Atomic number

Henry Gwyn-Jeffreys Moseley’s historic study in the 1910s gave rise to the concept of atomic number. Moseley used x rays to bombard a variety of chemical elements and observed the pattern generated by the reflected rays. He discovered that as atomic mass increased, the wavelength of reflected x rays reduced in a predictable fashion. The systematic change in wavelength from element to element, according to Moseley, was produced by an increase in the positive charge on atomic nuclei as one element became heavier than the next.

Atomic number: An overview

The number of protons in an atom’s nucleus is known as its atomic number. The total number of protons in an atom’s nucleus determines its atomic number. It is denoted by the letter ‘Z.’ The atoms of a specific element all have the same amount of protons and, as a result, the same atomic number. Different elements have different atomic numbers. Carbon atoms, for example, all have an atomic number of 6, while oxygen atoms all have an atomic number of 8.

 This concept was historically significant since it supplied the periodic law with a theoretical foundation. The discovery of the periodic law by Dmitri Mendeleev in the late 1860s was a great achievement. It supplied the chemical sciences with a crucial organizational notion. The inversion of certain elements in Mendeleev’s periodic table remained a difficulty in his final analysis. Elements are out of sequence according to their atomic weights in three locations where they are grouped according to their chemical properties, as stipulated by Mendeleev’s law.

It took approximately half a century for this challenge to be solved. Then it grew out of Wilhelm Roentgen’s x-ray studies, which he found in 1895. The discovery of this new type of electromagnetic radiation by Roentgen sparked a flurry of new research efforts targeted at understanding more about x rays and their effects on matter. One branch of x-ray study was started by Charles Grover Barkla, a physicist at the Universities of London and Cambridge.

Beginning in 1903, he studied how x-rays were scattered by gases in general and by elements in particular. He discovered that the farther up in the periodic table an element was, the more penetrating the rays it produced. He came to the conclusion that the number of electrons in an element’s atoms was related to the x-ray pattern he observed.

Atomic number’s history

Although we take atoms for granted, hardly one believed in them for generations. A Greek philosopher named Leucippus and his student Demokritos proposed the theory that the universe is made up of small indivisible particles called atoms some 2500 years ago. Unfortunately, Aristotle, the renowned Greek philosopher, disagreed with them. The theory of atoms was shelved for centuries because Aristotle’s beliefs were accepted throughout Europe for about 2000 years.

Atoms are the fundamental components of matter. They mix in a variety of ways to generate various compounds. Protons, neutrons, and electrons are found in all atoms except the common form of hydrogen. The number of protons in an element’s nucleus determines its atomic number. The number of protons in a neutral atom is equal to the number of electrons in shells, which is the energy level around the nucleus.

Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are called isotopes.

The standard atomic weight of an element is determined by the average isotopic mass of an isotopic mixture in a specific environment on Earth. The average isotopic mass of an isotopic mixture for an element in a defined environment on Earth determines the element’s standard atomic weight. 

Illustration of atomic number

The number of protons in an atom’s nucleus or the number of electrons in an electrically neutral atom equals the atomic number. The number of protons in an atom is called its atomic number.

A sodium atom, for example, has 11 electrons and 11 protons. As a result, the atomic number of the Na atom is 11 since the number of electrons equals the number of protons.

Atomic Orbital Energy levels

When an electron is at a certain energy level, it is more likely to be found in some parts of that level than in others. These parts are known as orbitals. Sublevels are orbitals that have the same energy. Each orbital consists of a maximum of 2 electrons.

The number of electrons in each energy level must be written down. An element’s atomic number indicates how many electrons are present in its atoms. Carbon, for example, has an atomic number of 6, which translates to six electrons as 2,4. So an atom with the atomic number 12 has an electronic structure of 2, 8, 2, with two electrons in the lowest energy level, eight in the next, and two in the highest energy level.

Atomic number list of first 20 elements

Conclusion

Because an element’s chemical characteristics are determined by the number and arrangement of electrons in its atoms, these issues disappear when atomic number rather than atomic mass is employed to generate a periodic table. The nuclear charge, in turn, determines the number of electrons in an atom. Thus, the chemical properties of an element are determined by the number of protons in its nucleus (also known as the nuclear charge or atomic number).