The atomic mass is the mass of an atom or molecule. To calculate the average mass of elements and molecules and to solve stoichiometry problems, atomic mass is used. It is also called atomic weight. In this article, we will study the definition of atomic mass and how can it be determined.
Atomic Mass- Definition
Atomic mass, also known as atomic weight, is a measure of the mass of an atom. This value is typically expressed in atomic mass units (amu), with one atomic mass unit being defined as 1/12th of the mass of a C-12 atom. The atomic mass can be found on the periodic table and is typically given as a decimal number.
1. Determination of Atomic Mass
The number of protons and neutrons in an atom's nucleus determines its atomic mass. The element to which the atom belongs is determined by the number of protons, also known as the atomic number. The number of neutrons in an atom of the same element, on the other hand, can vary. These variations are referred to as isotopes. An element's atomic mass is calculated by averaging the atomic masses of all of its naturally occurring isotopes. This is referred to as the relative atomic mass. The relative atomic mass of an element is usually given to four decimal places and is used to calculate the mass of an element sample.
Mass Number
The mass number of an element is the total number of protons and neutrons present in the atom. Mass number = Number of (protons + neutrons)
Mass Number Notation
In chemical notation, if the element is X, the mass number A is written as
The superscript is always used to represent the mass number. The atomic mass of an atom is also given by its mass number. This is because an atom's atomic mass is numerically equal to its mass number. For example, if an atom's mass number is 23, its atomic mass will be 23 u.
Average Atomic Mass and Isotopes
The average atomic mass is a measure of an atom's mass that accounts for the presence of different isotopes of an element. Isotopes are atoms of the same element with different numbers of neutrons in their nuclei. As a result, the atomic masses of isotopes of the same element differ. To determine an element's average atomic mass, the relative abundance of each isotope is multiplied by its atomic mass, and the sum of these values is divided by the total number of atoms. This calculation takes into account the natural occurrence of each isotope. For example, carbon has three isotopes: carbon-12, carbon-13, and carbon-14.
Carbon-12 is the most abundant isotope, making up 98.89% of naturally occurring carbon.
Carbon-13 makes up 1.11% of naturally occurring carbon.
Carbon-14 is a trace isotope that makes up only 0.0000000001% of naturally occurring carbon. The average atomic mass of carbon is calculated by multiplying the relative abundance of each of the isotopes by its atomic mass and then adding these values together. We would then divide the sum by the total number of atoms.
The average atomic mass of carbon is calculated by multiplying the relative abundance of each of the isotopes by its atomic mass and then adding these values together. We would then divide the sum by the total number of atoms.
Therefore, the average atomic mass of C is 12.0107 amu.
2. Application of Atomic
Mass One important application of atomic mass is in the field of chemistry.
The atomic mass of an element is used in stoichiometry to calculate the number of moles in a sample.
The atomic mass of a compound is also used to calculate its molar mass, which is the mass of one mole of the compound.
Atomic mass is important in nuclear physics and nuclear engineering.
The atomic mass of an atom is used to calculate the binding energy of the nucleus, which is the amount of energy required to hold protons and neutrons together. This binding energy is useful in understanding the stability of atomic nuclei and in calculating the energy released in nuclear reactions.
3. Importance of Atomic
Mass Atomic mass is an important concept in understanding the structure and properties of atoms.
It is used in a wide range of fields, from chemistry to nuclear physics, and plays a crucial role in many important applications.
The atomic mass of an element is used to calculate the number of atoms in a given sample, and can also be used to determine the element's place on the periodic table.
Atomic mass is also used to calculate the relative atomic mass of a molecule, which is important in determining the mole-to-mole ratios of reactants and products in chemical reactions.
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Key Takeaways
Atomic mass is also known as atomic weight.
The relative abundance of isotopes in a naturally occurring element is used to calculate the average mass of an element.
The atomic mass is the sum of the masses of its protons, neutrons, and electrons; an electron's mass is so small in comparison to the other particles that its mass is simply that of the nucleus (protons and neutrons).
FAQs
1. What is the unit of atomic mass?
The atomic mass unit (amu) is the standard unit used to express atomic mass. One atomic mass unit is defined as 1/12th of the mass of a carbon-12 atom, which is approximately 1.66 x 10-27 kg.
2. How is atomic mass calculated?
Atomic mass is typically calculated by taking into account the natural abundance of isotopes of an element and their individual masses. The weighted average of these isotopes is then used to determine the atomic mass.
3. What is the difference between atomic mass and atomic weight?
Atomic mass and atomic weight are used interchangeably and refer to the same concept. They both refer to the average mass of atoms of an element, but atomic weight is the term commonly used in chemistry, whereas atomic mass is used in physics.
4. Is atomic mass the same as an atomic number?
No, atomic mass and atomic number are different concepts. The atomic number of an atom is the number of protons present in the nucleus and is used to determine the element's place on the periodic table, whereas the atomic mass is the average mass of atoms of that element.
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