The Periodic Table Of Chemical Elements

Kate Onissiphorou

by Kate Onissiphorou

23rd February 2022

The periodic table of chemical elements is like the alphabet of chemistry. Similar to letters in the alphabet, elements can combine and react in many ways. 

In fact, the permutations of all possible chemical combinations of elements are greater than the estimated number of atoms in the visible universe! 

If we include the noble gases in the permutations, there would be 6.62×10184 possibilities. From these possibilities, the complex chemistry of life arose. In comparison, the estimated total upper number of atoms in the universe is only about 1×1082, or one hundred thousand quadrillion vigintillion atoms.

You can predict some reactions and combinations of elements if you know their properties based on the periodic table. And if you’re familiar with how the table is organised, you can describe at least some of the properties of an element by just looking at its position in the table.

What is the Periodic Table?

The periodic table arranges all known elements into periods and groups that correspond to specific chemical properties.

The Periodic Table

Trends are immediately obvious if you understand the way the periodic table is arranged. 

Here are some properties and trends of chemical elements as listed on the periodic table:

  • Atomic Radius You can determine the radius of an atom by measuring the distance between two nuclei of an ionic bond. The atomic radius tends to decrease as you move from left to right across the table. It increases as you go from top to bottom.
  • Ionisation Energy This is the energy needed to remove an electron from the outermost orbital of a gaseous atom or ion. The ionisation energy increases as you move from left to right and decreases from top to bottom of the periodic table.
  • Electron Affinity The opposite of ionisation energy, electron affinity is the quantity of energy that’s released as an electron is added to an atom. Electron affinity increases from left to right across the periodic table.
  • Electronegativity Electronegativity is how well an atom can attract a pair of bonding electrons in molecules. The strength of an atom’s electronegativity increases among the elements as you move from left to right across a period.
  • Metallic Characteristics – Metals are good conductors of heat and electricity. They’re ductile, malleable, and, with the exception of mercury, solid. The metallic characteristics of the elements increase diagonally from right to left. An illustration summarising the periodic table

What is the Periodic Table Used For?

The periodic table is used by chemists and other scientists as a comprehensive reference source.

It’s very useful to know the relative properties of the elements and be able to predict their reactivity based on their positions in the periodic table.

For example, you can use the periodic table to predict and compare the ionisation energies of different elements. Specific details such as atomic weight and electronegativity values can also be found pretty easily.

A scientist using the periodic table of elements in their lab work 

Printed periodic tables can only contain a very limited amount of information without becoming extremely large and impractical. Digital periodic tables, however, are not limited by physical space. This means they’re able to provide more information, including video content. Some digital periodic tables are also interactive and allow you to click on an element symbol to view further details.

How Are Elements Arranged in the Periodic Table?

As the name suggests, the elements in the periodic table are arranged into periods, or rows, of increasing atomic number. There are seven periods.

There are also 18 ‘groups’ that are represented by the different columns. Each period exhibits certain trends, such as increasing electron affinity. The groups categorise elements based on their shared properties. For example, Group 15 (5A) is the column for noble gases, which are the least reactive elements.

The periods mainly represent the number of orbitals. Elements that belong to the same period have the same number of orbitals. This means you can also write the electron configuration of these elements. The electron configuration describes how the electrons are distributed among the orbitals.

  • Period 1: one orbital, two elements
  • Period 2: two orbitals, eight elements
  • Period 3: three orbitals, eight elements 
  • Period 4: four orbitals, 18 elements
  • Period 5: five orbitals, 18 elements
  • Period 6: six orbitals, 32 elements
  • Period 7: seven orbitals, 32 elements

How Many Groups Are in the Periodic Table?

The periodic table of elements has 18 groups, each one representing a particular set of properties. The elements in a certain group or column all have the same number of valence electrons.

  • Group 1: This group is known as the alkali metals, with the exception of hydrogen. These metals are highly reactive and very sensitive to water, hence they are found in many compounds. Each element only has one valence electron.
  • Group 2: The alkaline earth metals are the second most reactive metals. They’re also very good reducing agents. Alkaline earth metals donate electrons during chemical reactions. Every element in this group has two valence electrons.
  • Groups 3-12: Also known as the transition metals, elements in these groups form two or more oxidation states. These metals are relatively stable and aren’t as reactive as the alkali and alkaline earth metals. Most transition metals are strong and hard but malleable. They’re also lustrous and have high melting points. Transition metals are good conductors of electricity and heat. They each have two valence electrons.
  • Group 13: This is the Boron group. The elements in this category have three valence electrons. They also have metalloid or metal properties. The elements in this group are boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and nihonium (Nh).
  • Group 14: This group is dubbed the carbon group and includes carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl). Each of these elements has five valence electrons. Most of these elements are fairly common on the earth’s crust. Carbon is the most important element because it serves as the backbone of organic compounds and life itself.
  • Group 15: This is the nitrogen group of elements. The elements in this group are nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and moscovium (Mc). Each of these elements has six valence electrons. They have common chemical behaviours but their physical properties vary.
  • Group 16: This group is known as the oxygen family, or the Chalcogens. The elements belonging to this group are oxygen (O), sulphur (S), selenium (Se), tellurium (Te), polonium (Po), and livermorium (Lv). Each of these elements has six valence electrons.
  • Group 17: This is the halogen group, named after their ability to form salts. The etymology of the name is Greek: hal or salt and -gen, which means to form. The elements in this group are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). They’re very reactive with alkali metals and alkaline earth metals. Each element has seven valence electrons.
  • Group 18: Otherwise known as the noble gases, the elements in this group are very stable because they all have eight valence electrons. The noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and oganesson (Og). They’re the least reactive of all the elements and are mostly found in an elemental state. Very few compounds are naturally formed from these elements. 

The History of the Periodic Table

Since ancient times, philosophers have wondered about the ultimate or fundamental composition of matter. For instance, the Greek philosopher Aristotle thought there were only four elements in nature earth, air, water, and fire.

The four elements: earth, air, water, fire

The Ancient Greeks believed that the four elements of earth, air, water, and fire made up all matter.

This belief became the foundation of alchemy and even medicine for thousands of years. However, the idea was disproven with the discoveries of many other elements. These breakthroughs also revealed the so-called four elements were not elements but rather mixtures and compounds.

The first scientific attempt to classify elements can be traced back to Antoine Lavoisier in 1789. He tried to classify the elements by grouping them into gases, non-metals and earths. These groupings still exist in the modern periodic table of elements.

It took more than four decades before the triad of elements was recognised by another scientist, Johann Döbereiner. In 1829, he realised that elements can be grouped into three according to their properties. This meant the properties of the middle element could be predicted based on the two known elements in the triad. It appears Döbereiner had an inkling of periodicity.

Three decades passed before real progress was made in discovering the periodicity of the elements. It was during a conference in Germany in 1860 that an accurate list of the atomic mass of the elements became available to the scientific community.

Who Invented the Periodic Table?

No one person invented the periodic table of chemical elements. Rather, the current arrangement of elements on a periodic table was discovered and developed by several scientists over several decades.

The development of the modern periodic table of elements can be mainly credited to the following scientists:

Alexandre Béguyer de Chancourtois de Chancourtois was a geologist who arranged the elements in a three-dimensional pattern using the ‘vis tellurique’ (telluric screw) published in 1862. This was based on the known atomic weights of the elements. As a result, elements with similar properties lined up in the diagram.

John Newlands About four years before Mendeleev published his periodic table of chemical elements (see below), Newlands proposed the Law of Octaves based on the similarities of elements that differ in weights by seven units. However, his system was awkward and did not provide any gaps for undiscovered elements. It was also criticised for being too arbitrary.

Julius Lothar Meyer Technically, Meyer could have been the one credited with the idea of the modern periodic table of chemical elements. However, his work was published much later than Mendeleev’s findings. Meyer grouped the elements based on their valency and in order of atomic weight. His table was very similar to Mendeleev’s table.

Dmtri Mendeleev Mendeleev is credited as the father of the modern periodic table of elements. Similar to the scientists before him, he arranged the elements based on their atomic weights but he noticed some inconsistencies. Instead, he grouped them according to their chemical properties. However, the true genius of his discovery was to include gaps that represented the undiscovered elements.

Henry Moseley Moseley’s main contribution was arranging the elements based on their atomic number instead of atomic weight. Although the weights correspond well with the atomic number in terms of periodicity of properties, there were some exceptions. Moseley solved this inconsistency.

The Periodic Table in 2022

The modern periodic table has 92 naturally-occurring elements and 26 synthetic elements. As the atomic number increases, the atom becomes less stable. The synthetic elements exist momentarily during atomic collisions. They are too unstable to exist in bulk and some can only be produced in a few atoms.

The current periodic table has remained the same for several years. The newest elements in the periodic table are:

  • Nihonium (Nh) – atomic number 113
  • Moscovium (Mc) – atomic number 115
  • Tennessine (Ts) – atomic number 117
  • Oganesson (Og) – atomic number 118.

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