Question

Identify the element and draw orbital diagrams for elements with these atomic numbers: (a) 22 (b) 18 (c) 33 (d) 35 (e) 25

Short answer

Element 22 (Ti): 1s^2 2s^2 2p^6 3s^2 3p^6 3d^2 4s^2; Element 18 (Ar): 1s^2 2s^2 2p^6 3s^2 3p^6; Element 33 (As): 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^3; Element 35 (Br): 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^5; Element 25 (Mn): 1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^2. Orbital diagrams are drawn based on these configurations following the rules of electron pairing and orbital filling.

Step-by-step solution

Identify the Elements

Using the periodic table, identify the elements with the given atomic numbers. (a) with atomic number 22 is Titanium (Ti), (b) atomic number 18 is Argon (Ar), (c) atomic number 33 is Arsenic (As), (d) atomic number 35 is Bromine (Br), and (e) atomic number 25 is Manganese (Mn).

Determine Electron Configurations

Write down the electron configurations of each element. (a) Ti: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^2 4s^2, (b) Ar: 1s^2 2s^2 2p^6 3s^2 3p^6, (c) As: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^3, (d) Br: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^5, and (e) Mn: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^2.

Construct Orbital Diagrams

Draw the orbital diagrams based on the electron configurations. For each element, fill orbitals in the order of their energy levels, and follow Hund's rule (maximize the number of unpaired electrons) and the Pauli exclusion principle (each orbital can hold a maximum of two electrons with opposite spins).

Key concepts

Electron Configurations

Understanding electron configurations is essential to grasp how atoms form bonds and the properties of elements. An electron configuration is a notation that shows the distribution of electrons among the atomic orbitals in an atom. These configurations are written with numbers indicating the energy level, the type of orbital, and superscripts showing the number of electrons in those orbitals.

For example, consider titanium (Ti) with an atomic number of 22. Its electron configuration is written as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d² 4s². This tells us that the first energy level (n=1) has 2 electrons in the 's' orbital (1s²), and so on until the 'd' and 's' orbitals of the third and fourth energy levels are reached, respectively.

Electron configurations are determined by a combination of principles, including the Aufbau principle, Hund's rule, and the Pauli exclusion principle, which determine the order in which orbitals are filled.

Hund's Rule

Hund's Rule relates to electron configurations and how electrons are distributed among orbitals of the same energy (degenerate orbitals). The rule states that when electrons fill subshells with more than one orbital (like 'p', 'd', or 'f'), one electron goes into each orbital before the second electron is added. The electrons prefer to have their own space and maintain parallel spins as long as possible.

For instance, in the case of manganese (Mn) with an electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s², the 3d subshell has five orbitals. According to Hund's rule, each of the five 3d orbitals will first receive one electron each (all with parallel spins), before any pairing occurs. This rule minimizes the repulsion between electrons, thus stabilizing the atom.

Pauli Exclusion Principle

The Pauli Exclusion Principle is a quantum mechanical concept that has profound implications for the structure and behavior of atoms. This principle states that no two electrons in an atom can have the same set of four quantum numbers. In essence, it means an atomic orbital can hold a maximum of two electrons, and they must have opposite spins.

When constructing electron configurations and orbital diagrams, we apply this principle by representing electrons in the same orbital with arrows pointing in opposite directions. This is evident in the provided exercise's step-by-step solution, where for each element, orbitals are filled according to their energy levels with arrows indicating the electrons' spins. Compliance with the Pauli exclusion principle ensures that we correctly predict electron arrangements and, therefore, the chemical behaviors of atoms.

Periodic Table

The periodic table is more than just a table of elements; it's a powerful tool that encapsulates the essence of chemistry. It organizes all known chemical elements in a systematic way, based on increasing atomic number (the number of protons in the nucleus of an atom). Each element's position in the table is significant and denotes particular properties, such as electronegativity, atomic mass, and reactivity, as well as the electron configuration of its atoms.

Elements in the same column, or group, typically have similar valence electron configurations, leading to similar chemical behaviors. For example, group 18, the noble gases (like argon), all have full outer electron shells, which explains their non-reactive nature. Understanding the arrangement of the periodic table helps in quickly identifying attributes of elements, such as the fact that arsenic (As) is a metalloid due to its position between metals and non-metals in the table, or bromine (Br) being a halogen and thus highly reactive.