What is an Atom ?

However, because most philosophers at the time — especially the very influential Aristotle — believed that all matter was created from earth, air, fire, and water, Democritus' atomic theory was put aside.

John Dalton, an 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 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.

Thomson, the British physicist who discovered the electron in 1897, proved that atoms actually can be divided, according to the Chemical Heritage Foundation.

He was able to determine the existence of the negatively charged particles by studying properties of electric discharge in cathode-ray tubes.

According to Thomson’s 1897 paper, the rays were deflected within the tube, which proved that there is 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," according to a 2013 article by Giora Hon and Bernard R. Goldstein published in the journal Annalen der Physik.

According to Thomson’s 1897 paper, the rays were deflected within the tube, which proved that there is 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," according to a 2013 article by Giora Hon and Bernard R. Goldstein published in the journal Annalen der Physik.

Atoms are not closed, encapsulated, surrounded by a strong shell sphere as it was believed.

The number of protons in an atom makes the difference between chemical elements and the number of neutrons in the nucleus distinguishes different isotopes of an element.

Atom’s electrons do all the chemical work and they are responsible for chemical reactions. Positive and negative ions exist because of the electrons.

The radius of an atom is one tenth of a billion of meter and a cube of sugar contains as many atoms as stars are in the universe.

The diameter of the biggest atom (cesium) is 9 times bigger than the diameter of the smallest atom (helium).

The nucleus of an atom can be split to form other elements. This is what happens in nuclear reactors and atomic explosions.

Most of the atom’s interior is empty space and 200 electrons can be fit inside of a proton.

There are 118 kinds of atoms which can be combined in different ways and create everything is created in the universe.

Atoms exist as electrically neutral (the same number of protons and electrons) or as ions (positive ions – more protons than neutrons; negative ions – more electrons than protons).

Super-dense
The nucleus which is located at the heart of every atom makes up more than 99.9 per cent of its mass, but only a trillionth of its total volume

Electrons are tiny
At only 1/1,836th the size of a proton or neutron, electrons contribute almost nothing to an atom’s mass, but are the most active component of an atom, responsible for bonding.

The rest is filler
More than 99.9 per cent of an atom’s volume is empty space. If an atom’s nucleus were the size of a basketball, its electrons would be zipping around several miles away.

The quantum leap
When electrons jump between energy levels, they don’t move through the space between. Instead, they disappear from one level and then instantly reappear on another level.

The force is strong
Atomic nuclei are held together by the strong force, which is 1038 times stronger than gravity, but only operates on the minute scale of a nucleus.