Organic Chemistry - How To Draw Lewis Structures

The Organic Chemistry Tutor
8 Apr 201811:55
EducationalLearning
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TLDRThis educational video script offers a comprehensive guide to drawing Lewis structures for organic chemistry, focusing on the bonding preferences of common elements. It explains the typical bonding patterns for hydrogen, carbon, nitrogen, oxygen, and halogens, and provides step-by-step examples for molecules like methane, methanol, ethylamine, ethyl chloride, dimethyl ether, acetaldehyde, ethene, acetylene, and hydrazine. The script also addresses how to adjust Lewis structures for charged molecules, emphasizing the importance of electron distribution and element valency.

Takeaways
  • πŸ”¬ Hydrogen can only form one bond, which is a fundamental rule in drawing Lewis structures.
  • 🌐 Elements like boron, carbon, nitrogen, oxygen, and fluorine can form multiple bonds, with boron typically forming three bonds in its neutral state.
  • πŸ”€ Carbon prefers to form four bonds, nitrogen usually forms three, and oxygen typically forms two bonds in organic chemistry.
  • 🌊 Halogens like fluorine, chlorine, bromine, and iodine generally form one bond and have seven valence electrons, needing one more to complete their octet.
  • 🌟 Sulfur often forms two bonds but can also form six, depending on its need to achieve an octet.
  • πŸ’§ Phosphorus and nitrogen both tend to form three bonds, while silicon and carbon both form four bonds.
  • πŸ™οΈ The Lewis structure for methane (CH4) involves carbon forming four single bonds with hydrogen atoms.
  • 🍺 Methanol (CH3OH) has a carbon bonded to three hydrogens and an oxygen, which forms two bonds and has two lone pairs.
  • 🌳 The Lewis structure for ethanamine (CH3CH2NH2) shows nitrogen forming three bonds and having one lone pair, while carbon forms four bonds.
  • πŸ’¦ Ethyl chloride (C2H5Cl) involves a carbon bonded to a chlorine atom, which forms one bond and has three lone pairs.
  • 🌈 Dimethyl ether has an oxygen in the middle forming two bonds with two methyl groups, each carbon in the methyl groups forms three bonds with hydrogens.
Q & A
  • What is the primary topic of the video?

    -The video is about how to draw basic Lewis structures within the realm of organic chemistry.

  • How many bonds can hydrogen form according to the video?

    -Hydrogen can only form one bond.

  • What is the typical number of bonds that carbon forms in its neutral state?

    -In its neutral state, carbon likes to form four bonds.

  • How does the number of bonds formed by boron differ when it has a charge?

    -When boron has a charge, it can deviate from its typical number of three bonds formed in its neutral state.

  • What is the Lewis structure for methane?

    -The Lewis structure for methane consists of a carbon atom bonded to four hydrogen atoms, each with a single bond.

  • How is the Lewis structure for methanol different from methane?

    -Methanol's Lewis structure includes a carbon atom bonded to three hydrogen atoms and one oxygen atom, which in turn is bonded to one hydrogen atom and has two lone pairs.

  • What is the general rule for elements that form three bonds?

    -Elements that form three bonds, like nitrogen, typically have one lone pair.

  • Why can't the Lewis structure for CH3CHO be drawn with a single bond between the carbon and oxygen?

    -A single bond would not satisfy the carbon's need for four bonds and the hydrogen's need for one bond, hence a double bond is required.

  • What is the functional group in C2H4 and what is its name?

    -The functional group in C2H4 is a double bond between two carbon atoms, and it is known as an alkene.

  • How does the Lewis structure for ethyl chloride differ from that of ethene?

    -In ethyl chloride, the chlorine atom forms a single bond with the carbon and has three lone pairs, whereas in ethene, there is a double bond between two carbon atoms.

  • How does the Lewis structure change for an oxygen atom when it gains or loses a hydrogen atom?

    -When oxygen gains a hydrogen atom, it loses a lone pair and acquires a positive charge. When it loses a hydrogen atom, it gains a lone pair and acquires a negative charge.

Outlines
00:00
πŸ§ͺ Basic Lewis Structures in Organic Chemistry

This paragraph introduces the fundamentals of drawing Lewis structures for organic chemistry, emphasizing the bonding preferences of common elements like hydrogen, carbon, nitrogen, oxygen, and halogens. Hydrogen forms one bond, while carbon and silicon aim for four, nitrogen and phosphorus for three, and oxygen for two. Halogens typically form one bond, needing one more electron to complete their octet. The paragraph illustrates the Lewis structures of methane and methanol, highlighting the step-by-step process of determining the correct arrangement of atoms and bonds.

05:02
πŸ“š Drawing Lewis Structures for Various Organic Molecules

The second paragraph delves into the Lewis structures of more complex organic molecules, including ethylamine (CH3CH2NH2), ethyl chloride (CH3CH2Cl), and dimethyl ether. It explains the process of drawing Lewis structures by starting with the most electronegative atoms and ensuring that all atoms achieve their preferred number of valence electrons. The paragraph also covers the Lewis structures of acetaldehyde (CH3CHO), ethene (C2H4), and acetylene (C2H2), introducing the concepts of alkenes and alkynes with double and triple bonds, respectively. Additionally, it discusses the Lewis structure of hydrazine, a molecule with nitrogen atoms forming both single and triple bonds.

10:03
πŸ”‹ Impact of Charges on Lewis Structures

The final paragraph addresses the impact of charges on the Lewis structures of molecules, specifically focusing on methanol and its anions and cations. It explains how the removal of a hydrogen atom from methanol results in a negatively charged oxygen with three lone pairs, while the addition of a hydrogen ion to methanol leads to a positively charged oxygen with one lone pair. The paragraph reinforces the idea that oxygen's bonding and lone pair count can vary depending on its charge state, providing a clear example of how to adjust Lewis structures to reflect ionic changes.

Mindmap
Methanol Cation (CH3OH+)
Methanol Neutral (CH3OH)
Methoxide Ion (CH3O-)
Hydrazine (N2H4)
Acetylene (C2H2)
Ethene (C2H4)
Acetaldehyde (CH3CHO)
Dimethyl Ether (CH3OCH3)
Ethyl Chloride (CH3CH2Cl)
Ethylamine (CH3CH2NH2)
Methanol (CH3OH)
Methane (CH4)
Silicon
Phosphorus
Sulfur
Halogens
Oxygen
Nitrogen
Carbon
Boron
Hydrogen
Molecular Symmetry
Implications of Electronegativity
General Trends and Exceptions
Charged Species
Lewis Structure Examples
Basic Bonding Principles
Organic Chemistry Lewis Structures
Alert
Keywords
πŸ’‘Lewis Structures
Lewis Structures are graphical representations of molecules that show the arrangement of atoms and the valence electrons around them. They are fundamental to understanding organic chemistry as they help visualize how atoms bond together. In the video, Lewis Structures are used to illustrate the bonding patterns in various molecules, such as methane and methanol, emphasizing their importance in depicting the connectivity and electronic arrangements in organic compounds.
πŸ’‘Hydrogen
Hydrogen is an element with one valence electron, which means it can form only one bond to achieve a stable electron configuration. In the context of the video, hydrogen's bonding capacity is highlighted as it can only form one bond, as seen in the Lewis Structures of methane (CH4) and methanol (CH3OH), where each hydrogen atom is bonded to a carbon or oxygen atom.
πŸ’‘Carbon
Carbon is a key element in organic chemistry, known for its ability to form four bonds due to its four valence electrons. The video explains that carbon typically forms four bonds in its neutral state, as demonstrated in the Lewis Structures of methane and ethylene (C2H4), where carbon atoms are bonded to four other atoms to satisfy the octet rule.
πŸ’‘Oxygen
Oxygen is another important element in organic chemistry, with six valence electrons, allowing it to form two bonds and have two lone pairs in its neutral state. The video script discusses how oxygen forms two bonds in methanol and how its bonding and lone pair configuration changes when it gains or loses a hydrogen atom, resulting in a negative or positive charge.
πŸ’‘Nitrogen
Nitrogen, with five valence electrons, tends to form three bonds to complete its octet. The video mentions nitrogen's bonding preference, as seen in the Lewis Structure of ethylamine (CH3CH2NH2), where the nitrogen atom forms three bonds and has one lone pair.
πŸ’‘Halogens
Halogens, such as fluorine, chlorine, bromine, and iodine, are elements that typically form one bond and have three lone pairs due to their seven valence electrons. The video script uses halogens as an example of elements that seek to gain one electron to achieve a stable octet, as seen in the Lewis Structure of ethyl chloride (CH3CH2Cl), where chlorine forms a single bond.
πŸ’‘Sulfur
Sulfur, with six valence electrons, can form two or six bonds depending on the situation. The video explains that sulfur can either gain two electrons to complete its octet or give away all six to form six bonds, as in the case of sulfate ions.
πŸ’‘Phosphorus
Phosphorus is similar to nitrogen in that it has five valence electrons and typically forms three bonds. The video script briefly mentions phosphorus's bonding preference, which is consistent with its need to achieve an octet.
πŸ’‘Silicon
Silicon, like carbon, has four valence electrons and tends to form four bonds. The video script notes that silicon's bonding behavior is analogous to that of carbon, as it also seeks to form four bonds to satisfy the octet rule.
πŸ’‘Aldehyde
An aldehyde is a functional group characterized by a carbon atom double-bonded to an oxygen atom (C=O), often with a hydrogen atom or an alkyl group attached to the carbon. The video script introduces acetaldehyde (CH3CHO) as an example of an aldehyde, highlighting the importance of the C=O double bond in its Lewis Structure.
πŸ’‘Charges
Charges in the context of the video refer to the positive or negative electrical properties of atoms or ions. The video script discusses how the presence of charges affects the Lewis Structures of molecules, particularly oxygen, which can have different numbers of lone pairs and bonds depending on whether it has a positive or negative charge.
Highlights

Introduction to drawing basic Lewis structures in organic chemistry.

Hydrogen can only form one bond.

Boron forms three bonds in its neutral state and can deviate when charged.

Carbon forms four bonds in its neutral state.

Nitrogen forms three bonds, oxygen two, and halogens one.

Halogens have seven valence electrons and need one more to complete their octet.

Sulfur can form two or six bonds depending on its valence electron configuration.

Phosphorus forms three bonds, and silicon forms four bonds like carbon.

Lewis structure of methane (CH4) is explained with carbon forming four bonds with hydrogen.

Lewis structure of methanol (CH3OH) is detailed, showing carbon, hydrogen, and oxygen bonding.

General trends for elements forming three bonds typically include one lone pair.

Oxygen forms two bonds and has two lone pairs when neutral.

Halogens form one bond and have three lone pairs.

Elements like carbon, nitrogen, oxygen, and fluorine aim for an octet of electrons.

Hydrogen, being in the first row, can only hold a maximum of two electrons.

Lewis structure of ethylamine (CH3CH2NH2) is explained with nitrogen forming three bonds.

Lewis structure of ethyl chloride (CH3CH2Cl) is detailed with chlorine forming one bond and having three lone pairs.

Lewis structure of dimethyl ether is explained with oxygen forming two bonds and having two lone pairs.

Lewis structure of acetaldehyde (CH3CHO) is detailed with a carbon-oxygen double bond.

Lewis structure of ethene (C2H4) is explained with a carbon-carbon double bond.

Lewis structure of acetylene (C2H2) is detailed with a carbon-carbon triple bond.

Lewis structure of hydrazine (N2H4) is explained with nitrogen forming three bonds and having one lone pair.

Impact of charges on Lewis structures, such as CH3O-, CH3OH, and CH3OH+, is discussed.

Oxygen's bonding changes with charge: one bond with a positive charge, three bonds with a negative charge.

Transcripts
00:00

in this video we're going to talk about

00:02

how to draw some basic lewis structures

00:04

within the realm of organic chemistry

00:07

so let's go over some basic things you

00:09

need to know

00:10

hydrogen can only form one bond

00:14

elements like boron carbon nitrogen

00:17

oxygen fluorine they could form multiple

00:20

bonds

00:21

boron likes to form three bonds

00:23

when it's in its neutral state

00:25

now when it has a charge it can deviate

00:27

from this number

00:28

carbon and its neutral state likes to

00:30

form four bonds

00:32

nitrogen likes to form two i mean three

00:34

oxygen likes to form two and a halogens

00:37

like to form one

00:39

so like fluorine chlorine bromine iodine

00:43

those elements they like to form one

00:44

bond they have seven valence electrons

00:47

and they only need one more to get to

00:48

eight

00:49

sulfur likes to form two bonds but

00:52

sometimes it could form six

00:54

it has six valence electrons it can

00:56

either

00:57

try to acquire two to get to eight so in

00:59

that case it's going to form two bonds

01:01

or it can give away its six valence

01:03

electrons and form six bonds in the case

01:05

of sulfate

01:07

phosphorus like nitrogen likes to form

01:09

three bonds

01:11

silicon like carbon likes to form four

01:13

bonds

01:16

but these are the most common elements

01:18

that you're going to be dealing with

01:20

in organic chemistry

01:24

so let's say if we want to draw the

01:26

lewis structure

01:28

for methane

01:29

you know that carbon likes to form four

01:31

bonds and hydrogen can only form one

01:33

bond

01:34

so the only way to put this together is

01:36

to do it like this

01:38

and so that is the lewis structure of

01:39

methane

01:44

what about this example

01:46

methanol

01:48

ch3oh a type of alcohol

01:51

how can we draw the lewis structure for

01:53

that molecule

01:55

so let's view the molecule from left to

01:57

right so we have a carbon

01:59

and that carbon has three hydrogens

02:01

attached to it

02:04

and each hydrogen can only form one bond

02:07

now the carbon is attached to an oxygen

02:10

and oxygen likes to form two bonds

02:13

so this is the typical structure of

02:14

oxygen

02:16

it likes to form two bonds and has two

02:18

lone pairs

02:21

and then we have a hydrogen

02:22

and so this is the lewis structure for

02:24

methanol

02:26

so make sure you know this hydrogen

02:28

likes to form one bond carbon

02:31

likes to form four bonds

02:33

nitrogen

02:34

likes to form three bonds

02:37

and for elements that form three bonds

02:38

typically they have one lone pair

02:41

these are the general trends there's

02:43

always some exceptions so keep that in

02:44

mind

02:46

now oxygen

02:47

which likes to form two bonds has two

02:50

lone pairs

02:53

and the halogens like fluorine and

02:55

chlorine and things like that

02:58

they like to form one bond but they're

02:59

going to have three lone pairs

03:03

elements like carbon nitrogen oxygen

03:06

fluorine they like to have eight

03:07

electrons around them

03:09

hydrogen is in the first row so it can

03:11

only hold a maximum of two electrons and

03:14

that's why it can only form one bond

03:17

let's try another example

03:19

ch3ch2

03:21

nh2

03:23

so go ahead and draw the lewis structure

03:25

for that molecule

03:27

so viewing it from left to right we're

03:28

going to start with the ch3 so we have a

03:30

carbon attached to three hydrogen atoms

03:34

and then we have a ch2

03:37

so that's a carbon that's attached to

03:39

two hydrogen atoms

03:40

and attached to that is an nh2

03:43

now nitrogen likes to form three bonds

03:47

and hydrogen can only form one

03:49

so this nitrogenous rebonds and

03:50

typically it has one lone pair with

03:53

those three bonds

03:55

so this is the structure of ethoamy

04:05

now go ahead and try this one

04:07

ethyl chloride

04:09

feel free to pause the video

04:12

so we're going to follow the same

04:13

pattern we have a ch3

04:16

attached to a ch2

04:18

and then that's attached to a chlorine

04:20

atom

04:22

now chlorine is a halogen and typically

04:24

they form one bond and they're going to

04:26

have two lone i mean three lone pairs

04:28

rather than two

04:29

and so this is the lewis structure for

04:31

ethyl chloride

04:34

now let's work on another example

04:36

dimethyl ether

04:38

go ahead and draw the lewis structure

04:39

for that

04:41

so i'm going to start with the oxygen in

04:43

the middle

04:44

oxygen likes to form two bonds and on

04:47

each side we have a methyl group or ch3

04:49

group

04:51

and we know each of those carbons

04:53

contain three hydrogens

04:56

an oxygen when it has two bonds it's

04:59

going to have two lone pairs

05:02

and so that's the lewis structure for

05:03

dimethyl ether

05:06

now what about this one ch3cho

05:11

how can we draw the lewis structure for

05:13

this molecule

05:16

so the left side ch3 at this point we're

05:18

pretty familiar with it it's just a

05:19

carbon with three hydrogens

05:22

now this carbon needs four bonds so

05:24

we're going to draw another bond

05:26

and the next thing that it's attached to

05:27

is a carbon atom

05:30

now how can we draw c h o

05:32

well we can't draw like this because

05:35

hydrogen will have two bonds and that's

05:36

not going to work and we can't draw this

05:39

way because

05:40

carbon won't have four bonds

05:42

the only way in which we can make carbon

05:46

to have four bonds and hydrogen to have

05:48

one and oxygen to have two

05:50

is to put a double bond between the

05:52

carbon and the oxygen and connect the

05:54

carbon directly to the hydrogen

05:56

as you can see every element has their

05:59

desired number of bonds

06:01

and so this is the lewis structure for

06:03

ch3cho

06:05

this is a type of aldehyde specifically

06:07

acetaldehyde

06:09

this is how you spell the name

06:16

aldehydes typically have this functional

06:18

group that you see here

06:26

next up is c2h4 go ahead and try that

06:30

draw the lewis structure for that

06:31

molecule

06:33

so how should we begin are the two

06:35

carbons connected to each other or

06:39

how do we even draw this thing

06:42

when you see something like this

06:44

draw the carbon atoms first

06:46

now there's four hydrogens

06:48

the best thing to do is to split the

06:50

number of hydrogens equally among the

06:52

two carbons

06:53

you don't want to put three hydrogens on

06:55

one carbon

06:57

and one hydrogen on the other

06:59

because the carbons are the same so

07:01

they're going to have the same

07:02

attraction to those hydrogen atoms

07:06

the best thing to do

07:08

is to draw the molecule of symmetry

07:10

so begin by putting two hydrogen atoms

07:12

on each carbon

07:14

now you know that carbon wants to have

07:16

four bonds and right now each carbon

07:18

atom has two

07:20

so the only way to make each carbon

07:22

atoms have four bonds is to put a double

07:24

bond in the middle

07:25

and so that is the structure of c2h4

07:28

also known as ethene

07:31

it's a type of alkene

07:34

so anytime you see

07:36

a double bond between two carbon atoms

07:39

the functional group is an alkene

07:42

now let's move on to our next example

07:44

and that is

07:45

c2h2

07:47

go ahead and try that one

07:50

so let's start with two carbon atoms

07:53

and we're going to put a hydrogen on

07:54

each one

07:56

now the only way for each carbon atom to

07:58

have four bonds is to put a triple bond

08:01

in the middle

08:02

and so this molecule is known as

08:04

acetylene

08:07

and a functional group

08:09

is an

08:10

alkyne which corresponds to a triple

08:13

bond between two carbon atoms

08:19

now what about this molecule hydrazine

08:22

how can we draw the lewis structure for

08:24

it

08:25

now this is going to be very similar to

08:27

c2h4

08:28

so we're going to put the two nitrogen

08:30

atoms in the middle

08:31

and we're going to start by placing two

08:34

hydrogen atoms

08:35

on each nitrogen atom now we know that

08:38

nitrogen likes to form three bonds so

08:41

right now each of them have two which

08:43

means that we need a single bond between

08:45

the two nitrogen atoms now nitrogen

08:47

likes to have one lone pair

08:49

so we can

08:50

draw it that way

08:53

so that's the structure of hydrazine

08:56

now let's talk about what to do when you

08:57

have charges

08:59

so i want you to draw these three

09:00

molecules ch3o minus

09:04

ch3oh

09:06

and ch3oh

09:08

plus

09:10

so let's start with a familiar example

09:11

one that we covered already methanol

09:17

you know what i'm not going to draw the

09:18

ch3 part

09:20

i'm just going to leave it like this ch3

09:23

now the oh part is what i'm going to

09:25

focus on

09:27

so we know that oxygen likes to form two

09:29

bonds

09:31

and so it's going to have two lone pairs

09:33

but what's going to happen if we take

09:35

off the hydrogen on the oxygen

09:45

the two electrons in this bond they're

09:47

going to be pulled back to the oxygen

09:49

oxygen is more electronegative than

09:52

hydrogen and so it has a partial

09:54

negative charge

09:56

and so when this bond breaks those

09:58

electrons will be returned to the more

10:00

electronegative elements can be pulled

10:02

by it and so this oxygen is going to

10:05

have three lone pairs

10:06

as opposed to two and now it has a

10:08

negative charge

10:11

now what about if the oxygen gains a

10:13

hydrogen what's gonna happen

10:16

what we're gonna do is react methanol

10:19

with a hydrogen ion

10:22

now we said that oxygen has a partial

10:24

negative charge and so it's attracted

10:26

to the positively charged hydrogen ion

10:29

and so it's going to use a lone pair to

10:32

form a bond between the oxygen and the

10:35

incoming hydrogen

10:36

and so we're going to get a structure

10:39

that looks like this

10:41

i'm running out of space here

10:47

so this lone pair is gone

10:49

and those electrons are now in this bond

10:52

and so this oxygen has one lone pair

10:54

left but now it bears the positive

10:56

charge

10:58

and so whenever you have an oxygen with

11:01

a positive charge

11:02

note that it loses a lone pair to form a

11:05

new bond and when it has a negative

11:07

charge

11:09

it gained a lone pair to break a bond

11:12

so as you can see whenever you have

11:13

charges

11:15

oxygen won't have two bonds when it has

11:17

a negative charge it typically has one

11:19

bond

11:20

when it has a positive charge it

11:21

typically has three bonds but when it's

11:23

neutral

11:24

it has its standard number of two bonds

11:29

so those are some things you want to

11:30

keep in mind but that's it for this

11:31

video that's all i got thanks for

11:32

watching

11:54

you

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