Question

Assuming that the seventh period of the periodic table has 32 members, what should be the atomic number of (a) the noble gas following radon (Rn); (b) the alkali metal following francium (Fr)?

Short answer

The atomic number of the noble gas following radon (Rn) is 118 and the atomic number of the alkali metal following francium (Fr) is 119.

Step-by-step solution

Identify the Atomic Numbers of Given Elements

The given elements are Radon (Rn), which is a noble gas and Francium (Fr), an alkali metal. The atomic number of Radon (Rn) is 86 and that of Francium (Fr) is 87.

Calculate the Atomic Number of Yet-to-Discover Noble Gas

Knowing that a period on the periodic table consists of 32 elements and that Radon (Rn) is the last element of the 6th period, it can be concluded that the next noble gas will be the last element of the next period. So the atomic number of the noble gas following radon (Rn) would be 86 (Radon’s atomic number) + 32 (Number of elements in a period) = 118.

Calculate the Atomic Number of the Alkali Metal

Francium (Fr) is the first element in the 7th period. It's an alkali metal. Therefore, the alkali metal following Francium (Fr) will be the first element in the 8th period. So, the atomic number of the alkali metal following francium (Fr) would be 87 (Francium’s Atomic number) + 32 (Number of elements in a period) = 119.

Key concepts

Atomic Number

The concept of the atomic number is a fundamental idea in understanding the organization of the periodic table. But what exactly is an atomic number? The atomic number is a unique identifier assigned to each chemical element, represented by a whole number. This number signifies the number of protons found in the nucleus of an atom of a particular element. For instance, the atomic number of hydrogen is 1, since each hydrogen atom has one proton in its nucleus.

The atomic number determines the identity of the chemical element and its position in the periodic table. As you move across the table from left to right, the atomic numbers increase sequentially, starting from 1 for hydrogen. This sequential order reflects the increase in protons, which in turn influences the chemical behavior of the elements. Understanding this helps in predicting how elements react and combine with others.

• Guides the arrangement of elements in the periodic table.
• Helps in understanding the chemical behavior of elements.

Noble Gases

Noble gases are fascinating elements found in group 18 of the periodic table. These gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and oganesson (Og). Each of these elements is characterized by a completely filled outer electron shell, making them highly stable and unreactive.

Noble gases are colorless, odorless, and tasteless under standard conditions. Their stability arises from the fact that they do not easily gain or lose electrons, which is why they have such low chemical reactivity. This unique property has led to their use in various applications like neon lights, helium balloons, and inert gas environments for conducting sensitive experiments.

• Helium is used in balloons because it is lighter than air.
• Neon is commonly used in bright signs due to its ability to emit light when electrified.

In our original exercise, we find radon (Rn) with an atomic number of 86. The next noble gas in sequence is oganesson (Og), expected to have the atomic number 118, following the same addition logic applied to periodic sequences.

Alkali Metals

Alkali metals are a fascinating group of elements occupying group 1 of the periodic table, which includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Characteristically, these metals are highly reactive, especially with water, due to their single valence electron ready to be shed in chemical reactions.

These metals are typically shiny and have lower melting points compared to most other metals. They are known for their role in biological systems, such as sodium in nerve transmission and potassium in cell function. Alkali metals are stored in oil to prevent reactions with moisture from the air.

• React strongly with water, producing heat and hydrogen gas.
• Form compounds such as salts with halogens.

In our specific context, francium (Fr) is the last known alkali metal, possessing an atomic number of 87. Following the same logic used in understanding the periodic table structures, the next alkali metal would have an atomic number of 119 if a new period begins.