Predicting and identifying reactions and products Study Guide

The periodic table organises elements into groups based on their similar chemical properties, largely determined by the number of electrons in their outer shell. We will focus on Groups 1 (alkali metals), 7 (halogens), and 0 (noble gases).

Group 1 elements are highly reactive metals. They have one electron in their outer shell, which they readily lose to form a positive ion with a +1 charge. This loss of an electron makes them very reactive. As you go down Group 1, the reactivity increases because the outer electron is further from the nucleus and shielded by more electron shells, making it easier to lose. They are soft metals, have low melting points (which decrease down the group), and react vigorously with water to produce hydrogen gas and a metal hydroxide, which is an alkaline solution.

Group 7 elements are known as halogens. They are non-metals with seven electrons in their outer shell. To achieve a stable electron configuration, they readily gain one electron to form a negative ion with a -1 charge. This tendency to gain an electron makes them highly reactive. As you go down Group 7, the reactivity decreases because the incoming electron is further from the nucleus and shielded by more electron shells, making the attraction to the nucleus weaker. They exist as diatomic molecules (e.g., Cl2, Br2) and their melting and boiling points increase down the group. They are toxic.

Group 0 elements are the noble gases. They are non-metals with a full outer shell of electrons (eight electrons, except helium which has two). This stable electron configuration means they do not readily gain, lose, or share electrons, making them very unreactive. They exist as monatomic gases, meaning their atoms do not bond with each other. Their boiling points are very low but increase slightly down the group. Their lack of reactivity makes them useful in applications where a non-reactive atmosphere is required, such as in light bulbs or welding.