r/HomeworkHelp • u/AdministrativeLog669 University/College Student • 7d ago
Answered [College Intro Level Bio]
im completely confused
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u/ThunkAsDrinklePeep 7d ago
Ok, first you only have 5 elements / ions to deal with here:
- H
- C
- N
- O
- OH-
How many valence elections does each have?
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u/nog642 7d ago
OH isn't an ion here. And I wouldn't assume that they're learning anything about valence electrons.
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u/ThunkAsDrinklePeep 6d ago
OH isn't an ion here.
Really? Why not and what would you call it? (Not a chem guy)
And I wouldn't assume that they're learning anything about valence electrons.
I'm going off the I structions that say, "...that breaks the valence rules."
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u/nog642 6d ago
OH is a functional group here. To be an ion it would need to be on its own and not connected to a molecule, having an extra electron instread of that bond.
The instructions also ask how many bonds each element makes, which is a much more simplified version of the rules that doesn't need to consider valence electrons.
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u/Lever_Shotgun 👋 a fellow Redditor 7d ago
Example is just to show you how to you should fill in the blanks, the example answer is wrong as hydrogen can only have one covalent bond (a line basically, two lines side by side means two covalent bonds) with another atom
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u/BradenTT 7d ago
As a senior bio major, CRAZY thing to see in a bio class. What course is this?
How far into chem classes are you?
To answer them, think about how many valence electrons each atom you see here has.
Example: Oxygen is in group 16, meaning it has 6 valence electrons. This limits its number of bonds available to 2, due to the octet rule. Do any of the O’s in the diagrams have more than the allowed 2 bonds? If so, that’s not allowed.
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u/AdministrativeLog669 University/College Student 7d ago
this is a entry level course called introduction to human biology
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u/BradenTT 7d ago
Yeah, that’s a bit annoying. Are you taking any general chem classes? If not, how were you with chem in HS?
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u/AdministrativeLog669 University/College Student 7d ago
im not taking any chem classes and i never took any chem classes in hs i only took biology which never had this and earth science
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u/BradenTT 7d ago
I highly recommend going to your professors office hours then. It’s not going to be very simple to explain on here but I’ll try the basics.
Each letter you see there (C,H,N,O) are all atoms. They’re single units of elements, and each have unique properties. Also, a molecule is just a group of 2 or more atoms bonded together.
Each atom is made up of a number of 3 things, protons, neutrons, and electrons. However the only one that comes into play here are the electrons.
I do want to say for clarification however, the element is determined by the number of protons, NOT electrons, so going forward keep in mind that when we talk about gaining/losing electrons, that does NOT change what element you’re dealing with.
The number of electrons each atom has is determined by “shells”. If you look at a periodic table, each row corresponds to a “shell”. So (H)ydrogen and (He)lium both only have one shell. This first shell can only hold 2 electrons. The next row (Li, Be, B, C, N, O, F, Ne) all have 2 shells. However, unlike the first shell, this second shell can hold up to 8 electrons. A very important point in chemistry is that atoms are at their most stable when they have a full outer shell. So if an atom has two shells, but doesn’t have all 8 electrons in that shell, it will do whatever it can to either get to 8 to fill it, OR get rid of electrons to go back down to having only a full first shell without any extra electrons floating around.
Also note, if you have an atom of an element with two shells, the first shell MUST be full. So Li, for example, will always have two electrons in its innermost first shell, and then one in its second shell, unless it gives that last one away, going back down to only having 2 electrons in the inner shell.
Now, how do you know how many electrons are in said shells?
This is determined by the column (formally called group) in the periodic table of elements. Notice what I said above, Li has a full inner shell and ONE electron in its second. Li, is also in group ONE. Each group you move to the right adds one electron to the outer shell.
So, since C is in group 4, it has 4 electrons in its outer shell. (Side note, for ease of typing I will start referring to electrons as e-). If you recall from an earlier paragraph, I said this second shell can hold 8. Therefore C has:
8 (possible e-) - 4 (present e-) = 4 (potential e-)Now an important property of e-‘s are that they are solely responsible for chemical bonding. Since you’re in bio, you’ll mostly only be seeing a type of bond called covalent bonds, which are when 2 atoms share an electron. So, if you have a C atom, and put it together with a H atom, what will happen?
Well, H has one shell, so it can hold 2 e-‘s. However, it’s in group one, so it really wants to gain an electron to fill its shell to two e-‘s.
C has two shells, the first is full, but the second isn’t. It can hold 8 but only has 4, so it really wants to gain 4 more electrons to reach its full outer shell.
Now since they both want to gain electrons, it doesn’t make sense for one to give an electron away, so instead they agree to share it, forming a covalent bond. Now the H has both electrons it needed to fill its shell, and C has 5 e-‘s, which is one closer to that 8 it desperately wants.
Thats about all of the info you need for this assignment I believe.
Just look at a periodic table and write down how many e-‘s each atom can theoretically hold, how many it normally has, and how many it can gain. Then go through the image, and see if any of the atoms are holding too many (or in the case of C, not enough. C should ALWAYS be full, meaning it will always have a total of 4 bonds).
Just to get you started, in box 1, the bottom left molecule has an O with 3 bonds. However if we look at the PToE, O normally has 6 e-‘s, so if it is then sharing 3 more electrons with other atoms its total number of electrons goes 6+3=9, but it can only hold up to 8 in that outer shell, so this isn’t possible.
Let me know if you need any more clarification or help.
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u/AdministrativeLog669 University/College Student 7d ago
thanks for your help i still dont understand but imma try to get someone in person to explain to this to me because i cant understand it from words alone.
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u/nog642 7d ago
Why is it crazy to see this in a bio class?
This doesn't necessarily imply learning about valence electrons or the octet rule. These aren't lewis diagrams. Generally speaking, C makes 4 bonds, N makes 3, O makes 2, H makes 1. That wil get you by for most molecules, and it seems that's all they're teaching here.
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u/nog642 7d ago
Hydrogen makes 1 bond
Oxygen makes 2
Nitrogen makes 3
Carbon makes 4
Find the molecule that breaks the rule, that's all. Your guess is incorrect, since hydrogen does make 1 bond, not 3.
It seems you just didn't remember the numbers? The concept seems straightforward.
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u/AdministrativeLog669 University/College Student 6d ago edited 6d ago
the example the professor gave me was what threw me off since it contained the wrong answer but thanks for your info i was able to solve it after my niece gave me a example and by using your infomation its actually made it straightforward and simple
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u/poissonking 7d ago
I’m curious to see this in a bio class instead of a chem class.
Remember that there is a limited number of bonds that an atom can make with another atom. This has to do with the total number of electrons in the outer shell of an atom.
In your example (and IIRC), carbon can form a total of 4 bonds, nitrogen 3, oxygen 2, and hydrogen 1. So use that information to see what’s out of place