How do valence electrons relate to the reactivity of an element

Considering the first three rows of the table, each row corresponds to the filling of a different electron shell: helium and hydrogen place their electrons in the 1n shell, while second-row elements like Li start filling the 2n shell, and third-row elements like Na continue with the 3n shell.

In general, the number of valence electrons is the same within a column and increases from left to right within a row. Group 1 elements have just one valence electron while group 18 elements have eight except for helium which has only two electrons total. Thus, group number is a good predictor of how reactive each element will be.

The periodic table can be broken up into different blocks based on which orbitals their valence electrons occupy. These are named after the orbitals, so there is an s-block, p-block, d-block and f-block. Inner-shell electrons: Those electrons that are not in the outer shell and are not involved in the reactivity of the element. Valence electrons: The electrons in the highest occupied principal energy level of an atom.

Next Trial Session:. Recorded Trial Session. This is a recorded trial for students who missed the last live session. Waiting List Details:. Due to high demand and limited spots there is a waiting list. You will be notified when your spot in the Trial Session is available. Next Trial:. Sign In. Valence electrons are the electrons in the highest occupied principal energy level of an atom.

Key Terms Inner-shell electrons: Those electrons that are not in the outer shell and are not involved in the reactivity of the element. Loading Notifications. Your Notifications Live Here. The valence electrons are the electrons in the outermost electron shell of an atom. That is why elements whose atoms have the same number of valence electrons are grouped together in the Periodic Table. This tendency is called the octet rule , because the bonded atoms have eight valence electrons.

An atom in Group 1 has only a single valence electron. A metal from Group 2 e. The valence electrons are less tightly bound and easier to remove, because they are farther away from the nucleus of the atom. It can either share electrons with a neighboring atom to form a covalent bond or it can remove electrons from another atom to form an ionic bond.

To form an ionic bond, a halogen atom can remove an electron from another atom in order to form an anion e. To form a covalent bond, one electron from the halogen and one electron from another atom form a shared pair e. Within each Group of nonmetals, reactivity decreases from top to bottom, because the valence electrons are at progressively higher energies and the atoms do not gain much stability by gaining electrons.

Although many decades remained before the details of atomic structure would be discovered, Mendeleev's table already organized elements in terms of their valence.

In Mendeleev's time atoms were thought to be indivisible, unique entities. Some were heavier than others, and it seemed reasonable to order the elements by increasing weight. There are two problems with this approach. First, measuring weight is a tricky task, and many of the accepted weights of Mendeleev's day were not correct. Second, it turns out that atomic weight is not really the relevant parameter.

Today's periodic tables place the elements in order of their atomic number, which is the number of protons in the nucleus. In Mendeleev's time, protons had not yet been discovered. Mendeleev wrote that "arrangement according to atomic weight corresponds to the valence of the element and to a certain extent the difference in chemical behavior.

Mendeleev combined the order of atomic weight with common valences to organize the elements in a table. That is, he organized the elements in groups according to their chemical characteristics. Because those properties repeat every so often, the result was a periodic table in which each vertical column, called a group, contains elements with similar characteristics, and each horizontal row, called a period, arranges the elements by weight, increasing from left to right and top to bottom.

About 50 years after Mendeleev's first periodic table, scientists discovered the atom was built around a nucleus with positively charged protons and neutral neutrons -- both of which are relatively heavy.