Difference Between Atomic Mass and Atomic Number

Introduction

The no. of protons presents in the nucleus of every element's atom, denoted by the letter Z, is the element's atomic number. Using only an atom's atomic number, an element can be identified as an atom. Any atom with the atomic number 8 represents an 𝑂 (Oxygen) atom, and a different element would be represented by an atom with a different proton no. The mass number, which is represented by the A, is neutrons plus protons in an atom.

Atomic Mass

It is the average mass of elements. The atomic mass, determined in amu (atomic mass unit), is equal to the mass of a mole of an element. This relationship between the atomic mass and the mole concept is important in chemistry. 1 mole of iron atoms would thus weigh 55.847 grams since the atomic mass of iron is 55.847 amu.

Atomic Number

It is equivalent to the no. of protons, which is also equivalent to no. of electrons in neutral atoms. The atomic no. of 𝐹𝑒 is 26 because a 𝐹𝑒 atom's nucleus has 26 protons. The atomic number may be shown as a left subscript in the symbol used to denote a specific nuclear or atomic species. For instance, 26𝐹𝑒 can be used to represent an atom or nucleus of Fe.

$$\mathrm{Z\:=\:e\:=\:p}$$

$$\mathrm{e\Rightarrow\:electrons\:no.}$$

$$\mathrm{Z\Rightarrow\:proton\:or\:atomic\:no.}$$

$$\mathrm{p\Rightarrow\:protons\:no.}$$

Importance of Atomic Numbers

The periodic table lists the elements in ascending sequence of atomic no. It is the no. of protons in an atom. An element's identity is determined by its protons no.; for eg, an element with six protons is a 𝐶 atom, regardless of how many neutrons it may have. How many electrons surround the nucleus depends on the protons no., and the arrangement of these electrons determines the majority of an element's chemical activity. In a periodic chart with rising atomic numbers, elements with similar chemical properties naturally line up in the same column.

Examples of Atomic Numbers

Calculating the atomic number has nothing to do with how many electrons & neutrons are present in an atom. The atomic no. is always calculated by the no. of protons. For instance, since carbon has a six-atomic-unit structure, each carbon atom has six protons. For example, an atomic number of hydrogen is 1, sodium is 11 and magnesium is 12.

Finding the Atomic Number

Any element's atomic number may be computed using the methods listed below.

• First off, the no, of protons in every atom of an element may be used to determine its atomic number.

• Second, if an element name/symbol is provided, a periodic table can be used to identify the element. Consider the case where the symbol Al (aluminium) is used. The periodic chart reveals that the atomic number of aluminium is 13. Since the elements are listed in ascending order in the periodic table, it is simple to determine.

Mass Number

It is the no. of neutrons & protons in the nucleus of an element. This mass estimate may be used to rapidly determine an element's neutron count by simply deducting the no. of protons from the mass no. The identical element's isotopes will share a relatively similar atomic number but vary in mass.

$$\mathrm{A\Rightarrow\:n\:+\:p}$$

$$\mathrm{A\Rightarrow\:Mass\:no.\:of\:atom}$$

$$\mathrm{n\Rightarrow\:no.\:of\:neutrons}$$

$$\mathrm{p\Rightarrow\:no.\:of\:protons}$$

Use of Mass Number

The isotopic mass, which is expressed in atomic mass units, may be calculated using an element's mass number. An element's isotope will have a similar atomic number but a distinct mass number. Neutron count is the primary difference between isotopes. The mass number of several isotopes of the identical element will vary.

Properties of Mass Number

• A particular element is designated by its mass no., which is the total no. of its protons & neutrons.

• Nucleons are the collective name for protons and neutrons.

• Different elements may have different neutron counts. Even yet, the no.of protons in every atom of an element is the same. So, the definition of an isotope is an atom of a comparable element with an equivalent atomic no. but a different mass no.

Difference Between Atomic Number and Mass Number

Atomic Mass	Atomic Number
The neutrons plus protons in a specific element's nucleus are known as atomic mass.	The proton’s no. in an element's nucleus is often indicated by its atomic number.
It is the element’s average mass.	In the atom, it refers to the total amount of protons.
Represented by A	Denoted by Z
Additionally, it is employed to categorise several isotopes of a similar element.	The atomic number is the same among isotopes.

Conclusion

It can be concluded that the total proton no. in an atom is its atomic number. On either hand, the number of neutrons in an element may vary. The total no. of neutrons & protons in an element yields its mass no. Distinct isotopes of similar elements can be distinguished from one another using their atomic masses. Atomic mass is often measured using the atomic mass unit (amu). A periodic table of elements is organised according to their atomic numbers.

FAQs

1. Twenty neutrons and twenty electrons are found in the calcium atom. Find the calcium atom's atomic and mass numbers?

Atomic no. is equal to the total count of protons or electrons in a neutral atom so it will be 20 for Ca. The mass number is the sum of protons plus neutrons. Proton’s number is equal to no. of electrons so, no. of protons are 20. So mass number= 20 + 20 = 40.

2. How much is a mass of 1 atom?

Mass of 1 atom is 1.66 × 10−24. It is 1/12 the mass of Carbon-12 atoms. It is referred to as amu.

3. What is the mole of substance?

A mole is the mass of a substance that includes 6.022 × 1023 of that substance's particles. The mole is the SI unit. It has the designation mol.

4. A mole has how many atoms?

12 grams of pure Carbon-12 weigh precisely one mole, or 6.022 × 1023atoms, making one mole equivalent to 12 grams of pure carbon-12. Avogadro's No.is the no. of particles included in 1 mol(6.022 × 1023).

5. Where do electrons reside in atoms?

Electrons are present outside the atom's nucleus, in contrast to protons & neutrons, which are contained inside the nucleus at its centre. Negative electrons are drawn to the positive nucleus as the electric charges of opposite polarity attract one another.