Mass Number

An element is a particle that cannot be changed or broken down through chemical means. There are 118 elements in the periodic table. Atoms are subdivisions of the elements. The main constituents of atoms include protons, neutrons, and electrons. The atoms of an element each have the same number of protons. Protons have a positive charge, while electrons have a negative charge. However, neutrons are electrically neutral. The number of protons distinguishes each element from another. The number of neutrons and electrons may vary. Changes in the number of electrons generate a charged element or ion. However, changes in the number of neutrons result in isotopes.

Atomic structure

An atom can be defined as the smallest amount of matter which retains its characteristics as a chemical particle. The atom has two clear regions. These are the nucleus and the outer region. The nucleus holds the protons and neutrons at the centre of the atom. The protons are positively charged, while the neutrons are neutral.

On the other hand, the outer region contains electrons orbiting around the nucleus. These electrons are negatively charged. The number of electrons equals the number of protons. The positive charge of the protons balances the negative charge of the electrons. 

What is the atomic number?

The arrangement of elements in the modern periodic table follows the order of increasing atomic numbers. Thus, the first element has fewer protons than the next element, and so forth. The atomic number refers to the total number of protons in the nucleus of an atom. All the neutral atoms of a single element have the same number of protons and electrons. Therefore, the atomic number of a neutral atom can be the number of protons or the number of electrons.

The atomic number determines an element’s identity. For instance, an unknown element has eleven protons in its atoms. This element can only be sodium. The elements are discernable according to their atomic number. The number of protons also governs the number of electrons that orbit its nucleus. Therefore, the atomic number influences the chemical reactivity of an atom. The chemical characteristics of the various elements are related to the number and arrangement of electrons in the atom structure.

A left subscript denotes the atomic number with the symbol representing the specific element. 

For example:

47Ag for silver

History of the periodic table

Dimitri Mendeleev pioneered the creation of the periodic table in 1869. His table arranged elements according to their increasing atomic mass. At this time, scientists were yet to study the atomic structure and were unaware of the existence of the nucleus. The atomic mass compared to that of hydrogen, which has an atomic mass of one, was the only relevant information scientists could rely on. Once scientists discovered the nucleus, they determined that the atomic number was responsible for the chemical properties of elements. Therefore, the atomic number was the best figure to provide an accurate periodic table. 

What is the mass number?

The mass number is the sum of the total number of protons and neutrons present in the nucleus of an atom. The number of electrons is not accounted for while calculating the mass number. Only the protons and neutrons were considered because the bulk of the atomic mass concentrated on the nucleus. 

The mass number varies from one element to another due to neutrons. The varying number of neutrons results in the formation of isotopes. Isotopes are a group of atoms of the same element that have the same atomic number but different mass numbers. 

For instance;

The carbon atom has six protons. Its atomic number is six.

However, the carbon atom exists as several isotopes. These include carbon-12, carbon-13, and carbon-14. Carbon-12 has six protons and six neutrons, while carbon-13 has six protons and seven neutrons. Only the number of neutrons changes. 

Even a minor increase or decrease in the number of neutrons causes a significant change in the atom’s chemical reactivity. Carbon-12 is stable and does not decay. However, carbon-14 is unstable and undergoes radioactive decay. Carbon-14 is used in the study of fossils through carbon dating. It has a long half-life of more than 5,000 years, suitable for fossil dating.

Isotopes have multiple uses in treatment and diagnosis, nuclear medicine, oil exploration, and nuclear explosives generation.

How to calculate and denote the mass number?

Consider the element boron.

Boron has an atomic number of 5. That means it has five protons within its structure. 

An isotope of boron has six neutrons within its nucleus. How do you calculate the mass number?

Mass number = number of protons + number of neutrons

Therefore, mass number = 5 + 6 = 11

This boron isotope has a mass number of 11 and an atomic number of 5.

The following illustrates how the isotope will be presented.

511B

B is the symbol for the element boron. 5 is its atomic number, and 11 is its mass number.

Conclusion:

Understanding the concepts of mass and atomic numbers enables students to master chemistry better. These concepts constitute the fundamental basics of science. The comprehension of atoms is important as they form components of the human body. These atoms and elements are the primary facilitators of chemical reactions with the body. Another key reason to study the atomic structure is to refine our understanding of isotopes and radioactivity. There are 245 known isotopes. Furthermore, radioactivity can be harnessed for positive uses if stabilised. Furthermore, atoms join to form large structures known as molecules. Many molecules interact to develop solids, gases, and liquids.