The Octet Rule states that main-group elements will generally form enough bonds to obtain 8 electrons in their valence shell.
The Octet Rule
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concept
Octet Rule
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When you hear the term octet rule, just realize it's a tendency of most main group elements in achieving 8 octet electrons by way of chemical bonding. Now we're going to say they do so to us, to have the same number of octet electrons as a noble gas. And realize that each covalent bond formed between 2 elements equals the sharing of 2 valence electrons between them. Now we talked about octet electrons. Now valence electrons are electrons an element possesses based on group number. So aluminum being in group 3 a means it has 3 valence electrons. Now shared electrons are the electrons and element gains through a chemical bond. And when we talk about octet electrons, octet electrons equals these valence electrons plus your shared electrons. In by combining the valence and shared, this justifies a need to get to 8 total octet electrons for majority of the main group elements. Remember hydrogen doesn't fit this definition neatly, It only needs one valence electron to get the noble gas configuration of Helium. So we don't talk about hydrogen when it comes to the octet rule. Now that we've learned about these 3 different classes of electrons, click on to the next video and let's take a look at an example question.
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example
Octet Rule Example 1
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In this example question, it says, which of the following statements is true in terms of the following compound? In the following compound, we have a nitrogen atom in the center, and it is surrounded by 3 fluorines. Realize here that nitrogen, it's a man group element, and the drive of mangrove elements is trying to get to 8 octet electrons. So that means that the answer could be b or c. Now, we can look at its valence electrons. Its valence electrons are the electrons tied to its group number. We're gonna say Nitrogen's in group 5 a, so it should have 5 valence electrons. These are the electrons that it brings to the table in order to contribute to this chemical compound. So Nitrogen's in group 5 a, so this is 1, 2, 3, 4, 5 electrons, it's brought in. The shared electrons are the electrons that it gains from chemical bonding to fluorine atoms. So we'd say here that it's shared electrons, if we take a look, it is gaining 1, 2, 3 additional electrons from the fluorine atoms. And that 5 plus 3 is what gives us 8 octet electrons. So here the best answer would be option b. So just keep in mind, elements come in with their electrons and to in order to get to the 8 octet electrons, they can share electrons from the surrounding elements around them.
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Problem
Problem
How many shared electrons are around the oxygen atom?
a) 4
b) 2
c) 6
d) 10
e) 8
A
4
B
2
C
6
D
10
E
8
4
Problem
Problem
Which of the following atoms has the most valence electrons?
a) O
b) Be
c) He
d) N
e) Si
A
O
B
Be
C
He
D
N
E
Si
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concept
Octet Rule
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Now how could it be chemistry without some exceptions? We learned that a majority of the main group elements wanna have 8 octet electrons around themselves to resemble more like the noble gases. But now we're going to see that some elements can have a non octet number of electrons and be completely fine and stable. So we're gonna say these elements are stable with a non octet number of electrons. We talk about incomplete octets and expanded octets. In an incomplete octet, an element is able to maintain its stability when having less than 8 octet electrons around itself. And in an expanded octet, another element is able to maintain the stability when it has more than 8 octet around octet electrons around itself. Now we're gonna say here that their non octet number of electrons typically is twice their group number. So if we take a look, if we're looking at a group 2 a element twice, so 2 times 2, will mean that it's okay with having 4 electrons for its number of octet electrons. Here group 3 a is okay with having 6 octet electrons, 10 octet electrons for 6 on 5 a, 12 octet electrons from element in group 6 a, and then we have 14 and then 16. We take a look here, the elements that typically have, an incomplete octet are hydrogen, helium, beryllium, and then in group 3 a's, boron, aluminum, gallium, and indium. The elements that typically can have an expanded octet, they are found in row 3 or period 3 and lower. So we're talking about phosphorus, sulfur, chlorine, arsenic, selenium, bromine, krypton, tellurium, iodine, xenon, and radon. Now remember, noble gases are very stable. They tend not to wanna get involved in bonding preferences because they're perfect. But these ones that are lower down, since they're so much lower they have larger shells, so they can form bonds, if needed. And just realize here that when it comes to their non octet number, they're not gonna have 8 octet electrons. They tend to have this twice the value of their group number. So keep that in mind when examining these different types of elements that have non octet number of electrons.
Some elements can have less or more than 8 octet electrons around them while still maintaining stability.
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example
Octet Rule Example 2
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Here it says how many octet electrons around the phosphorus atom in the following compound? So remember, your octet electrons equals your valence electrons plus your shared electrons. If we take a look here, your valence electron number is based on your group number. Phosphorus is in group 5 a so it has 5 valence electrons. So 1, 2, 3, 4, 5. And then the shared electrons are the electrons you gain by forming a chemical bond with another element. So here, our shared electrons would be the ones that we're gaining from forming a bond with the hydrogen atom. So 1, 2, 3, 4, and 5. So here we'd see that phosphorus has 10 total octet electrons. Here, this makes sense because we said that when we're dealing with a non octet number of electrons, it's typically twice the group number of the element. Phosphorus is in group 5 a and if you multiply that by 2, we typically can see it go all the way up to 10 valence electrons. So that means option b would be our correct choice.
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Problem
Problem
Which of the following contains an atom that may have an incomplete octet?