M2, S2 Polarity and intermolecular forces

Question 1

What is electronegativity?

Answer 1

An atom’s ability to attract the electron pair in a covalent bond.

Question 2

How does position in the periodic table affect electronegativity?

Answer 2

Electronegativity increases across periods and decreases down groups ( ignoring the noble gases).

Question 3

How is electronegativity measured? What is the most electronegative element?

Answer 3

On the Pauling scale. Greater pauling value = higer electronegativity. Flourine is the most electronegative element.

Question 4

What is:

• polarity
• a dipole

Answer 4

polarity - the property of havng two poles (opposite aspects)

a dipole - the difference in charge between two atoms caused by a shift in electron density in the bond.

Question 5

What makes a covalent bond polar?

Answer 5

A covalent bond is polar if its bonding electrons are pulled towards the more electronegative of its two atoms.

Question 6

Result of a polar bond?

Answer 6

In a polar bond, the difference in electronegativities between two atoms causes a permanent dipole. The greater the difference in electronegativity, the more polar the bond.

Question 7

What do you need to remember about the covalent bonds in diatomic gases?

Answer 7

The covalent bonds in diatomic gases are (e.g. H₂, Cl₂) are non- polar because the atoms have equal electroegativities and so the electrons are equally attracted to both nuclei.

Question 8

how does a similar electronegativity between two elements affect the bond between them?

Answer 8

The bonds between elements with similar electronegativities, e.g. C and H, are essentially non-polar.

Question 9

What type of dipole does a polar bond have?

Answer 9

A permanent dipole

Question 10

What determines whether or not a molecule has a permanent dipole?

Answer 10

The arrangement of polar bonds in a molecule determines whether or not it has a permanent dipole.

Question 11

What are the arrangements of polar bonds?

Answer 11

1. If polar bonds are are arranged symmetrically so that the diploles cancel each other out, then the molecule has no overall dipole and is non-polar. e.g. CO₂
2. If the polar bonds are arranged so that they don’t cancel each other out, the charge is arranged unevenly across the whole molecule, and it will have an overall dipole.

Question 12

What are molecules with an overall dipole known as?

Answer 12

Polar. e.g. water is polar as the negative charge is positioned towards the oxygen atom.

Question 13

How do work out whether a molecule has an overall dipole?

Answer 13

To work out whether a molecule has an overall dipole you first need to draw it in 3D . Then label the partial charges on each atom, and look to see if they cancel each other out.

Question 14

Which are the only bonds that are purely covalent?

Why?

Answer 14

The only bonds that are purely covalent are the bonds between atoms of a single element e.g. diatomic gases.

This is because the electronegativity difference between the atoms is zero and so the bonding electrons are arranged completely evenly with the bond.

Question 15

What do you need to remember about the properties of most compounds?

Answer 15

Very few compounds are purely covalent or completely ionic. Really, most compounds are somewhere in between the two extremes -meaning they’ve got ionic and covalent properties.

e.g. covalent hydrogen chloride gas molecules dissolve to form hydrochloric acid which is an ionic solution.

Question 16

How can you use electronegativity to predict what type of bonding will occur between two atoms?

Answer 16

The greater the difference in electronegativity, the more ionic in character the bonding becomes.

Question 17

What do you need to emeber about intermolecular forces?

What are the different types of intermolecular forces?

Answer 17

Intermlecular forces are much weaker than covalent, ionic or metallic bonds.