Question

Define valence shell and valence electron.

Short answer

Question: Define valence shell and valence electron, and provide the valence shell and number of valence electrons for sodium and oxygen. Answer: The valence shell is the outermost shell of an atom that contains electrons, and these electrons are responsible for chemical bonding. A valence electron is an electron present in the valence shell that determines the atom's chemical behavior. For sodium (Na), the valence shell is the third shell (3s¹), with one valence electron. For oxygen (O), the valence shell is the second shell (2s² 2p⁴), with six valence electrons.

Step-by-step solution

Definition of Valence Shell

The valence shell is the outermost shell (energy level) of an atom that contains electrons. These electrons are involved in chemical bonding, which leads to the formation of molecules and compounds. The valence shell is important because it determines an atom's reactivity and how it will interact with other atoms.

Definition of Valence Electron

A valence electron is an electron present in the valence shell of an atom. These electrons are responsible for an atom's chemical behavior, as they are used to form bonds with other atoms. The number of valence electrons affects the reactivity and stability of an element, as atoms typically strive to have a full valence shell (usually eight electrons, following the octet rule).

Example: Sodium

In the case of sodium (Na), it has an atomic number of 11. Its electron configuration is 1s² 2s² 2p⁶ 3s¹. The valence shell would be the third shell, as it is the outermost shell occupied by electrons (3s¹). The valence electron is the single electron in this third shell (3s¹).

Example: Oxygen

For oxygen (O), with an atomic number of 8, the electron configuration is 1s² 2s² 2p⁴. The valence shell is the second shell containing 2s² and 2p⁴ electrons. Oxygen has six valence electrons in the second shell, consisting of two 2s electrons and four 2p electrons.