1.2.6 Transition Metals

In this lesson, we will explore the unique properties of halogens, their reactions with metals and non-metals, the trends in molecular mass, melting point, and boiling point down the group, and the trend of decreasing reactivity. We will also discuss how more reactive halogens can displace less reactive halogens from their salts.

The Halogens - Group 7

The elements in Group 7 of the periodic table are known as the halogens. This group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Halogens share similar properties because they all have seven electrons in their outer shell.

Properties and Outer Shell Electrons

The properties of elements in Group 7 depend on the outer shell of electrons in their atoms. The outer shell, also known as the valence shell, is the outermost energy level where electrons are located. It plays a crucial role in determining the chemical behaviour and physical properties of an element.

Seven Electrons in Outer Shell

Halogens have seven valence electrons in their outermost energy level. This electron configuration makes halogens highly reactive, as they require one additional electron to achieve a stable electron configuration. The presence of seven valence electrons contributes to the characteristic properties and reactivity of halogens.

Nature of Halogen Compounds

Halogens are non-metals and typically form molecules made of pairs of atoms. These diatomic molecules include fluorine (F₂), chlorine (Cl₂), bromine (Br₂), iodine (I₂), and astatine (At₂). The atoms within these molecules are held together by covalent bonds.

Reactions with Metals and Non-Metals

Halogens react with both metals and non-metals to form compounds:

• Reactions with Metals: Halogens readily react with metals to form ionic compounds called metal halides. During these reactions, the halogen atom gains one electron from the metal atom to achieve a stable electron configuration. For example, chlorine (Cl₂) reacts with sodium (Na) to form sodium chloride (NaCl), a common salt.
• Reactions with Non-Metals: Halogens can also react with non-metals to form covalent compounds. These reactions typically involve the sharing of electrons between the halogen atom and the non-metal atom. For example, chlorine (Cl₂) reacts with hydrogen (H₂) to form hydrogen chloride (HCl), a colourless gas.

Trends in Molecular Mass, Melting Point, and Boiling Point

As you move down Group 7, the molecular mass, melting point, and boiling point of the halogens increase. This trend occurs because the atoms become larger and have more electrons, resulting in stronger intermolecular forces between the molecules. The larger molecules experience stronger London dispersion forces, which require more energy to overcome and lead to higher melting and boiling points.

Decreasing Reactivity

The reactivity of halogens decreases as you move down the group. This trend occurs because the outer shell electrons are further away from the nucleusA membrane-bound organelle in eukaryotic cells that contains DNA., experiencing weaker attractive forces. Consequently, it becomes more difficult for halogens to gain an additional electron and achieve a stable electron configuration.

DisplacementThe forced removal of people from their land. Reactions

A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt. This is known as a displacement reaction. For example, chlorine (Cl₂) can displace bromine (Br₂) from an aqueous solution of potassium bromide (KBr) to form potassium chloride (KCl).

Conclusion

In conclusion, the halogens in Group 7 of the periodic table exhibit characteristic properties due to the presence of seven electrons in their outer shell. Halogens are non-metals and form diatomic molecules. They react with metals and non-metals to form compounds, and their reactivity decreases as you move down the group.