Question

Which of the following properties show a clear periodic variation: (a) first ionization energy, (b) molar mass of the elements, (c) number of isotopes of an element, (d) atomic radius?

Short answer

(a) First ionization energy and (d) atomic radius show clear periodic variation.

Step-by-step solution

Identify Periodic Properties

In this step, we will discuss what periodic properties are. Periodic properties are those that show a repeating pattern or trend across periods (rows) and groups (columns) of the periodic table. Common periodic properties include ionization energy and atomic radius, as these properties are influenced by the arrangement of electrons around the nucleus.

Analyze Each Given Property

Let's examine each property to determine if it has a periodic variation: (a) First Ionization Energy: The energy required to remove the outermost electron. The first ionization energy typically increases across a period and decreases down a group, showing a clear periodic trend. (b) Molar Mass: This is the mass of one mole of a substance. Molar mass increases with increasing atomic number and does not show periodic variation. (c) Number of Isotopes: This value varies without a predictable pattern; elements can have varying numbers of isotopes, and this does not follow a periodic trend. (d) Atomic Radius: The distance from the nucleus to the outer boundary of the electron cloud. Atomic radius decreases across a period and increases down a group, showing a periodic trend.

Select Properties with Periodic Variation

From the analysis: - First Ionization Energy shows periodic variation. - Atomic Radius also shows periodic variation. Thus, the properties that exhibit a clear periodic variation are first ionization energy and atomic radius.

Key concepts

Ionization Energy

Ionization energy refers to the amount of energy required to remove the outermost electron from a gaseous atom or ion. This property exhibits a clear periodic trend, reflected in the arrangement of the periodic table. The first ionization energy typically increases as you move across a period from left to right. This increase is due to the increasing positive charge of the nucleus, which holds the electrons more tightly. Thus, more energy is needed to remove an electron.

As you move down a group in the periodic table, the ionization energy decreases. This happens because the outermost electron is farther from the nucleus, thanks to added electron shells, which results in a weaker attraction between the nucleus and the outermost electrons. This makes it easier to remove an electron.

• Periodic Trend: increases across a period, decreases down a group
• Influence: Number of protons and electron shielding
• Importance: Determines reactivity and chemical properties of an element

Atomic Radius

Atomic radius is the measure of the size of an atom from its nucleus to the outer boundary of its electron cloud. It is another property that shows a periodic trend. As we observe the periodic table, the atomic radius decreases from left to right across a period. This decrease is due to the increasing nuclear charge, which pulls the electron cloud closer to the nucleus, making the atom smaller.

Conversely, when traveling down a group, the atomic radius increases. This increase results from the addition of electron shells. Each added shell places the outermost electrons further from the nucleus, leading to a larger atomic radius.

• Periodic Trend: decreases across a period, increases down a group
• Effect: Increased nuclear charge and additional electron shells
• Significance: Influences chemical bonding and element interaction

Molar Mass

Molar mass is defined as the mass of one mole of a substance, typically expressed in grams per mole. Unlike ionization energy and atomic radius, molar mass does not exhibit a periodic trend. Instead, it continuously increases as you move down the periodic table.

Molar mass is directly related to the atomic number of an element, which increases in a linear fashion from left to right and top to bottom in the periodic table. Each additional proton and neutron contribute to a higher molar mass, making it non-periodic.

• Relationship: Increases with atomic number
• Use: Important for stoichiometry and calculating amounts in chemistry
• Non-periodic: No repetition across periods or groups