Write Lewis structures that obey the octet rule for each of the following molecules and ions. (I

Write Lewis structures that obey the octet rule for each of...

Key Concepts

Lewis Structures

Lewis structures are diagrams that represent the arrangement of electrons among atoms in a molecule or ion. They are used to show how atoms are bonded together by covalent bonds and to depict any lone pairs of electrons. These drawings provide a simplified visualization of the electron distribution, which is foundational for predicting molecular geometry and reactivity.

Octet Rule

The octet rule is a guideline in chemistry which states that atoms tend to form bonds until they are surrounded by eight electrons in their valence shell, achieving a noble gas configuration. This rule is particularly useful for constructing Lewis structures of many main group elements, ensuring that each atom reaches a stable state through shared or lone pairs.

Valence Electrons

Valence electrons are the electrons present in the outermost shell of an atom and are crucial for chemical bonding. In creating Lewis structures, the total number of valence electrons available—accounting for any extra electrons due to negative charges or the loss of electrons from positive charges—determines how electrons can be distributed to satisfy the octet rule.

Formal Charge Calculation

Calculating formal charges helps in determining the most appropriate Lewis structure among possible alternatives. It involves comparing the number of electrons assigned to each atom in the Lewis structure with the number of electrons the atom would have in its neutral, isolated state. Structures with formal charges closest to zero are generally more stable and are preferred when multiple valid Lewis structures exist.

Structural Variability with the Same Electron Count

Even when species have the same number of atoms and valence electrons, they can exhibit different Lewis structures due to variations in the arrangement of bonds and lone pairs. This concept highlights that identical overall electron counts can lead to isomers or alternative bonding scenarios, each with distinct formal charge distributions, which in turn can influence the physical and chemical properties of the molecules or ions.

Transcript

00:02 This question has multiple molecules or ions for which you need to draw lewis structures.

00:08 So let's begin and i'll review the steps that are oftenly followed in order to determine the lewis structure.

00:18 First we have p .o .c .l .3.

00:20 What we need to do is sum up the number of valence electrons for each element found in the molecule.

00:28 Phosphorus contains five valence electrons.

00:30 Oxygen has six.

00:32 Chlorine has seven.

00:33 There are three of them, so it'll be seven times three.

00:36 This gives us 32 valence electrons.

00:40 This question specifically asks us to draw lewis structures that obey the octet rule.

00:46 Although there are many of these that could be better explained with an expanded octet, we will stick to the octet rule that was specified in the problem.

00:58 So we've got phosphorus in the middle, we've got one oxygen, and then we've got three chlorine surrounding it.

01:07 We see that phosphorus has an octet with the four bonds that are surrounding it, each bond having two electrons, and then each oxygen has an octet with the one bond and the three lone pairs.

01:21 The next one is s .o4 -2 minus.

01:24 Sulfur has six valence electrons, oxygen has six, but there are four of them, and then we've got a minus two charge, so we add on the additional two electrons.

01:33 This also gives us a total number.

01:34 Of valence of electrons of 32.

01:37 So we'll put sulfur in the middle, put our oxygens around it, and then add in all of our valence electrons, recognize this is an ion, and put brackets around it with its charge of minus 2.

01:50 We'll see that sulfur has eight valence electrons around it because of the four bonds, each bond having two valence electrons, and then each oxygen has one bond in three lone pairs, which gives each oxygen an octet.

02:05 The next one is xenon tetroxide.

02:10 Xenon has eight valence electrons, oxygen has six, and there are four of them.

02:14 So we get a total of 32.

02:16 So we'll put xenon in the middle, and we're going to have a very similar structure with the central atom having four single bonds and all peripheral atoms having one bond with three loan pairs.

02:29 The next one is phosphate, p .o .4 .3 minus.

02:33 Phosphorus has five valence.

02:34 Electrons, oxygen has six, there are four of them, and then we add on the three additional electrons because it has a three minus charge, and we also get 32.

02:44 So we'll put phosphorus in the middle, and then again use the rest of the electrons to give an octet to everything, and make sure to put it in brackets and identify its charge.

02:56 For the last one, we have perchlorate, c .l .o .4 minus.

03:01 Chlorine has seven valence electrons, oxygen has six, there are four.

03:05 Of them plus the additional electron because of its minus one charge.

03:09 We get 32 valence electrons.

03:12 So like all the other ones, we're going to put our chlorine in the middle because it's found first.

03:19 Bond, all of the oxygens.

03:21 We just used up eight valence electrons, so that means that we have 24 left over.

03:27 If we put six electrons as lone pairs around each of them, each oxygen, then there being four oxygens, then six times four is the 24 electrons that we have left over.

03:40 And that gives us our final lewis structure, as shown here.

03:44 We'll put it in brackets and identify its charge outside of the brackets.

03:51 For part b, we'll start with nitrogen trifluoride.

03:54 Nitrogen has five valence electrons.

03:57 Fluorine has seven, but there are three of them.

03:59 So that gives us 26 valence electrons...

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