is an increased attraction for the outer electrons
And so the bonding pair of electrons are attracted more strongly

Question 6

Why does electronegativity increase up a group?

Answer 6

Down the group the bonding pair of electrons is held increasingly further away from the nucleus,
The number of shells increases
So the distance of the outer electrons from the nucleus increases
And so the bonding pair of electrons are attracted less strongly

(Sum up, it’s shielding)

Question 7

What are polar bonds?

Answer 7

When one atom is more electronegative than the other (and they are bonded)

Question 8

What is an example of polar bonds?

Answer 8

Chlorine is more electronegative than the hydrogen
Cl has a greater attraction for the electrons than H in the bond
The electrons are closer to the Cl than the H

-paulings scale readings-
Chlorine: 3.0
Hydrogen:2.1

So Cl>H in electronegativity
If you want a visual representation look at the video at 3:42

As a result the Chlorine becomes slightly negative and the reverse for hydrogen
This is a permanent dipole and the charge difference is always present

Question 9

What are dipoles?

Answer 9

The differing attraction for the pair of electrons allows there to be a small charge difference between the atoms.

Question 10

What are the conditions for a polar bond to form

Answer 10

If the two bonding atoms are different, their attraction for the shared pair of electrons is unequal
The bonding atom with a greater attraction for the shared pair of electrons is more electronegative
The bond is polarised

Question 11

What are the conditions for a non polar bond to form?

Answer 11

If the two bonding atoms are identical, their attraction for the shared pair of electrons are equal
The electrons are equally distributed between the bonding atoms
The bond is perfectly covalent

Question 12

What is the spectrum of bonds?

Answer 12

Rather than bonds existing as discreetly ionic and covalent they exist on a spectrum

Question 13

Where is ionic bonding on the spectrum Of bonds and why?

Answer 13

The far left as the difference in electronegativity is so great that one atom effectively takes the electron from the other

(Left is greatest right is leastest which I’m aware isn’t a word)

Question 14

Where is polar-covalent bonding on the spectrum of bonds?

Answer 14

The middle as the difference in electronegativity is small so the atoms share the electrons unequally and the bond is polarised

Question 15

Where is covalent bonding on the spectrum of bonds?

Answer 15

At the far right as there is no difference in electronegativity so the molecule is electronically symmetrical

Question 16

What is the difference between polar and non polar bonds

Answer 16

Molecules containing polar bonds are not always polar

The symmetry of polar bonds can cancel the effect of any permanent dipole

Question 17

What are features of non symmetrical molecules?

Answer 17

A difference in charge exists across the molecule
There is an overall dipole
The molecule is polar

Question 18

What are the features of symmetrical molecules?

Answer 18

The symmetry of the molecule means that the effect of any permanent dipoles is cancelled out
Linear, trigonal planar or tetrahedral shape (occurs in)
All atoms attached to the central atom are identical
No difference in charge exists across the molecule
The molecule is non polar

Question 19

What is a non polar bond

Answer 19

The two bonding atoms are identical and the electrons are equally distributed between the bonding atoms

Question 20

What is a polar bond?

Answer 20

The two bonding atoms are different and their attraction for the shared pair of electrons is unequal

Question 21

What is a polar molecule

Answer 21

A difference in charge exists across the molecule

Question 22

What is a non polar molecule

Answer 22

The symmetry of the molecule means that the effect of any permanent dipoles is cancelled out and there is no difference in charge exists across the molecule

Question 23

Which of the following molecules is polar?
A: SiCl4
B: CO2
C: NH3
D: BF3

Answer 23

CccCcCccccccccCccccccccCcC

It’s c

Question 24

In magnesium iodide, some polarisation of the bond occurs. Explain, in terms of magnesium iodide, what the term polarisation means.

Answer 24

There is a small difference in electronegativity between Mg and I , as a result, the pair of electrons are shared unequally and there is an uneven distribution of charge . The bond is polarised

Question 25

Both NF3 and BF3 molecules contain polar bonds. However, only one of these molecules is polar. State which molecule is polar and explain the difference.

Answer 25

NF3 is polar. It had a pyramidal shape and is not symmetrical, meaning that the dipoles do not cancel. BF3 is not overall polar it has a trigonal planar shape and is symmetrical so the dipoles cancel

Question 26

Define the term electronegativity

Answer 26

The ability of an atom to attract electrons in a covalent bond

Question 27

Chlorine is more electronegative than carbon and hydrogen, which have roughly equal electronegativity.
- they can form the molecule dichloromethane, CH2Cl2. Explain why it is a polar molecule

Answer 27

The molecule is not symmetrical and dipoles do not cancel out overall