Atom | Definition, History, Structure | Explanation, Examples

Atom

Definition

An atom is the smallest unit of matter that retains the properties of an element. It is made up of three types of subatomic particles: protons, neutrons, and electrons. The protons and neutrons are found in the nucleus, which is the central part of the atom, while the electrons orbit the nucleus in shells.

History

The history of the atom can be traced back to ancient Greece, where philosophers such as Leucippus and Democritus proposed the idea of indivisible particles that make up matter. However, it wasn’t until the 19th century that scientists began to provide a more detailed understanding of the structure of atoms.

• 19th century: John Dalton, a British chemist, and physicist, proposed the first modern atomic theory in 1803. He stated that all matter is made up of atoms, atoms of a given element are identical and atoms of different elements have different properties.
• Early 20th century: JJ Thomson, a British physicist, discovered the electron in 1897 and proposed the “plum pudding” model of the atom. In which the atom was a positively charged sphere with negatively charged electrons embedded in it. Ernest Rutherford, a New Zealand-born British physicist, proposed the nuclear model of the atom in 1911, which stated that the majority of an atom’s mass is concentrated in a small, dense nucleus.
• Early 20th century: Niels Bohr, a Danish physicist, proposed a quantum mechanical model of the atom in 1913, which incorporated the principles of quantum mechanics to explain the behavior of electrons in atoms. This model explained the observed patterns in the emission spectra of atoms and improved our understanding of the structure of atoms.
• Mid-20th century: Erwin Schrödinger, an Austrian physicist, proposed the wave mechanical model of the atom in 1926, which explained the behavior of electrons in terms of probability waves. This model was later refined by other scientists and led to the development of the field of quantum mechanics.
• Late 20th century and beyond: Scientists continue to study the properties of atoms and their role in the universe using advanced technologies such as particle accelerators and electron microscopes. They also developed theories that explained the behavior of subatomic particles such as protons and neutrons and the fundamental interactions that govern the behavior of matter in the universe. Today, scientists continue to explore the properties of atoms in different conditions and discover new atomic species in the universe.

Atoms can gain or lose electrons to form ions, which are atoms that have a net electrical charge. Atoms that have lost electrons are called cations and have a positive charge, while atoms that have gained electrons are called anions and have a negative charge.

Examples

1. Carbon atom: Carbon atoms have 6 protons and 6 electrons in their nucleus and in their outermost shell. Carbon atoms can bond with other atoms to form compounds such as carbon dioxide (CO2) and methane (CH4). In these compounds, the carbon atoms are held together by chemical bonds, which are formed by the sharing or exchange of electrons between atoms.

2. Hydrogen atom: Hydrogen atoms have 1 proton and 1 electron in their nucleus and in their outermost shell. Hydrogen atoms are the lightest and most abundant elements in the universe, and they can form chemical bonds with other atoms to create compounds such as water (H2O) and hydrogen gas (H2).

In summary, an atom is the basic unit of matter that makes up all physical objects. It is made up of protons, neutrons, and electrons. The number of protons in an atom’s nucleus determines the element to which it belongs, while the number of electrons in its outermost shell determines its chemical properties and how it interacts with other atoms. Atoms can gain or lose electrons to form ions, and they can bond with other atoms to form compounds.