The Student Room Group

a level chemistry drawing moelceules

for AQA do need to include wedges and broken lines.
Reply 1
Yeah
Original post by nnn121337
for AQA do need to include wedges and broken lines.


Yes. Especially when drawing tetrahedral and trigonal pyramidal shapes.
Reply 3
Original post by NoxDuck
Yeah

how do you know where to draw it for unknown molecules how do you know where to put wedge and line broken for unknown molecules.
Reply 4
Original post by TypicalNerd
Yes. Especially when drawing tetrahedral and trigonal pyramidal shapes.

how do you know where to draw it for unknown molecules how do you know where to put wedge and line broken for unknown molecule
Reply 5
Original post by nnn121337
how do you know where to draw it for unknown molecules how do you know where to put wedge and line broken for unknown molecule


1. Work out the number of bonds, and the number of lone pairs of electrons there are around the central atom.
2. Work out the shape. There's quite a nice summary table here: https://alevelchemistry.co.uk/notes/shapes-of-molecules-and-ions/ (note that the tetrahedral bond angle is usually 109.5°, and remember that the wedged bonds should be filled in)
3. Normal line = in the plane of the paper. Wedged bond (long thin black triangle) = sticking out of the paper towards you. Dashed bond (in a vaguely small –> big order, kind of like a stripey triangle) = sticking out of the paper away from you.

I find it really helps to visualise things if you use a molecule model kit, or a ball of blu-tack with some pins stuck into it :smile:
Reply 6
Original post by bl0bf1sh
1. Work out the number of bonds, and the number of lone pairs of electrons there are around the central atom.
2. Work out the shape. There's quite a nice summary table here: https://alevelchemistry.co.uk/notes/shapes-of-molecules-and-ions/ (note that the tetrahedral bond angle is usually 109.5°, and remember that the wedged bonds should be filled in)
3. Normal line = in the plane of the paper. Wedged bond (long thin black triangle) = sticking out of the paper towards you. Dashed bond (in a vaguely small –> big order, kind of like a stripey triangle) = sticking out of the paper away from you.

I find it really helps to visualise things if you use a molecule model kit, or a ball of blu-tack with some pins stuck into it :smile:

sorry i am still confused where do you draw the wedge and broken line after the shape and angle is filled in for molecules you have not seen before.
Reply 7
Original post by nnn121337
sorry i am still confused where do you draw the wedge and broken line after the shape and angle is filled in for molecules you have not seen before.


Do you have an example "unseen molecule"? It's probably easier to work through things that way rather than trying to guess or make general assumptions :smile:
Reply 8
e.g dichlorodifluormethane(C Cl2 F2)
Reply 9
Original post by nnn121337
e.g dichlorodifluormethane(C Cl2 F2)

Ok, so you can work out the central atom this is the carbon. Each molecule consists of one carbon atom, which has 2 x Cl atoms and 2 x F atoms attached to it.

Around this carbon atom, there are 4 bonds, and no lone pairs of electrons (can you work out why this is the case?)

This means that the molecule is tetrahedral around the C.

Spoiler


And then at the ends of the bonds just stick F or Cl :smile:

Spoiler


Spoiler

(edited 3 months ago)
Reply 10
Original post by bl0bf1sh
Ok, so you can work out the central atom this is the carbon. Each molecule consists of one carbon atom, which has 2 x Cl atoms and 2 x F atoms attached to it.

Around this carbon atom, there are 4 bonds, and no lone pairs of electrons (can you work out why this is the case?)

This means that the molecule is tetrahedral.

Spoiler


And then at the ends of the bonds just stick F or Cl :smile:

Spoiler


Spoiler


so it does not matter which atom you attach the wedge and line broken all that matters is you placed the wedge and broken line in the set place based on the shape of the molecule. answer to your question carbon has four outer electron each are used in covalent bond to fluorine and chlorine so no lone pairs. another method is 4+2+2=8
8/2=4
4 bond available however they all used by cl2 and f2 therefore no one pairs. thank you for the help appreciate it a lot.
Reply 11
Original post by nnn121337
so it does not matter which atom you attach the wedge and line broken all that matters is you placed the wedge and broken line in the set place based on the shape of the molecule. answer to your question carbon has four outer electron each are used in covalent bond to fluorine and chlorine so no lone pairs. another method is 4+2+2=8
8/2=4
4 bond available however they all used by cl2 and f2 therefore no one pairs. thank you for the help appreciate it a lot.

By "which atom" I'm guessing you mean "which out of the Cl atoms and F atoms"? In this case, no, it does not matter.

Like I said, in the case of optical isomerism, it will matter (relative to the positions of the other atoms), but you'll usually be given clues on this if you needed to draw, say, (R)-butan-2-ol. I can't remember if you're supposed to know this at A-level or not, but here's a useful link: https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(Wade)_Complete_and_Semesters_I_and_II/Map%3A_Organic_Chemistry_(Wade)/06%3A_Stereochemistry_at_Tetrahedral_Centers/6.03%3A_Absolute_Configuration_and_the_(R)_and_(S)_System. Wikipedia also has a decent page on this: https://en.wikipedia.org/wiki/Cahn–Ingold–Prelog_priority_rules
Reply 12
Original post by bl0bf1sh
By "which atom" I'm guessing you mean "which out of the Cl atoms and F atoms"? In this case, no, it does not matter.

Like I said, in the case of optical isomerism, it will matter (relative to the positions of the other atoms), but you'll usually be given clues on this if you needed to draw, say, (R)-butan-2-ol. I can't remember if you're supposed to know this at A-level or not, but here's a useful link: https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(Wade)_Complete_and_Semesters_I_and_II/Map%3A_Organic_Chemistry_(Wade)/06%3A_Stereochemistry_at_Tetrahedral_Centers/6.03%3A_Absolute_Configuration_and_the_(R)_and_(S)_System. Wikipedia also has a decent page on this: https://en.wikipedia.org/wiki/Cahn–Ingold–Prelog_priority_rules

i don't think i need to know about optical isomerism also by atoms i mean any others atom(when i am given a different atom for different molecules ) except the central atom to which everything is attached.

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