Question

For each of the following pairs, indicate which element has the smaller first ionization energy: (a) Ti, Ba; (b) Ag, Cu; (c) Ge, Cl; (d) Pb, Sb.

Short answer

The elements with the smaller first ionization energies in each pair are: (a) Ba, (b) Ag, (c) Ge, and (d) Pb.

Step-by-step solution

Pair (a): Ti, Ba

Ti is found in Group 4 and Period 4, while Ba is in Group 2 and Period 6. Since Ba is further down the periodic table, it will have a smaller ionization energy. The element with the smaller first ionization energy is Ba.

Pair (b): Ag, Cu

Ag and Cu are both in Group 11. Ag is in Period 5, while Cu is in Period 4. Since Ag is in a lower period, it will have a smaller ionization energy. The element with the smaller first ionization energy is Ag.

Pair (c): Ge, Cl

Ge and Cl are both in Period 4. Ge is in Group 14, while Cl is in Group 17. Since Ge is to the left of Cl in the periodic table, it will have a smaller ionization energy. The element with the smaller first ionization energy is Ge.

Pair (d): Pb, Sb

Pb is found in Group 14 and Period 6, while Sb is in Group 15 and Period 5. Since Pb is further down the periodic table (despite being one group to the left of Sb), it will have a smaller ionization energy. The element with the smaller first ionization energy is Pb.

Key concepts

Periodic Table Trends

The periodic table displays elements in an organized manner, where each row is called a 'period' and each column a 'group'. One essential trend to understand is the change in first ionization energy as we move across or down the table.

Ionization energy is the energy required to remove an electron from an atom in its gaseous phase. Typically, the first ionization energy increases as we move from left to right across a period due to the increasing positive charge in the nucleus which attracts electrons more strongly. Conversely, as we go down a group, the ionization energy decreases. This happens because additional electron shells are added, which shield the outer electrons from the nucleus, making them easier to remove.

Understanding these trends helps us predict the reactivity and bonding behavior of elements. For instance, elements with low ionization energies tend to lose electrons easily and participate in ionic bonds, while those with higher ionization energies are less likely to give up electrons and may form covalent bonds instead.

Atomic Structure

The atomic structure of an element greatly influences its ionization energy. Atoms consist of a nucleus, containing protons and neutrons, surrounded by electrons in various shells. The number of protons (the atomic number) defines the element.

However, it's not just the number of protons that matters, but also the electron configuration. Elements strive for a stable configuration, which typically resembles that of noble gases. The valence electrons, those in the outermost shell, are the ones involved during ionization. Elements that are close to achieving a full valence shell (like those on the right side of the periodic table) generally have higher ionization energies because losing an electron would make them less stable.

When looking at elements within the same group, the number of inner electron shells plays a role in shielding the outer electrons from the pull of the nucleus. This shielding effect influences ionization energy alongside the effective nuclear charge—the net positive charge experienced by the valence electrons.

Chemical Properties

Chemical properties of an element are deeply connected to its first ionization energy. Elements with smaller ionization energies tend to be metals because they can easily lose an outer electron to form positive ions, or cations. This is why metals are often good conductors of electricity and heat; the delocalized electrons are free to move and carry energy.

On the other hand, elements with higher ionization energies, such as nonmetals, show reluctance to lose electrons and often gain electrons in reactions, forming anions. Across the periodic table, nonmetals are found on the right side, and their higher ionization energies contribute to properties like higher electronegativities and the tendency to form negative ions.

A knowledge of these properties allows for a better understanding of reaction mechanisms and the predictability of an element's behavior in chemical processes, which is fundamental to various scientific disciplines, from analytical chemistry to pharmacology.