Question

How many electrons does a halogen atom need to complete its octet? Give examples of the ways a Cl atom can do so.

Short answer

A halogen atom needs one electron to complete its octet. A chlorine atom can either gain one electron or share one electron to achieve this.

Step-by-step solution

Identify the Group of Halogens

Halogens are located in Group 17 of the periodic table. They include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).

Determine the Valence Electrons

Atoms of halogens have seven valence electrons. This can be deduced from their group number, 17, where the last digit (7) indicates the number of valence electrons.

Calculate Electrons Needed for Octet

An octet requires eight electrons in the outer shell. Since halogens have seven valence electrons, they need one more electron to complete their octet.

Example - Chlorine Gaining an Electron

A chlorine atom (Cl) can gain one electron to complete its octet. For example, it can gain an electron from a sodium atom (Na) to form NaCl.

Example - Chlorine Sharing Electrons

A chlorine atom can share one electron with another atom, forming a covalent bond. For instance, two chlorine atoms can share electrons to form Cl₂.

Key concepts

Halogen Group

The halogen group is located in Group 17 of the periodic table. This group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Halogens are highly reactive non-metals. Their high reactivity stems from their tendency to gain one electron to achieve a stable electronic configuration.

Valence Electrons

Valence electrons are the outermost electrons of an atom. They are crucial because they determine how an atom can bond with other atoms.
Halogens have seven valence electrons. The number of valence electrons in halogens can be deduced from their group number in the periodic table. For example, chlorine (Cl) is in Group 17, and the last digit, 7, shows it has seven valence electrons.

Octet Rule

The octet rule is a principle in chemistry which states that atoms tend to bond in such a way that they have eight electrons in their outermost shell, achieving a stable electron configuration similar to noble gases.
Halogens, which have seven valence electrons, need just one more electron to complete their octet. This is why they are highly reactive and readily form bonds to achieve a stable electronic structure.

Electron Gain

Electron gain refers to the process by which an atom acquires additional electrons. Halogens typically gain one electron to complete their octet. For example, a chlorine atom (Cl) can gain an electron from a sodium atom (Na). This results in the formation of sodium chloride (NaCl), a stable compound.
When a chlorine atom gains an electron, it becomes a chloride ion (Cl^-), achieving a stable electronic configuration with eight electrons in its outer shell.

Covalent Bonding

Covalent bonding occurs when two atoms share one or more pairs of electrons. Halogens can form covalent bonds to complete their octet.
For instance, two chlorine atoms can share one electron each to form a chlorine molecule (Cl₂). By sharing electrons, each chlorine atom achieves a stable octet configuration. Covalent bonds are common among non-metals, especially within the halogen group, due to their similar electronegativities and valence electron configurations.