Write Lewis structures for the species in Exercise 105 that involve minimum formal charges.

Name: Problem 106, Chapter 8: Chemistry
Uploaded: 2019-08-22T17:43:18-08:00
Duration: 12 min 4 s
Channel: Lena Jake
Description: Write Lewis structures for the species in Exercise 105 that involve minimum formal charges.

Write Lewis structures for the species in Exercise 105 that...

Key Concepts

Minimization of Formal Charges

Minimization of formal charges involves selecting the Lewis structure in which the distribution of electrons results in the smallest possible magnitude of formal charges on the atoms. This concept is important because structures with minimal formal charges (or a distribution where any negative charges reside on more electronegative atoms) are generally more stable and represent the true electronic structure of the molecule or ion.

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom that are available for bonding. The total number of valence electrons determines how atoms bond with each other and is used as the starting point in constructing a Lewis structure, ensuring that all electrons are properly accounted for in the molecular structure.

Lewis Structures

Lewis structures are diagrams that represent the arrangement of valence electrons among atoms in a molecule or ion. They show how electrons are shared or transferred between atoms to form chemical bonds and provide a visual representation of the molecule's bonding and lone pairs.

Formal Charge

Formal charge is a calculated charge assigned to an atom in a molecule based on the assumption that electrons are shared equally in chemical bonds. It is determined by comparing the number of valence electrons in the free atom to the number of electrons assigned to it in the Lewis structure, and it helps in evaluating the stability and the most likely arrangement of electrons in the molecule.

Octet Rule

The octet rule is a chemical guideline that atoms tend to form bonds until they are surrounded by eight electrons in their valence shell, achieving a noble gas electron configuration. This rule is used when drawing Lewis structures, particularly for main group elements, to determine the arrangement of electrons that leads to a stable configuration.

Transcript

00:01 So in this video, we're going to work through question 106 from chapter 8, which says right -lous structures for the species and exercise 105 that involve minimum formal charges.

00:10 So in a of exercise 105, we're given p .o.

00:14 Cl3.

00:15 So our phosphorus atom brings five valence electrons.

00:18 Our oxygen atom brings six valence electrons, and each of our chlorine atoms brings seven valence electrons.

00:24 So we have a total of 32 electrons.

00:27 So let's go ahead and make the least electronegative atom, our central atom.

00:31 Make the phosphorus atom or central atom.

00:34 And then we have oxygen, chlorine, chlorine, and chlorine.

00:39 Let's go ahead and bond all of these and fill in the octet.

00:51 So that makes our chlorine atoms happy.

00:53 That makes the formal charges 7 minus 6 minus 1 is 0.

00:58 So the formal charges on all of our chlorine atoms are zero.

01:02 But our oxygen atom serves out with six valence electrons, so it's going to be happier making two bonds rather than just one.

01:10 So we're going to double bond that, and then we'll fill in the octet by adding two more lone pairs of electrons.

01:18 And that should use up all 32 of our electrons.

01:22 Now, what's the formal charge on this oxygen atom? well, it's six minus four minus two, that's zero.

01:27 And the formal charge on our central phosphorus atom is five minus six.

01:32 Minus 5.

01:34 So we have a formal charge of zero there too.

01:38 So all of our formal charges of zero, i would say that's minimum.

01:42 So this is the lewis structure for p .o .c .l .3.

01:45 Next we have in part b, s .o .4 minus 2.

01:48 So our sulfur atom and each of our oxygen atoms bring six valence electrons, and then we get two more because of our negative 2 charge.

02:01 So let's go ahead and make our sulfur atom, the central atom, and then we are bonded to four oxygen atoms.

02:13 I can go ahead and fill in the octet on each of these oxygen atoms.

02:18 That's going to use up all 32 of my electrons.

02:22 But then when i do that, my formal charges aren't very good.

02:25 So what are the formal charges? well, in each of the oxygen atoms, it's 6 minus 6 minus 1.

02:32 So that's a formal charge of minus 1.

02:34 And then on the central sulfur atom, it's 6 minus 4.

02:37 That's plus 2.

02:38 So i have minus 1, minus 1, minus 1, minus 1, and plus 2.

02:42 So instead of just having each of the oxygen atoms singly bonded, what if i took two of them and double bonded them? then fill in my octets.

02:59 So what are my formal charges like now? well, on each of these oxygen atoms, it hasn't changed.

03:05 It's minus 1, and then on each of our double bonded oxygens, it's 6 minus 4 minus 2.

03:10 So that's 0 and 0.

03:13 And then on my central sulfur atom, i have 6 minus 6.

03:18 So that's also 0.

03:21 So that's about as low as our formal charges can get.

03:23 We need both of these oxygen atoms to have a minus 1 formal charge, because remember, the formal charges on all of your atoms should sum to the overall charge on the molecule or ion, which in this case is minus 2.

03:37 So these have to add equal minus 2.

03:39 So these formal charges are minimized.

03:42 And c, we have clo4 minus.

03:44 So our chlorine atom brings seven valence electrons, each of our oxygen atoms bring 6, and then we get one more for our minus 1 charge.

03:50 So we have 32 electrons.

03:52 So let's make our chlorine atom, our chlorine atom, our central atom, and then bond each of our oxygen atoms.

04:05 If i just fill in the octet on these, my formal charges on the oxygen atoms are going to be 6 minus 6 minus 1 so that's minus 1 on each of these and then my formal charge on the central chlorine atom is 7 minus 4 so that's plus 3 so i have minus 1 minus 1 minus 1 minus 1 minus 1 and plus 3 so that's not very good so rather than making all single bonds to my oxygen atoms let's try making 3 of these double bonds so what happens then the formal charges on those oxygen atoms are 0, 0, and 0, because we have 6 minus 4 minus 2.

04:51 On one of my oxygen atoms, it's 6 minus 6 minus 1.

04:55 That's a formal charge of minus 1.

04:57 And on my central chlorine atom, i have 7 minus 7.

05:01 So that's 0.

05:03 So our formal charges are all 0 except for on our oxygen atom where we have our minus 1 charge.

05:08 So this is a good lewis structure.

05:12 Next we have p .o .4 minus 3.

05:15 So our phosphorus atom brings five electrons.

05:17 Each of our oxygen atoms brings six.

05:19 And then we get three more for our minus three charge.

05:22 So we have 32 electrons in total...