Question

From the following list of elements \(-\mathrm{Ar}, \mathrm{H}, \mathrm{Ga}, \mathrm{Al}, \mathrm{Ca}, \mathrm{Br}, \mathrm{Ge},\) \(\mathrm{K}, \mathrm{O}\) - pick the one that best fits each description. Use each element only once: (a) an alkali metal, (b) an alkaline earth metal, \((\mathbf{c})\) a noble gas, \((\mathbf{d})\) a halogen, \((\mathbf{e})\) a metalloid, \((\mathbf{f})\) a nonmetal listed in group \(1 \mathrm{~A},(\mathrm{~g})\) a metal that forms a \(3+\) ion, \((\mathbf{h})\) a nonmetal that forms a \(2-\) ion, (i) an element that resembles aluminum.

Short answer

(a) K, (b) Ca, (c) Ar, (d) Br, (e) Ge, (f) H, (g) Ga, (h) O, (i) None from the provided list.

Step-by-step solution

Identify the categories

We first need to understand the different categories given in the problem, and their characteristics: (a) An alkali metal - These are found in Group 1 of the periodic table and always form +1 ions. (b) An alkaline earth metal - These are found in Group 2 of the periodic table and always form +2 ions. (c) A noble gas - These are found in Group 18 of the periodic table and do not form any ions as they have a completely filled valence electron shell. (d) A halogen - These are found in Group 17 of the periodic table and always form -1 ions. (e) A metalloid - These elements have properties of both metals and non-metals. (f) A non-metal in group 1A - These are non-metal elements in Group 1 of the periodic table. (g) A metal that forms a 3+ ion - These are elements that form ions with a +3 charge. (h) A nonmetal that forms a 2- ion - These are non-metal elements that form ions with a -2 charge. (i) An element that resembles aluminum - This is an element that has similar properties to aluminum.

Identify the elements

Now that we have identified the categories, we can start classifying the elements according to their properties. (a) An alkali metal: Potassium (K) is found in Group 1 and is an alkali metal. (b) An alkaline earth metal: Calcium (Ca) is found in Group 2 and is an alkaline earth metal. (c) A noble gas: Argon (Ar) is found in Group 18 and is a noble gas. (d) A halogen: Bromine (Br) is found in Group 17 and is a halogen. (e) A metalloid: Germanium (Ge) is a metalloid, as it has properties of both metals and non-metals. (f) A non-metal in group 1A: Hydrogen (H) is found in Group 1 and is a non-metal. (g) A metal that forms a 3+ ion: Gallium (Ga) forms a +3 ion (Ga³⁺). (h) A nonmetal that forms a 2- ion: Oxygen (O) forms a 2- ion (O²⁻). (i) An element that resembles aluminum: Aluminum (Al) is a metal in Group 13. Gallium (Ga) is also in Group 13 and shares similar properties with aluminum. Ga has already been used in (g), so the next best option is Indium (In). However, Indium is not in the provided list of elements. Thus, there is no element in the provided list that hasn't been used and also resembles aluminum.

Key concepts

Alkali Metal

Alkali metals are fascinating elements located in Group 1 of the periodic table. They are known for their highly reactive nature, particularly with water, and they form +1 ions when bonding with other elements. A classic example of an alkali metal is Potassium (K), which reacts forcefully with water to form potassium hydroxide and hydrogen gas.

These metals are soft and have low melting points compared to other metals. Additionally, they're shiny and can be easily cut with a knife. The reactivity of alkali metals increases as you go down the group, meaning francium (Fr) is the most reactive alkali metal. Alkali metals are also great conductors of electricity and are used in various applications, including batteries, such as lithium (Li) batteries, which are common in electronic devices.

Halogen

Halogens make up Group 17 in the periodic table and have a very distinctive characteristic: they eagerly grasp for electrons to achieve a full outer shell, thus forming -1 ions. These elements include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Bromine, for instance, is unique for being a liquid at room temperature among the halogens.

H4 The Reactive Nature of Halogens
Halogens are highly reactive, with fluorine being the most aggressive. These elements play a substantial role in everyday life; for example, chlorine is a critical component in water purification processes, and iodine is essential in dietary needs to prevent deficiencies. Halogens are also notorious for forming salts when they react with metals, such as sodium chloride (table salt), which is a compound of chlorine.

Noble Gas

Noble gases, inhabiting Group 18, are the pacifists of the periodic table, rarely engaging in chemical reactions due to their complete valence electron shells. This inertness makes them very stable and non-reactive under normal conditions. Argon (Ar), for instance, makes up almost 1% of the Earth's atmosphere and is often used as a non-reactive shield gas in welding and in light bulbs to prevent the rapid oxidation of the filament.

From helium (He), used in balloons and as a safe breathing gas in deep-sea diving mixtures, to xenon (Xe), used in high-quality light sources, noble gases are applicable in a diverse range of industries despite their inert nature.

Metalloid

Metalloids straddle the border between metals and nonmetals on the periodic table. Possessing a combination of both metallic and non-metallic properties, they are semiconductors, which means they partially conduct electricity. This makes them extremely valuable in the field of electronics. Germanium (Ge) and silicon (Si) are prime examples, both of which play an integral role in the making of semiconductors for computer chips.

Metalloids often exhibit versatility, appearing shiny like metals but brittle like nonmetals. Arsenic (As), for example, has been historically used in pesticides and lead alloys, but also possesses semiconductor properties. Understanding the distinctive nature of metalloids is key in science and technology, especially for advancements in electronic devices.