Problem 115 - Chemistry Matter and Change

Question

What element has the electron configuration \([\mathrm{Ar}] 4 \mathrm{s}^{1} 3 \mathrm{d}^{5} ?(\text {Chapter } 5)\)

Step-by-Step Solution

Answer

The element with the electron configuration \([\mathrm{Ar}] 4 \mathrm{s}^{1} 3 \mathrm{d}^{5}\) is Chromium (Cr).

Step 1: Identify the core electron configuration of Argon

To find the core electron configuration of Argon, we need to locate it on the periodic table. Argon (Ar) has 18 electrons and is in group 18 (VIII) and period 3. Its electron configuration is \[1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6}\] which corresponds to the \([\mathrm{Ar}]\) notation.

Step 2: Add the specified valence electrons

Now we have to include the given valence electrons in the given electron configuration \([\mathrm{Ar}] 4 \mathrm{s}^{1} 3 \mathrm{d}^{5}\). Adding these valence electrons to argon's core electron configuration, we get: \[1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{1} 3d^{5}\]

Step 3: Determine the total number of electrons

Count the total number of electrons in this electron configuration: 2 (1s) + 2 (2s) + 6 (2p) + 2 (3s) + 6 (3p) + 1 (4s) + 5 (3d) = 24 electrons

Step 4: Identify the element with 24 electrons

To find the element that corresponds to this electron configuration, look for the element with an atomic number of 24 in the periodic table. The element with 24 electrons is Chromium (Cr), which is in group 6 (VI) and period 4. The answer is: Chromium (Cr) has the electron configuration \([\mathrm{Ar}] 4 \mathrm{s}^{1} 3 \mathrm{d}^{5}\).

Key Concepts

Chromium

Chromium is a fascinating element, primarily known for its unique electron configuration. Its electron configuration is represented as \([\mathrm{Ar}] 4 \mathrm{s}^{1} 3 \mathrm{d}^{5}\). This might seem a bit unusual compared to the expected \([\mathrm{Ar}] 4 \mathrm{s}^{2} 3 \mathrm{d}^{4}\). The reason for this configuration is chromium's tendency to achieve a more stable, lower-energy state. This involves having a half-filled \(3d\) subshell, which is more stable than other possible configurations.

Chromium is located in group 6 on the periodic table and has an atomic number of 24. This indicates that it has 24 electrons and is situated in period 4.

• Chromium's shiny appearance makes it valuable in decorative and industrial uses.
• It is also known for its high corrosion resistance and hardness, making it useful in the manufacturing of stainless steel and other alloys.

Understanding chromium's electron configuration helps us explain its chemical properties and behavior.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial in determining how an element will react with others. In the case of chromium, it has only one electron in the \(4s\) orbital and five electrons in the \(3d\) orbital after argon’s core configuration. These electrons are considered its valence electrons because they are involved in bonding and chemical reactions.

The unique electron configuration of chromium, with one electron in the \(4s\) orbital, is an exception to the usual pattern seen in other elements nearby on the periodic table. This is because the \(3d\) subshell is stabilized by having a half-filled configuration, which provides chromium with distinctive properties such as multiple oxidation states. These characteristics are important for its role in various chemical reactions and its use in industrial applications.

• It can have oxidation states ranging from +1 to +6, although +3 and +6 are the most common.
• This variability makes it versatile in forming compounds and being an essential part of different catalysts.

Periodic Table

The periodic table is a systematic arrangement of elements, organized based on their atomic number, electron configuration, and recurring chemical properties. It is a crucial tool for understanding how elements interact and predicting their behavior.

Each element on the periodic table has a unique electron configuration that provides information about its chemical properties and reactivity. For instance, chromium's position in group 6 and period 4 reflects its electron configuration which is unlike many others in its row and group.

• Groups, or columns, in the periodic table indicate elements with similar valence electron configurations and similar chemical properties.
• Periods, or rows, represent elements with the same number of electron shells. As you move across a period, each element gains one more proton in the nucleus and one more electron in the outer shell.

The arrangement of the periodic table allows chemists to easily identify patterns and make predictions about elements' behavior during chemical reactions. Understanding chromium's specific place helps us to infer much about its chemical attributes and potential use.