Difference Between Electron & Valence Shells - Explained

In summary, electron shells are defined by quantum number n and contain a certain number of electrons, with 2e in n=1, 8e in n=2, 18e in n=3, 32e in n=4 and so on. Valence shells, on the other hand, are the outermost orbitals available for chemical reactions and are limited due to the number of non-metallic elements. The order of filling for shells follows a pattern, with the s orbital filling before the d and f shells in subsequent periods. This explains why element 19 starts with 4s^1 even though the 3d orbitals are not filled yet. The concept is further explained in Linus Pauling's book
  • #1
Ratzinger
291
0
I would like to get clarified the difference between electron shells and valence shells.
Electron shell is defined by quantum number n, the energy level. So there are 2e in n=1, 8e in n=2, 18e in n=3, 32e in n=4 and so on.
But what is the exact defintion of valence shells, ecxept that the 1st takes 2, the 2th 8, the 3th 8, the 4th 18 electrons and so on?

Why does element 19 start with 4s^1 even though all the 3d orbitals are not filled yet? Why is not first one entire electron shell completed before starting to fill a new one?

thank you
 
Physics news on Phys.org
  • #2
The valence 'shells' or 'orbitals' are the outermost 'orbitals' and are available for chemical rections. Also remember that there are limited chemical reactions due to the limited number of non-metallic elements, e.g. halides, O, S, P, C, and so on. When metals are mixed, the result is an alloy, which is different than a chemical compound.

If one looks at the orbital wave equations for the 3d and 4s, the 4s would show lower energy levels than the 3d shells. Similarly for periods 5, 6 and 7, the s orbital fills before the d and f shells of the previous periods.

See the order in which shells are filled here -

http://en.wikipedia.org/wiki/Periodic_table#Explanation_of_the_structure_of_the_periodic_table
 
  • #3
thanks Astronuc

I also found a nice explanation to my problem in Linus Pauling "General Chemistry" on page 138 (Dover). Great book and a cheap buy.
 

1. What is the difference between an electron shell and a valence shell?

An electron shell refers to the energy levels or orbitals in an atom where electrons can be found. These shells are labeled as K, L, M, N, etc. A valence shell specifically refers to the outermost energy level in an atom, which contains the valence electrons that are involved in chemical bonding.

2. How many electrons can each shell hold?

The first shell, K, can hold a maximum of 2 electrons. The second shell, L, can hold a maximum of 8 electrons. The third shell, M, can hold a maximum of 18 electrons. The number of electrons that can be held in the higher shells increases as you go further from the nucleus. This is due to the increasing distance from the positively charged nucleus, which makes it easier for electrons to occupy higher energy levels.

3. Why are valence electrons important?

Valence electrons are important because they are the electrons involved in chemical bonding between atoms. These bonds are responsible for creating molecules and compounds, which make up all matter in the universe. The number and arrangement of valence electrons determine an atom's reactivity and its ability to form chemical bonds with other atoms.

4. How do electron shells and valence shells affect an atom's properties?

The number of electron shells and the number of electrons in the valence shell can affect an atom's properties in various ways. The more electron shells an atom has, the larger its atomic radius and the more shielding effect it has on the valence electrons. This makes it easier for the atom to lose or gain electrons, making it more reactive. Additionally, the number of valence electrons determines the type of chemical bonds an atom can form, which ultimately affects its chemical properties.

5. Can an atom's electron and valence shells change?

Yes, an atom's electron and valence shells can change through various processes such as ionization, where an atom gains or loses electrons, or through chemical reactions where atoms share or transfer electrons to form new bonds. These changes can alter an atom's properties and ultimately affect the behavior and characteristics of the substance it makes up.

Similar threads

  • Biology and Chemistry Homework Help
Replies
5
Views
644
  • Biology and Chemistry Homework Help
Replies
1
Views
1K
Replies
8
Views
929
Replies
2
Views
967
Replies
7
Views
4K
Replies
3
Views
2K
  • Biology and Chemistry Homework Help
Replies
1
Views
14K
  • Quantum Physics
Replies
4
Views
1K
  • Biology and Chemistry Homework Help
Replies
1
Views
3K
Replies
5
Views
2K
Back
Top