Breaking Down the Periodic Table

The periodic table is an essential resource for all chemistry students, as it supplies you with vital information that you will need to solve a variety of problems. Hence, it is imperative that you familiarise yourself with it and learn how to read it quickly and accurately. The more adept you are at gleaning information from the periodic table, the better you will become at chemistry as a whole.

The periodic table features over a hundred different elements, and at first glance, it is not always easy to find patterns. Luckily, the periodic table is designed to be highly systematic, and you can learn to read it quickly using a few common strategies.

But first, it is important to understand what exactly the periodic table is and familiarise yourself with some of its key characteristics.

The Basics

The periodic table, also known as the periodic table of elements, is a chart that displays all known chemical elements in an organised, systematic way. There are currently 118 different elements represented on the periodic table, each with their own structure, properties and characteristics.

Reading Rows (Periods)

The rows on the periodic table are known as periods, and there are 7 periods in total, each containing a different number of elements.

Number of elements

The first period only contains two, hydrogen (H) and helium (He). The second and third periods contain 8 elements each, and the fourth and fifth periods contain 18 elements each.

The last two periods are somewhat unique, because they contain the lanthanide and actinide series. The lanthanide series includes elements with atomic number 57 to 71, and is included between barium and lutetium in the sixth period. Similarly, the actinide series includes elements with atomic number 89 to 102, and is included between radium and lawrencium in the seventh period.

Lanthanide and actinide series

The lanthanide and actinide series are usually presented as two separate rows beneath the main periodic table, and represent the inner transition metals. The lanthanide series includes elements such as lanthanum (La), europium (Eu) and ytterbium (Yb), while the actinide series includes elements such as uranium (U), plutonium (Pu) and even einsteinium (Es)!

Properties of periods

All the elements in the same period have the same number of electron shells. This is where the electrons within the element are stored. The row number corresponds to the number of electron shells within each element in that row. For example, hydrogen and helium have 1 electron shell each, while lithium, carbon and fluorine in the second row have 2 electron shells each.

As you move across the period from left to right, the number of protons (subatomic particles with positive charge) increases. This is called “reading across a period”.

Reading Columns (Groups)

The columns on the periodic table are known as groups, and there are 18 groups in total. Elements in the same group share a number of physical and chemical properties.

Charge

Elements in the same group have the same number of electrons in their outer electron shell. This means that their ions will have the same positive or negative charge. For example, sodium (Na) and potassium (K) are both in Group 1, and have 1 electron in their outer shell and lose 1 electron to form a cation. Hence, they will become the ions Na⁺ and K⁺, with a charge of +1.

Chemical properties

Elements in the same group also react to things in the same way. For example, Group 1 elements are known as “alkali metals” and are known to explode when coming into contact with water. You may have seen your chemistry teacher perform this experiment in the lab: when you drop a piece of lithium, sodium or potassium metal into a tub of water, they produce a volatile, explosive reaction.

This is because the electrons from the metal flow into the surrounding water to form a hydroxide and hydrogen gas, in an extremely fast reaction that produces a significant amount of heat. Other experiments will show that elements in other groups also share properties similar to one another.

Reading Individual Elements

Each individual element has its own element box, which contains important information about it that differentiates it from other elements. You can also form your own inferences based on the information given in this box. Generally, there are four important pieces of information included in each element box.

Atomic number

This is the small number at the top of the box, indicating the number of protons or electrons in the atom. Each atom contains the same number of protons and electrons, until it becomes ionised through the gain or loss of electrons.

Chemical symbol

The letter or pair of letters directly below the atomic number is the chemical symbol of the element. This is usually an abbreviated form of the element name; for example, the chemical symbol for lithium is Li. However, some chemical symbols are not derived from the common element name at all; for example, the chemical symbol for tungsten is W (which is the first letter of the element’s Latin name, “Wolfram”). Hence, it is important to familiarise yourself with the chemical symbols for the most commonly encountered elements.

Element name

This is the full name of the element located under the chemical symbol. It is the name that the element is commonly referred to.

Atomic mass

Finally, the atomic mass is the small number at the bottom of the element box, indicating the average mass of all of the element’s isotopes (atoms and ions). Due to differences in the percentage of abundance of each element’s isotopes, this is usually a decimal rather than a whole . It is a rough estimate of how many protons and neutrons there are in the nucleus of the atom.

Looking for Patterns

The periodic table is organised systematically to enable you to glean information at a glance. Here are some important patterns that can help you refer to the table more quickly and easily.

Metals, metalloids and non-metals

With the exception of hydrogen, elements closer to the left-hand side of the periodic table are metals and elements closer to the right-hand side are non-metals. The metalloids, which serve as a transition between them, include boron (B), silicon (Si) and antimony (Sb).

Noble gases

The 6 noble gases are found in Group 18, the very last column in the periodic table. They are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). They form a group because they are all odourless, colourless and have low reactivity.

Halogens

The 5 halogens are found in Group 17, and include fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). The name “halogen” means “salt-producing”, and the 5 halogens produce a wide range of salts when they react with metals.

Natural occurrence

The elements with atomic numbers 1 through 94 are said to be naturally occurring; that is, they can be found in nature without the need for synthesising. The elements with atomic numbers 95 through 118 do not occur naturally and exist because they were successfully synthesised in labs, nuclear reactors and nuclear explosions.

The TSA Approach

These strategies provide a good overview of how to read the periodic table. However, more information can be derived from the periodic table which can serve as immediate visual guide for other chapters, further aiding a student’s ability to apply information during examinations. If you are still confused about how to break it down, The Science Academy has just the solution for you. Our O Level chemistry tuition classes have helped countless students master the subject, as well as develop a deep-seated passion for chemistry.

With over 20 years of combined experience, our experienced science tutors are committed to helping our students get the most of their science education, and instilling in them a passion for general science, physics, chemistry and biology.