Differences Between Atomic Mass and Molecular Mass
Each particle of matter has some measure of mass related to it whether little or huge. Everything is composed of atoms. The mass of an atomic particle is known as the atomic mass. This is usually expressed according to the international arrangement as far as a brought together atomic mass unit (amu).
It very well may be best characterized as 1/12th of the mass of a carbon-12 atom in its ground state. The mass of an atom can be represented by the whole of the mass of protons and neutrons which is practically equal to the atomic mass. This little change is because of the coupling energy mass misfortune.
1 amu = 1.66 x 10-24 g
Atomic Mass of an Atom
The atomic weight of an atom is a dimensionless number when it is isolated by bound together atomic weight or Daltons.
This is known as the total isotopic mass.
The atomic masses of elements change from 1.008 amu for hydrogen up to 250 amu for elements that have an extremely high atomic number.
Mass of molecules can be dictated by including the normal atomic mass of every atom in the molecule.
In this article, we will learn about atomic mass and molecular mass, what is the atomic mass of iron, what is the atomic mass of potassium, and learn in general about the atomic and molecular masses.
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Atomic Mass of Different Elements
Given below are atomic masses of different elements.
What is Molecular Mass?
Let us now look at what molecular mass is.
The molecular mass of a compound refers to the total of all the atomic masses of the atoms which form a compound.
Molecular mass is the measure of mass related to a molecule. It is likewise called atomic weight. It tends to be determined by including the mass of every atom duplicated by the number of atoms of the element present in the molecule. For example, water consists of 2 hydrogen atoms and 1 oxygen atom. Mass of the water molecule is equal to the normal atomic mass of hydrogen increased by two or more the atomic mass of oxygen. The molecular mass of elements relies on the constituent atoms of the molecule.
The molecular mass of molecules can be controlled in the following way:
Mass Spectrometry: This technique is commonly utilized in deciding the mass of little molecules. This is accounted for as monoisotopic mass.
Hydrodynamic Strategy: The weight is resolved according to Mark-Houwink relations. This technique requires calibration; subsequently it is likewise depicted as a relative atomic weight determination strategy.
Static Light Scattering: Molecular weight is resolved from the measure of light dispersed utilizing the Zimm technique.
Key Takeaway Points
All matter is composed of atoms.
Elements are substances composed of just one sort of atom.
Atoms have a focal nucleus which contains protons and neutrons.
Electrons tend to move in orbits around the nucleus.
Protons’ relative mass is 1 and they have a positive charge.
Neutrons’ relative mass is 1 and they are neutral.
Electrons have a very negligible mass and a negative charge.
Every particle of matter, no matter how small or large, has a mass associated with it. Atoms are the building blocks of everything.The mass of an atomic particle is its atomic mass. As far as a brought together atomic mass unit, this is normally expressed according to the international agreement. It's possible that it's best described as 1/12th the mass of a carbon-12 atom in its ground state. The total mass of protons and neutrons, which is nearly equal to the atomic mass, can be used to represent the mass of an atom. The coupling energy mass imbalance is responsible for this minor variation. When an atom is isolated by bonded together atomic weight or Daltons, its atomic weight is a dimensionless number. The total isotopic mass is the term for this. Elements' atomic masses range from 1.008 amu for hydrogen to 250 amu for elements with extraordinarily high atomic masses.
The normal atomic mass of each atom in a molecule can be used to determine the mass of the molecule. We will study atomic mass and molecular mass in this post, as well as what the atomic mass of iron is and what the atomic mass of potassium is, as well as the atomic and molecular masses in general.
Overview of Molecular Mass
The combined atomic masses of the atoms that make up a compound are referred to as molecular mass. The mass of a molecule is measured by its molecular mass. It's also known as atomic mass. It is usually calculated by multiplying the mass of each atom by the number of atoms of the element present in the molecule. Two hydrogen atoms and one oxygen atom, for example, make up water. Water molecules have a mass equal to the standard atomic mass of hydrogen multiplied by two or more times the atomic mass of oxygen. The atoms that make up a molecule determine the molecular mass of an element.
Molecules' molecular masses can be manipulated in the following way:
Mass Spectrometry: This method is often used to determine the mass of small compounds. Monoisotopic mass is used to account for this.
The weight is resolved using Mark-Houwink relations in a hydrodynamic strategy. Because this technique necessitates calibration, it is sometimes referred to as a relative atomic weight determination strategy.
Static Light Scattering: The Zimm approach is used to determine the molecular weight from the amount of light dispersed.
Solved Example
Question: What is the molar mass of sulfur trioxide SO3, an atomic compound?
Solution: By definition, the molar mass of SO3 equals its atomic mass in grams. Hence, the calculation of the molar mass of SO3 is needed first.
The molecular mass (also called formula mass) of a compound refers to the total atomic masses of the apparent multitude of atoms in the molecule. The molecular mass of SO3 with 4 atoms in its molecule, is given by,
1S = 1 x 32.07 amu
= 32.07amu
3O = 3 x 16.00 amu
= 48.00amu
Therefore, the molecular mass of SO3 is 80.07 amu.
FAQs on Atomic Mass and Molecular Mass: Definitions, Formulas & Examples
1. What is the fundamental difference between atomic mass and molecular mass?
The fundamental difference lies in the entity they describe. Atomic mass refers to the mass of a single atom of an element, expressed in atomic mass units (u). It is the weighted average mass of all naturally occurring isotopes of that element. For example, the atomic mass of Carbon is approximately 12.011 u. Molecular mass, on the other hand, is the mass of a single molecule of a substance. It is calculated by summing the atomic masses of all the atoms present in the molecule's formula. For instance, the molecular mass of a water molecule (H₂O) is the sum of the atomic masses of two hydrogen atoms and one oxygen atom.
2. How is the molecular mass of a compound calculated? Provide an example.
To calculate the molecular mass of a compound, you need to sum the atomic masses of every atom in its chemical formula. Let's take the example of sulphuric acid (H₂SO₄):
- First, identify the number of atoms of each element: 2 Hydrogen atoms, 1 Sulphur atom, and 4 Oxygen atoms.
- Next, find the atomic mass of each element from the periodic table (approximate values: H = 1.008 u, S = 32.06 u, O = 16.00 u).
- Finally, multiply the number of atoms by their respective atomic masses and add them together:
- Molecular Mass of H₂SO₄ = (2 × 1.008 u) + (1 × 32.06 u) + (4 × 16.00 u) = 2.016 u + 32.06 u + 64.00 u = 98.076 u.
3. What is the key distinction between atomic mass and mass number?
While they sound similar, atomic mass and mass number are distinct concepts. The mass number (A) is a whole number that represents the total count of protons and neutrons in an atom's nucleus. It is always an integer. In contrast, atomic mass is the actual measured mass of an atom (or the weighted average for an element), which is rarely a whole number because it accounts for the exact mass of protons, neutrons, electrons, and the mass defect from nuclear binding energy. It is also a weighted average of the masses of an element's natural isotopes.
4. Why are the atomic masses of most elements on the periodic table not whole numbers?
The atomic mass of an element is not a whole number primarily because of the existence of isotopes. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. The atomic mass listed on the periodic table is a weighted average of the masses of all its naturally occurring isotopes, based on their relative abundance. For example, Chlorine has two main isotopes: Chlorine-35 (abundance ~75.77%) and Chlorine-37 (abundance ~24.23%). This results in an average atomic mass of approximately 35.45 u, which is not a whole number.
5. When should you use the term 'formula mass' instead of 'molecular mass'?
The term 'molecular mass' is correctly used for substances that exist as discrete molecules, typically covalent compounds like water (H₂O) or methane (CH₄). The term 'formula mass' is used for ionic compounds, such as Sodium Chloride (NaCl) or Calcium Carbonate (CaCO₃). This is because ionic compounds do not form individual molecules but exist as a crystal lattice structure. 'Formula mass' refers to the sum of the atomic masses of the atoms in the compound's empirical formula unit. While calculated in the same way, the terminology reflects the different chemical structures.
6. What is the importance of understanding atomic and molecular mass in chemistry?
Understanding atomic and molecular mass is crucial for quantitative chemistry, particularly in the field of stoichiometry. It forms the bridge between the microscopic world of atoms and molecules and the macroscopic world of grams that we can measure in a lab. Key applications include:
- Converting between the mass of a substance and the number of moles (using the mole concept).
- Determining the empirical and molecular formulas of unknown compounds.
- Calculating the theoretical yield of products in a chemical reaction.
- Preparing solutions of a specific concentration (molarity).
7. What is an Atomic Mass Unit (amu or u) and why is it used?
An Atomic Mass Unit (amu or u) is the standard unit used to express the masses of atoms and molecules. It is defined as exactly one-twelfth (1/12th) the mass of a single, neutral atom of the Carbon-12 isotope in its ground state. Using grams to describe the mass of a single atom would involve extremely small and inconvenient numbers. The atomic mass unit provides a convenient relative scale where the mass of a Carbon-12 atom is exactly 12 u, making it easier to compare the masses of different atoms and molecules.
