Problem 172 - Chemistry An Atoms First Approach

Question

Answer the following questions based on the given electron configurations and identify the elements. a. Arrange these atoms in order of increasing size: \([\mathrm{Kr}] 5 s^{2} 4 d^{10} 5 p^{6} ;[\mathrm{Kr}] 5 s^{2} 4 d^{10} 5 p^{1} ;[\mathrm{Kr}] 5 s^{2} 4 d^{10} 5 p^{3}\). b. Arrange these atoms in order of decreasing first ionization energy: \([\mathrm{Ne}] 3 s^{2} 3 p^{5} ;[\mathrm{Ar}] 4 s^{2} 3 d^{10} 4 p^{3} ;[\mathrm{Ar}] 4 s^{2} 3 d^{10} 4 p^{5}\).

Step-by-Step Solution

Answer

The order of increasing atomic size for the given electron configurations is: Tl < Tm < Hf, and the order of decreasing first ionization energy is: Cl > Br > As.

Step 1: Identify the elements from their electron configurations

The first task is to find the elements corresponding to the given electron configuration. Using the periodic table, we can find the elements as follows: 1. \([\mathrm{Kr}] 5 s^{2} 4 d^{10} 5 p^{6}\): This element has the electron configuration of krypton, with 2 extra electrons in the 5s orbital, 10 in the 4d orbital, and 6 in the 5p orbital. The total number of electrons equals 54 (Kr) + 2 (5s) + 10 (4d) + 6 (5p) = 72. The element with 72 electrons is Hafnium (Hf). 2. \([\mathrm{Kr}] 5 s^{2} 4 d^{10} 5 p^{1}\): This element has the electron configuration of krypton, with 2 extra electrons in the 5s orbital, 10 in the 4d orbital, and 1 in the 5p orbital. The total number of electrons equals 54 (Kr) + 2 (5s) + 10 (4d) + 1 (5p) = 67. The element with 67 electrons is Thallium (Tl). 3. \([\mathrm{Kr}] 5 s^{2} 4 d^{10} 5 p^{3}\): This element has the electron configuration of krypton, with 2 extra electrons in the 5s orbital, 10 in the 4d orbital, and 3 in the 5p orbital. The total number of electrons equals 54 (Kr) + 2 (5s) + 10 (4d) + 3 (5p) = 69. The element with 69 electrons is Thulium (Tm).

Step 2: Compare the elements in terms of atomic size

Now that we have identified the elements, we can arrange them by increasing atomic size. The atomic size increases down a group and decreases across a period (from left to right) in the periodic table. Since all three elements are in the same period, their atomic size will decrease from left to right. Therefore, the order of increasing atomic size is: Tl < Tm < Hf b. Arrange these atoms in order of decreasing first ionization energy:

Step 1: Identify the elements from their electron configurations

The same procedure as before, we identify the elements corresponding to the given electron configurations: 1. \([\mathrm{Ne}] 3 s^{2} 3 p^{5}\): This element has the electron configuration of neon, with 2 extra electrons in the 3s orbital and 5 in the 3p orbital. The total number of electrons equals 10 (Ne) + 2 (3s) + 5 (3p) = 17. The element with 17 electrons is Chlorine (Cl). 2. \([\mathrm{Ar}] 4 s^{2} 3 d^{10} 4 p^{3}\): This element has the electron configuration of argon, with 2 extra electrons in the 4s orbital, 10 in the 3d orbital, and 3 in the 4p orbital. The total number of electrons equals 18 (Ar) + 2 (4s) + 10 (3d) + 3 (4p) = 33. The element with 33 electrons is Arsenic (As). 3. \([\mathrm{Ar}] 4 s^{2} 3 d^{10} 4 p^{5}\): This element has the electron configuration of argon, with 2 extra electrons in the 4s orbital, 10 in the 3d orbital, and 5 in the 4p orbital. The total number of electrons equals 18 (Ar) + 2 (4s) + 10 (3d) + 5 (4p) = 35. The element with 35 electrons is Bromine (Br).

Step 2: Compare the elements in terms of first ionization energy

First ionization energy, the energy required to remove the outermost electron, generally increases across a period (from left to right) and decreases down a group in the periodic table. Since all three elements are in the same period, their ionization energy will increase from left to right. Therefore, the order of decreasing first ionization energy is: Cl > Br > As

Key Concepts

Periodic Table

The periodic table is a chart that organizes all known chemical elements in a structured way. Each element is placed according to its atomic number, electron configurations, and recurring chemical properties. Elements are arranged in rows called periods and columns called groups or families. This systematic organization helps to predict an element's chemical behavior based on its position.

For instance, as you move from left to right across a period in the periodic table, each element has a higher atomic number and typically a smaller atomic size due to increasing nuclear charge attracting the electron cloud more strongly. Conversely, moving down a group usually increases atomic size since additional electron shells are added.

Key takeaways include:

• Periods are horizontal rows in the periodic table.
• Groups are vertical columns with elements having similar chemical properties.
• Atomic number increases from left to right and top to bottom.

Understanding the layout of the periodic table is crucial for interpreting electron configurations and predicting elements' behaviors.

Atomic Size

Atomic size, or atomic radius, refers to the distance from the nucleus of an atom to the outermost shell of electrons. It is an important parameter because it affects how atoms interact with each other. Generally, the atomic size decreases from left to right across a period due to increased nuclear charge pulling electrons closer. On the other hand, it increases down a group as more electron shells are added, making the atom larger.

This trend in atomic size is important for predicting how elements might bond or react with one another. In the given exercise, the elements hafnium, thallium, and thulium were compared based on their atomic size. Knowing that these are arranged across a period, the trend of decreasing atomic size from thallium to hafnium could be expected.

Points to remember:

• Atomic size decreases across a period from left to right.
• Atomic size increases down a group.
• Comprehending atomic size trends aids in predicting reactivity and bonding characteristics.

Ionization Energy

Ionization energy is the energy required to remove the outermost electron from a neutral atom in the gaseous state. This concept is crucial in understanding how atoms participate in chemical reactions. Across a period, ionization energy generally increases with rising nuclear charge, as the electrons are more tightly bound to the nucleus. In contrast, ionization energy decreases down a group because the outer electrons are further from the nucleus and are less tightly held.

In the step-by-step solution, we saw how ionization energies for chlorine, bromine, and arsenic were compared. Since these elements are in the same period, their ionization energy trends upward, placing the less reactive chlorine highest in ionization energy due to a more substantial ability to hold onto its electrons.

Remember these key trends:

• Ionization energy increases from left to right across a period.
• Ionization energy decreases down a group.
• Higher ionization energy often means less reactivity.

Understanding ionization energy helps explain the reactivity of different elements.

Chemistry

Chemistry is the scientific discipline that studies substances, their properties, and the changes they undergo. It seeks to understand the composition of matter and the principles governing its interactions and transformations. By utilizing basic units like atoms and molecules, chemistry explores everything from the simple interactions of hydrogen and oxygen forming water to complex organic reactions in living organisms.

The concepts of electron configuration, atomic size, and ionization energy are fundamental in chemistry. They help explain how elements will react and bond with each other. In the exercise, these concepts were vital for identifying and comparing elements using electron configurations and predicting chemical behaviors based on their trends on the periodic table.

Key insights include:

• Electron configurations determine how elements interact.
• Understanding periodic trends allows prediction of chemical properties and reactivities.
• Chemistry spans a wide range of topics from basic atomic study to complex organic reactions.

The essence of chemistry lies in explaining how the world works on an atomic and molecular level.