Atomic structure is the structure of the atom. Atoms are the smallest constituent of matter. All substances- solid, liquid and gas are made of atoms. Atoms are incredibly small- about 100 picometres or 10 billionths of a metre.
The atomic structure is comprised of the protons, neutrons and electrons arranged in a particular pattern. However, the atomic structure is not a clearly defined map or diagram. The boundaries of the atom are not well defined and depending on the energy level of the individual constituents; the atomic structure can vary significantly.
Every atom has the following three components- protons, neutrons and electrons.
The protons and neutrons are concentrated at the centre of the atom- the nucleus. The core constitutes over 99% of the mass of the atom. The proton is positively charged while the neutron does not carry any charge. The proton and the neutron are held together by nuclear forces- an unyielding force.
The proton is 1836 times as massive as the electron and is positively charged. The number of protons in an atom corresponds to the atomic number of the element.
The neutron is the heaviest component of the atomic structure. It is 1839 times as massive as the electron. The neutron does not carry any charge. The sum of the protons and the neutrons is the mass number of the element. A mass number is just a number, i.e. It is dimensionless. The actual mass of an atom at rest is measured differently. The unified atomic mass unit is the actual mass of an atom at rest. The Dalton (Da) is the unit used to measure the unified atomic mass unit. One Dalton is equal to one-twelfth of the mass of a free neutral atom of carbon-12.
The electrons are the smallest particles in the atomic structure. Electrons always rotate in an orbit around the nucleus. However, they (electrons) do not follow distinct paths. Electrons exist more like a cloud around the nucleus- the electron cloud. As the atomic structure is not well defined, the dimensions of an atom are described by the atomic radii. The atomic radius is the distance from the centre of the atom to the more out end of the electron cloud. The atomic structure is assumed to be spherical. However, the spherical fabric of the atom is correct only in a vacuum. Everywhere else, the atomic structure is subject to many variations due to external forces acting on the atom.
The electrons are negatively charged. Therefore, they are attracted to the protons by a strong electromagnetic force. The electrons continuously rotate in an orbit around the nucleus to counteract the electromagnetic force exerted by the protons in the nucleus.
Electrons behave as both a particle and a wave. In certain positions within the atomic structure, an electron can form a three-dimensional standing wave- a wave that does not move about the nucleus. The probability of an electron occupying such a position can be calculated using mathematical models- the atomic orbital. Only a few, discrete sets of orbitals are present around the nucleus (the other waves rapidly decay into more stable forms). Within the atomic structure, each orbital corresponds to a particular energy level. Electrons can move to a higher orbital by acquiring energy from a photon. Similarly, electrons can move to a lower orbital by spontaneously emitting energy in the form of photons. The phenomenon of movement of electrons can be readily observed by heating a metal rod. When the metal cylinder is exposed to fire, the electrons acquire energy and move to a higher orbital. When the rod is removed from the fire, the electrons lose energy by emitting photons and rapidly move back into lower orbitals. The hot red colour of the bar is due to the emission of photons by the electrons that are moving to a lower orbital.