Elements are pure substances that cannot be broken down any further by chemical reactions. For example, oxygen (O) and hydrogen (H) are both types of elements. Whereas compounds, such as water (H2O), are made of two or more elements combined.
An element is made of only one type of atom, and has electrons, protons, and neutrons. The protons and neutrons are located in the nucleus, while electrons occupy electron shells surrounding the nucleus.
Each element has a different number of protons, neutrons, and electrons. These determine the final properties of the element, and are also responsible for its position in the Periodic Table of the Elements.
For example, oxygen is heavier than hydrogen because the total number of protons and neutrons in its nucleus is greater than that of hydrogen.
Protons, neutrons and electrons are the basic building blocks of an atom. To see how they work, let’s look at two simple elements.
First, let’s look at hydrogen.
In contrast, let’s look at the element carbon (C).
The first version of the Periodic Table was created by Dmitri Mendeleev, and he arranged the known elements based on their atomic mass. However, elements on the current periodic table are arranged in order of their increasing atomic mass.
The Periodic Table is categorised by:
The periodic table arranges elements based on their atomic number, which represents the number of protons in the nucleus. Each element has the same number of protons and electrons. So in a neutral atom, you can use the atomic number to determine the number of electrons or the number of protons.
The mass number of an element is the sum of its protons and neutrons, so it is always higher than the atomic number. On the periodic table, the mass number is usually below the element’s symbol and the atomic number is above it.
This information is important, as it allows you to determine how many protons, neutrons and electrons each element has.
Hydrogen has an atomic number of 1 and a mass number of approximately 1. So, we can work out that:
Carbon has an atomic number of 6 and a mass number of approximately 12, so, we can calculate that: