Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The Halogens are the elements in Group 7 of the Periodic Table. They are non-metals and exist as diatomic molecules, such as , , , and .
Physical properties change down the group: melting and boiling points increase, and the colors of the elements become darker ( is a pale yellow gas, is a green gas, is a red-brown liquid, and is a grey-black solid).
Chemical reactivity decreases down the group. This is because the atomic radius increases and there is more shielding, making it harder for the nucleus to attract the one electron needed to fill the outer shell.
Halogens react with metals to form ionic compounds called halides. In these reactions, the halogen atom gains one electron to form a halide ion with a charge (e.g., , ).
Displacement reactions occur when a more reactive halogen replaces a less reactive halogen from its aqueous salt solution. For example, will displace and .
Halogens act as oxidizing agents because they gain electrons () during reactions.
📐Formulae
💡Examples
Problem 1:
Predict the result and write the ionic equation when aqueous bromine () is added to a solution of sodium iodide ().
Solution:
The solution turns from colorless to brown. Ionic equation:
Explanation:
Bromine is higher in Group 7 than iodine, meaning it is more reactive. Therefore, displaces the ions. The brown color is caused by the formation of molecular iodine () in the solution.
Problem 2:
Explain why the reactivity of the Halogens decreases down the group from Fluorine to Astatine.
Solution:
As you move down the group, the number of electron shells increases, which increases the atomic radius and the 'shielding' effect. The nucleus has a weaker electrostatic attraction for an incoming electron, making it harder for the atom to gain an electron to form a stable ion.
Explanation:
Reactivity in Group 7 depends on the ease with which an atom can attract and capture an electron to complete its outer shell.