Chemistry (Part-1)

John Dalton's atomic theory, proposed in the early 19th century, stated that all matter is made up of extremely small particles called atoms, which are indivisible and indestructible.

While we now know that atoms are indeed divisible into subatomic particles (protons, neutrons, and electrons), Dalton's theory was a foundational concept in the development of modern chemistry.

John Dalton, an English chemist and physicist, formulated his atomic theory around the early 1800s.

This theory proposed fundamental ideas about the nature of matter, including that all matter is made of atoms, atoms of a given element are identical, and chemical reactions involve the rearrangement of atoms.

While some aspects of his original theory have been modified over time with further discoveries, Dalton's work laid the essential groundwork for our modern understanding of atoms and molecules.

This principle is known as Dalton's Law of Partial Pressures, which he formulated in the early 19th century. This law states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases. 

The partial pressure of a gas in a mixture is the pressure that the gas would exert if it occupied the same volume alone at the same temperature.

The atomic number (often denoted by the symbol Z) is a fundamental property of a chemical element. It uniquely identifies the element and determines its place in the periodic table.

The number of protons in the nucleus of an atom defines which element it is. For example, all atoms with 6 protons are carbon atoms.

While a neutral atom has an equal number of protons and electrons, the atomic number is specifically based on the count of protons, as this number remains constant for all isotopes of a particular element, whereas the number of neutrons can vary (leading to isotopes), and the number of electrons can change (leading to ions).

An atom is the smallest indivisible particle of matter, which can take part in a chemical change or chemical reaction, i.e. It is the smallest particle representing matter in a chemical reaction.

Atoms are composed of three main subatomic particles:

Protons: Positively charged particles located in the nucleus (the atom's central core).
Neutrons: Neutrally charged particles (no electric charge) also located in the nucleus.
Electrons: Negatively charged particles that orbit the nucleus in specific energy levels or shells.

Atomic Mass:
The atomic mass is approximately the sum of the number of protons and neutrons in the nucleus. Isotopes of the same element have the same number of protons but differ in the number of neutrons. This difference in the number of neutrons leads to different atomic masses for the isotopes of that element.

For example, Carbon-12, Carbon-13, and Carbon-14 are all isotopes of carbon. They all have an atomic number of 6 (6 protons), but they have 6, 7, and 8 neutrons respectively, resulting in different atomic masses.

Atoms of the same element, which have the same atomic number but different atomic mass or mass numbers, are called isotopes.

An isotope atom has the same number of protons and a different number of neutrons. Atoms of different elements having different atomic numbers but the same mass number are called isobars.

Isobars are atoms of different chemical elements that have the same number of nucleons (protons + neutrons), which means they have the same mass number.

However, because they are different elements, they must have a different number of protons, and therefore a different atomic number.

For example, Argon-40 (atomic number 18) and Calcium-40 (atomic number 20) are isobars. They both have a mass number of 40, but they are different elements due to their different numbers of protons.