Problem 21 - Chemistry Matter and Change

Question

Write ground-state electron configurations for the following elements. a. bromine (Br) c. antimony (Sb) e. terbium (Tb) b. strontium (Sr) d. rhenium (Re) f. titanium (Ti)

Step-by-Step Solution

Answer

a. Br: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵ b. Sr: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² c. Sb: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p³ d. Re: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d⁵ e. Tb: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁹ f. Ti: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d²

Step 1: a. Bromine (Br)

Bromine has an atomic number of 35, meaning it has 35 electrons. We'll follow the order of the periodic table and fill the orbitals accordingly. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵ This is the ground-state electron configuration of bromine (Br).

Step 2: b. Strontium (Sr)

Strontium has an atomic number of 38, meaning it has 38 electrons. We'll follow the order of the periodic table and fill the electron orbitals accordingly. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² This is the ground-state electron configuration of strontium (Sr).

Step 3: c. Antimony (Sb)

Antimony has an atomic number of 51, meaning it has 51 electrons. We'll follow the order of the periodic table and fill the electron orbitals accordingly. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p³ This is the ground-state electron configuration of antimony (Sb).

Step 4: d. Rhenium (Re)

Rhenium has an atomic number of 75, meaning it has 75 electrons. We'll follow the order of the periodic table and fill the electron orbitals accordingly. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d⁵ This is the ground-state electron configuration of rhenium (Re).

Step 5: e. Terbium (Tb)

Terbium has an atomic number of 65, meaning it has 65 electrons. We'll follow the order of the periodic table and fill the electron orbitals accordingly. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁹ This is the ground-state electron configuration of terbium (Tb).

Step 6: f. Titanium (Ti)

Titanium has an atomic number of 22, meaning it has 22 electrons. We'll follow the order of the periodic table and fill the electron orbitals accordingly. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d² This is the ground-state electron configuration of titanium (Ti).

Key Concepts

The Periodic Table

The periodic table is a tabular arrangement of the chemical elements, organized based on their atomic number, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number, which is the number of protons in an atom's nucleus.

The table has rows called periods and columns known as groups. Elements within the same group typically have similar properties and electron configurations in their outer shell. Understanding the periodic table's layout helps with predicting the behavior of elements, their possible chemical reactions, and bonding patterns.

The periodic table is split into blocks, such as the s, p, d, and f blocks, which tells us where to find the outermost electrons of the elements. In learning about electron configurations, one must become familiar with the arrangement and logic of the periodic table as it directly influences how electrons are distributed in atoms.

Atomic Number

The atomic number is a fundamental characteristic of an element and defines the type of atom. It is equal to the number of protons in the nucleus of an atom and, in a neutral atom, also equals the number of electrons orbiting the nucleus. This number is crucial because it controls the chemical behavior of the element and thereby its position on the periodic table.

For instance, every carbon atom contains six protons, so the atomic number of carbon is 6. When identifying an element's ground-state electron configuration, we start by looking at its atomic number then fill the electron orbitals in sequence until we have accounted for all the electrons corresponding to that number.

Electron Orbitals

Electron orbitals are the areas within an atom where electrons are most likely to be found. They come in several shapes and sizes, which include s, p, d, and f orbitals, each able to hold a certain number of electrons.

For example, an s orbital can hold up to two electrons, a p orbital can hold six, a d orbital can hold ten, and an f orbital can hold fourteen. These orbitals are filled according to a set of rules known as the Aufbau principle, the Pauli exclusion principle, and Hund's rule. These rules help determine the order in which the electron subshells are filled, with lower energy subshells filling up before higher energy ones. This orderly filling of orbitals emerges in the step-by-step electron configuration of all known elements.

Ground-State

An atom's ground-state electron configuration is the arrangement of electrons around its nucleus that has the lowest energy level. It is the most stable configuration and the one in which atoms exist when they are not excited by energy input.

Electrons fill the orbital shells in a predictable order, which can be gleaned from their position on the periodic table. The ground-state electron configuration is written by noting the occupied orbitals and the number of electrons in each, expressed in a shorthand notation that lists the energy levels, types of orbitals, and the quantity of electrons in each orbital.

Understanding an element's ground-state helps predict its reactivity, the types of chemical bonds it can form, and its behavior in different chemical reactions. When talking about electron configurations for homework exercises, we always refer to the ground-state unless otherwise specified.