Question

Show how using the periodic table helps you find the expected electron configuration of any element.

Short answer

The periodic table can help find the expected electron configuration of any element by highlighting the arrangement of elements in rows (energy levels) and columns (valence electrons). To determine the electron configuration of an element, follow the rows from left to right and top to bottom, filling electrons in the orbitals s, p, d, and f according to their maximum capacity. For example, the electron configuration of Chlorine (Cl) from the 3rd period with 17 electrons is \(1s^2 2s^2 2p^6 3s^2 3p^5\).

Step-by-step solution

Understand electron configuration

Electron configuration is a method of describing the distribution of electrons in an atom through a series of numbers and letters. It allows us to understand how the electrons are arranged in different energy levels and orbitals around the nucleus of the atom. The electron configuration is based on the principle that electrons will fill the available space in the lowest energy levels and orbitals first before moving to higher energy levels.

Understand the relationship between electron configuration and the periodic table

The periodic table is an arrangement of all known elements, organized by atomic number (the number of protons in the nucleus of the atom). In addition, the layout of the periodic table can help us determine an element's electron configuration. The rows (periods) in the periodic table represent different energy levels, and the columns (groups) represent the number of valence electrons (electrons in the outermost energy level) the element has.

Understand electron orbitals and their arrangement in energy levels

Before we determine the electron configuration of an element using the periodic table, we must first understand electron orbitals. There are four types of orbitals: s, p, d, and f. Each orbital has a specific shape and can hold a certain maximum number of electrons: 1. s orbitals can hold up to 2 electrons 2. p orbitals can hold up to 6 electrons 3. d orbitals can hold up to 10 electrons 4. f orbitals can hold up to 14 electrons These orbitals exist in different energy levels, and each energy level can hold different combinations of orbitals. The periodic table is organized in such a way that it helps in determining which orbital is being filled for a particular element.

Example: Find the electron configuration of an element using the periodic table

Let's find the electron configuration of the element Chlorine (Cl). Its atomic number is 17, which means it has 17 electrons. 1. Follow the rows (periods) of the periodic table from left to right and top to bottom. Chlorine is located in the 3rd period and the 17th group. 2. The first and second periods contain only the s orbital. So, starting from hydrogen (H), fill electrons in the 1s orbital. The 1s orbital holds up to 2 electrons, so the configuration is \(1s^2\). 3. Move on to the 2s orbital in the second period, which can also hold 2 electrons: \(1s^2 2s^2\). 4. Next, fill the 2p orbital in the second period, which can hold up to 6 electrons: \(1s^2 2s^2 2p^6\). 5. In the 3rd period, fill the 3s orbital with 2 electrons: \(1s^2 2s^2 2p^6 3s^2\). 6. Finally, fill the 3p orbital in the 3rd period with the remaining 5 electrons (since Chlorine has 17 electrons in total): \(1s^2 2s^2 2p^6 3s^2 3p^5\). So, the electron configuration of Chlorine (Cl) is \(1s^2 2s^2 2p^6 3s^2 3p^5\).

Key concepts

Periodic Table

The periodic table is a vital tool in chemistry that organizes all known elements based on their atomic number. It is more than just a list; it is a roadmap that indicates how elements relate to each other based on their electron configuration.

Understanding the **trend and layout** is crucial:

• **Periods:** Horizontal rows on the periodic table indicate the element’s principal energy level. As we move down the periods, the principal energy level increases, meaning electrons are being added to a new, outer shell.


• **Groups:** Vertical columns, also known as groups, show the number of valence electrons — the electrons that are found in the outermost shell. Valence electrons are critical because they determine an element’s chemical properties and reactivity.

By using the periodic table efficiently, you can swiftly predict electron configurations and gain insights into how elements might combine chemically.

Energy Levels

Energy levels refer to the fixed distances from the nucleus where electrons may be found orbiting the atom. They are analogous to the rungs of a ladder: electrons can only exist on a rung, not between them. Each energy level can hold a certain maximum number of electrons, and electrons fill the lowest available energy levels before occupying higher ones.

The **quantum numbering system** helps in understanding energy levels:

• The principal energy level is represented as "n". For example, in the electron configuration notation, 1s refers to the first energy level.


• Within a given energy level, there are one or more sublevels – known as orbitals – that also have specific shapes and capacities for electrons.

Energy levels are crucial for predicting the atom's reactivity and the formation of ions. As the period increases, so does the energy level, meaning the electrons are further from the nucleus and often more reactive in chemical reactions.

Electron Orbitals

Electron orbitals are regions within an atom where electrons are likely to be found. These orbitals arise from the solutions of the Schrödinger equation, which determines the probability distribution that describes an electron's position. Understanding electron orbitals is key to understanding how atoms bond and how molecules form.

There are four main types of orbitals:

• **s orbital:** Spherical in shape and can hold up to 2 electrons.
• **p orbitals:** Dumbbell-shaped and can hold up to 6 electrons across three degenerate orbitals (px, py, pz).
• **d orbitals:** More complex shapes and can accommodate up to 10 electrons across five degenerate orbitals.
• **f orbitals:** Even more complex shapes, holding up to 14 electrons across seven orbitals.

The way these orbitals are filled – by either the **afbau principle, Hund's rule** or **Pauli's exclusion principle** – influences the electron configuration of an atom and ultimately its chemical behavior.