What is an atom?

An atom is the smallest unit of matter that has characteristic properties of a chemical element. It is the building block of chemistry. Atoms mostly consist of an empty space, surrounded by negatively charged electrons and positively charged nucleus of protons and neutrons. 

What are the basic properties of an atom?

The basic properties of an atom are:-

1. Atomic number- The number of units of positive charged protons in the nucleus, which is denoted by the letter Z. This number determines the place of the chemical element in the periodic table. For example, the atomic number of hydrogen is 1, carbon is 6, that is any atom with 6 protons is an atom of carbon. 
2. Atomic mass- The atomic mass unit (amu) indicates the mass of the atom. Each proton or neutron weighs about 1 amu thus the atomic mass is close to mass, which indicates the number of particles within the core of an atom. 
3. Electronegativity- Electronegativity measures the inclination of an atom to pull the electric cloud in the direction during chemical bonding with another atom. It was propounded by Pauling, he devised a scale to order chemical elements on the basis of electronegativity. 
4. Density- The number of units of mass of an element that are present in a certain volume of medium. Temperature and air pressure influence density. Traditionally density is expressed through the Greek letter ‘ro’ and in the SI system in kilograms per cubic metre (kg/m³). 
5. Melting point- The temperature at which the solid form of element is at equilibrium with the liquid form is called the melting point. For example- the melting point of water is 0° C.
6. Ionic radius- Ionic radius is the radius that an ion has in an ionic crystal. The orbital is an area surrounding the atom where probability of finding an electron is greatest. 
7. Isotopes- Atoms of the same element that differ in atomic mass are called isotopes. With heavier atoms there may be higher atomic numbers. The great number of isotopes is not stable. They fall apart during the radioactive decay process. Radioactive isotopes are called radioisotopes. Isotopes have identical chemical properties but different nuclear properties. For example- there are three isotopes of hydrogen. Two are stable but tritium is unstable.
8. Electronic shell- The wave-like pattern of circles that circle around the core is the electronic configuration of an atom. The circles are divided up in shells and subshells which are numbered by means of quantities. 

What is an atomic orbital?

The mathematical function describing location and wave-like behaviour of an electron in an atom. It also refers to the physical region where electrons can be calculated to be present. Each orbital is characterised by three quantum numbers ‘n, l and m’ which respectively correspond to the electron’s energy, angular momentum and vector component. 

Atomic orbitals can be hydrogen-like orbitals that are derived from exact solutions of Schrodinger equation for one electron and a nucleus. These are still used as pedagogical tools. The Slater type orbital is a form without radial nodes but decays from the nucleus as does the hydrogen orbital. Gaussian type orbital has no radial nodes and decays. It is propounded that combinations of many Gaussians can attain accuracy of hydrogen-like orbitals.

The term “orbital” was coined by Robert Mulliken as an abbreviation for one electron orbital wave function. The development of quantum physics had an explanation of behaviour of these electron orbits as one of its driving forces. The ‘plum pudding model’ was the most widely accepted explanation of atomic structure during the 19th century. 

Orbitals are given names such as X type where the X is the energy level corresponding to principal quantum number. The set of orbitals for given n and l is called a subshell. Denoted by X type to the power y. The exponent y shows the number of electrons in the subshell. 

Atomic orbitals are the quantum states of the individual states of individual electrons in an electron cloud around a single atom. Classically the electrons were believed to orbit the atomic nucleus like the planets revolve around the sun. However the electrons cannot be described as solid particles rather the atmosphere around a planet would be a better comparison for the same. 

Describe the atomic structure.

An atom is an intricate grouping of negatively-charged electrons organised in positively-charged nucleus shells. The nucleus bears the atomic mass and it constitutes neutrons and protons. The size of every atom is identical.The diameter of a single atom is known to be around 2-3 À.

9. J Thompson discovered the existence of electrons that marked the emergence of advanced atomic physics. The majority of properties regarding atoms are based on either their number or their arrangement of electrons. The atomic mass of each electron is known to be around 9.1 × 10-³¹kilograms. 

The existence of positively-charged particles observed in the nucleus is called proton. The charge within a proton is identical but opposite to that of the negatively-charged electrons. The volume of protons within a nucleus dictates the variety of a particular chemical element. 

Neutrons bear no charge and at the same time, they have the identical atomic mass as protons. It was discovered by Sir James Chadwick. The neutrons are not repulsed by the electron clouds or even the nucleus just because it lacks electrical charge, rendering it as a helpful instrument for examining the atomic structure.

Explain Einstein’s equation E = mc².

The mass defect and binding energy are related to Albert Einstein’s formula. In 1905, Einstein developed a special theory of relativity.  One of its implications was that mass and energy are interchangeable. This equation states that mass can be converted into energy where c is the speed of light. This equation is the key to power of nuclear weapons and nuclear reactors.

Conclusion

Atoms are the extremely small particles that are basic building blocks of ordinary matter. Atoms join to form molecules. Atoms consist of positively charged nuclei surrounded by clouds of negatively charged electrons. Nuclei is made up of positively charged protons and neutral neutrons held by nuclear force, this is the atomic structure.