Question

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

Step-by-step solution

(Step 1: Identify the alkali metal)

Elemental K is an alkali metal as it belongs to group 1A of the periodic table.

(Step 2: Identify the alkaline earth metal)

Elemental Ca is an alkaline earth metal because it belongs to group 2A of the periodic table.

(Step 3: Identify the noble gas)

Elemental Ar is a noble gas since it belongs to group 8A of the periodic table.

(Step 4: Identify the halogen)

Elemental Br is a halogen because it belongs to group 7A of the periodic table.

(Step 5: Identify the metalloid)

Elemental Ge is a metalloid as it is located along the diagonal line between metals and nonmetals in the periodic table.

(Step 6: Identify the nonmetal in group 1A)

Elemental H is the nonmetal in group 1A of the periodic table.

(Step 7: Identify the metal that forms a 3+ ion)

Elemental Ga is a metal from group 3A that forms a 3+ ion.

(Step 8: Identify the nonmetal that forms a 2- ion)

Elemental O is a nonmetal from group 6A that forms a 2- ion.

(Step 9: Identify the element that resembles aluminum)

Elemental Al resembles aluminum because they are the same element.

Key concepts

Alkali Metals

Alkali metals are a fascinating group of elements located in Group 1A of the periodic table. They include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). These metals are known for being highly reactive, especially with water.

• **Characteristics:** Alkali metals have a single electron in their outermost shell, which they readily lose to form positive ions, or cations (e.g., K⁺).
• **Reactivity:** Their reactivity increases as you move down the group. For example, potassium is more reactive than lithium.
• **Uses:** Alkali metals are used in various industries, such as sodium in table salt and potassium in fertilizers.

Their high reactivity and characteristic property of forming +1 ions make alkali metals distinct and easily identifiable.

Alkaline Earth Metals

Alkaline earth metals can be found in Group 2A of the periodic table, directly next to the alkali metals. This group includes beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

• **Characteristics:** Each element in this group has two electrons in its outer shell. These electrons are lost in reactions to form +2 ions, which are called cations.
• **Reactivity:** Alkaline earth metals are less reactive than their Group 1A neighbors but still react with water, albeit slower. Calcium, for example, reacts with water at room temperature.
• **Applications:** Magnesium and calcium are essential for biological functions, such as bone development, and are widely used in alloys and construction.

These elements share common attributes due to their electron configurations and their important uses in various fields.

Noble Gases

Noble gases occupy Group 8A of the periodic table, consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These gases are known for their lack of reactivity.

• **Characteristics:** Noble gases have a complete set of electrons in their outermost shell, making them stable and often unreactive.
• **Inertness:** This group is known for not forming compounds easily due to their stable electron configurations.
• **Uses:** Argon is used in light bulbs, neon in lighting signs, and helium in balloons. Their chemical inertness lends to many of their applications in industry and technology.

Despite being considered chemically uninteresting due to their low reactivity, noble gases are crucial for various technological applications.

Halogens

The halogens form a group of elements located in Group 7A of the periodic table. This includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).

• **Characteristics:** These elements have seven electrons in their outer shell and are just one electron short of a full shell, making them highly reactive.
• **Reactivity:** Halogens typically gain an electron to form negative ions, or anions (e.g., Cl⁻), which are extremely reactive, especially with alkali and alkaline metals.
• **Uses:** Chlorine is used for water purification and in household products, while iodine is vital in medicine and nutrition.

Opting to gain one electron to achieve a full valence shell renders halogens highly reactive, paving the way for their widespread use in various applications.

Metalloids

Metalloids, or semimetals, are located along the "stair-step" line on the periodic table. This line divides metals and nonmetals. They include boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te).

• **Characteristics:** Metalloids have properties that are intermediate between metals and nonmetals, such as semiconducting properties.
• **Applications:** Silicon and germanium are widely used in semiconductors, which are essential components in electronics, like computers and smartphones.

The dual characteristic of metalloids, having both metallic and nonmetallic qualities, makes them extremely valuable in technology, particularly in the electronics industry.

Chemical Ions

Chemical ions are atoms or molecules that have gained or lost one or more electrons, giving them a net charge. Ions are crucial in various chemical processes and are categorized based on their charge.

• **Types of Ions:**
  • Cations are positive ions formed by losing electrons, such as Na⁺ or Ca²⁺.
  • Anions are negative ions formed by gaining electrons, evident in ions like Cl⁻ or O²⁻.
• **Formation:** Ions form during chemical reactions, particularly bonding, where atoms gain or lose electrons to achieve stable electron configurations.
• **Importance:** They are important in various fields from biology to chemistry; for instance, ions are crucial in nerve signal transmission and cellular processes.

Understanding ions and their roles in chemical reactions helps us grasp chemical behavior and processes across different scientific disciplines.