Problem 74 - Chemistry: The Central Science in SI Units, Global Edition

Question

For each element, indicate the number of valence electrons, core electrons, and unpaired electrons in the ground state: (a) sodium, (b) sulfur, (c) fluorine.

Step-by-Step Solution

Answer

In summary: a) Sodium: - Valence electrons: 1 - Core electrons: 10 - Unpaired electrons: 1 b) Sulfur: - Valence electrons: 6 - Core electrons: 10 - Unpaired electrons: 2 c) Fluorine: - Valence electrons: 7 - Core electrons: 2 - Unpaired electrons: 1

Step 1: Electron Configuration

Sodium has an atomic number of 11, which means it has 11 electrons. The electron configuration for sodium in its ground state is 1s²2s²2p⁶3s¹. Step 2: Identify the valence and core electrons

Step 2: Valence and Core Electrons

The valence electrons are the electrons in the outermost energy level. In this case, there is only one valence electron (3s¹). The remaining 10 electrons are core electrons (1s²2s²2p⁶). Step 3: Determine the unpaired electrons

Step 3: Unpaired Electrons

Sodium has only one unpaired electron in its 3s orbital. a) Summary for Sodium: - Valence electrons: 1 - Core electrons: 10 - Unpaired electrons: 1 b) Sulfur Step 1: Determine the electron configuration

Step 4: Electron Configuration

Sulfur has an atomic number of 16, which means it has 16 electrons. The electron configuration for sulfur in its ground state is 1s²2s²2p⁶3s²3p⁴. Step 2: Identify the valence and core electrons

Step 5: Valence and Core Electrons

The valence electrons are the electrons in the outermost energy level. In this case, there are six valence electrons (3s²3p⁴). The remaining 10 electrons are core electrons (1s²2s²2p⁶). Step 3: Determine the unpaired electrons

Step 6: Unpaired Electrons

Sulfur has two unpaired electrons in its 3p orbitals. b) Summary for Sulfur: - Valence electrons: 6 - Core electrons: 10 - Unpaired electrons: 2 c) Fluorine Step 1: Determine the electron configuration

Step 7: Electron Configuration

Fluorine has an atomic number of 9, which means it has 9 electrons. The electron configuration for fluorine in its ground state is 1s²2s²2p⁵. Step 2: Identify the valence and core electrons

Step 8: Valence and Core Electrons

The valence electrons are the electrons in the outermost energy level. In this case, there are seven valence electrons (2s²2p⁵). The remaining two electrons are core electrons (1s²). Step 3: Determine the unpaired electrons

Step 9: Unpaired Electrons

Fluorine has one unpaired electron in its 2p orbitals. c) Summary for Fluorine: - Valence electrons: 7 - Core electrons: 2 - Unpaired electrons: 1

Key Concepts

Electron Configuration

Understanding electron configuration is crucial for determining the distribution of electrons in an atom. Each atom has a number of electrons equal to its atomic number, and these electrons occupy various energy levels or shells around the nucleus. The electron configuration is a method of writing out these energy levels to showcase how electrons are arranged.

Typically, electrons fill the available orbital spaces in a predictable pattern based on energy levels and subshells: 1s, 2s, 2p, 3s, 3p, and so on, following the Aufbau principle. Let's illustrate this with examples:

• **Sodium (Na)**: With an atomic number of 11, the configuration is 1s²2s²2p⁶3s¹.
• **Sulfur (S)**: Atomic number 16 makes its configuration 1s²2s²2p⁶3s²3p⁴.
• **Fluorine (F)**: With an atomic number of 9, its configuration is 1s²2s²2p⁵.

This step-by-step fill allows us to easily determine other electron properties, such as those involving core and valence electrons.

Core Electrons

Core electrons refer to the electrons not involved in chemical bonding. They reside in the inner shells, beneath the valence shell, and are generally more stable due to being closer to the nucleus.

These electrons effectively shield the valence electrons from the full charge of the nucleus, making them less reactive compared to valence electrons. Here's how to determine core electrons for each element mentioned:

• Sodium: 10 core electrons (1s²2s²2p⁶).
• Sulfur: 10 core electrons (1s²2s²2p⁶).
• Fluorine: 2 core electrons (1s²).

Core electrons remain constant for elements in the same period until a new energy shell starts being filled, then the count of core electrons includes these previously unpaired, unstable configurations.

Unpaired Electrons

Unpaired electrons play an essential role in determining an element's magnetic properties and reactivity. These are electrons that do not pair up with another electron in an orbital.
The presence of unpaired electrons can make an atom or a molecule paramagnetic (attracted to magnetic fields). To identify unpaired electrons, you should observe the electron configuration:

• Sodium: 1 unpaired electron in the 3s orbital.
• Sulfur: 2 unpaired electrons located in two of the 3p orbitals.
• Fluorine: 1 unpaired electron in the 2p orbital.

It's critical to remember that unpaired electrons matter particularly in transitions between elements or bonding scenarios. For instance, having an unpaired electron can increase the likelihood of forming ionic or covalent bonds. Observing these electrons helps chemists predict and explain the behavior of elements in different chemical reactions.