Valence vs. Valency

Attribute	Valence	Valency
Definition	Refers to the number of electrons an atom can gain, lose, or share in a chemical bond	Refers to the combining power of an element, determined by the number of electrons it can donate, accept, or share
Electrons involved	Valence electrons	Valence electrons
Measurement	Measured in terms of the number of electrons in the outermost shell of an atom	Measured by the number of bonds an atom can form
Chemical behavior	Determines how an atom will react with other atoms to form compounds	Determines the number of bonds an atom can form with other atoms

Definition

Valence and valency are two terms that are often used interchangeably in chemistry, but they actually have distinct meanings. Valence refers to the combining capacity of an atom, which is determined by the number of electrons in its outer shell. Valency, on the other hand, is the number of bonds an atom can form with other atoms. In simpler terms, valence is the number of electrons an atom can gain, lose, or share, while valency is the number of bonds it can form.

Electron Configuration

Valence is related to the electron configuration of an atom. The valence electrons are the electrons in the outermost shell of an atom, also known as the valence shell. These electrons are the ones involved in chemical bonding and determine the reactivity of the atom. Valency, on the other hand, is determined by the number of electrons an atom needs to gain, lose, or share to achieve a stable electron configuration. For example, an atom with four valence electrons will typically have a valency of four, as it can form four bonds to achieve a stable octet.

Chemical Bonding

Valence plays a crucial role in chemical bonding. Atoms tend to bond with other atoms in order to achieve a full outer shell of electrons, which is the most stable configuration. The number of valence electrons an atom has determines the type of bond it can form. For example, atoms with one, two, or three valence electrons tend to lose those electrons to form positive ions, while atoms with five, six, or seven valence electrons tend to gain electrons to form negative ions. Valency, on the other hand, determines how many bonds an atom can form in a molecule. For example, carbon has a valency of four, which means it can form up to four covalent bonds with other atoms.

Periodic Table

The periodic table is organized based on the valence electrons of the elements. Elements in the same group have similar valence electron configurations and therefore similar chemical properties. For example, all the elements in Group 1 have one valence electron, while all the elements in Group 18 have a full outer shell of electrons. Valency, on the other hand, can vary within a group of elements. For example, in Group 14, carbon has a valency of four, while silicon has a valency of four or six, depending on the compound it forms.

Chemical Reactions

Valence and valency are important concepts in understanding chemical reactions. The valence of the reactants determines the type of bonds that will be formed in the products. For example, in a reaction between sodium and chlorine to form sodium chloride, sodium with one valence electron will lose that electron to chlorine with seven valence electrons, forming an ionic bond. Valency, on the other hand, determines the stoichiometry of the reaction. For example, in the reaction between hydrogen and oxygen to form water, hydrogen with one valence electron will share that electron with oxygen with six valence electrons, forming a covalent bond.

Conclusion

In conclusion, while valence and valency are related concepts in chemistry, they have distinct meanings and applications. Valence refers to the combining capacity of an atom based on its outer shell electrons, while valency refers to the number of bonds an atom can form. Understanding these concepts is essential in predicting the behavior of atoms and molecules in chemical reactions.