Define atomic mass, atomic number, mass number and isotones.
Answers
Answer:
The primary building blocks of atoms are protons, neutrons, and electrons. It is convenient to describe the composition of an atom in terms of the number of protons and neutrons in its nucleus (Fig. 1). The term atomic number, conventionally denoted by the symbol Z, indicates number of protons present in the nucleus of an atom, which is also equal to the number of electrons in an uncharged atom. The number of neutrons is represented by the neutron number ( N). Because the mass of these nuclear particles is each approximately equal to one unified atomic mass unit (u), the sum of the protons plus neutrons is designated as the mass number ( A). The mass of the electron is more than 1800 times smaller than the proton mass and, therefore, can be neglected in calculating the mass number. For any element, the mass number is equal to the atomic weight rounded off to the nearest integer value.
The atomic mass of an element is the average mass of the atoms of an element measured in atomic mass unit (amu, also known as daltons, D). The atomic mass is a weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope.
★ Atomic number:
The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus.
★ Mass number:
The mass number, also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. It is approximately equal to the atomic mass of the atom expressed in atomic mass units.
★ Isotopes:
Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom.