Question

Refer to the periodic table and select the symbol of the element that fits each of the following descriptions: (a) the fourth-period representative element with properties similar to $\mathrm{O}$ (b) the sixth-period transition element with properties similar to $\mathrm{Ni}$ (c) the rare earth element whose atomic mass is lowest (d) the radioactive noble gas

Short answer

(a) Se, (b) Pt, (c) La, (d) Rn

Step-by-step solution

Identify Fourth-Period Similar to Oxygen

Oxygen ( ext{O} ) is in Group 16 of the periodic table, also known as the chalcogens. The fourth-period element in the same group is Selenium ( ext{Se} ). Therefore, the element that fits this description is Selenium.

Identify Sixth-Period Similar to Nickel

Nickel ( ext{Ni} ) is a transition metal in Group 10 of the periodic table. In the sixth period, the transition element with similar properties in the same group is Platinum ( ext{Pt} ). Thus, the element fitting this description is Platinum.

Lowest Atomic Mass Rare Earth Element

The rare earth elements are the lanthanides. The lanthanide with the lowest atomic mass is Lanthanum ( ext{La} ), which has an atomic mass of approximately 138.91 u. Therefore, Lanthanum fits this description.

Identify Radioactive Noble Gas

The noble gases are found in Group 18 of the periodic table. The radioactive noble gas is Radon ( ext{Rn} ), which is known for its radioactivity and is located at the bottom of the group. Hence, Radon is the element described here.

Key concepts

Representative Elements

The representative elements, also known as main-group elements, are found in the s and p blocks of the periodic table. These elements include those in Groups 1, 2, and 13 to 18. They are called representative because they display a wide range of chemical and physical properties that are typical of elements.

• Group 1 elements are known as alkali metals (e.g., Lithium, Sodium).
• Group 2 elements are called alkaline earth metals (e.g., Magnesium, Calcium).
• Groups 13 to 18 include a variety of nonmetals, metals, and metalloids.

Representative elements are characterized by the filling of the outermost s and p orbitals. For example, Selenium (Se), a representative element, is in Group 16 and shares chemical similarities with Oxygen (O). This resemblance is primarily due to having six valence electrons in their outermost shell, influencing their reactive nature.

Transition Metals

Transition metals occupy the center of the periodic table in Groups 3 to 12. These metals are known for their ability to form compounds with vivid colors, due to their d electrons that can easily shift between different energy levels.

• They often have multiple oxidation states.
• Transition metals are good conductors of heat and electricity.
• Examples include Iron (Fe), Copper (Cu), and Nickel (Ni).

A distinctive feature of transition metals is their partially filled d orbitals. This means they can form a variety of complex compounds. Platinum (Pt), a sixth-period transition metal, is known for its robustness and catalytic properties, similar to Nickel (Ni). Their similarities stem from belonging to the same group, where shared electron configurations offer comparable chemical behaviors.

Lanthanides

Lanthanides, sometimes referred to as rare earth elements, are found in the periodic table's f block. These elements include 15 elements from Lanthanum (La) to Lutetium (Lu).

• They are known for their high magnetic susceptibility and ability to produce phosphorescent compounds.
• Lanthanides often exhibit similar chemical properties due to their similar ionic radii.
• They are generally shiny and silvery-white metals.

One notable lanthanide is Lanthanum (La), the first element in this series, which possesses the lowest atomic mass among the lanthanides. This property makes it a crucial starting point for studying the properties of other lanthanides. Lanthanides play essential roles in modern technology, found in everything from smartphones to electric car motors.

Noble Gases

Noble gases reside in Group 18 of the periodic table. Known for their chemical inertness, they have a complete set of outer electrons, making them highly stable.

• Includes Helium (He), Neon (Ne), and Argon (Ar).
• They are colorless, odorless, and tasteless gases under standard conditions.
• These elements have low chemical reactivity because of their full valence electron shells.

Among noble gases, Radon (Rn) is unique because of its radioactivity. It occurs naturally from the decay of Uranium and is found in the earth's crust. Although hazardous, Radon has been studied for potential therapeutic uses in medicine. Understanding noble gases helps illuminate their use in lighting, welding, and as coolants in nuclear reactors.