How to Read the Periodic Table — Overview & Components

Reading the Periodic Table

The periodic table is a chart with all the known elements. We've all seen this table, but do you know how to read it?

Each row on the table is called a period. All the elements in a period have the same number of orbitals. This starts from one orbital at the top row, to seven orbitals at the bottom row. Each row increases by one orbital. Elements in the same period have similar physical properties.

Each column on the table is called a group. All the elements in each group have the same number of electrons in their outer shell, also called valence electrons. Elements in the same group react with other elements in similar ways.

---

Element Boxes

The atomic number, the number at the top of each element box, is the number of protons in the nucleus and the number of electrons in the atom.

The elemental symbol is an abbreviation of the element name. Some periodic tables do not include the element names, only the symbols.

The atomic weight is the average mass of all the element's isotopes. It is the average number of all the protons and neutrons in the nucleus. Generally, the atomic mass increases as you move down or across each group or period. Of course, there are exceptions to this rule.

Check out this series by TED-Ed to learn more about each element with an interactive periodic table!

What Does the Periodic Table Tell Us?

The periodic table contains an immense amount of information, but if read correctly it can be a powerful tool for chemistry.

There are primarily three ways that people navigate the periodic table: group, period, and atomic number.

Groups

The columns of the periodic table are called groups. It may seem strange to call columns groups, but this is done because elements of the same group have similar properties. In fact, the periodic table organizes elements into groups based on their properties. This is one reason for the strange shape of the table. The group number is listed on top of each column. The table shown above shows 18 groups. Some tables only show eight groups, while others show up to 32 groups. 18 groups is the most common, but the number of groups does not have a significant impact on the information the table provides.

Periods

The rows of the periodic table are called periods. This may seem silly, but let's think about why they are named periods for a bit. When we think about waves, orbits, circular motion, or really anything that repeats, the time that it takes to do one cycle is called a period. Examine the sine wave depicted below.

At every interval of $1$ ($0-1$, $1-2$, $2-3$, etc), the graph of the sine wave exactly repeats itself. The sine wave is said to be periodic with an interval of $1$. Well, the periodic table is periodic through the properties of the elements. If we go across a period of the table from the left to the right, the properties of the elements change drastically until we get to the end of the row. The next element is directly below the element we started at. This means they are in the same group. Think back to what we learned about groups: elements in the same group have similar properties. This means these two elements have similar properties. As we can see, the cycle of properties repeats itself with every period.

The periods are numbered on the left side of each row. There are seven periods overall. The two rows on the bottom actually belong in periods $6$ and $7$. They are typically taken out like this in order to improve the readability of the table.

Atomic number

The atomic number is the number of protons an element has. The atomic number increases by one as we move one element to the right. That is to say, if an element has an atomic number of 25, the element directly on its right will have the atomic number 26. When we reach the end of a period, the next element is the leftmost element of the next period.

---

Information on Elements

Each box on the periodic table represents an element. The table shown above gives more information than many tables, but reading it can be difficult. Below is a cropping of the key provided on the table.

We are mostly concerned with the atomic number, chemical symbol, atomic mass, and name. In this example, the atomic number is 26, the chemical symbol is Fe, the atomic mass is $55.845$ (this mass is always given in daltons, or its equivalent, grams per mole), and the name is iron. These four pieces of information will be used significantly more than the rest, and you should feel comfortable with what they mean and how to read them.

Other Information

The other information provided on this table is first ionization energy, electronegativity, electron configuration, and oxidation states.

First ionization energy is how much energy must be put into a gaseous atom in order to knock off the outermost electron. It is typically expressed in kilojoules per mole.

Electronegativity is how strongly an atom attracts electrons. It is rated on a scale of $0$ to $4$, and it increases as you proceed up and to the right on the table. Fluorine is the most electronegative element, and francium is the least.

The electron configuration is how the electrons are organized into sub-shells. A more in-depth explanation is beyond the scope of this page, but the electron configuration is strongly linked to the properties of the element.

Oxidation states are the ionic states where the atom is stable. Using iron as an example, iron will commonly lose either two or three electrons, but it is stable losing up to six electrons, or gaining up to two electrons.

$$\color{#D73D75}{\text{Vocabulary Review:}}$$

$\color{#D73D75}{\text{Group}}$: The columns of the periodic table$\\$

$\color{#D73D75}{\text{Period}}$: The rows of the periodic table$\\$

$\color{#D73D75}{\text{Atomic number}}$: The number of protons of an element$\\$

(Video) Kim's How to Read an Element in the Periodic Table of Elements in Plain English Video

by dancemonkey1033

This video will teach you how to understand the symbols and numbers that you find on the periodic table. It's also a good review of atomic number, atomic weight, mass number, protons, neutrons, and electrons.

How Is the Periodic Table Organized?

The periodic table is organized based on the amount of electrons a neutral atom of each element has. This is the same as the number of protons in that atom. This value is called the atomic number and is listed above each element on the periodic table. Even though protons define the identity of an element, the number of electrons determines the reactivity of each element, allowing the periodic table to sort elements by similar properties.

Electrons are found in different spaces around an atom, which we call electron shells. Each row of the Periodic Table of Elements, called a period, represents a new outer shell of electrons. The elements in each column, called a group, have the same amount of electrons in their outer shell, causing them to have similar properties. These predictable properties are so important that they were what allowed Mendeleev to come up with the modern periodic table in the first place!

(Video) How Does The Periodic Table Work | Properties of Matter | Chemistry | FuseSchool

by FuseSchool - Global Education

In this video, you will learn about how the periodic table is organized. You will also see some trends among certain groups like the alkali metals, the halogens, and the noble gases.

Throughout the table, we can observe many traits like metallic character, atomic radius size, differences in ionization energy, and changes in electronegativity.