The Atom – The Basic Building Block of Matter


Atoms are the basic building blocks of matter, making up every visible thing we see, feel and touch. Atoms form the backbone of all chemical compounds by binding together in large numbers to form molecules.

Atoms contain positively charged protons, neutral neutrons and negatively charged electrons; these particles play an essential part in creating chemical bonds between substances and determine their physical properties.

The History of the Atom

The atom is the basic unit of matter. Consisting of protons, neutrons and electrons arranged in specific arrangements that work together for stability, it first appeared as a theory by Greek philosophers Leucippus and Democritus who suggested all things are composed of hard, innumerable particles called atoms. John Dalton revived this idea around 1800 through scientific experiments with gases; using his model from this evidence alone he demonstrated that some dissolve more easily in water than others due to having different masses among their constituent parts atoms.

Dalton realized that atoms possess a neutral electric charge, and modelled this by visualizing an atom as an positively charged sphere with negative electrons scattered randomly within it – often known as the Plum Pudding Model. Here in America however, most don’t eat plum pudding very often so Thomson’s model may be easier understood if thought of likening it to a Chocolate Chip Cookie instead.

Ernest Rutherford modified the Dalton model in 1911 when he discovered that some elements give off positive particles known as alpha particles, and conducted his Gold Foil Experiment by shooting a beam of alpha particles at a sheet of gold foil. He observed how some were deflected to either side while most collected at its center – leading him to conclude that its center contained the nucleus of an atom.

James Chadwick was another key contributor in Rutherford’s atomic study. He first discovered that an atom’s nucleus cannot consist exclusively of protons; to achieve this he fired alpha particles at Beryllium; upon impact, these alpha particles knocked out protons that he measured against its mass; this difference is what defines an element’s atomic number; its core corresponds to its mass.


Protons are one of the three basic subatomic particles–along with neutrons and electrons–that make up atoms, the building blocks of matter and chemistry. Protons are positively charged, making up part of an atom’s nucleus (an ordinary hydrogen atom contains one proton). Neutrons do not carry any charge, meaning their positive charges cancel each other out in neutral atoms.

Protons were one of the earliest achievements in atomic structure studies. Wilhelm Wien (1898) and J.J. Thomson (1910) observed streams of ionized gaseous atoms and molecules which lost electrons to form neutral atoms; from these, they determined that any positive charges on these neutral atoms came from protons, and that an atom’s overall mass depended upon both neutrons and protons present within its nucleus.

Ernest Rutherford demonstrated in 1919 and 1925 that nitrogen, when bombarded by alpha particles, produced nuclei that are similar to hydrogen nuclei. Furthermore, Rutherford established that an element’s atomic number is determined primarily by its nucleus’ number of protons; hence giving this particle its name: proton.

Protons weigh only 1.673 x 10-27 kilograms – this makes them 1,836 times as massive as electrons, but only account for a tiny fraction of total mass in an atom (which consists of both its nucleus and cloud of electrons). Protons are part of larger particles called hadrons; hadrons are composite particles comprised of smaller quarks held together by strong interaction forces – one of the fundamental forces found within nature.

While middle schoolers might not need all of the details, it would be beneficial for them to know that an electron with its negative charge attracts positively charged proton particles, leading them to draw closer together until electrostatic forces create close associations and bonds between atoms that ultimately trap an electron within their nucleus. The energy stored up during electron’s journey to proton converts into binding energy for that atom as its bound electron gets caught within it – ultimately becoming part of its binding energy and becoming trapped within.


Neutrons are particles found within an atom’s nucleus that do not possess either positive or negative electric charges, but do possess more mass than protons. Neutrons play an essential role in maintaining its stability by keeping protons from repelling each other like positively charged magnets; additionally, neutrons help create nuclear binding energy which holds together its nucleus.

Neutrons are created in nuclei during nuclear fusion or fission reactions, but can also be released in certain reactions. Neutrons do not possess an electrical charge and therefore remain neutral towards other particles such as protons, electrons, and photons. Neutrons play an essential role in isotope formation by helping balance out positive and negative charges on protons that make up isotopes of an element.

As with protons, neutrons are fundamental subatomic particles composed of quarks and gluons. First discovered by Ernest Rutherford in 1911 – who first recognized that an atom contained a small positively charged nucleus surrounded by negatively charged electrons – neutrons play an essential role in many aspects of physical science.

But he failed to recognize that within its nucleus was another, much larger subatomic particle: the neutron.

Each neutron consists of three quarks, represented in this diagram by colored circles, and three streams of gluons (represented by wavy lines). The gluons produce or absorb energy that modifies the electric force repulsion between protons within its core; this process of eliminating electrostatic repulsions is known as strong nuclear force.

Splitting an atom requires enormous amounts of energy. Nuclear fusion, in which two nuclei collide to become one nucleus, allows neutrons from each nucleus to lose some mass that is converted to nuclear binding energy.

Neutrons give the atom its stability and allow it to form isotopes and undergo chemical reactions that result in our familiar elements. Studies using neutrons have led to groundbreaking, Nobel Prize-winning discoveries and measurements; such findings have helped develop vaccines against diseases, build more efficient turbines and engines, create quantum materials and more.


Electrons are one of three fundamental subatomic particles, along with protons and neutrons, that make up an atom. Electrons possess negative electrical charges and are far smaller than its positively charged nucleus.

Electrons may either be bound to an atom, or free-floating (not bound). Bound electrons form orbitals around its nucleus that look like cloud-like structures called orbitals; this structure may take the shape of a circle (s orbital), dumbbell (p orbital), or more complex shapes like d and f orbitals; each orbital can hold two electrons maximum. Electrons are lightest of subatomic particles with negative electrical charge attracted towards positive nuclei; as such they form their core along with protons and neutrons as protons/electrons determine its chemical properties.

Democritus proposed the hypothesis that all matter was composed of indestructible units called atoms, as part of his theory about material nature. He believed that cutting stones into two would eventually reduce them too small to further divide. From here came their name – from Greek meaning “indivisible.”

As the universe began to cool after the Big Bang, conditions became ideal for quarks to coalesce and form atoms, according to CERN. Electrons joined protons, neutrons and other particles in creating nuclei for each atomic nucleus.

Early in the 1800s, English physicist J.J. Thomson created an atom model depicting a nucleus surrounded by electron clouds of various shapes resembling plum pudding’s raisins suspended within its round cake-like ball form. Thomson’s model helped introduce people across society to the idea of atoms.

Electrons are lepton particles, meaning that they react only with electromagnetic and weak forces rather than short-range strong forces such as those found within an atomic nucleus. Electrons can be found in all elements’ atoms and are responsible for its colors as well as serving as the basis of all chemical reactions; additionally, streams of electrons may even produce certain forms of radiation such as X-rays or radioactivity.

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