An atom has a central, dense, tightly packed nucleus with a diameter of 10-15 m compared to an atom at 10-10 m, a size equivalent to a marble in a football stadium. Therefore, the nucleus makes up less than 0.01 % of the atom's volume.
The nucleus contains positively charged protons and neutral neutrons as subatomic particles bound firmly by the nuclear force.
Molecular mass is the sum of the masses of all the atoms in the molecule, denoted as m.
The mass of the atoms is measured in the average atomic mass unit, a weighted average of all the element's naturally occurring isotopes.
The sum is represented in amu (μ) or Da unit.
The joining of two or more uncharged atoms by a linkage known as a covalent bond creates molecules such that changing the connection, or the arrangement will change the molecule and its properties.
For example, joining two Cl atoms give a Cl-Cl molecule. Changing the linkage to form H-Cl gives a new molecule with different properties altogether.
The matter is composed of invisible, indivisible, innumerable particles called atoms. Atoms are responsible for giving each matter its unique properties and identity. The uniqueness comes from the nature of the atom and its composition. Atoms are composed of three subatomic particles- electron, neutron, and proton. For example, an Oxygen atom has 8 electrons, 8 protons, and 8 neutrons.
The Average Atomic mass of an element is the weighted average of the atomic masses of all naturally occurring isotopes of an element. It is also known as the atomic weight and is expressed in amu.
The weighted average gives a more accurate value than the normal average by considering all isotopic forms of an element.
The unit used to describe the mass of an atom is the unified atomic mass unit, symbolized as amu or μ.
The standard used for measuring the mass of an atom is a 12C atom. Carbon-12 (12C) is an isotope of Carbon with 6 protons, 6 neutrons, and 6 electrons.
The mass number is the total count of the number of protons and neutrons present in the nucleus of an atom, denoted as A.
For example, 12C has 6 protons and 6 neutrons; its mass number is 12.
A mass number is always a whole number. The mass number is also known as the atomic mass number or nucleon number.
The Atomic number (symbol Z) uniquely identifies an element and is equal to the number of protons present in the nucleus of an atom.
For example, atomic number 6 identifies the Carbon atom with 6 protons in its nucleus. An uncharged Carbon atom will also have 6 electrons in the outer nuclear region, equal to its atomic number.
Isotopes are a group of atoms belonging to an element with the same atomic number but a different mass number. Such a group of atoms have the same number of protons in their nuclei but differ only in the number of neutrons.
A Neutron is an uncharged, neutral subatomic particle found in an atom's nucleus, denoted as n or n0.
