Difference Between AMU and Grams

Main Difference – AMU vs Grams

The terms amu and grams are used to measure the mass of substances. Therefore, grams can be converted into amu units and amu units can be converted into grams as well. Gram is a larger unit when compared to amu, but gram is a smaller unit compared to other units used for the measurement of mass. The term amu stands for “atomic mass unit” and is used for the measurements of very small substances such as atoms. The amu is the unit that is used to express the atomic mass of a chemical element. The main difference between amu and grams is that amu is used to express the mass in atomic level whereas gram is used as a metric unit of mass.

Key Areas Covered

1. What is AMU
      – Definition, Explanation, Calculation, Applications
2. What are Grams
      – Definition, Symbol, Applications
3. What is the Relationship Between AMU and Grams
      – How to Convert Grams into AMU
4. What is the Difference Between AMU and Grams
      – Comparison of Key Differences

Key Terms: Amu, Atom, Atomic Mass, Grams, Mass, Neutrons, Nucleus, Protons

What is AMU

The term amu can be defined as a unit of mass that is equal to exactly one twelfth of the mass of carbon-12 atom. The term amu stands for “atomic mass units”. The value of one twelfth of the mass of carbon-12 atom is 1.660538921 x 10−27 kg. Therefore, 1amu is equal to 1.660538921 x 10−27 kg of mass. This is approximately equal to the mass of a proton or a neutron. (One carbon atom of caron-12 isotope is composed of 12 protons. Then the mass of one twelfth of that atom is equal to the mass of a proton).

Figure 1: A diagram of carbon-12 atom

When the mass of an atom is given in the units of amu, it gives the sum of the masses of all protons and neutrons that are in the nucleus of the atom. Electrons have a negligible mass when compared to protons and neutrons. However, since the number of protons is a unique characteristic for any given chemical element, the mass of that number of protons should also be unique for each element. The total mass of the protons is named as the atomic number of an element. Therefore, both atomic number and atomic mass are given in the terms of amu.

The concept amu was introduced because the masses of atoms are minute and cannot be measured by the units that we use to measure heavy substances. For example, the mass of a proton in grams or kilograms is a very little amount that is not that easy to be handled. But when it is given in amu, it is very easy to handle.

What are Grams

Gram is a unit used to measure a mass of a substance. It can be defined as the mass that is equal to one thousandth of a kilogram (1/1000 kg). The symbol for this unit is “g”. The older definition for gram is “the mass of one cubic centimeter of water at 4^oC. The gram is used in measuring solid substances in the day to day life.

Figure 2: Grams is a measuring unit used in day to day life

When using the symbol with a value, one should use a space between the value and the symbol. For example, if there is a compound having a mass of 450 of grams, then it is given as “450 g”. The gram was a fundamental unit for measuring the mass according to the “centimeter-gram-second system of units”. But later it was replaced with kilogram (kg) in the SI unit system.

Relationship Between AMU and Grams

The terms amu and grams can be interconverted. This means amu can be converted into grams and grams can be converted into amu as well.

For example, the atomic weight of carbon-12 isotope is 12 g/mol. That means one mole of carbon-12 isotope weighs 12 g. The atomic mass of carbon-12 isotope is 12 amu. Therefore,

1 mol of carbon-12 = 12 g
12 amu = 12 g / 1 mol
= 12 g / 6.023 x 10²³
Then, 1 amu = 1.66 x 10^-24 g

Definition

AMU: Amu can be defined as a unit of mass that is equal to exactly one twelfth of the mass of carbon-12 atom.

Gram: Gram can be defined as the mass that is equal to one thousandth a kilogram (1/1000 kg).

Symbol

AMU: The symbol used to express “atomic mass unit” is amu.

Gram: The symbol for grams is “g”.

Applications

AMU: The unit amu is used for measurements in atomic level.

Gram: Gram is used in measuring large substances when compared to amu.

Conclusion

The terms amu and grams are used in measuring masses of substances. Gram is used in our day to day life to express the mass of goods that we use whereas amu is used for minute scale measurements. The main difference between amu and grams is that amu is used to express the mass in atomic level whereas gram is used as a metric unit of mass.

References:

1. Helmenstine, Anne Marie. “What Is an Atomic Mass Unit or amu?” ThoughtCo, Available here. Accessed 13 Sept. 2017.
2. “Gram.” Wikipedia, Wikimedia Foundation, 5 Sept. 2017, Available here. Accessed 13 Sept. 2017.
3. “How to Convert Grams to AMU.” Sciencing, Available here. Accessed 13 Sept. 2017.

Image Courtesy:

1. “1636489” (Public Domain) via Pixabay
2. “2222968” (Public Domain) via Pixabay