There are 15 protons and 22 neutrons in the nucleus of an element. What is its mass number?
37
Finding the Mass Number of an Element
The question asks us to find the mass number of an element given the number of protons and neutrons in its nucleus. Let's break down the concepts involved.
Understanding Protons, Neutrons, and Mass Number
- Protons: These are positively charged particles found in the nucleus of an atom. The number of protons uniquely identifies an element and is also called the atomic number ($Z$).
- Neutrons: These are neutral particles also found in the nucleus. They contribute to the mass of the atom but do not have an electric charge.
- Mass Number: The mass number ($A$) is the total number of protons and neutrons in the nucleus of an atom. It represents the approximate total mass of the atom in atomic mass units (amu), as protons and neutrons each have a mass close to 1 amu.
Calculating Mass Number
The relationship between mass number, protons, and neutrons is given by the simple formula:
$A = Z + N$
Where:
- $A$ is the Mass Number
- $Z$ is the number of Protons (Atomic Number)
- $N$ is the number of Neutrons
Applying the Formula to Find the Mass Number
We are given the following information:
- Number of protons = 15
- Number of neutrons = 22
Using the formula for mass number:
Mass Number ($A$) = Number of Protons ($Z$) + Number of Neutrons ($N$)
$A = 15 + 22$
$A = 37$
So, the mass number of the element is 37.
| Particle | Location | Charge | Contributes to |
|---|---|---|---|
| Proton | Nucleus | Positive (+1) | Atomic Number, Mass Number |
| Neutron | Nucleus | Neutral (0) | Mass Number |
| Electron | Outside Nucleus (Orbitals) | Negative (-1) | Chemical Properties |
Confirming the Result
The calculation shows that an element with 15 protons and 22 neutrons has a mass number of 37.
Revision Table: Atomic Structure Basics
| Term | Definition | How to Find |
|---|---|---|
| Atomic Number ($Z$) | Number of protons in the nucleus. Defines the element. | Given directly, or found on the Periodic Table for a specific element. |
| Mass Number ($A$) | Total number of protons and neutrons in the nucleus. | $A = Z + N$ (Number of Protons + Number of Neutrons) |
| Number of Neutrons ($N$) | The count of neutral particles in the nucleus. | $N = A - Z$ (Mass Number - Atomic Number) |
Additional Information: Isotopes and Mass Number
Atoms of the same element always have the same number of protons (the same atomic number). However, they can have different numbers of neutrons. Atoms of the same element with different numbers of neutrons are called isotopes.
Since the mass number is the sum of protons and neutrons, isotopes of an element have different mass numbers. For example, Carbon-12 and Carbon-14 are isotopes of carbon. Both have 6 protons, but Carbon-12 has 6 neutrons (mass number 12) while Carbon-14 has 8 neutrons (mass number 14).
The mass number is always a whole number because it is a count of particles. The atomic mass (often listed on the periodic table) is usually a decimal because it is the weighted average of the masses of all the naturally occurring isotopes of that element.
Similar Questions
- When a positively charged alpha particle is passed through a thin gold foil, most of the particles pass straight through without deflection. Based on Thomson's model of the atom, which of the following best explains this observation?
Which of the following is the last element in the Newlands Law of Octaves classification?
How many atoms are present in a (NH4)2SO4 molecule?
In Mendeleev’s periodic table, the properties of the elements are considered a periodic function of their:
Which of the following is essential for the synthesis of thyroxin?
If the atomic number of Krypton is 36, then its electronic configuration is:
The maximum number of electrons that can be accommodated in M shell is:
Which of the following is the third member of the Dobereiner triad, that also features Lithium and Sodium?
Atomic numbers of four elements are as follows: F (9), P (15), Cl (17), Ar (18).
Which of the following two elements would be chemically similar?
The number of neutrons present in a nitrogen atom is ________.
Important Questions from Structure of Atom
α particles are doubly charged ions of ________.
Which non-metal among the following is poly-atomic?
The elements belonging to the same group of periodic table have the same-
The sum of the total number of protons and neutrons present in the nucleus of an atom is known as-
A chemical equation is said to be balanced if number of ________.
