Problem 41 - Chemistry: The Central Science in SI Units, Global Edition

Question

(a) What is the general relationship between the size of an atom and its first ionization energy? (b) Which element in the periodic table has the largest ionization energy? Which has the smallest?

Step-by-Step Solution

Answer

(a) As the atomic size increases, the ionization energy decreases. This is because larger atoms have their outermost electrons farther from the nucleus and experience less attractive force from the protons in the nucleus, requiring less energy to be removed. (b) The element with the largest ionization energy is Helium (He), while the element with the smallest ionization energy is Francium (Fr).

Step 1: (a) Understanding ionization energy and atomic size

Ionization energy is the energy required to remove an electron from a neutral atom in the gaseous state. Atomic size is the distance from the center of an atom's nucleus to its outermost electron shell.

Step 2: (a) Relationship between atomic size and ionization energy

As the atomic size increases, the ionization energy decreases. This is because the outermost electrons are farther from the nucleus, and thus, they experience less attractive force from the protons in the nucleus. Consequently, it requires less energy to remove an electron from a larger atom as compared to a smaller atom. Now, let's move to the second part of the question.

Step 3: (b) Identifying the element with the largest ionization energy

In the periodic table, ionization energy generally increases as one moves from left to right across a period and decreases as one moves downwards in a group. The reason for this is that when moving from left to right, the number of protons in the nucleus increases, making the positive charge of the nucleus stronger. This increases the attractive force between the nucleus and the electrons, making it harder to remove an electron. The element with the largest ionization energy is the one that has the smallest atomic size and is located in the upper-right corner of the periodic table. The element is Helium (He), located in group 18 and period 1.

Step 4: (b) Identifying the element with the smallest ionization energy

Conversely, the element with the smallest ionization energy is the one that has the largest atomic size and is located in the lower-left corner of the periodic table. The element is Francium (Fr), located in group 1 and period 7. In summary: - There is an inverse relationship between atomic size and ionization energy: as atomic size increases, ionization energy decreases. - The element with the largest ionization energy is Helium (He), while the element with the smallest ionization energy is Francium (Fr).

Key Concepts

Atomic Size

Atomic size refers to the overall shape and size of an atom, determined by the boundary within which an atom's electrons reside. This boundary is not a fixed surface, but rather a space where the probability of finding an electron is highest. The atomic size can be described by atomic radii, which is the distance from the nucleus of an atom to its outermost electron shell. Generally, atomic size can increase with the addition of electrons and energy levels.

In the periodic table, atomic size increases when moving down a group because additional electron shells are added, distancing the outermost electrons from the nucleus. However, moving across a period from left to right results in a decrease in atomic size. This is due to the increasing number of protons in the nucleus, which pulls the electron cloud closer, effectively reducing the size of the atom.

Understanding atomic size helps in predicting how much energy is needed to remove an electron during ionization, as smaller atoms with electrons closer to the nucleus generally require more ionization energy.

Periodic Table

The periodic table is a comprehensive chart organizing all known chemical elements by increasing atomic number, electron configuration, and recurring chemical properties. The layout of the periodic table includes periods (rows) and groups (columns), which help in illustrating trends such as atomic size, ionization energy, and electronegativity.

As you move across a period from left to right, elements exhibit increasing ionization energy due to enhanced nuclear charge from more protons. This increase in positive charge strengthens the attraction between the nucleus and the outer electrons, making it harder to remove an electron, which increases the ionization energy. Conversely, moving down a column decreases ionization energy, due to the larger atomic size and relatively weak attraction of the electrons to the nucleus.

Periodic table trends are a useful tool for predicting the chemical behavior of elements, especially in regards to their ability to gain or lose electrons.

Electrons

Electrons are subatomic particles found outside the nucleus of an atom, carrying a negative charge. They play a crucial role in determining the chemical properties of an atom, as they are involved in forming chemical bonds. Electrons are organized into regions known as electron shells or energy levels, typically represented in their electron configuration.

In the context of ionization energy, the outermost electrons (or valence electrons) are most significant. These are the electrons that participate in chemical reactions and are removed during the ionization process. The easier it is to remove an electron, the lower the ionization energy of an element.

Understanding how electrons behave and interact with the nucleus of their atoms is key to comprehending other atomic properties, such as atomic size and ionization energy. Higher energy levels house electrons that are further from the nucleus, experiencing weaker attraction, and are easier to remove, indicating lower ionization energy. This behavior is predictable based on an element's position on the periodic table.