Question

Write electron configurations for these atoms. (a) Strontium (Sr), named for a town in Scotland. (b) Tin (Sn), a metal used in the ancient world. Alloys of tin (solder, bronze, and pewter) are important.

Short answer

Sr: \[ 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 \] ; Sn: \[ 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^2 \]

Step-by-step solution

Identify the Atomic Number

First, we need to identify the atomic number of each element. For Strontium (Sr), the atomic number is 38. For Tin (Sn), the atomic number is 50.

Understand Electron Configuration Basics

Electron configuration describes the distribution of electrons among the various atomic orbitals. The order of orbital filling is determined by the Aufbau principle, and the configuration is written according to the increasing order of energy levels: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, and so on.

Write Electron Configuration for Strontium (Sr)

Begin filling electrons according to the order of orbital energies, starting with 1s. Strontium has 38 electrons: 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s². So, the complete electron configuration for Strontium is: \[ \text{Sr: } 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 \]

Write Electron Configuration for Tin (Sn)

Now, do the same for Tin, which has 50 electrons: 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p². Therefore, the electron configuration for Tin is:\[ \text{Sn: } 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^2 \]

Key concepts

Atomic Number

The atomic number is a fundamental property of an element, defining the number of protons in the nucleus of an atom. Essentially, it determines the identity of an element. This number also equals the number of electrons in a neutral atom. Remember, electrons have a negative charge that balances the positive charge of the protons. The atomic number is unique for each element, allowing us to distinguish between different elements.
For example:

• Strontium (Sr) has an atomic number of 38, meaning it has 38 protons and, in its neutral form, 38 electrons.
• Tin (Sn) carries an atomic number of 50, thus having 50 protons and 50 electrons when neutral.

Understanding atomic numbers is crucial for writing electron configurations, as it tells us how many electrons we need to place into the available atomic orbitals.

Aufbau Principle

The Aufbau Principle is an essential rule in chemistry. It helps us figure out the electron arrangement within an atom in a specific order. According to this principle, electrons fill atomic orbitals of the lowest energy first before moving on to higher energy levels. This filling order is often remembered by the sequence: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, and so forth.
The Aufbau principle ensures that electrons are added in a way that creates the lowest possible energy configuration for the atom.

• For Strontium (Sr), we start filling from the 1s orbital and continue according to the order, resulting in its electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s².
• For Tin (Sn), similarly, we fill up to 5p², giving: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p².

This principle is vital to correctly assigning electrons to their respective orbitals based on energy levels.

Atomic Orbitals

Atomic orbitals are regions around an atom's nucleus where electrons are likely to be found. Each orbital can hold a specific number of electrons and has a distinct shape and energy level. Orbitals are organized into different types based on their shapes: s, p, d, and f.

• The **s-orbital** is spherical and can hold up to 2 electrons.
• The **p-orbitals** are dumbbell-shaped, exist in sets of three (
• The **d-orbitals** have more complex shapes and occur in sets of five, accommodating up to 10 electrons.
• Finally, the **f-orbitals**, known for even more complex shapes, occur in sets of seven, holding up to 14 electrons.

The concept of atomic orbitals is critical in understanding the distribution of electrons in an atom. This distribution is depicted by the electron configuration which is determined by filling these orbitals in the order prescribed by the Aufbau principle.