Why doesn't helium have 8 electrons instead of 2?

Since helium is the second element in the table, a neutral helium atom can't have 8 electrons as it only has two. The other elements have an atomic number greater than 8.

How many electrons can fill each shell?

first shell is 2, second shell is 8, third shell is 18, and then 32.

How many electrons can fill each shell?

2, 8, 18, 32, 32, 18, 2. IT follows the rule of 2n^2, where n is equal to the position of the shell.

so how many valence electrons does group 3-12 have? or do they have none at all?

It varies. Also, they have a weird habit of being able to have more than one oxidation state. Iron (26) is in the 8th group and usually has a charge of +2 or +3.

What about the elements at the bottom who can't really fit in so they left it out? How much valence electrons do they have?

They have three to four valence electrons, according to my research.

Main content

Course: High school chemistry > Unit 1

Lesson 4: The periodic table and Lewis diagrams

Determine valence electrons using the periodic table

Google Classroom

Learn how to determine the number of valence electrons for an element using the periodic table.

An atom's valence electrons are the electrons in its outermost shell. In the chlorine model below, the valence electrons are shown in

red

The number of valence electrons determines most of an atom's chemical behaviors. So, it's important to be able to identify how many valence electrons atoms of different elements have.

Fortunately, we can use the periodic table to quickly determine the number of valence electrons for main group elements.

Valence electrons on the periodic table

Bohr models for the first three periods of the periodic table are shown below. The valence electrons are shown in

red

Do you notice any patterns in the number of valence electrons?

The number of valence electrons increases going left to right across a period. But, with the exception of

He

, the number of valence electrons remains the same going down a group.

For example,

H

Li

, and

Na

are in group 1 and all have one valence electron. Both

N

and

P

are in group 15 and have five valence electrons.

This is why elements in the same group have similar chemical properties—they have the same number of valence electrons!

This pattern allows us to quickly identify the number of valence electrons for main group elements on the periodic table, even if we don't have Bohr models to reference. The diagram below shows the number of valence electrons (VE) for the main group elements.

To summarize, we can use an element's group on the periodic table to determine how many valence electrons its atoms have:

Main group	1	2	13	14	15	16	17	18
Valence electrons	1	2	3	4	5	6	7	8*

*except helium, which has 2

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Steve
Posted 4 months ago. Direct link to Steve's post “Why doesn't helium have 8...”
Why doesn't helium have 8 electrons instead of 2?
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- vincent.wang11
  Posted 4 months ago. Direct link to vincent.wang11's post “Since helium is the secon...”
  Since helium is the second element in the table, a neutral helium atom can't have 8 electrons as it only has two. The other elements have an atomic number greater than 8.
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lydia.ashenafi.277
Posted 4 months ago. Direct link to lydia.ashenafi.277's post “At 12:29, what about the ...”
At
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, what about the 2 8 8 method?
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kristine.aboloje
Posted 4 months ago. Direct link to kristine.aboloje's post “How many electrons can fi...”
How many electrons can fill each shell?
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- Anushka
  Posted 2 months ago. Direct link to Anushka's post “first shell is 2, second ...”
  first shell is 2, second shell is 8, third shell is 18, and then 32.
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Susan Everly
Posted 25 days ago. Direct link to Susan Everly's post “so how many valence elect...”
so how many valence electrons does group 3-12 have? or do they have none at all?
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- Zayan
  Posted 24 days ago. Direct link to Zayan's post “It varies. Also, they hav...”
  It varies. Also, they have a weird habit of being able to have more than one oxidation state. Iron (26) is in the 8th group and usually has a charge of +2 or +3.
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alexa araujo
Posted 3 months ago. Direct link to alexa araujo's post “How many electrons can fi...”
How many electrons can fill each shell?
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- Pierce, Greyson
  Posted 3 months ago. Direct link to Pierce, Greyson's post “2, 8, 18, 32, 32, 18, 2. ...”
  2, 8, 18, 32, 32, 18, 2. IT follows the rule of 2n^2, where n is equal to the position of the shell.
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Squirrel
Posted 3 months ago. Direct link to Squirrel's post “What about the elements a...”
What about the elements at the bottom who can't really fit in so they left it out? How much valence electrons do they have?
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- Zayan
  Posted a month ago. Direct link to Zayan's post “They have three to four v...”
  They have three to four valence electrons, according to my research.
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Moonwatcher
Posted 14 days ago. Direct link to Moonwatcher's post “This is the "1A,2A,3A..."...”
This is the "1A,2A,3A..." scale right?
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