Question

Write the electron configuration for each of the following elements. (a) silicon (b) lithium (c) magnesium

Short answer

Electron configurations are Silicon (Si) - \(1s^2, 2s^2, 2p^6, 3s^2, 3p^2\), Lithium (Li) - \(1s^2, 2s^1\), Magnesium (Mg) - \(1s^2, 2s^2, 2p^6, 3s^2\).

Step-by-step solution

Identify the Atomic Number

Find each element's atomic number on the periodic table. The atomic numbers are: Silicon (Si) - 14, Lithium (Li) - 3, Magnesium (Mg) - 12.

Electron Configuration for Silicon

Silicon has 14 electrons. Writing the electron configuration, we follow the order defined by the Aufbau principle. The electron configuration for Silicon (Si) is \(1s^2, 2s^2, 2p^6, 3s^2, 3p^2\). This configuration shows that there are 2 electrons in the 1s subshell, 2 electrons in the 2s subshell, 6 in the 2p subshell, 2 in the 3s subshell, and finally 2 in the 3p subshell.

Electron Configuration for Lithium

Lithium has 3 electrons. The Aufbau principle sets the electron filling order. The electron configuration for Lithium (Li) is \(1s^2, 2s^1\). This configuration shows that there are 2 electrons in the 1s subshell, and 1 electron in the 2s subshell.

Electron Configuration for Magnesium

Magnesium has 12 electrons. As per the Aufbau principle, the electron configuration for Magnesium (Mg) is \(1s^2, 2s^2, 2p^6, 3s^2\). This configuration shows that there are 2 electrons in the 1s orbital, 2 in the 2s, 6 in the 2p, and 2 in the 3s orbital.

Key concepts

Understanding the Aufbau Principle for Electron Configuration

Learning the electron configuration of elements is crucial for understanding their chemical properties and behavior. One of the foundational principles guiding electron configuration is the Aufbau Principle. According to the Aufbau Principle, electrons fill orbitals starting at the lowest available energy level before moving to higher levels.

Imagine the energy levels within an atom as a building with floors; electrons would fill the rooms from the ground floor up. This orderly progression moves through the orbitals in the following sequence: 1s, 2s, 2p, 3s, and so forth. Each orbital can only hold a set number of electrons: two electrons in s orbitals, six in p orbitals, ten in d orbitals, and fourteen in f orbitals.

Applying the Aufbau Principle

Referring back to the exercise, silicon (Si) with an atomic number 14 fills each energy level according to the Aufbau Principle: beginning with 1s, following with 2s, then 2p, and so on until all 14 electrons are accounted for. This results in the electron configuration of Si as: 1s², 2s², 2p⁶, 3s², 3p². Following this orderly progression is essential in ensuring accurate electron configuration for elements.

Navigating the Periodic Table

The periodic table is a systematic arrangement of the chemical elements, organized on the basis of their atomic numbers, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number, which is the count of protons within an atom's nucleus; it is also equivalent to the electron count in a neutral atom.

The table is divided into periods (horizontal rows) and groups/families (vertical columns). Each row signifies a new energy level for electrons. Consequently, elements in the same group exhibit similar chemical behavior due to the same valence electron configurations, for instance, the alkaline metals in group 1 or the noble gases in group 18.

Using the Periodic Table for Electron Configuration

Whenever you're completing an exercise for electron configuration, the periodic table becomes a key tool. For example, when identifying the electron configuration of magnesium (Mg) with its atomic number of 12, refer to its position on the periodic table. This will indicate that magnesium is in the third period and the second group, which leads to its electron arrangement as: 1s², 2s², 2p⁶, 3s².

The Significance of Atomic Number

The atomic number of an element is perhaps the most fundamental characteristic that defines an element's identity. It is denoted by the letter 'Z' and represents the number of protons present in the nucleus of an atom. Since elements are defined by the number of protons they possess, the atomic number is unique to each element and determines its position in the periodic table.

The atomic number also tells us about the number of electrons in a neutral atom. For instance, lithium has an atomic number of 3, which means that a neutral lithium atom contains 3 electrons.

Importance in Electron Configuration

Knowing the atomic number is essential when writing the electron configuration for an element. For lithium, with its atomic number of 3, the electron configuration would begin by filling the 1s orbital followed by the 2s orbital, resulting in the notation: 1s², 2s¹. This atomic number acts as a guide for determining how the electrons are distributed across different orbitals in line with the Aufbau Principle.