Question on Chemical bonding

bonkysleuth SG

the table below shows some of the physical properties of some 'unknown' substancese, P, Q, R and S

Substance M.P/deg cel boiling point Elect.Cond. Solubilit

P 122 550 Poor(s)Poor(l) insoluble

Q 690 1790 Poor(s)Good(l)soluble

R 1510 2489 Poor(s)Poor(l) insoluble

S 1453 2730 Good(s)good(l) insoluble

by the water the last column is "solubility in water" and for electrical conductivity Poor(s) means poor conductor in solid state

which of the following statements about the 4 substances is coorect?

1. P is a simple molecular compounds with weak covalent bonds

2. Q is an ionic compound with mobile electrons in liquid state

3. R is a macromolecule with immmobile electrons held by strong electrostatic forces

4. S is a macromolecule with mobile electrons.

I eliminated option 1 and 3. Let me explain first. First, the melting and b.p of P is simply too high for it to be a simple molecular compound, which usually have -ve values for melting points

As for 3, the term forces are used for ionic compounds. Macromolecules are covalent compounds

Left with choice 2 and 4. 2 sounds quite right to me. By the way, do macromolecules have high m.p and b.p? Are diamond and graphite considered macromolecules? I know diamond is, so graphite is probably one too. Option 4 looks fine but I just want to know whether macromolecules ahve high m.p and b.p.

2.the proton numbers of elements X , Y and Z are 4 , 6,8 respectively. Which of the following lists gives the correct formulae of the compounds formed between them?

1 XZ YZ2 XYZ3

2 XZ YZ2 XYZ4

My answer is 1. XYZ3 contains both covalent and ionic bonds as XZ is an ionic compound with YZ2 is covalent compound. Please screen through my answers. thanks.

ThunderFbolt SG

lest i'm mistaken, macromolecules are like protein and fat molecules, where the molecules are formed by monomers polymerising. diamond and graphite are lattice structures? so they should have low melting and boiling points.

it is possible that they have mobile electrons in molten state or aqueous state depending on the atoms in the molecule.

2. you are right. in such questions, when they give the proton number, it is much easier to correct your answer by referring to their corresponding elements as we are used to seeing them. in 1, the compounds are BeO, CO(2), and BeCO(3)

wishboy SG

Q1.

S can be graphite which has a macromolecular covalent layered lattice structure.
Reason for having high mp/bp is because a large amount of energy is required to break the numerous strong covalent bonds between atoms.
It is also insoluble.

Macromolecules generally have high mp/bp.

While for Q,
Ionic compounds usually dissociate into its constituent ions in water (if they are soluble), rather than releasing its electrons.
Charge carriers (for electrical conductivity) in liquid state should be mobile ions instead of mobile electrons.
Hence, Q is not a possible option.

Q2.

X is a metal with 2 valence electrons.
Y is a non-metal with 4 valence electrons.
Z is also a non-metal with 6 valence electrons.

Both options have XZ and YZ2 (kind of redundant) so we do not need to look at them.

An ion of X has a charge of 2+. Y and Z can form an ion (with covalent bonds), YZ3 2-, having a charge of 2-.
Therefore, X 2+ can form a compound with YZ3 2-, resulting in XYZ3. So, option 1 is correct.

For option 2, there will be 2 extra electrons which are neither shared nor transferred, so a possible compound can be [XYZ4] 2- and not XYZ4.

Disclaimer: My answer may not be correct.

bonkysleuth SG

Q1.

Macromolecules generally have high mp/bp.

Q2.

X is a metal with 2 valence electrons.
Y is a non-metal with 4 valence electrons.
Z is also a non-metal with 6 valence electrons.

Both options have XZ and YZ2 (kind of redundant) so we do not need to look at them.

For option 2, there will be 2 extra electrons which are neither shared nor transferred, so a possible compound can be [XYZ4] 2- and not XYZ4.

Disclaimer: My answer may not be correct.

" an ion (with covalent bonds)"

Hi, what do you mean by the above phrase? thanks. with ionic bonds?

Darkness_hacker99 SG

An ion is a charged atom.

it does contain bonds .

wishboy SG

" an ion (with covalent bonds)"

Hi, what do you mean by the above phrase? thanks. with ionic bonds?