3.1.3.6 Bond polarity

Question 1

What is electronegativity?

Answer 1

The power of an atom to attract the electron density in a covalent bond towards itself

Question 2

What is the Pauling scale?

Answer 2

Used as a measure of electronegativity, ranges from 0 to 4. The greater the number, the more electronegative the atom. Noble gasses do not have a number because they do not usually form covalent bonds.

Question 3

What does electronegativity depend on?

Answer 3

The nuclear charge
The distance between nucleus and outer shell electron
The shielding of the nuclear charge by electrons in inner shells

Question 4

How does the distance between nucleus and outer shell electron affect electronegativity?

Answer 4

The smaller the atom, the closer the nucleus is to the shared outer main level electrons and greater its electronegativity

Question 5

How does nuclear charge affect electronegativity?

Answer 5

For a given shielding effect, the larger the nuclear charge, the larger the electronegativity.

Question 6

How do trends in electronegativity change going up a group?

Answer 6

Electronegativity increases; atoms get smaller and there is less shielding by electron in inner shells

Question 7

How do trends in electronegativity change going across a period?

Answer 7

Electronegativity increases; nuclear charge increases, number of inner main levels remains the same (no change in shielding) and atoms become smaller.

Question 8

Where are the most electronegative atoms found?

Answer 8

Top of the periodic table (exclude noble gasses)

Question 9

What are the most electronegative atoms?

Answer 9

Nitrogen, Oxygen and Fluorine

Question 10

What is polarity?

Answer 10

The unequal sharing of electrons between atoms that are bonded together covalently. It is a property of a bond

Question 11

How can you use the electronegativity difference to work out the type of bond between two atoms?

Answer 11

Difference less than 0.5 = non-polar covalent bond
Difference more than 0.5 but less than 2.1, it is polar covalent bond
Difference greater than 2.1, it is ionic bond

Question 12

What are examples of non-polar bonds?

Answer 12

Diatomic molecules
C-H bonds

Question 13

How is a dipole caused?

Answer 13

The difference in electronegativity between two atoms

Question 14

What is a dipole?

Answer 14

A bond or molecule whose ends have different charges
or
A difference in charge between two atoms caused by a shift of electron density in the bond

Question 15

What shapes do symmetrical molecules have?

Answer 15

Linear, trigonal planar, tetrahedral, octahedral, trigonal bipyramid

Question 16

Why are some molecules with a larger electronegativity non-polar?

Answer 16

Dipole charges can cancel each other out due to molecules being completely symmetrical

Question 17

What are the properties of non-polar molecules?

Answer 17

Include things like elements, symmetrical molecules, hydrocarbons.
Dipoles can cancel out
No permanent dipole
Charge (electron density) is distributed evenly

Question 18

What are the properties of polar molecules?

Answer 18

Non-symmetrical molecules
Dipoles don’t cancel out
Has a permanent dipole
Charge (electron density) is distributed unevenly

Question 19

Why do permanent dipoles not cancel out in polar molecules?

Answer 19

Molecule is asymmetrical - e.g. different elements or different groups attached to the central atom, or the same element is attached to the central atom, but it has lone pairs, e.g. NH3 or H2O