Article on Atoms and it’s history by Dr. Hsb

Thinking about how we came to know atoms, what is an atom, how it was made, how it behaves, theories behind it, to get all the answers read the article!!!

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Journey of an AtomThis Article on the Facts about atoms, the building blocks of matterAtoms are the smallest part or basic units of matter and the defining structure of elements. The term “atom” comes from the Greek Adjective “Atomos” known as indivisible, because it was once thought that atom was the smallest things in the universe and could not be subdivided.

We now know that atoms are made up of three particles: protons, neutrons and electrons — which are composed of even smaller quarks like particles.Atom was created after the Big Bang 13.7 billion years ago.

As the hot, dense new universe cooled, conditions became suitable for quarks and electrons to form.

According to CERN Quarks came together to form protons and neutrons, and these particles combined into nuclei within the first few minutes of the universe’s existence. It took 380,000 years for the universe to cool enough to slow down the electrons so that the nuclei could capture them to form the first atoms. According to Jefferson Lab, the earliest atoms were primarily hydrogen and helium, which are still the most rich elements in the universe,

Gravity eventually caused clouds of gas to coalesce and form stars, and heavier atoms were created within the stars and sent throughout the universe when the star exploded.

Atomic particlesMass of Protons and neutrons are heavier than electrons and reside in the nucleus of the atom. Electrons are extremely lightweight and exist in a cloud around the nucleus. According to the Los Alamos National Laboratory the electron cloud has a radius 10,000 times higher than the nucleus.Mass of Protons and neutrons is nearly the same. However, mass of one proton is about 1,835 times higher than an electron. Number of protons and electrons is always same in an atom, and the number of protons and neutrons is may or may not same.

Adding a proton to an atom makes a new element, while adding a neutron makes an isotope which heavier than original atom.

Nucleus was discovered in 1911 by Ernest Rutherford, a physicist from New Zealand by alpha particle experiment. In 1920, Rutherford proposed the name proton for the positively charged particles of the atom discovered by Goldstein. He also theorized that there was a neutral particle within the nucleus discovered(in 1932) by British physicist James Chadwick who was the student of Rutherford.The nucleus is held together by the strong binding force, one of the four basic forces in nature. This force between the protons and neutrons overcomes the repulsive electrical force that would otherwise push the protons apart, according to the rules of electricity.

Some atomic nuclei are unstable because the binding force varies for different atoms based on the size of the nucleus of the atom. These atoms will then decay into other elements by decay process.ElectronsElectrons are tiny compared to protons and neutrons and also over 1,800 times smaller than either a proton or a neutron.

According to Jefferson Lab Electrons are about 0.054% as massive as neutrons. According to the Science History Institute electron was discovered by the British physicist Joseph John (J.J.) Thomson in 1897. Originally known as “corpuscles,” electrons have a negative charge calculated by Oildrop experiment and are electrically attracted to the positively charged protons.

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Electrons around the atomic nucleus in clouds called orbitals, an idea that was put forth by Erwin Schrödinger, an Austrian physicist, in the 1920s. Today, this model is known as the quantum model or the electron cloud model. The inner orbitals surrounding the atom are spherical but the outer orbitals are much more complicated and in different shape.

Electronic configuration of an atom refers to the locations of the electrons in a typical atom. According to the Los Alamos National Laboratory, using the electron configuration and principles of physics, chemists can predict the properties of atom, such as stability, boiling point and conductivity etc.NeutronsAccording to the American Physical Society Rutherford theorized that there was a neutral particle within the nucleus discovered (in 1932) by British physicist James Chadwick who was the student of Rutherford. Neutrons were found during experiments when atoms were shot at a beryllium foil and subatomic particles with no charge were released which is the neutron.Neutrons are neutral particles exist within all atomic nuclei (except for hydrogen).

A neutron’s mass is slightly larger than that of a proton. Like protons, neutrons are also made of quarks — one “up” quark (with a positive 2/3 charge) and two “down” quarks (each with a negative one-third charge).

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History of the atomThe theory of the atom dates at least as far back as 460 B.C. to Democritus, a Greek philosopher. Democritus most likely built his theory of atoms upon the work of past philosophers, according to Andrew G. Van Melsen, author of “From Atomos to Atom: The History of the Concept Atom” (Duquesne University Press, 1952) accepted by scientific comunity.

A stone cut in half gives two halves of the same stone explain by Democritus. If the stone were to be continuously cut, at some point there would exist a piece of the stone small enough that it further unable to cut. His explanation included the ideas that atoms exist separately from each other, that there are an infinite amount of atoms, that atoms are able to move, that they can combine together to create matter but unable to merge to become a new atom, and that they cannot be subdivided, according to Universe Today. However, because most philosophers at the time — especially the very influential Philosopher Aristotle — believed that all matter was created from earth, air, fire and water, Democritus’ atomic theory was put aside.John Dalton, a British chemist, built upon Democritus’ ideas in 1803 when he put forth his own atomic theory, according to the chemistry department at Purdue University. Dalton’s theory included several ideas from Democritus, such as atoms are indivisible and indestructible and that different atoms form together to create all matter. Dalton’s additions to the theory included the following ideas: That all atoms of a certain element were identical, that atoms of one element will have different weights and properties than atoms of another element that atoms cannot be created or destroyed and that matter is formed by atoms combining in simple whole numbers.

According to the Chemical Heritage Foundation J.J.Thomson, the British physicist who discovered the electron in 1897 by Cathode ray experiment and proved that atoms can be subdivided. According to Thomson’s 1897 paper, the rays were deflected within the tube, which proved that there was something that was negatively charged within the vacuum tube. In 1899, Thomson published a description of his version of the atom, commonly known as the “plum pudding model.” An excerpt of this paper is found on the Chem Team site. Thomson’s model of the atom included a large number of electrons suspended in something that produced a positive charge giving the atom an overall neutral charge. His model resembled plum pudding, a popular British dessert that had raisins suspended in a round cake-like ball.The next scientist to further modify and advance the atomic model was Rutherford, who was the student of J.J.Thomson, according to the chemistry department at Purdue University. In 1911, Rutherford published his version of the atom, which included a positively charged nucleus by planetary model or spiral model. This model arose when Rutherford and his assistants fired alpha particles at gold foil. According to the Jefferson Lab an alpha particle is made up of two protons and two neutrons basically positively charged Helium, all held together by the same strong nuclear force that binds the nucleus.The scientists noticed that a small percentage of the alpha particles were scattered at very large angles to the original direction of motion while the majority passed right through hardly disturbed. Rutherford was able to approximate the size of the nucleus of the gold atom, finding it to be at least 10,000 times smaller than the size of the entire atom with much of the atom being empty space. Rutherford’s model of the atom is still the basic model till date.Several other scientists furthered the atomic model, including Niels Bohr (base on Rutherford’s model to include properties of electrons based on the hydrogen spectrum) known as Borh’s atomic model is the best model, Ultimately, Erwin Schrödinger (developed the quantum model of the atom), Werner Heisenberg (stated that one cannot know both the position and velocity of an electron simultaneously), and Murray Gell-Mann and George Zweig (independently developed the theory that protons and neutrons were composed of quarks) .

Additional resources:www.livescience.com

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