Historically, the modern periodic table of elements is based on the framework developed by the Russian chemist, Dmitri Mendeleev, in 1869. He arranged the elements in increasing order of atomic number, leaving gaps for the undiscovered elements.
Although previous attempts were made to create a systematic periodic table of elements, Mendeleev’s version was the best. It was the first to consider the ascending order based on the atomic number of elements. At the same time, it grouped the elements into rows (known as periods) and columns (called groups). He started new rows every time the chemical properties were repeated.
The modern periodic table of elements has 118 entries but only 92 elements occur naturally – those following uranium are all created artificially in particle accelerators.
What is the periodic table of elements?
The periodic table of elements is a systematic arrangement of chemical elements based on characteristics including an element’s atomic number and chemical properties. The elements are arranged into periods with corresponding columns that pertain to a group of elements with similar properties.
Periodic tables usually contain details such as the name, symbol, atomic number, atomic weight, and electron configuration. However, printed periodic tables are limited by space, which makes it difficult to include more detailed information about each element. One solution to this problem is to publish an interactive periodic table online, complete with hyperlinks that lead to individual pages for each element.
The periodic table of elements can help both chemistry students and professional chemists analyse compounds and predict chemical reactions. For example, you can determine the reactivity of an element or compound based on its position in the periodic table. As alkali metals are more reactive than other metals, they can easily displace them in a single displacement reaction.
Why are elements arranged in a table?
The elements are arranged in a table because this makes it easier to understand their relationship with one another, as well as their general properties and trends. For example, as you move from left to right, the electron affinity of the elements increases.
How many elements are in the periodic table?
The modern periodic table of elements has 118 entries. However, only 92 elements are naturally occurring; elements with atomic numbers above 92 are artificially created in particle accelerators. Elements from 1 to 82 (excluding technetium and promethium) have at least one stable isotope.
Different groups on the periodic table
The modern periodic table of elements is arranged in ascending order of atomic number. It has 18 columns (groups) and seven rows (periods). The 18 groups of elements share common properties. For example, all the noble gases are very stable, virtually inert and don’t normally combine with other elements.
Here’s a brief overview of the different groups of elements on the periodic table:
- Group 1: Alkali metals (excluding hydrogen) – this group contains the most reactive metallic elements, which are typically found as part of compounds. Some are extracted in pure forms and then stored in inert liquids and containers. Alkali metals react violently with water to form alkaline solutions or strong bases. The elements in group 1 include sodium, potassium, lithium, rubidium, caesium, and francium.
- Group 2: Alkaline earth metals – the elements in this group are the second most reactive. Like group 1 elements, they also form hydroxides or strong bases when they react with water. Their oxide compounds, on the other hand, are very stable and commonly found in the earth’s crust. The alkaline earth metals include calcium, magnesium, and strontium.
- Groups 3-12: Transition and inner transition metals – these elements reduce in metallicness as you move from left to right. They’re grouped into the inner elements and the outer elements with two sub-periods – the lanthanides and the actinides. Transition metals are good conductors of electricity and heat. They each have two valence electrons.
- Group 13: Boron group – these elements all have three valence electrons and metalloid or metal properties. The elements in this group include boron, aluminium, and thallium.
- Group 14: Carbon group – with four valence electrons each, group 14 in the periodic tables consists of carbon, silicon, germanium, tin, and lead. Carbon is the most important element because it serves as the backbone of organic compounds.
- Group 15: Nitrogen group – the elements in group 15 all have five valence electrons. However, their chemical and physical properties vary widely. For example, nitrogen is a gas at room temperature, while phosphorus is a powdery solid. Many of the elements in the nitrogen group form transparent compounds but they can either be diamagnetic or paramagnetic at room temperature.
- Group 16: Oxygen group – the elements belonging to this group each have six valence electrons. They also have small atomic radii and large ionic radii. Examples of group 18 elements include oxygen, sulphur, selenium, tellurium and polonium.
- Group 17: Halogen group – the elements in this group form salts with alkali metals, alkaline earth metals, and other metals. Highly reactive and toxic, they also produce strong acids when combined with hydrogen. Halogens have seven valence electrons in their outer shell.
- Group 18: Noble gases group – the elements in this group have fully-filled outer orbitals, which makes them very stable. As a result, they’re inert or unreactive with other elements and compounds at standard conditions. The six noble gases are neon, argon, xenon, helium, radon, and krypton, all of which occur naturally.
The history of the periodic table
The history of the periodic table of elements can be traced back to 1789. It was during this time that the French scientist Antoine Lavoisier tried to group known elements into metals and non-metals.
However, it took about four decades before another significant discovery was made. The German scientist Johann Wolfgang Döbereiner noticed that there are similarities in the chemical and physical properties of certain elements. He arranged the elements into groups of three based on their atomic weight. He called them triads.
Another significant breakthrough came in 1860 when scientists at the International Conference of Chemistry decided that hydrogen should be assigned an atomic weight of one. The atomic weights of all other elements were then determined based on their relative atomic weight to hydrogen.
Meanwhile, British chemist John Newlands discovered the law of octaves. He was the first person to arrange the elements into periods. He also observed that the chemical properties are similar for every eighth element in the period. However, his system was awkward and did not provide any gaps for undiscovered elements.
It wasn’t until 1869 that Dmitri Mendeleev came up with the idea for 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.
It took more than four decades before the elements were arranged by atomic number rather than atomic weight. In 1913, the British physicist Henry Moseley used X-rays to measure the wavelengths of elements. These correlated with the atomic number.
The periodic table in 2023
The current periodic table in 2023 contains 92 naturally-occurring elements and 26 synthetic elements. There haven’t been any significant changes to the periodic table over the last few years. However, many online versions have now become more detailed and interactive.