Question

Refer to the periodic table and select the symbol of the element that fits each of the following descriptions: (a) the third-period alkaline earth metal (b) the halogen that exists as a reddish-brown liquid at normal conditions (c) the rare earth element whose atomic number is greatest (d) the actinide with properties similar to Ce.

Short answer

(a) Mg, (b) Br, (c) Lu, (d) U

Step-by-step solution

Identify the Element for (a)

Alkaline earth metals are found in Group 2 of the periodic table. The third period corresponds to elements with atomic numbers 11 through 18. The alkaline earth metal in this period is magnesium (Mg).

Identify the Element for (b)

Halogens are located in Group 17 of the periodic table. Among these, bromine (Br) is the only one that exists as a reddish-brown liquid at room temperature.

Identify the Element for (c)

Rare earth elements include the lanthanides and the actinides after lanthanum. The element from these with the highest atomic number is lutetium (Lu) with atomic number 71.

Identify the Element for (d)

Actinides are found between atomic numbers 89 to 103. Cerium (Ce) is similar in properties to thorium (Th), which is commonly associated with having similar properties to lanthanides like Ce, but thorium itself is not an answer here. We usually refer to another in a chemical property context similar to Ce - Uranium (U).

Key concepts

Alkaline Earth Metals

Alkaline Earth Metals are a fascinating group of elements located in Group 2 of the periodic table. These elements are known for their importance in both biology and industry.
Some properties they universally share include:

• Shiny appearance
• Good conductors of electricity
• High melting points

In everyday terms, one of their standout qualities is their ability to form strong, stable compounds. For instance, magnesium, found in this group, plays a critical role in many biological systems.
They are typically less reactive than the neighboring alkali metals but more so than most others you find on the periodic table, ready to react by losing two valence electrons to form +2 charges. Calcium, another member of this family, is crucial in human bone development. Additional members of the alkaline earth metals include strontium and barium, each contributing uniquely to various chemical industries and manufacturing processes. These metals are essential and continue to be a subject of intrigue for chemists and students alike.

Halogens

The Halogens make up Group 17 of the periodic table. They include elements like fluorine, chlorine, bromine, iodine, and astatine.
Notably reactive, halogens are eager to gain an electron to achieve a stable octet configuration, which makes them highly electronegative. Bromine stands out in this group for its unique physical state. Unlike most non-metals, bromine is a liquid at room temperature with a distinctive reddish-brown color. Halogens have

• High electronegativities
• Varied physical states (solid, liquid, gas)
• High reactivity, especially with alkali and alkaline earth metals

Bromine, due to its state and color, has found uses in applications like flame retardants and photographic chemicals. The entire family's capability to form halides, compounds with elements from Group 1 or 2, is groundbreaking in chemical synthesis and household uses.

Rare Earth Elements

Rare Earth Elements, although not rare per se, are challenging to extract because they are widely dispersed rather than concentrated in ores. They divide into two families: the lanthanides and early actinides, known for their unique magnetic, luminescent, and electrochemical properties. Lutetium, with atomic number 71, marks the end of the lanthanide series. It showcases characteristics typical of these elements:

• Strong metallic properties
• Silvery-white appearance
• High melting points

The practical applications of rare earth elements are broad. For instance, they are crucial in manufacturing powerful magnets used in wind turbines and electronics. Lanthanides like lutetium specifically stand out in their use in advanced computing technologies and medical imaging equipment. Their growing necessity in advancing technology makes them continually significant in modern science and industry.

Actinides

Actinides reside in the bottom row of the f-block on the periodic table, ranging from atomic numbers 89 to 103. Known for their large atomic and ionic sizes, they play crucial roles in nuclear chemistry. Elements within this group are largely characterized by their radioactivity, with uranium and thorium being the most discussed. Uranium, in particular, has properties similar to those of cerium, which places it among those actinides with notable practical use.
Its natural radioactive characteristics allow for applications in power generation.

• Highly dense materials
• Radioactive properties
• Complex electron configuration

Beyond energy production, actinides have uses in medicine, particularly in radiation therapy for cancer treatment. Despite the challenges in managing and storing these materials due to their radioactivity, they remain invaluable to both scientific advancements and societal needs.