Problem 9 - Chemistry: The Central Science

Question

(a) True or false: An element's number of valence electrons is the same as its atomic number. (b) How many valence electrons does a nitrogen atom possess? (c) An atom has the electron configuration \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{2}\). How many valence electrons does the atom have?

Step-by-Step Solution

Answer

(a) False: An element's number of valence electrons is not the same as its atomic number. (b) Nitrogen possesses \(5\) valence electrons. (c) The atom with electron configuration \(1s^2 2s^2 2p^6 3s^2 3p^2\) has \(4\) valence electrons.

Step 1: Answer (a): Analyzing the Relationship between Valence Electrons and Atomic Numbers

The atomic number of an element represents the number of protons in the nucleus of an atom. Meanwhile, valence electrons are the electrons in an atom's outermost electron shell. The number of valence electrons determines an element's chemical properties and reactivity. It is crucial to understand that the atomic number does not directly correspond to the number of valence electrons. The number of valence electrons can be found using the periodic table and identifying the group number (column) of the element. Hence, the statement is false.

Step 2: Answer (b): Finding Valence Electrons in Nitrogen

Since we've established that the number of valence electrons is not equal to the atomic number, we need to find the number of valence electrons in a nitrogen atom. Nitrogen's atomic number is \(7\), which means it has \(7\) protons and \(7\) electrons. To determine the number of valence electrons, we can analyze nitrogen's position in the periodic table. Nitrogen belongs to Group \(15\) (also known as Group \(5A\)). Elements in Group \(15\) have \(5\) valence electrons. Therefore, nitrogen possesses \(5\) valence electrons.

Step 3: Answer (c): Analyzing Electron Configuration for Valence Electrons

To find the number of valence electrons in the given electron configuration (\(1s^2 2s^2 2p^6 3s^2 3p^2\)), we need to identify the electrons in the atom's outermost shell. In this case, the outermost shell is the third shell, which consists of both 3s and 3p subshells. The 3s subshell has \(2\) electrons, and the 3p subshell has \(2\) electrons. Adding these together, the atom has \(2 + 2 = 4\) valence electrons.

Key Concepts

Atomic Number

The atomic number is a fundamental concept in chemistry. It represents the number of protons found in the nucleus of an atom. This number not only identifies the element but also helps in understanding the arrangement of electrons in an atom.

Each element on the periodic table has a unique atomic number. For instance, nitrogen has an atomic number of 7, meaning every nitrogen atom is comprised of 7 protons. Concepts related to atomic numbers serve as a foundation for more complex topics in atomic structure.

However, the atomic number alone does not dictate the number of valence electrons. Valence electrons are located in the outermost shell of an atom and play a crucial role in chemical bonding and reactivity. This is why understanding the placement of elements in the periodic table is essential, as it assists in determining the valence electrons.

Electron Configuration

Electron configuration describes the distribution of electrons among the various orbitals in an atom. It helps understand how electrons populate different energy levels and subshells following the rules of quantum mechanics.

To determine the electron configuration of an element, it's helpful to start at the beginning of the periodic table and "build up" each element by adding electrons one by one across increasing energy levels. The configuration helps predict an element's chemical properties and bonding behavior.

• The notation begins with the lowest energy level (n=1) and follows the sequence s, p, d, and f subshells.
• Subshells are written with the number corresponding to their energy level and the number of electrons they contain. For example, in the electron configuration for nitrogen \(1s^2 2s^2 2p^3\), the orbitals in the 2nd energy level contain five electrons total.

Understanding the electron configuration is essential for predicting the arrangement of electrons and identifying valence electrons, which are the electrons available for forming chemical bonds.

Periodic Table

The periodic table is a powerful tool in chemistry that organizes all known elements in order of increasing atomic number. It showcases trends in chemical properties and electron configurations in a structured layout.

Each row in the periodic table corresponds to a principal energy level, while each column represents a group or family of elements sharing similar characteristics. Notably, elements within the same group often have the same number of valence electrons.

• Group numbers can be used to determine the number of valence electrons. For example, elements in Group 15, like nitrogen, have five valence electrons.
• The table also allows easy visualization of trends, such as atomic size and electronegativity, as you move across periods and down groups.

For students and chemists alike, using the periodic table effectively can provide insights into elemental behavior and chemical reactivity.