Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The Group 1 elements, known as the Alkali Metals, include , , , , , and .
They all possess a single electron in their outermost shell ( configuration), which dictates their chemical properties.
Physical properties: They are soft (can be cut with a knife), have low densities (Lithium, Sodium, and Potassium float on water), and have relatively low melting and boiling points compared to other metals.
Trend in Reactivity: Reactivity increases down the group. This is because the outer electron is further from the nucleus, the atomic radius increases, and there is more shielding, making it easier to lose the .
Trend in Physical Properties: Melting points and boiling points decrease down the group as the metallic bonding becomes weaker due to increased atomic size.
Reaction with Water: They react vigorously with water to produce a metal hydroxide and hydrogen gas. The resulting solution is alkaline ().
Reaction with Oxygen: They tarnish quickly in air to form metal oxides, such as , , and .
Flame Test Colors: Lithium () produces a red flame, Sodium () produces a yellow/orange flame, and Potassium () produces a lilac flame.
📐Formulae
💡Examples
Problem 1:
Write the balanced chemical equation for the reaction between Potassium and water, including state symbols, and describe the observations.
Solution:
Explanation:
Observations include: Potassium melts into a shiny ball, moves rapidly on the surface of the water, produces a lilac-colored flame, and eventually disappears with a 'pop' or small explosion. The resulting solution of is strongly alkaline.
Problem 2:
Explain why Cesium () is more reactive than Lithium ().
Solution:
Cesium has a larger atomic radius than Lithium. In , the valence electron in the shell is much further from the nucleus than the valence electron in the shell of .
Explanation:
Due to increased distance and electron shielding from inner shells, the electrostatic attraction between the nucleus and the outer electron is weaker in . Therefore, less energy is required to remove the electron ( is lower), making more reactive.