A Comprehensive Overview of Atomic Mass and Atomic Weight
What is Atomic Mass?
When it comes to Chemistry, there are many things that students have to learn. One important Chemistry topic that all students should learn is the topic of atomic mass and atomic weight.
Students always seem to have thousands of questions about atomic weight vs atomic mass. This is why today we are going to look into all important aspects related to the topic of atomic weight vs atomic mass.
In this article, students will be able to learn about atomic mass and relative atomic mass. We will also talk about the difference between atomic mass and atomic mass numbers, along with the difference between atomic weight and molecular weight.
So, let’s begin by first looking at what atomic mass means. According to experts, atomic mass can be defined as the total number of protons and neutrons present in an atom. It is important to remember that, ideally, the mass of electrons is also counted. However, since the size of the electrons is very small, their mass is often neglected.
The unit for atomic mass is Dalton. This unit is represented by ‘Da.’ Also, students should know that Dalton is the standard unit that is used for indicating the mass of an atom. The atomic mass of different elements varies as the number of protons and neutrons is different for different elements.
Relative Isotopic Mass
Now, let’s look at the meaning of relative isotopic mass. While atomic mass is an absolute mass, relative isotopic mass is a dimensionless number that has no units.
This loss of units is the result of using a scaling ratio concerning the carbon-12 standard. Further, it is interesting to note that the word ‘relative’ in the term relative isotopic mass refers to this scaling of the carbon-12 standard.
Based on this information, it can be said that the relative isotopic mass is the mass of any given isotope when the final value is scaled by the mass of carbon-12. It is important to remember that the mass of carbon-12 should always be determined experimentally in this case.
On a similar note, it can also be stated that the relative isotopic mass of a nuclide or isotope is the mass of the isotope relative to 1/12th of the mass of a carbon-12 atom.
Learn to View the Atomic Mass and Other Details in the Periodic Table
Students must now have a basic idea of the meaning of atomic mass and relative atomic mass. The next important step is to learn about atomic weight and the difference between atomic mass and atomic mass number. However, before that, students need to know how to spot some details in the periodic table.
What we mean by this is that all students must know how to spot the atomic number, atomic symbol, and atomic mass of an element on the periodic table. To help students succeed in this task, we have attached a labelled image below. Students can refer to this image to learn how to spot the atomic number, atomic symbol, and atomic mass of an element on the periodic table.
(image will be uploaded soon)
What is Atomic Weight?
It is a commonly known fact that a single element can have several isotopes. This means that if one wants to calculate the atomic weight, then it is important to consider the masses of different isotopes. The percentage of different isotopes might also vary.
It is also important to remember the values of isotope relative abundance and isotope mass while calculating the atomic weight. Also, atomic weight is known as the relative atomic mass. It can be defined as the ratio of the mean mass of the atoms of a chemical element to a certain standard.
Further, the normal unit of atomic weight has been 1/12th of the atomic mass of the carbon-12 isotope since the year 1961. An isotope can also be referred to as one of two or more species of atoms with different atomic mass numbers of the same chemical element.
Students should also be aware of the fact that atomic weight is also measured in the units of atomic mass. This is usually abbreviated to AMU. It is also known as Daltons. Before we proceed to discuss the difference between atomic weight and molecular weight, some students might also be interested to learn about the history of this concept.
A Brief History of Atomic Weight
According to various sources, John Dalton was the first scientist who considered that the value of one should be allotted to the hydrogen atom. This was considered as the base of his scale of atomic weights.
After that, for several decades, nuclidic masses were explained on a scale based on 1/18th the mass of neutral atom oxygen. The chemical atomic weight unit at that time was 1.000272 times the physical atomic mass unit.
This period of confusion was eventually brought to an end in 1961. This was done after the acceptance of the 1/12th mass of carbon as the unit for both atomic weights and nuclidic masses.
Differences between Atomic Mass and Atomic Weight
Till now, we have discussed the meaning of atomic mass and atomic weight. We have also looked at various aspects related to both of these topics. Now, it’s time to look at the difference between both of these concepts.
To make it easier for students, we have created a table that highlights the differences that exist between atomic mass and atomic weight. That table is mentioned below.
The Differences Between Atomic Mass and Atomic Weight
Fun Facts About Atomic Mass and Atomic Weight
Did you know that there were two groups of scientists who discovered the concept of relative atomic masses? John Dalton and Thomas Thomson discovered this concept in 1803 and 1805, respectively, while Jons Jakob Berzelius discovered this concept between 1808 and 1826.
Further, earlier, the relative atomic mass was defined with that of the lightest element. However, Prout’s hypothesis stated that the atomic mass of all elements would have to be proven to be exact multiples of the lightest element. Many other theories and experiments were carried out before finally arriving after using the 1/12th carbon-12 standard.
Composition of the Atom
Atoms are the smallest particles of any element. But the atom is also composed of 3 particles. These particles are neutrons, protons, and electrons. Every atom has 1 nucleus that binds 1 or many electrons around it and the nucleus typically has the same number of protons and neutrons. Protons and neutrons together are known as nucleons.
The protons are positively charged, neutrons are neutral and electrons are negatively charged.
Different Kinds of Atoms
The different kinds of atoms are-
Stable Atoms- Most atoms on the earth are stable and their protons, neutrons, and electrons are balanced. If there are no external forces to a stable atom, it will always stay the same.
Isotopes- Isotopes contain a different number of neutrons but the same number of protons and electrons. These are also called atom's cousins. Having extra neutrons might make isotopes radioactive.
Ions- Atoms with additional or absent electrons are called ions and they have a positive or negative electric charge. Ions are responsible for many chemical reactions in elements.
Radioactive- Radioactive Atoms are atoms that have multiple neutrons in the nucleus, which makes them very unstable. Radioactive atoms give off particles to eventually become stable.
Antimatter- All atomic particles have a twin anti-particle, with an opposite electric charge, they are antimatter. Antimatter is very infrequent and delicate.
Types of Subatomic Particles
The 3 types of subatomic particles are-
Electrons
Electrons have a negative charge. This charge is -1e which approximates \[ - 1.602 \times 10 ^ {-19} \].
The mass of an electron is nearly \[ 9.1 \times 10 ^ {-31} \].
Electrons have relatively negligible mass and that's why they are not counted when calculating the mass of an atom.
Protons
The positively charged subatomic particles are called protons. The charge on a proton is 1e, which is approximately \[ 1.602 \times 10 ^ {-19} \].
The mass of this subatomic particle is approximately \[ 1.672 \times 10 ^ {-24} \].
Protons are 1800 times heavier than electrons.
The atomic number of the element is always equal to the number of protons in the atoms of a given element.
Neutrons
The electrically neutral particles which carry no charge at all are called neutrons.
The mass of a neutron is nearly the same as the mass of a proton that is \[ 1.674 \times 10 ^ {-24} \].
Isotopes of an element have the same number of protons but differ in the number of neutrons.
Atomic Structure of Isotopes
Each element has a unique number of protons, which is described by its atomic number. But many atomic structures of any element can exist which disagree with the total number of nucleons. These variants are the Isotopes of the element which have different nucleon numbers ( mass number). The isotopes of an element have the exact number of protons but counter in the total number of neutrons. Nucleons are members of the nucleus, present in the atom. Any of the protons or a neutron can be nucleons. The atomic structure of an isotope is described with the help of the 3 things. They are
The chemical symbol of the given element
The atomic number of the given element
The mass number of the given isotope.
Photoelectric Effect
During the photoelectric effect, electrons escape from the surface of a given material. The surface of the material is composed of both positive and negative ions and when light is made to be incident on the given metal surface, some of the electrons which are there near the surface of the metal will absorb sufficient energy from the incident radiation. Thus, they overcome the attraction of the positive ions and when the electrons gain as much sufficient energy as required, they will run out of the metal surface into the surrounding area. This forms the basis for the Photoelectric Effect. Some energy points are-
Work Function - Work Function is the minimum energy that is required to remove an electron from the surface of the given metal.
Threshold Frequency - Threshold frequency is the minimum frequency of light that can force an electron to radiate from the surface of a given metal.
Threshold Wavelength - Threshold wavelength is the maximum wavelength of light that can displace a photoelectron from the surface of a given metal.
Conclusion
The study notes on the Differences between Atomic Mass and Atomic Weight provides a comprehensive overview of the topic including definitions of both Atomic Mass and Atomic Weight, the differences between them, composition of the atom, atomic structure of isotopes and the photoelectric effect.
FAQs on Difference Between Atomic Mass and Atomic Weight for JEE Main 2024
1. Explain the Topics of Atomic Number and Atomic Weight in Brief.
Atomic number is the number of protons that are present in a chemical element. It is also defined as the number of electrons present in an element. Atomic weight, on the other hand, is defined as the total number of protons plus the number of neutrons present in a chemical element. Atomic Weight is also called relative atomic mass. The unit, Daltons, is used to measure Atomic Weight and Atomic Mass and is also called Atomic Mass Unit or AMU.
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2. Where is the Atomic Mass of an Element Present?
According to various experimental evidence, the large majority of an atom’s mass is present in its nucleus. This is because the nucleus contains both protons and neutrons. The mass number of a chemical element is also represented by the letter ‘A,’ and it is the total number of protons and neutrons present in an atom. The unit of atomic mass denoted by 'u' is called the Unified Atomic Mass unit. Atomic Mass Unit is characterised as the mass which is equal to \[\frac{1}{12}\] of the mass of one carbon-12 atom
3. What is Atomic Weight also known as? Why is the Concept of Atomic Mass Important?
Atomic weight is also known as the relative atomic mass. In other words, the bonding ability of an atom is determined by the number of electrons. And in chemistry, the concept of atomic mass is vital because it is the relation between mass and moles. The value for mass can be calculated in the laboratory, and moles can be calculated by referring to the atomic numbers. Further, a lot of research that is carried out in chemistry is done based on atomic ratios.
4. What is the Difference Between Mass and Weight?
According to sources, the mass of an object can be defined as the measure of the inertial property of the object. It can also be defined as the sum of matter that is found within the object. The weight of an object, on the other hand, is the measure of the force that is exerted by gravity on the object. It can also be viewed as the force that is required to sustain that force. These are the major differences between Weight and Mass.
5. What is Valency?
Valency is the number of electrons gained/lost by an atom to achieve its outermost shell. In other words, the combining capacity of an atom is called the valency of the atom. The total number of bonds that an atom can constitute is expressed by its valency. The atoms become more and more stable by achieving their outermost shell or completing the octet. Atoms tend to combine with other atoms or participate in chemical reactions in which they give or lose electrons to other atoms, to get into a stable state by completing their octet.
