Properties of organic compounds

Question 1

What is the meaning of polarity?

Answer 1

Separation of charge

Question 2

Describe polar molecules

Answer 2

They have a positively charged region and a negatively charged region

Question 3

Describe non-polar molecules

Answer 3

They have no real difference in charge across the molecule

Question 4

What is electronegativity?

Answer 4

Electronegativity is a measure of an atom’s tendency to attract electrons to itself.
All atoms are attracted to bonding electrons, but some are more attracted to them than others.

Question 5

What is the polarity of two hydrogen atoms? explain

Answer 5

There is no difference in charge so their covalent bond is non-polar.
-Since they are both the same, they pull on the electrons with the same amount of strength so they end up spending the same amount of time around the nucleus both hydrogen atoms

Question 6

What is the polarity of a hydrogen atom and a chlorine atom? explain

Answer 6

There is a difference in charge so the covalent bond is polar
-Chlorine is more electronegative than hydrogen so it as a larger tendency to attract electrons to itself. although the bonding electrons ar shared, chlorine pulls more tightly on them causing the electrons to spend more time around the chlorine nucleus than the hydrogen
Bond dipoles(chlorine is partially negative, hydrogen is partially positive)

Question 7

What compounds are always non-polar? - Why?

Answer 7

Alkanes, alkenes, and alkynes. This is because they have a symmetrical shape and therefore any dipoles between C-H bonds are cancelled out

Question 8

Why are haloalkanes also considered to be non-polar?

Answer 8

This is because the non-polar carbon chain overtakes the halogen atoms, even though it is highly electronegative( same properties as alkanes, alkenes, and alkynes) - the dipole is cancelled out by the symmetry of the carbon chain

Question 9

Which compounds are polar? - what do they contain that allow for this?

Answer 9

Alcohol, carboxylic acid, amine. Compounds that contain oxygen or nitrogen are usually polar overall because they are very electronegative atoms, more than carbon and hydrogen atoms. When one of these atoms attaches to the main carbon chain, there is a negative charge region, giving the molecule polarity.

Question 10

What are the polar compounds and why are they small?

Answer 10

Only small alcohols, amines, and carboxylic acids are polar( less than 5 carbon atoms) This is because when these organic molecules are small, there is a large enough proportion to make the molecule polar.

Question 11

What are large molecules of alcohol, carboxylic acid, and amine considered to be in terms of polarity?

Answer 11

As more carbon atoms are added to the main carbon chain, the polar functional group takes up a smaller proportion of the molecule
This means that large molecules with generally more the 5 carbons in the main chain are considered to be non-polar because the carbon chains are more strongly non-polar and cancel out the dipoles

Question 12

What is the state change for melting point?

Answer 12

Solid to liquid

Question 13

What is the state change for boiling boint?

Answer 13

Liquid to gas

Question 14

What is the general rule for melting/boiling point?

Answer 14

The stronger the force of attraction, the more heat energy required to break it

Question 15

When the temperature increases….

Answer 15

the energy of the molecule increases. This will cause state changes from a state with less energy to one with more ie solid to liquid, liquid to gas

Question 16

Which compounds have low melting and boiling points?- explain

Answer 16

Alkanes, alkenes, alkynes, and haloalkanes due to them being non-polar and have weak intermolecular forces between molecules. This doesn’t require much heat energy to break them and change their state

Question 17

Why do haloalkanes have slightly higher melting/boiling point than alkenes, alkanes, alyknes?

Answer 17

Because the halogen atom gives it slightly more polarity

Question 18

Which compounds have higher melting and boiling points?- explain

Answer 18

Alcohols, amines, carboxylic acids due to them being polar molecules held together by strong intermolecular forces of attraction. This is due to the attraction between positively charged and negatively charged regions of neighbouring molecules which is higher than non-polar organic compounds

Question 19

What is the general trend for all organic molecules?- why

Answer 19

For all organic molecules, the melting and boiling point increases as the length of the carbon chain increases.
- This is due to the number of electrons that determine the strenth of intermolecular forces. When the number of electrons increases when the molecular mass does, it leads to stronger attractive forces between molecules. This requires more heat to break the bonds

Question 20

What is a solute and solvent?

Answer 20

A solute is the thing that gets dissolved in liquid while the solvent in the liquid something dissolves in(like water)

Question 21

What is the rule of solubility?

Answer 21

Polar molecules will dissolve in polar molecules and non-polar molecules will dissolve in non-polar molecules (like dissolves like) - a thing will only dissolve in something that has the same existence of polarity

Question 22

Which compounds DO NOT dissolve in water? - why

Answer 22

Alkanes, alkenes, alkynes and haloalkanes don’t dissolve in water. This is because they are all non-polar molecules due to being symmetrical. Non polar molecules will be insoluble in polar liquids like water

Question 23

What do non polar molecules do when mixed with a polar molecule?

Answer 23

They will form seperate layers making alkanes, alkenes, alkynes and halokalkanes immicisble in water

Question 24

Which compounds are soluble in water? - why only some

Answer 24

some alcohols, amines, and carboxylic acids that are between 1-4 carbon atoms in their main chain. They are all polar molecules so they will dissolve in water as it is polar ( like dissolves like)
- With 5 or more carbon atoms in the main chain, they begin to resist and instead of mixing, they form separate layers with the water due to the non-polarity cancelling out the polar nitrogen and oxygen atoms ( the bigger the molecule, the less polar it becomes)- the large molecules become insoluble in water