Question

Use the periodic table to determine each quantity. $$ \begin{array}{l}{\text { a. the number of } 3 \text {s electrons in Mg }} \\\ {\text { b. the number of } 3 d \text { electrons in } \mathrm{Cr}} \\ {\text { c. the number of } 4 d \text { electrons in } \mathrm{Y}} \\ {\text { d. the number of } 6 p \text { electrons in } \mathrm{Pb}}\end{array} $$

Short answer

a. 2 3s Electrons in Mg, b. 5 3d Electrons in Cr, c. 1 4d Electron in Y, d. 2 6p Electrons in Pb

Step-by-step solution

- Determine Number of 3s Electrons in Mg

Locate magnesium (Mg) on the periodic table. It is in the third period and second group of the s-block. It has an atomic number of 12, which means it has 12 electrons. Electron configuration of Mg can be written as 1s^2 2s^2 2p^6 3s^2. Therefore, the number of 3s electrons in Mg is 2.

- Determine Number of 3d Electrons in Cr

Locate chromium (Cr) on the periodic table. It is in the fourth period and the d-block of the table. Chromium has an atomic number of 24, implying 24 electrons. The electron configuration for Cr is an exception to the standard order; it is [Ar] 3d^5 4s^1. Hence, there are five 3d electrons in Cr.

- Determine Number of 4d Electrons in Y

Identify yttrium (Y) on the periodic table. It is located in the fifth period and is part of the transition metals in the d-block. Y has an atomic number of 39. The configuration is [Kr] 4d^1 5s^2. Therefore, Y has one 4d electron.

- Determine Number of 6p Electrons in Pb

Find lead (Pb) on the periodic table. It is in the sixth period and in the p-block. Pb has an atomic number of 82. Its electron configuration ends in 6p^2. As a result, Pb has two 6p electrons.

Key concepts

Electron Configuration

Electron configuration is a representation of the distribution of electrons in the atomic orbitals of an atom. It is fundamental to understanding the chemical behavior of elements. Electrons are arranged in shells around the nucleus, and these shells are further divided into subshells called s, p, d, and f. The 'aufbau principle' guides their arrangement, which states that electrons fill orbitals starting from the lowest available energy levels before moving to higher ones.

For example, magnesium (Mg) has an electron configuration of 1s² 2s² 2p⁶ 3s². This indicates that Mg has two electrons in the 3s subshell. However, there are exceptions to the electron filling order, such as chromium (Cr), where the configuration, [Ar] 3d⁵ 4s¹, reflects a more stable arrangement due to half-filled d subshell. Understanding these patterns is crucial for predicting the chemical properties of elements.

Transition Metals

Transition metals are located in the d-block of the periodic table and are known for their ability to form various oxidation states and colored compounds. This is because they have partially filled d orbitals that can accept or donate electrons during chemical reactions.

A characteristic property of transition metals like yttrium (Y) is their complex electron configuration, which, for Y is [Kr] 4d¹ 5s²; indicating a single electron in the 4d orbital. These metals play vital roles in many biological processes and are widely used in industry and technology. Their unique electron configurations contribute to their diversity of uses.

Atomic Structure

Atomic structure refers to the organization of protons, neutrons, and electrons in an atom. At the center is the nucleus, consisting of protons and neutrons, while electrons orbit the nucleus in regions called electron shells.

The atomic number of an element determines its position in the periodic table and represents the number of protons in the nucleus. For instance, lead (Pb) has an atomic number of 82, signifying it has 82 protons and, when neutral, 82 electrons. These electrons are distributed as per the element's electron configuration, ending in 6p² for Pb, implying it has two electrons in the 6p subshell. The atomic structure largely influences the chemical reactivity and properties of the element.

Periodic Table Trends

The periodic table displays elements in order of increasing atomic number and shows recurring trends in their physical and chemical properties. These trends can be predicted by the location of an element in the table. For example, atomic size generally decreases across a period and increases down a group.

Electronegativity, the ability of an atom to attract electrons when forming a compound, generally increases across a period and decreases down a group. Elements like magnesium (Mg) and lead (Pb), although in different groups, show distinct properties based on their position. Mg, being closer to the start of a period, exhibits a smaller size and higher ionization energy than Pb which is near the end of another period. Understanding these trends is essential for explaining the behavior of elements during chemical reactions and their roles in various applications.