Question

An unknown element is a nonmetal and has a valence-electron configuration of \(\mathrm{n} s^{2} \mathrm{n} p^{4}\) a. How many valence electrons does this element have? b. Possible identities for this element include which of the following? $$ \mathrm{Cl}, \mathrm{S}, \mathrm{Pb}, \mathrm{Se}, \mathrm{Cr} $$

Short answer

a. The unknown element has 6 valence electrons. b. Two possible identities for the unknown element are Sulfur (S) and Selenium (Se).

Step-by-step solution

Determine the number of valence electrons

In the given electron configuration, \(\mathrm{n} s^{2} \mathrm{n} p^{4}\), n represents the principal quantum number corresponding to the highest energy level occupied by electrons. For valence electrons, we consider the electrons in the outermost energy level. Thus, the valence electrons in this configuration are those in the s and p orbitals. Valence electrons are given by \(\mathrm{ns^{2}}\) and \(\mathrm{np^{4}}\). To find the total number of valence electrons, sum the exponents 2 and 4: _valence electrons_ = 2 + 4 = 6 a. The unknown element has 6 valence electrons.

Identify possible elements from the given list

Now, let's examine the given elements and determine their valence-electron configurations: 1. Cl (Chlorine) - Group 17 (VIIA); Valence electron configuration: \(\mathrm{3s^2 3p^5}\) 2. S (Sulfur) - Group 16 (VIA); Valence electron configuration: \(\mathrm{3s^2 3p^4}\) 3. Pb (Lead) - Group 14 (IVA); Valence electron configuration: \(\mathrm{6s^2 6p^2}\). Pb is a metal, so it does not fit the criteria of being a nonmetal. 4. Se (Selenium) - Group 16 (VIA); Valence electron configuration: \(\mathrm{4s^2 4p^4}\) 5. Cr (Chromium) - Group 6 (VIB); Valence electron configuration: \(\mathrm{3d^5 4s^1}\). Cr is a metal, so it does not fit the criteria of being a nonmetal. The requirement for this element is that it must be a nonmetal and have valence-electron configuration \(\mathrm{ns^{2} np^{4}}\) with 6 valence electrons. b. Based on the given criteria and the list of elements, two possible identities for the unknown element are Sulfur (S) and Selenium (Se) since both have a valence-electron configuration of \(\mathrm{ns^2 np^4}\) and are nonmetals.

Key concepts

Electron Configuration

The electron configuration of an element details how its electrons are distributed among the various orbitals around the nucleus. Electrons fill orbitals starting from the lowest energy level, following a set of rules known as the Aufbau principle, the Pauli exclusion principle, and Hund’s rule.

Understanding electron configurations is crucial because it helps explain an element’s chemical properties and the types of chemical bonds it can form. Every element has a unique electron configuration that can be predicted using the periodic table.

For instance, when we see a valence electron configuration of 입니다. can predict its chemical properties and reactivity.

Principal Quantum Number

The principal quantum number, symbolized by 'n', indicates the main energy level occupied by an electron within an atom. It defines the approximate distance of an electron from the nucleus and its energy.

입니다. The higher the value of 'n', the higher the energy and the larger the orbitals, which means electrons are more distant from the nucleus.

This concept is critical when determining valence electrons, as only the electrons in the outermost energy level, which corresponds to the highest principal quantum number, are considered.

Chemical Elements

Chemical elements are the simplest forms of matter that cannot be broken down using chemical means. Each element has a unique number of protons in its nucleus, known as the atomic number, which determines its position on the periodic table and its chemical behavior.

Elements are classified into metals, nonmetals, and metalloids based on their physical and chemical properties. For example, nonmetals, which include elements like sulfur (S) and selenium (Se), typically have higher electronegativities and form covalent bonds, whereas metals are good conductors of heat and electricity.

In the step-by-step solution, the distinction between metal and nonmetal is crucial in identifying that the unknown element with the electron configuration 중! 입니다. Knowing the chemical properties, such as nonmetallicity, guides us toward the correct identity of an element.

Periodic Table Groups

The periodic table organizes all known chemical elements into a coherent format where elements are arranged by increasing atomic number. Importantly, the elements are grouped into columns known as groups or families. Elements within the same group share similar chemical properties because they have the same number of valence electrons.

For example, the valence electron configuration of 중! 입니다. Examining element groups on the periodic table allows us to narrow down the search when we’re given a set of properties to match, such as in the exercise where identifying the group tells us about the valence electron configuration and the metal or nonmetal nature of the element.