Structure of an Atom

Smallest unit of ordinary matter, an atom, is the building block of the chemical element. Each solid, liquid, gas, and plasma are made of atoms that are either neutral or ionised. Atoms are incredibly minuscule, often measuring less than 100 picometers in diameter. They are so small that using classical physics to precisely anticipate their behavior—as if they were tennis balls, for example—is impossible due to quantum phenomena.

Each atom is made up of a nucleus and one or more electrons that are attached to the nucleus. The nucleus consists of one or more protons and a significant number of neutrons. Only the most abundant form of hydrogen is neutron-free. The nucleus contains more than 99.94 percent of an atom’s mass. The Protons possess positive charge, the electrons have negative charge, and the neutrons have no charge. When the protons and electrons in an atom are equal, the atom is electrically neutral. If an atom contains more electrons than protons, it has a net negative or positive charge — these atoms are referred to as ions.

The Electromagnetic force attracts the atom’s electrons to its protons in the atomic nucleus.  Nuclear force attracts the neutrons and the protons in the nucleus. This force is typically stronger than the electromagnetic force that attracts positively charged protons. The repelling electromagnetic force can become stronger than the nuclear force in some conditions. In this situation, the nucleus fragments and separates into distinct parts. This is a type of radioactive decay.

The atomic number is the number of protons in the nucleus; it indicates the chemical element the atom belongs to. For instance, every atom with 29 protons is copper. The number of neutrons in an element indicates its isotope. Atoms can form chemical compounds such as molecules or crystals when they create chemical bonds with one or more other atoms. Atoms’ ability to associate and disassociate accounts for the majority of physical changes observed in nature. Chemistry is the science that investigates these transformations.

Structure

The majority of matter is composed of agglomerations of molecules that can be easily separated. Molecules, in turn, are made up of atoms connected by more difficult-to-break chemical bonds. Each atom is composed of smaller particles known as electrons and nuclei. These particles are electrically charged, and it is the electric forces acting on the charge that keep the atom together. Separation of these smaller constituent particles requires a growing amount of energy and results in the generation of new subatomic particles, the majority of which are charged.

Nucleus is the atom’s positively charged nucleus, which holds the majority of its mass. It is made of  the neutral-charged neutrons and the positive-charged protons. Protons, neutrons, and the electrons that orbit them are all extremely stable particles found in all naturally occurring atoms. Additional subatomic particles may coexist with these three types of particles. They are, however, formed only by the injection of massive amounts of energy and are extremely brief in duration.

All atoms have approximately the same size, regardless of whether they have three or ninety electrons. A row of approximately 50 million atoms of solid matter would measure 1 cm (0.4 inch). The angstrom(Å), defined as 10⁻¹⁰ metre, defined as 10^-10 metre, is a handy measure of length for  measuring atomic sizes. Radius of the atom lies between 1 and 2 Å. The nucleus is even more minute when compared to the overall size of the atom. It is proportional to an atom in the same way as the marble proportional to the football field. The nucleus occupies only 10^-14 metres of the atom’s volume, or one part in 100,000. The femtometre (fm), which equals 10^-15 metre, is a handy unit of 

length for measuring nuclear sizes. The diameter of a nucleus is proportional to the number of particles it contains and ranges between approximately 4 and 15 fm for a light nucleus such as carbon and lead. Despite its modest size, the nucleus contains nearly all of the atom’s mass. Protons are huge, positively charged particles, whereas neutrons are massless and somewhat larger than protons. The fact that nuclei can contain anywhere between one and roughly 300 protons and neutrons explains their wide range of mass. The lightest nucleus, hydrogen, has a mass 1,836 times that of an electron, while heavier nuclei have a mass approximately 500,000 times that of an electron.

Basic Properties

Atomic Number

The most fundamental property of an atom is its atomic number (often symbolised by the letter Z), which is defined as the number of positive charge units (protons) contained in the nucleus. For instance, an atom with a Z of 6 is carbon, while one with a Z of 92 is uranium. A neutral atom contains an equal number of protons and electrons, resulting in an exact balance of positive and negative charges. Because electrons dictate how one atom interacts with another, the chemical characteristics of an atom are ultimately determined by the number of protons in the nucleus.

Atomic Mass and Isotopes

The number of neutrons in an atom’s nucleus has an effect on its mass but not on its chemical characteristics. Thus, a nucleus with six protons and six neutrons will have the same chemical characteristics as one with six protons and eight neutrons, despite their different masses. The Isotopes are nuclei having the same number of protons but having a different number of neutrons. Each chemical element has a large number of isotopes.

Typically, isotopes are described by the total of their protons and neutrons in the nucleus—a quantity called the atomic mass number. The first atom in the preceding example would be designated as carbon-12 or 12C (due to its six protons and six neutrons), whereas the second would be designated as carbon-14 or 14C.

Atomic mass is expressed in terms of the atomic mass unit, which is defined as 1/12 of the mass of a carbon-12 atom, or 1.660538921 10^-24 grams. Because the mass of an atom is composed of the nucleus and electrons, the atomic mass unit is not identical to the mass of a proton or neutron.

Conclusion

Since the late nineteenth century, scientists have known that the electron carries a negative electric charge. Between 1909 and 1910, American physicist Robert Millikan determined the value of this charge for the first time. Millikan’s oil-drop experiment involved suspending microscopic oil drops in an oil mist chamber. He determined the weight of the oil drips by observing the rate at which they fell. Oil drops that had accumulated an electric charge (for example, by friction as they travelled through the air) could then be slowed or halted by providing an electric force. Millikan determined the charge on each drop by comparing applied electric force to variations in motion. After measuring numerous drops, he discovered that their charges were all simple multiples of a single number. The charge on an electron was used as the fundamental unit of charge, and the various charges on the oil drops corresponded to those with 2, 3, 4… more electrons. The electron’s charge is currently widely agreed to be 1.602176565 x 10^-19 coulomb. Millikan was given the 1923 Nobel Prize in Physics for this achievement.

The charge on the proton is equivalent to the charge on the electron in magnitude but opposite in sign—the proton possesses a positive charge. Because opposite electric charges attract one another, electrons and protons are attracted to one another. This force is responsible for keeping electrons in orbit around the nucleus, much like gravity keeps the Earth in orbit around the Sun.

The electron weighs approximately 9.109382911 x 10^-28 grams. A proton or neutron has a mass approximately 1,836 times greater. This explains why the mass of an atom is governed mostly by the protons and neutrons contained within the nucleus.