The Periodic Table - Group I properties (3)
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1.
Sodium (Na) is a highly reactive metal that reacts vigorously with water to produce hydrogen gas and sodium hydroxide. Predict the properties of potassium (K), calcium (Ca), and magnesium (Mg) based on this information. Consider their reactivity with water, their appearance, and their reactions with other substances.
Based on the reactivity of sodium, we can predict the following properties for potassium, calcium, and magnesium:
- Potassium (K): Potassium is expected to be even more reactive than sodium. It will also react vigorously with water, producing hydrogen gas and potassium hydroxide. Potassium is a soft, silvery-white metal and is also highly reactive with air, tarnishing quickly. It is more reactive than calcium and magnesium.
- Calcium (Ca): Calcium is expected to be less reactive than sodium but more reactive than magnesium. It will react with water, although the reaction will be slower than that of sodium. Calcium is a strong, white metal. It reacts with acids and is used in various applications, including in the human body.
- Magnesium (Mg): Magnesium is expected to be less reactive than calcium. It will react with water, but the reaction will be relatively slow. Magnesium is a lightweight, silvery-white metal. It is often used in alloys and is also used in fireworks.
Key Prediction: As you move down Group I, reactivity with water increases. Appearance tends to remain silvery-white, but reactivity decreases.
2.
Lithium (Li) is a solid at room temperature and is less reactive than sodium. It is used in batteries and is relatively soft. Considering this information, predict the properties of rubidium (Rb) and cesium (Cs). Include in your answer how their properties compare to lithium.
Based on the information provided about lithium, we can predict the following properties for rubidium and cesium:
- Rubidium (Rb): Rubidium is expected to be a solid at room temperature, similar to lithium. It will be more reactive than lithium, and therefore less soft. It will react with water, although the reaction will be faster than that of lithium. Rubidium is a soft, silvery-white metal.
- Cesium (Cs): Cesium is expected to be a solid at room temperature and will be even more reactive than rubidium. It will react vigorously with water, producing hydrogen gas and cesium hydroxide. Cesium is a soft, silvery-white metal and is the most reactive of the alkali metals.
Comparison to Lithium: Rubidium and cesium will be more reactive than lithium. They will be less soft than lithium. Their reactivity with water will be greater than that of lithium. They will also be more likely to tarnish in air than lithium.
3.
Describe the physical properties of lithium, sodium and potassium, as they appear down Group I. Your description should include changes in melting point, density and reactivity.
As you move down Group I (Lithium, Sodium, Potassium), there are clear trends in the physical properties of these metals.
- Melting Point: The melting point decreases as you go down the group. Lithium has the highest melting point (180°C), while potassium has the lowest (60°C). This is because the metallic bonding becomes weaker with increasing atomic size. Larger atoms have a greater distance between their valence electrons and the nucleus, resulting in weaker attraction and therefore lower melting points.
- Density: The density increases as you move down the group. Lithium is the least dense (0.53 g/cm³), and potassium is the most dense (0.89 g/cm³). This is also related to the increasing atomic size. While the number of protons and neutrons increases, the volume increases more significantly, leading to a higher density.
- Reactivity: The reactivity increases down the group. Lithium is relatively unreactive, sodium is reactive, and potassium is the most reactive. This is because the outermost electron is further from the nucleus in larger atoms, making it easier to remove and form a positive ion. The ease of losing an electron increases down the group, leading to greater reactivity with water and other substances.