Unit 1 - Bonding

Question 1

What is a covalent bond?

Answer 1

A shared pair of electrons, between two positively charged nuclei.

Question 2

Arrange ionic, polar, and pure bonds in a bonding continuum in order of increasing difference in electronegativity.

Answer 2

At the start, there’s pure covalent, zero difference.

In the middle, there’s polar covalent, low difference.

At the end, there’s ionic, high difference.

https://prnt.sc/LwOMDjHIssa6

Question 3

What are the types of bonding & structure that can exist in elements?

Answer 3

Ionic Bonds
Pure Covalent Molecular
Polar Covalent Molecular
Covalent Network
Metallic

Question 4

Draw a diagram to show metallic bonding, and describe why metals conduct electricity.

Answer 4

https://prnt.sc/1MCqQXfgozEI
(Positive metal ions interlaced with a sea of free moving electrons)

They can conduct, since electrons are delocalised, so they can move freely within the metal structure.

Question 5

Describe a pure covalent bond, and provide an example.

Answer 5

Pure covalent bonds are covalent bonds that exist between two atoms with the same electronegativities.

Any of the diatomic molecules are good examples, e.g. H-H

Question 6

Describe a polar covalent bond, and provide an example.

Answer 6

Polar covalent bonds form when a shaired pair of electrons are not shared equally, due to one element having a higher electronegativity than the other.

An example can be H - Br where H has an electronegativity of 2.2, and Br has an electronegativity of 3.0

Question 7

Draw a molecule of HCl and label the partial charges present

Answer 7

https://prnt.sc/EGE0Gyx6JwZH
(Don’t need to draw the larger size of the other)

Question 8

When will an ionic bond be formed?
When do they usually form?

Answer 8

Ionic bonds when there is a high enough difference in electronegativities, higher than polar covalent bonds.

They usually occur between metals and non-metals with high differences in electronegativities
e.g. Sodium chloride

Question 9

How are ionic compounds held together and what type of structure will they have?

Answer 9

The electrostatic force of attraction between the oppositely charged ions in the lattice.

Question 10

Which elements in the first 20 have a metallic structure?

Answer 10

Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, and Calcium.

Question 11

Which elements in the first 20 have a covalent network structure?

Answer 11

Boron, Carbon (in the form of graphite, or diamond), Silicon.

Question 12

Which elements in the first 20 have a covalent molecular structure?

Answer 12

Phosphorus, Sulfur, Fullerenes

Question 13

How do London Dispersion Forces arise?

Answer 13

LDFs are caused by an uneven distribution of electrons within an atom.

This gives rise to temporary dipoles.

Question 14

Which elements in the first 20 have a monatomic structure?

Answer 14

Noble Gases (Helium, Neon, Argon)

Question 15

What happens to the strength of LDFs as the size of the atom/molecule increases?

Why does this happen?

Answer 15

Larger atoms and molecules exhibit stronger dispersion forces than smaller and lighter ones.

This is because, in a larger atom/molecule valence (outer) electrons are farther from the nucleui than smaller ones, they’re less tightly held so can form a temporary dipole easier.

Question 16

How does a dipole form?

Answer 16

When an atom or molecules electrons are distributed unsymmetrically about the nucleus.

Question 17

What are permanent dipole - permanent dipole interactions? How do they compare to LDFs?

Answer 17

An intermolecular bond stronger than LDFs that form in polar molecules.

Compared to LDFs, they are permanent due to the polarity, and are stronger than them.

Question 18

Why do some substances with polar bonding not have dipoles?

Answer 18

If we take the vectors of the bond dipoles and draw them out,

If we draw out CO2, the C-O bond dipoles are equal in magnitude but oriented oppositely, and so their vector sum is zero.

Whereas H2O, O-H bonds are also equal in magnitude, but are oriented 104.5degrees to each other, hence why their vector sum is not zero.

https://prnt.sc/Zkd9FFG3k_Lg

Question 19

Which of the following will be polar, explain.

CCl4
CH4
HCl4

Answer 19

CCl4 is non polar, this is because it’s net dipole is zero, as the geometrical structure is symmetrical.

In CH4 (non polar), the net dipole is zero, as the geometrical structure is symmetrical.

In H-Cl (polar), the net dipole is more than zero, and the geometrical structure is not symmetrical.

Question 20

Which of the following will be polar, explain.

Carbon dioxide
Chloromethane
Hexane

Answer 20

Carbon dioxide is non polar, because the net dipole is zero, as the geometrical structure is symmetrical.

Chloromethane is polar, because the net dipole is more than zero, with an unsymmetrical geometrical structure.

Hexane is nonpolar because of its symmetrical structure (net dipole 0), but carbon and hydrogen also have low electronegativity differences.

Question 21

When will hydrogen bonding occur? Give three compounds that will exhibit hydrogen bonding.

Answer 21

Hydrogen bonding occurs when a hydrogen atom is covalently bonded to a highly electronegative element such as nitrogen, oxygen, or flourine.

They work like PD-PD interactions

H2O, NH3, CHCl3

Question 22

What anomalous properties of water arise from hydrogen bonding?

Answer 22

Ice is less dense than water, since hydrogen bonds create an open lattice structure

Relatively high melting point, since more energy is required to overcome hydrogen bonds because hydrogen bonds are strong.

Question 23

What anomalous properties of water arise from hydrogen bonding?

Answer 23

Ice is less dense than water, since hydrogen bonds create an open lattice structure

Relatively high melting point, since more energy is required to overcome hydrogen bonds because hydrogen bonds are strong.

Question 24

List the Van Der Waal forces in order of strength starting from weakest

Answer 24

1. London Dispersion Forces
2. Permanent Dipole - Permanent Dipole Interactions
3. Hydrogen bonding

Question 25

Explain why the boiling point of Ammonia NH3 is higher than methane CH4

Answer 25

This is because Nitrogen and Hydrogen have high differences in electronegativities, giving rise to Hydrogen bonding, which is strong and takes more energy to break therefore higher boiling point.

CH4 does not exhibit Hydrogen bonding, as C and H have very similar electronegativities.

Question 26

Explain how viscosity (a fluid’s resistance to flow) is affected by hydrogen bonding

Answer 26

Hydrogen bonds increase viscosity.

For example, take a non hydrogen bonded and hydrogen bonded liquid and throw a ball into it, if it takes longer to fall the viscosity is higher.

Question 27

Why is ethanol C2H5OH miscible with water, whereas ethane C2H6 is not?

Answer 27

Hydrogen bonds affect solubility. The more polar the molecule is due to hydrogen bonding, the higher will be the solubility.

The polar molecules are attracted by water molecules through hydrogen bonding and thus they dissolve easily in water.

Question 28

Why does sulfur S8 have a higher boiling point than phosphorus (P4)?

Answer 28

S8 molecules have higher boiling points than P4 molecules

This is because Van der waal forces are stronger on larger molecules (because valence electrons are less tightly held) and so it takes more energy to break them.

Question 29

Which type of solvents will dissolve polar compounds or molecules?

Answer 29

Polar solvents.

Because like dissolves like, when we dissolve polar solute in polar solvent forces holding the components of polar solute is replaced by the similar forces.

Question 30

What type of solvent will dissolve non-polar compounds or molecules?

Answer 30

non-polar solvent.

Because like dissolves like, when we dissolve non-polar solute in non-polar solvent, forces holding the components of polar solute are replaced with similar forces.

Question 31

What intermolecular force is responsible for ice floating on water?

Answer 31

Hydrogen Bonding, as they cause spacing that causes ice to be less dence than liquid water.

Question 32

Explain why diamond has a high melting point

Answer 32

Diamonds have very high melting points, because a large amount of energy is required to overcome the strong covalent bonds.

Question 33

Why is the melting point of Argon larger than Helium

Answer 33

Logically, Argon has a larger mass than helium, and so the london dispersion forces are much greater.

Question 34

Write Ionic formula for Magnesium Chloride

Answer 34

MgCl2

Mg is on the closer side for valency rule so 2(+)

Cl is on the farther side of valency rule so 2(-)

Mg2+(Cl2-)2

Question 35

Write Ionic formulae for sodium bromide

Answer 35

Na+Br-

Na is on the closer side for valency rule so 1(+)

Cl is on the farther side of valency rule so 1(-)

Question 36

Is Iodine likely to dissolve in hexane or water best?

Answer 36

Water is polar, and hexane is non-polar.

Iodine is non-polar as its geometrical shape is symmetrical and so the net is zero.

Like dissolves like, and therefore it will likely dissolve in hexane.