Валентні електрони

Valence electrons are considered one of most important parts of chemistry as they define an atom's behavior with others, which is essentially what chemistry is about.

Valence electrons are the outermost electrons of an atom. These electrons are important as they govern that atom's electronegativity, electron affinity, and ionization energy, which leads to things such as covalent and ionic bonds.

These can be found by looking at the number of the group, or family that they are in on the periodic table. For instance, Magnesium (Mg), is in Group 2, which denotes that it has 2 valence electrons.

Valence Electrons

What are Valence Electrons?

• Valence electrons are located in the outermost shell of an atom

• Not every atom has the same number of valence electrons, it depends on the location of the element on the periodic table. The groups on the periodic table typically notes the number of valence electrons an element has (with some exceptions).

How do Valence Electrons Form Bonds?

Valence electrons are the electrons occupying the "valence shell," or outermost shell of the atom. For the main block elements, the valence electron equal the group number.

These electrons, in essence, determine the properties of the atom. The reason for this is that atoms really like having a filled valence shell. A filled shell usually means 8 electrons (this is called the octet rule). How can an atom achieve a full valence shell? By gaining, losing, or sharing electrons. When atoms gain or lose valence electrons, we create two charged particles. The electrostatic attraction between the ions pulls the atoms together. So, we've formed an ionic bond. A covalent bond is formed when atoms share valence electrons. So, both participating atoms effectively "gain" 1 electron per bond. Atoms that need more than one electron can form multiple bonds.

But how can we predict what an atom might do with its valence electrons? This task is actually very simple. We look at the periodic table!

• Groups 1 and 2 are the alkali and alkaline earth metals. They lose electrons and form ionic bonds.

• Groups 13-15 contain the metalloids, the post-transition metals, and some nonmetals. All of these elements mostly form covalent bonds.

• Groups 16 and 17 finish the nonmetals and also contain the halogens. They can form ionic or covalent bonds depending on what other elements they bond with. They also contain most of the diatomic elements.

• Group 18 comprises the noble gases. They already have a full valence shell. So, they generally don't undergo chemical reactions. There are a few noble gas compounds. But, they are octet rule exceptions.

• Groups 3-12 are the transition metals. Their d-orbitals make their chemistry more complicated. They have variable oxidation states and form coordination complexes. We'll study them more in future lessons.

• At the bottom of the periodic table are the lanthanides and actinides. They have f-orbitals. So, their chemistry is even more complicated. Also, many of them have unstable nuclei. So, they are radioactive. We'll learn more about them when we look at nuclear chemistry.

These rules are not steadfast for every element. But, they does apply in the majority of cases.

As with everything in chemistry, the rule does not hold in every scenario. Let's consider a few molecules and their atoms. Oxygen has 6 valence electrons, so we would expect it to gain 2 electrons. This is true for MgO. However, in CO2, we see each oxygen making 2 covalent bonds. In each of these cases, oxygen obtains a full octet.

(Video) Concept of Valency - Introduction | Atoms And Molecules | Don't Memorise

by Don't Memorise

What is valency? When are atoms in a stable state? If they're not stable, how do they become stable? Find out all of these answers and more in this video by Don't Memorise.

(Video) Finding the Number of Valence Electrons for an Element

by Wayne Breslyn

This short video by Dr. B will teach you how to find the number of valence electrons quickly in elements from groups $1$ through $8$.