How to Read the Periodic Table of Elements

The periodic table of elements contains the building blocks that make up the objects in our world. Water is a combination of hydrogen and oxygen atoms. Carbon atoms are in all living things. As of 2016, the periodic table contains 118 unique elements. Scientists are trying to create new elements by using particle accelerometers, but this can be a tricky process. Once you’re familiar with the element key, layout and structure, it’s easy to read the periodic table.

What is the Element Key?

The box containing each element’s information is known as the element key. Each key contains an element’s name, unique symbol, atomic weight and atomic number. Oxygen, for example, has an atomic number of 8, an atomic weight of 15.996 and a unique symbol, O.What do each of these sections on the element key tell us?

Atomic Number

The element’s atomic number lets you know how many protons are in the nucleus, and how many electrons are in orbit around it. With oxygen, that tells you that there are eight positive protons in the center of each atom, and eight negative electronics orbiting it. Every element on the periodic table has an atomic number assigned to it. Not only does it let you count the protons and electrons, but it also determines the element’s place on the table.

Atomic Mass

The atomic mass is the number located at the bottom of an element key. This number is the average mass of the element’s isotopes, including all electrons, protons and neutrons. Isotopes have the same number of protons, but a different number of neutrons.

Scientists created elements 93 through 118 in a laboratory. These artificial elements don’t exist naturally and haven’t survived longer than several milliseconds at a time. The atomic weight of these elements is based on the element that survived longest when it was created. Future research can change the listed atomic weight of these elements.

Atomic Symbol

Finally, an element’s name determines the atom’s symbol. In most cases, like oxygen or carbon, it’s simply the first letter of the element’s name. In others, like potassium or mercury, scientists have to look back into history. Potassium has the designation K because of its Neo-Latin name — Kalium. Mercury has the designation Hg because of its Greek name — hydrargyrum, which means ‘liquid silver.” Silver meanwhile has the designation Ag, for its Latin name — Argentum which later became the French word for the same color: argent. How many elements can you guess just by looking at their atomic symbol?

Classifying Elements Helps You Read the Periodic Table

The structure of the periodic table might seem strange to the casual observer, but its design serves a purpose. Each element is placed according to its atomic weight and number. The vertical columns are groups, and the horizontal rows are periods.

Group

Elements are grouped into columns based on their chemical properties. A Roman numeral, or in modern tables, an Arabic numeral, designates each column. This is the number of electrons an element has in its outer shell, which are known as valence electrons.

Valence electrons are the number of electrons an element has available to bond with other elements to make molecules.

Group 1 consists of Alkali Metals — things like sodium, potassium, and cesium which are not as dense as other metals and are highly reactive. Some of them even explode when they come into contact with water or air.

Group 2 includes the Alkaline Earth Metals like calcium and magnesium, which bond easily. Their atoms are small than those in Group 1.

Groups 3 through 12 are the Transition Metals. This group makes up most of the periodic table. On the far right, you’ll find some metals, as well as metalloids and nonmetals. The most common nonmetals are Group 17, the Halogens and Group 18, the Noble Gases that don’t bond with anything.

Want to learn more about one of these groups? Check out our Everyday Uses of Element Series to learn more about a group’s properties, traits, and common uses: 

Alkali Metals | Alkaline Earth Metals | Transition Metals | Actinides | Lanthanides | Basic Metals | Metalloids | Nonmetals | Halogens | Noble Gases

Period

Surrounding each element’s nucleus is a shell which can only hold a certain number of electrons. Elements in the periodic table are broken out into rows based on the number of shells they have.

Neon is in the second row, or period, which means it has two shells. The first shell can only hold two electrons, while the second shell can hold up to eight electrons, for a total of 10.

On the bottom of the periodic table, you’ve got the lanthanides and actinides. Lanthanides all have an atomic number larger than that of lanthanum and are almost all soft silvery metals. Actinides are in the very bottom row of the periodic table, and all have atomic numbers higher than that of actinium. Every one of these elements is highly radioactive.

Color-Coding

To make it easier to read the periodic table, modern versions include color-coding. Each color breaks out elements into their different groups. Elements 57 through 71 and 89 through 103 are in separate rows to improve readability as well.

Periodic Trends

Once you learn how to read the periodic table, it becomes easier to see the trends that are presented there. For example, if you follow the table from left to right, you’ll see that electronegativity increases. Electronegativity occurs where the valence shell carrying the electrons is less than half full.

Moving from the top to the bottom shows a decrease in electronegativity. This doesn’t apply to noble gasses, which always have a full valence shell or the lanthanides and actinides at the bottom of the table.

Going from right to left shows an increase in atomic radius or the distance between the element’s nucleus, and its valence shells. The group one elements have the largest radius, while the noble gasses have the smallest.

This radius also increases as you move from the top of the table to the bottom. Moving this direction also shows increasing metallic characteristics — the further left you get on the chart, the more metallic the elements become. Noble gasses, which are distinctly non-metallic, are on the far right and alkaline metals are on the far left.

By using the guide above, you’ll be able to read the periodic table with ease in no time!

Why does the periodic table look that way? Check out my latest article, Who Made the Periodic Table and Why? to see what historic periodic tables looked like. You won’t believe how different they were!

This article originally published 10/27/2017. We first updated it on 02/18/2019 to include more information about the periodic table, it’s classifications and trends. The article was also updated 12/23/2019 to improve heading layout and 07/10/2020 to add missing resources about the actinides and lanthanides.