Atoms – The Basic Building Blocks of Matter

Democritus’ theory on what matter was composed of was that it consisted of tiny and eternal particles he called atomos – this name stuck.

An atom is the basic unit of any chemical element. It consists of a nucleus made up of protons and neutrons surrounded by negatively charged electrons that compose its outermost shell.


Atoms are the building blocks that compose all matter around us. Although small in size, atoms contain even smaller particles known as protons, neutrons and electrons. When joined together with other atoms they form ions and molecules – the fundamental building blocks of matter.

Through history, philosophers and scientists alike have long explored the nature of matter. Since at least 5th century BCE when Democritus first suggested that all matter is composed of microscopic particles called atomos – meaning uncuttable or indivisible in Greek – the concept has persisted until today’s definition of the modern atom is still based upon this ancient philosophy.

John Dalton first developed modern atomic theory during the 19th century. Noticing how chemical elements combined in set whole number ratios, he proposed a model of an atom comprising of a central nucleus surrounded by electrons. Though his work represented an important advance, it wasn’t until later in 20th century when physicist Erwin Schrodinger significantly advanced our knowledge about how atoms functioned and developed our understanding further.

Ernest Rutherford conducted an experiment that confirmed and supported his theory that atoms consist of a central nucleus surrounded by an electromagnetically bound swarm of electrons in 1911, using alpha particles shot through gold foil and deflected by an alpha particle collider to show this relationship between nuclei and electrons as well as their total lack of space within each atom – a landmark event on our journey toward understanding quantum mechanics today.


Atoms are tiny particles that serve as the building blocks for all forms of matter in our universe – be it solid, liquid or gas. Atoms consist of trillions and trillions of smaller subatomic particles such as protons, neutrons and electrons; all living and nonliving things come together from these subatomic particles to make the world what it is today.

The term atom first made its debut in scientific literature during the late 18th century and denoted something which cannot be divided into smaller particles. At that time, scientists understood there to be a central part to an atom called its nucleus where protons and neutrons co-existed alongside electrons; there was also an electron cloud located outside its perimeter; but none knew yet that protons and neutrons themselves contained smaller particles called quarks that are made up of protons and neutrons.

In 1913, British physicist J. J. Thomson conducted experiments using cathode rays and discovered that positively charged objects such as atoms caused deflections that led him to theorize that an atom consisted of a positively charged nucleus with negatively charged electrons revolving around its center in circular orbits – this theory later known as the plum pudding model was widely adopted until 1915 when Niels Bohr proposed his more precise yet simpler model of the atom.

Bohr’s model placed the nucleus at the heart of an atom, where most of its charge and mass are concentrated. He demonstrated how electrons in an atom were organized into circles or “energy levels”, with each energy level holding specific numbers of electrons; for instance, an innermost energy level can only hold two electrons while outermost shell (valence shell) may contain up to eight.


Protons are positively charged subatomic particles found within an atom’s nucleus. As part of its three main subatomic particles, proton has an electrical charge equivalent to one elementary electric charge +1e and forms nearly all of an atom’s mass.

Protons in an atom define its elemental makeup; hydrogen has one proton and thus stands as one of the lightest elements. Ernest Rutherford first discovered this fundamental particle and gave it its name based on Greek meaning for first: proton.

Protons, like electrons, possess positive electrical charges. Unlike neutrons, however, protons are relatively stable: they do not break down or decay on their own and form the basis for all atomic nuclei.

Protons possess an extremely small mass, just 1.673 x 10-27 kilograms – or approximately one billion trillion trillionth of a kilogram or roughly 1,836 times greater than an electron (according to their mass ratio).

Protons are lepton particles with multiple particle and wavelike characteristics, including quantum mechanical spin. Their quantum mechanical properties include half-integer angular momentum according to Pauli exclusion principle. Other leptons include muons, tau neutrinos and pions; their less stable particle and wavelike properties allow them to orbit their nucleus’ energy levels known as shells; these shells determine an atom’s chemical properties and chemical bonds between atoms as they bond through interactions called the valence shell; this behavior determines chemical reactions that cause physical changes that influence nature changes such as bonds among atoms themselves and physical changes between other physical changes as a whole.


Neutrons are neutral subatomic particles that, along with protons and electrons, compose the nuclei of every atom except hydrogen (which only has one proton and no neutrons). Since neutrons don’t carry charges themselves, their neutral nature helps avoid electrostatic repulsion between protons in the nucleus as well as increase binding energy for stability under normal circumstances.

A neutron weighs approximately one hundred eight times that of a proton due to their different electrical charges; protons possess positive charges while neutrons don’t. Neutrons don’t interact with electromagnetic fields while protons do, enabling detection without moderators – though the technique used may differ slightly than with alpha or beta particles.

Because of the properties of neutrons, their presence is typically indicative of nuclear reactors or fission processes. Neutrons also play a vital role in weapon design as they can trigger fission reactions even in regular non-weapon grade fissile materials.

Just like protons, neutrons do not easily ionize and can pass easily through solid objects without becoming ionized themselves, making them ideal for probing dense materials such as lead or concrete blocks. Once inside such materials, the fast neutron slows down considerably when passing through and may produce radioactive isotopes when it absorbs an electron in its vicinity.

Neutrons can also be utilized in medical applications, including positron emission tomography (PET). PET uses neutron radiation to produce images of human anatomy; however, its usage is less widespread due to being both penetrating and ionizing, potentially causing permanent damage to living tissue.


An atom’s positively charged nucleus attracts negatively charged electrons that orbit around it in orderly orbitals; their attraction allows them to overcome their mutual repulsion and keep moving around in this fashion. Orbitals form concentric shells which gradually widen outward from its center with each successive shell having more electron subshells.

An atom is composed of electrons arranged so that those in its innermost shells can form bonds easily with neighboring atoms, making molecules and all other things we see in nature possible. Electrons in outermost orbitals also interact to form chemical bonds between various atoms belonging to the same element.

Traditional views of an atom depict electrons as orbiting around its nucleus like planets orbit the Sun; this simplistic model does not accurately represent their behavior, as electrons more commonly reside in shells and subshells of an atom; each shell/subshell has a specific energy depending on its distance from its nucleus.

At every atom, their number of electrons is determined by the protons present within their nucleus. This number, known as their atomic number, determines what element the atom belongs to and helps define its properties.

Valency of an element determines its outer electrons, which determine how easily chemical bonds form between different atoms. Helium (He) and neon (Ne), two members of Group 18 family of elements, have outer electron shells which have all been filled to their octet limits, making them exceptionally stable single atoms that will only rarely form chemical bonds with other atoms.

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