Chem 1/2 thread!

[dreambig]

Hey guys, Im a bit confused with how to determine if a covalent molecule is polar or non polar by looking at symmetry? Can anyone explain it to me?

Also does a dipole molecule mean the same thing as a polar molecule?


Thanks

[Limista]

Hey guys, Im a bit confused with how to determine if a covalent molecule is polar or non polar by looking at symmetry? Can anyone explain it to me?

Also does a dipole molecule mean the same thing as a polar molecule?


Thanks

We can tell if a covalent molecule is polar or non-polar by looking at it's shape/symmetry.

Let's say you have drawn the structural formula for hydrogen chloride. You'll note that the angle between the 3 bonds/lines on the Cl atom is about 30 degrees, and these lines are relatively close to each other. Each of these lines represent an electron pair and electrons are negatively charged.
Now look at the hydrogen atom - it doesn't have any bonds/lines surrounding it, apart from the bond line connecting it to Cl. Therefore, H has less electron pairs surrounding it compared to Cl. We can conclude that H is more postively charged than Cl, or that Cl is more negatively charged than H. The electronegativity of each atom in HCl is different and not the same. There is not an equal balance of electronegativity; therefore HCl is a polar molecule.

On the other hand, H2 gas is a non-polar molecule, because there is equal balancing of electronegativity between the H atoms, as you can make out by drawing the structural formula.

In short - you can tell if a molecule is polar or non-polar by drawing its structural formula.

There is no such thing as a dipole molecule. A dipole is caused when there is an uneven distribution of charge in the molecule (so basically you will have a dipole if it is a polar molecule).

[psyxwar]

Hey guys, Im a bit confused with how to determine if a covalent molecule is polar or non polar by looking at symmetry? Can anyone explain it to me?

Also does a dipole molecule mean the same thing as a polar molecule?


Thanks

I assume you're referring to how a molecule with polar bonds (ie. a bond between atoms that have a relatively large difference in electronegativity, think it was 0.5-1.7 on Pauling's scale) can be polar or non polar, which is as you said dependent on its shape.

Okay, so lets take CO2 for example. The bonds between the Cs and the Os are infact polar bonds, due to the difference in the electronegativities of the two. But, CO2 is nonpolar. Why? Well, it's a linear shaped molecule, meaning that these slight charges cancel out resulting in an overall nonpolar molecule. (Your slightly negative oxygens on each side cancel each other out)

Another example is water, or H2O. Water also has two polar bonds, but its a polar molecule. Why? Well, as you probably know water is V shaped, meaning that the negative charges of the two oxygens don't cancel out because they're not in the same plane (as opposed to CO2, where the two negatives are in opposite directions along the same "line" and therefore cancel out. If you do Physics you can think of it as two equal but opposite vectors)

[Homer]

how would i draw the structural formula of methylbutane?

[Limista]

how would i draw the structural formula of methylbutane?

1. draw a butane straight chain isomer
2. notice there are 4 carbon atoms - number them 1,2,3,4 from left to right or from right to left (does not matter)
3. on 2nd carbon atom (according to how you've numbered), replace one of the hydrogen atoms with methyl group in tetrahedral orientation

[teletubbies_95]

Bump! Post all your questions up here chem 1/2rs!

[psyxwar]

A diatomic molecule bromine has two isotopes, 79Br and 81Br, of which each is approximately 50% abundant. After undergoing high energy electron bombardment, the number of 1+ ions is likely to be detected by mass specstroscopy is?

The answer is 5; I have no idea why.

[Sach1_K]

A diatomic molecule bromine has two isotopes, 79Br and 81Br, of which each is approximately 50% abundant. After undergoing high energy electron bombardment, the number of 1+ ions is likely to be detected by mass specstroscopy is?

The answer is 5; I have no idea why.

just a note I don't think we have to know how the thing works for this exam.

[saba.ay]

A diatomic molecule bromine has two isotopes, 79Br and 81Br, of which each is approximately 50% abundant. After undergoing high energy electron bombardment, the number of 1+ ions is likely to be detected by mass specstroscopy is?

The answer is 5; I have no idea why.

Well the only way I see it as being 5 is because there are 5 different positive ion fragments which can be created.
We know the molecule is diatomic, so there must be 2 Br atoms in each molecule. So when bombarded with electrons, the molecular ion which forms can be any of the following:

1. [79Br and 79Br]+
2. [79Br and 81Br]+
3. [81Br and 81Br]+

After this, the following 2 fragments can be created through further bombardment:
4. [79Br]+
5. [81Br]+

In total, there are 5 different 1+ ions which the mass spec will detect.

[yuzy]

How many possible jumps could arise if an electron jumps back from the 6th to the 3rd subshell?

There's a diagram of an atom with a nucleus (black dot) and 6 shells around it

[Sach1_K]

How many possible jumps could arise if an electron jumps back from the 6th to the 3rd subshell?

There's a diagram of an atom with a nucleus (black dot) and 6 shells around it

6
Cuz it can jump up to 3 shells yeah
So you use 3! Which is 6.

[andymanine]

Hey guys, just wondering if there is an easy way to learn and remember molar mass?
Been trying to learn a simple way to understand it for ages and I just keep getting confused!

Thanks

[Yacoubb]

Hey guys, just wondering if there is an easy way to learn and remember molar mass?
Been trying to learn a simple way to understand it for ages and I just keep getting confused!

Thanks

What do you mean by Molar Mass? Like what it is, how to calculate it.

Molar mass = grams/mol. Its like exactly the same as the relative molecular mass of a compound, just adding g/mol at the end.

E.g. Water has a relative molecular mass of 18. The molar mass is 18 g/mol.

[andymanine]

What do you mean by Molar Mass?

Sorry! I meant like the whole concept of Mole, not just molar mass!

[SocialRhubarb]

I don't know if this can really be taught over the internet but...

Basically a mole a unit of counting. Just like we use a dozen to mean twelve eggs or twelve loaves of bread or twelve hydrogen bombs, we use moles to count numbers of atoms. A particular number of atoms: 6.02 * 10^23 atoms. Why do we use it? Because it makes calculations easier. Atoms are really small, so a small sample of a chemical, say 12 grams of carbon would have so many particles that it would be impractical to do calculations with it. So rather than count each individual particle and do calculations with numbers like 6.02 * 10^23, we can do calculations with much simpler numbers like '1'.

Is there anything special about the number 6.02*10^23? Not really. It's the number of atoms in 12 grams of carbon, because carbon is used as a standard for a variety of scales, but more importantly it's essentially just a convenient number to use.

Molar mass is then just the mass in grams of one mole of a particular substance. Hydrogen has a molar mass of 1. This means that 1 mole of hydrogen weighs 1 gram. And that is basically why we use moles. Because it is a helluva lot easier to say 1 mole of hydrogen weighs 1 gram than to say that 6.02*10^23 atoms of hydrogen weighs 1 gram.