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# Elementary concepts: Bonding + Periodicity +Stoichio

Hi guys! I'm doing chem after a while so there's a lot I've forgotten I hope you don't mind helping me!

1) Can someone explain the mathematical logic behind the formula for natural abundance of an isotope?

The calculation goes like this: Relative atomic mass= ( Isotope 1 * x) + Isotope 2(1-x)

What I don't understand is the 1-x part, was always bad at math

2) Why does hybridization occur only after excitation of one of the 2s electrons to the unfilled 2p orbital?

3) What decides which hybrid is formed? This really puzzles me, how does carbon decide what it needs ?

4) I don't get the textbook explanation for why transitional metals have variable oxidation states. Is there a picture or video that you use to understand this? (I'm a visual learner)

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Hi guys! I'm doing chem after a while so there's a lot I've forgotten I hope you don't mind helping me!

1) Can someone explain the mathematical logic behind the formula for natural abundance of an isotope?

The calculation goes like this: Relative atomic mass= ( Isotope 1 * x) + Isotope 2(1-x)

What I don't understand is the 1-x part, was always bad at math

2) Why does hybridization occur only after excitation of one of the 2s electrons to the unfilled 2p orbital?

3) What decides which hybrid is formed? This really puzzles me, how does carbon decide what it needs ?

4) I don't get the textbook explanation for why transitional metals have variable oxidation states. Is there a picture or video that you use to understand this? (I'm a visual learner)

This guy has done every video on the syllabus, extremely helpful! I haven't done hybridisation yet so I won't be able to help you, but he definitely will.

If you only have two isotopes, that means those two must add up to one. If you had 20% abundance of one isotope and there was only one other isotope, the other isotope would have 80% abundance, 100-20=80. The number 1 is just a substitute for 100.

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Hi guys! I'm doing chem after a while so there's a lot I've forgotten I hope you don't mind helping me!

1) Can someone explain the mathematical logic behind the formula for natural abundance of an isotope?

The calculation goes like this: Relative atomic mass= ( Isotope 1 * x) + Isotope 2(1-x)

What I don't understand is the 1-x part, was always bad at math

2) Why does hybridization occur only after excitation of one of the 2s electrons to the unfilled 2p orbital?

3) What decides which hybrid is formed? This really puzzles me, how does carbon decide what it needs ?

4) I don't get the textbook explanation for why transitional metals have variable oxidation states. Is there a picture or video that you use to understand this? (I'm a visual learner)

Hybridization is a mixing of atomic orbitals that occur when the atoms are bonding. They take however many orbitals are involved in the process and "combine" them to form however many orbitals needed that are all of the same energy. The exact reasoning behind this is based off of quantum mechanics which is not necessary to understand, and probably can't be understood, at the IB level.

But think about it this way. When you have neutral atoms with electrons in the ground state, they won't really be doing much of anything. They can't form bonds or whatever because they don't have enough energy to do so. When you excite the electrons to a higher energy state they have more energy which is enough to form hybrid orbitals. The orbitals alone are just places for the electrons to reside (i.e. where you're most likely to find an electron in an atom, it relates back to Heisenberg's uncertainty principle and Schrodinger's equations) but when you mix orbitals together you can form overlaps of some configuration that allow for bonds to form.

Carbon (and any element really) decides what hybridization it takes based on the atoms involved and the bond character. The most basic orbital mixing is that of two s orbitals, which are formed from hydrogen atoms because hydrogen's electron resides only in the 1s orbital. This also happens with s and p orbitals, and the hybridization you make will relate back to the bonding. The most common hybrids you will see with these will be sp3, sp2, and sp. Sp3 involves the mixing of four orbitals, one that's s and three that are p. Sp2 is three orbitals, one s and two p, and sp is two orbitals, one s and one p. You can deduce the hybridization based off the bonds present in your molecule (you count them). If you have all single bonds surrounding your carbon molecule, you know it is sp3 hybridized because there are four bonds. If you have a double bond present, it will be sp2 hybridized. You count the double bond as one bond, and since there's only two other bonds present you get a total of three. With a triple bond you count the triple bond as one bond and then the other bond as one, giving two bonds. This works for any molecule, but in the IB you'll see it mostly with carbon.

This video will probably help you with the variable transition states of the transition metals, which is because of unfilled d orbitals and the electrons that fill these orbitals being able to move around in them: https://www.youtube.com/watch?v=E3Ok1qaXK_g

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Thank you!

The video was nice but oddly he didn't really answer the question he set out to.

I have two new queries, yet again all help is greatly appreciate since everything on the fast-track right now, thank you!

1) Why exactly does vapor pressure affect the boiling point? I says vapor pressure is pressure exerted by a gas on it's liquid molecules so the external pressure was never in question to begin with. What have I missed here?

2) Can someone solve this sum? I'm stumped!

1. We have 45g pure KCL (100%). How many ml H2O must we add to prepare a 20% solution?

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Thank you!

The video was nice but oddly he didn't really answer the question he set out to.

I have two new queries, yet again all help is greatly appreciate since everything on the fast-track right now, thank you!

1) Why exactly does vapor pressure affect the boiling point? I says vapor pressure is pressure exerted by a gas on it's liquid molecules so the external pressure was never in question to begin with. What have I missed here?

2) Can someone solve this sum? I'm stumped!

1. We have 45g pure KCL (100%). How many ml H2O must we add to prepare a 20% solution?

1) I looked up the answer for you Vapour pressure is actually not the pressure exerted by vapour on its liquid molecules. Vapour pressure is actually the upward pressure of the vapour against the atmosphere in an open system (I didn't know this either ). So in order for the liquid to boil, the pressure against the atmosphere must be equal to the pressure that the atmosphere exerts on the system (i.e external pressure). Interesting question as I didn't think about this before.

2) Well I would have gone about it in this way:

- Find the amount of KCL in moles: g/M=n => 45/74= 0.61 moles

- How many moles of water do we need for 0.61 to exist as 20% of the solution: 0.61/0.20 = 3.05 moles water

- How many ml of water is that? First convert moles into grams then grams into ml. We know that density of water 1 g /cm^3, and 1cm^3 = 1 ml:

3.05*18 = 54.9 grams of water which is 54.9 ml

Do you have the correct answer somewhere? I'm only 90 % sure that this is correct. It's at least the way I would try to solve this problem.

Edited by Kaushalz
1 person likes this

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Thank you!

The video was nice but oddly he didn't really answer the question he set out to.

I have two new queries, yet again all help is greatly appreciate since everything on the fast-track right now, thank you!

1) Why exactly does vapor pressure affect the boiling point? I says vapor pressure is pressure exerted by a gas on it's liquid molecules so the external pressure was never in question to begin with. What have I missed here?

2) Can someone solve this sum? I'm stumped!

1. We have 45g pure KCL (100%). How many ml H2O must we add to prepare a 20% solution?

1) I looked up the answer for you Vapour pressure is actually not the pressure exerted by vapour on its liquid molecules. Vapour pressure is actually the upward pressure of the vapour against the atmosphere in an open system (I didn't know this either ). So in order for the liquid to boil, the pressure against the atmosphere must be equal to the pressure that the atmosphere exerts on the system (i.e external pressure). Interesting question as I didn't think about this before.

2) Well I would have gone about it in this way:

- Find the amount of KCL in moles: g/M=n => 45/74= 0.61 moles

- How many moles of water do we need for 0.61 to exist as 20% of the solution: 0.61/0.20 = 3.05 moles water

- How many ml of water is that? First convert moles into grams then grams into ml. We know that density of water 1 g /cm^3, and 1cm^3 = 1 ml:

3.05*18 = 54.9 grams of water which is 54.9 ml

Do you have the correct answer somewhere? I'm only 90 % sure that this is correct. It's at least the way I would try to solve this problem.

HI! Thanks for taking the time to solve this it's killing me!

Sadly the website provides only the questions

What formula/logic is it exactly that you've used for this step, I'm not familiar with it and I've looked up the percent concentration formula but that only deals with masses, step: How many moles of water do we need for 0.61 to exist as 20% of the solution: 0.61/0.20 = 3.05 moles water

##### Share on other sites

Thank you!

The video was nice but oddly he didn't really answer the question he set out to.

I have two new queries, yet again all help is greatly appreciate since everything on the fast-track right now, thank you!

1) Why exactly does vapor pressure affect the boiling point? I says vapor pressure is pressure exerted by a gas on it's liquid molecules so the external pressure was never in question to begin with. What have I missed here?

2) Can someone solve this sum? I'm stumped!

1. We have 45g pure KCL (100%). How many ml H2O must we add to prepare a 20% solution?

1) I looked up the answer for you Vapour pressure is actually not the pressure exerted by vapour on its liquid molecules. Vapour pressure is actually the upward pressure of the vapour against the atmosphere in an open system (I didn't know this either ). So in order for the liquid to boil, the pressure against the atmosphere must be equal to the pressure that the atmosphere exerts on the system (i.e external pressure). Interesting question as I didn't think about this before.

2) Well I would have gone about it in this way:

- Find the amount of KCL in moles: g/M=n => 45/74= 0.61 moles

- How many moles of water do we need for 0.61 to exist as 20% of the solution: 0.61/0.20 = 3.05 moles water

- How many ml of water is that? First convert moles into grams then grams into ml. We know that density of water 1 g /cm^3, and 1cm^3 = 1 ml:

3.05*18 = 54.9 grams of water which is 54.9 ml

Do you have the correct answer somewhere? I'm only 90 % sure that this is correct. It's at least the way I would try to solve this problem.

HI! Thanks for taking the time to solve this it's killing me!

Sadly the website provides only the questions

What formula/logic is it exactly that you've used for this step, I'm not familiar with it and I've looked up the percent concentration formula but that only deals with masses, step: How many moles of water do we need for 0.61 to exist as 20% of the solution: 0.61/0.20 = 3.05 moles water

You need a 20 % solution right? Which in an aqueous solution (any substance mixed with water) means that the substance must exist as 20 % of the whole solution. In this case KCL must exist as 20 % of the whole solution. Hence, we have to calculate what 3.05 moles is 20 % off to find the total moles of water present. So I used this formula: moles of KCL/moles of water = 0.20, since we know the moles of KCL in this case we can calculate the moles of water to make a 20 % solution.

1 person likes this

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Thank you!

The video was nice but oddly he didn't really answer the question he set out to.

I have two new queries, yet again all help is greatly appreciate since everything on the fast-track right now, thank you!

1) Why exactly does vapor pressure affect the boiling point? I says vapor pressure is pressure exerted by a gas on it's liquid molecules so the external pressure was never in question to begin with. What have I missed here?

2) Can someone solve this sum? I'm stumped!

1. We have 45g pure KCL (100%). How many ml H2O must we add to prepare a 20% solution?

1) I looked up the answer for you Vapour pressure is actually not the pressure exerted by vapour on its liquid molecules. Vapour pressure is actually the upward pressure of the vapour against the atmosphere in an open system (I didn't know this either ). So in order for the liquid to boil, the pressure against the atmosphere must be equal to the pressure that the atmosphere exerts on the system (i.e external pressure). Interesting question as I didn't think about this before.

2) Well I would have gone about it in this way:

- Find the amount of KCL in moles: g/M=n => 45/74= 0.61 moles

- How many moles of water do we need for 0.61 to exist as 20% of the solution: 0.61/0.20 = 3.05 moles water

- How many ml of water is that? First convert moles into grams then grams into ml. We know that density of water 1 g /cm^3, and 1cm^3 = 1 ml:

3.05*18 = 54.9 grams of water which is 54.9 ml

Do you have the correct answer somewhere? I'm only 90 % sure that this is correct. It's at least the way I would try to solve this problem.

HI! Thanks for taking the time to solve this it's killing me!

Sadly the website provides only the questions

What formula/logic is it exactly that you've used for this step, I'm not familiar with it and I've looked up the percent concentration formula but that only deals with masses, step: How many moles of water do we need for 0.61 to exist as 20% of the solution: 0.61/0.20 = 3.05 moles water

You need a 20 % solution right? Which in an aqueous solution (any substance mixed with water) means that the substance must exist as 20 % of the whole solution. In this case KCL must exist as 20 % of the whole solution. Hence, we have to calculate what 3.05 moles is 20 % off to find the total moles of water present. So I used this formula: moles of KCL/moles of water = 0.20, since we know the moles of KCL in this case we can calculate the moles of water to make a 20 % solution.

I see the mix up, you've calculated mole percent as opposed to the more common weight percent, am I right? Thanks !

Here's my attempt at the calculation using mass percent:

45g of KCL/ xg of H20 =0.2

-> 225 g

->1gm/cm3 therefore 225 ml.

Gah! I hate these people for not providing the answer, I posted the question on Yahoo and one of the answerers provided 2 completely different unlike either of ours so far so that's 4 speculations so far, good god! :'D Have a look: https://answers.yahoo.com/question/index?qid=20140428093211AATynly

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Gah! I hate these people for not providing the answer, I posted the question on Yahoo and one of the answerers provided 2 completely different unlike either of ours so far so that's 4 speculations so far, good god! :'D Have a look: https://answers.yaho...28093211AATynly

Hmmm... The last calculation he did uses the same method as mine actually, I just forgot to make KCl 20 % of the whole solution. Hence the 0.8 number for H20 as there should be 80 % of water in solution. Also, when the task ask for 20 % (not stating wheather it should be mole percentage or mass percentage) im pretty sure we should calculate in mole percentage. I might be wrong though...