How to find the number of protons, electrons, and neutrons?
Everything in the world is matters. Just like matter is made up of tiny indivisible particles called atoms, these atoms further consist of a large number of subatomic particles. Electrons, protons, and neutrons are the most important subatomic particles present in an atom.
These three control the physical and chemical properties of the atomic elements. In this article, you will learn everything there is to know about these subatomic particles.
Especially how to find the protons, neutrons, and electrons present in a particular atom or an element. So, let’s start reading!
Protons are positively charged particles present inside the nucleus of an atom.
Neutrons are neutral particles present inside the atomic nucleus.
Electrons are negatively charged particles circulating around the atomic nucleus.
The basic atomic structure consists of a dense positively charged nucleus present at the center. The positive charge comes from the positively charged protons. The nucleus is surrounded by negatively charged electrons, held in specific energy levels called shells. Oppositely charged subatomic particles attract each other by a force known as the nuclear force of attraction.
A neutral atom consists of an equal number of protons (p) and electrons (e). So, the total positive charge gets canceled by the total negative charge which leads to an overall zero charge on the atom, and it stays stable.
The mass of a proton is equal to the mass of a neutron while the electrons possess a negligible mass i.e., 1/1836th times the mass of a proton or neutron.
Subatomic particle
Symbol
Charge
Relative mass (amu)
Actual mass (kg)
Proton
p+
+1
1
1.67 x 10-27
Neutron
n
0
1
1.67 x 10-27
Electron
e–
-1
1/1836
9.11 x 10-31
The abbreviation amu represents atomic mass units.
How do find the number of electrons, protons, and neutrons from the Periodic Table?
The protons present in the nucleus of an atom can be determined from its atomic number (symbol Z).
On the other hand, the total number of protons and neutrons present in the atomic nucleus is represented as its mass number (symbol A).
The Periodic Table is an arrangement of atomic elements in an order of increasing atomic number.
The following steps will lead you in finding the number of protons, electrons, and neutrons of an element from the Periodic Table.
Step I: Read the Periodic Table from left to right and identify the given element from its symbol.
For example, the symbol for sodium element is Na. It is located at the beginning of the Periodic Table in the first column (Group IA) and third row (Period no. 3).
Step II: The number at the top of the elemental symbol represents the atomic number (Z). Find the protons present in the element by using equation 1.
Atomic number Z= number of protons present in the atoms of that element. (Equation1)
The number at top of Na is 11. So, 11 protons are present in a sodium atom.
Step III: Find the number of electrons present in this element. In an uncharged neutral atom, the number of electrons= number of protons.
So, there are 11 electrons present in a neutral sodium atom.
Step IV: Find the number of neutrons present in the element by using formula 1.
A number of neutrons= Mass number (A)- Atomic number (Z). (Formula 1)
The mass number is the nearest whole number value of the number written at the bottom of the elemental symbol in the Periodic Table. As the mass number is the sum of protons and neutrons so the neutrons present in an atomic element can be determined by subtracting Z from A.
The mass number of sodium is 23. So, the sodium atom has 23-11=12 neutrons.
Thus, an atom of sodium (Na) has 11 electrons, 11 protons, and 12 neutrons respectively.
How do find the number of electrons, protons, and neutrons present in an isotope?
Isotopes are different forms of the same element that have the same atomic number, but their mass numbers are different. By this definition, two or more isotopes of an element have the same number of protons and electrons, but the number of neutrons present in them differs.
Once we know the isotopic notation, and the atomic and mass numbers of the different isotopes of an element we can conveniently find the number of electrons, protons, and neutrons present in them by following all those steps as discussed in the previous section.
Let’s understand this concept further with the help of some relevant examples.
Example #1:
Protium (1 1H), deuterium (1 2H), and tritium (1 3H) are three isotopes of the hydrogen element.
For protium (1 1H)
Number of protons = atomic number = 1
Number of electrons = Number of protons = 1
Number of neutrons = Mass number – atomic number = 1-1 =0.
For deuterium (1 2H)
Number of protons = atomic number = 1
Number of electrons = Number of protons = 1
Number of neutrons = Mass number – atomic number = 2-1 =1.
For tritium (1 3H)
Number of protons= atomic number = 1
Number of electrons= Number of protons = 1
Number of neutrons= Mass number-atomic number =3-1=2.
So, now you can see that all the isotopes of hydrogen have the same number of protons and electrons present in them (i.e., 1 and 1) while the neutrons present in them differ i.e., 0,1, and 2 respectively.
Example#2:
6 12C, 6 13C, and 6 14C are the three main isotopes of carbon.
Let’s find their protons, electrons, and neutrons.
For 6 12C
Number of protons = atomic number = 6
Number of electrons = number of protons =6
Number of neutrons= mass number – atomic number = 12-6 = 6.
For 6 13C
Number of protons = atomic number = 6
Number of electrons = number of protons = 6
Number of neutrons = mass number – atomic number = 13-6 = 7.
For 6 14C
Number of protons= atomic number = 6
Number of electrons = number of protons = 6
Number of neutrons= mass number -atomic number = 14-6=8.
All the elements are usually a combination of their many isotopes, but the relative abundance of a specific isotope may be much greater than the others. Therefore, you must have noticed that the relative atomic mass (Ar) of an element is generally recorded in decimal points while its mass number is taken as a whole number.
For example, the Ar of carbon is 12.011. But the mass number (A) written as a superscript on C is 12 because 12C is present in a much greater proportion than any of 13C or 14C isotopes in the carbon element. The relative abundance of the 12C isotope in carbon is 98.89 % while that of its 13C isotope is 1.11 %. However, the 14C isotope is present only in a trace amount.
The mass number of an element is its relative atomic mass (Ar) rounded off to the nearest whole number value. Therefore, one should always keep in mind that we use the mass number and not the relative atomic mass of an element to calculate the number of neutrons present in it.
Neutrons are sub-atomic particles; they always exist as an integer value and cannot be represented using fractions or decimal points.
How do find the number of electrons, protons, and neutrons present in an ion?
We have already told you that a neutral atom has an equal number of protons and electrons present in it. But, this is not the case in an ion.
Atoms acquire electric charges and change into ions by the gain or loss of one or more electrons. The gain of electrons results in negatively charged ions called anions. On the other hand, the loss of electrons produces positively charged ions called cations.
The number of protons and neutrons present in an atom stays unchanged in its ionic form. Contrarily, the number of electrons present in it changes based on the acquired charge.
To find the electrons present in an ion:
If the charge is positive: Subtract the magnitude of the charge from the atomic number.
If the charge is negative: Add the magnitude of the charge to the atomic number.
Example #1:
Sodium ion (Na+) is formed from sodium atom (Na)
A positive charge is present on Na+
The magnitude or amount of charge present = 1
The atomic number (Z) of the sodium atom is 11
Number of electrons present in Na+ ion= Atomic number – magnitude of charge = 11 -1 = 10
The number of protons and neutrons present in Na+ ion stays the same i.e., 11 and 12 respectively.
Neutrons are electrically neutral particles, so they stay uninvolved in the calculations. However, the loss of one electron develops an electron deficiency consequently the Na+ ion has more protons than electrons.
Example #2:
Nitride (N3-) ion is formed from nitrogen atom (N)
A negative charge is present on N3-
The magnitude or amount of charge present = 3
The atomic number (Z) of the nitrogen atom is 7
Number of electrons present in N3- ion = Atomic number + magnitude of charge = 7+3 = 10
Number of protons present in N3- = Atomic number (Z) = 7.
Number of neutrons present in N3- = Mass number – atomic number = 14-7 =7
The gain of three electrons makes N3- an electron-rich species so it has more electrons than protons present in it.
How do find the number of electrons, protons, and neutrons in a compound?
A compound is defined as a chemical substance formed by the combination of atoms belonging to two or more different elements.
Example:
Carbon dioxide (CO2) is a compound consisting of one carbon atom and two atoms of oxygen.
Let us discuss how can we find the total number of electrons, protons, and neutrons present in this compound.
Step I: Find the number of electrons, protons, and neutrons present in an atom of each individual element from the compound.
CO2 has two individual elements i.e., carbon (C) and oxygen (O)
Carbon
Number of protons = atomic number = 6
Number of electrons = number of protons = 6
Number of neutrons = mass number – atomic number = 12- 6 = 6
Oxygen
Number of protons= atomic number = 8
Number of electrons = number of protons = 8
Number of neutrons = mass number -atomic number = 16-8 =8
Step II: Identity how many atoms of each element are present in the compound.
There is 1 atom of carbon while two atoms of oxygen are present in CO2.
Step III: Multiply the number of protons, electrons, and neutrons calculated in step I with the number of atoms of each element.
1 atom of carbon
1 x ( 6 protons) = 6 protons
1 x (6 neutrons ) = 6 neutrons
1 x (6 electrons ) = 6 electrons
2 atoms of oxygen
2 x ( 8 protons ) = 16 protons
2 x (8 neutrons ) = 16 neutrons
2 x (8 electrons) = 16 electrons
Step IV: Take the sum of all the protons, neutrons, and electrons calculated.
Total number of protons = 6 + 16= 22
Total number of neutrons = 6 +16 = 22
Total number of electrons = 6 + 16 = 22
So, there are a total of 22 protons, 22 neutrons, and 22 electrons present in CO2.
The number of protons, electrons, and neutrons present in the first 30 elements of the Periodic Table?
Periodic Element
Atomic number
Mass number
Protons
Electrons
Neutrons
Hydrogen (H)
1
1
1
1
0
Helium (He)
2
4
2
2
2
Lithium (Li)
3
7
3
3
4
Beryllium (Be)
4
9
4
4
5
Boron (B)
5
11
5
5
6
Carbon (C)
6
12
6
6
6
Nitrogen (N)
7
14
7
7
7
Oxygen (O)
8
16
8
8
8
Fluorine (F)
9
19
9
9
10
Neon (Ne)
10
20
10
10
10
Sodium (Na)
11
23
11
11
12
Magnesium (Mg)
12
24
12
12
12
Aluminum (Al)
13
27
13
13
14
Silicon (Si)
14
28
14
14
14
Phosphorus (P)
15
31
15
15
16
Sulfur (S)
16
32
16
16
16
Chlorine (Cl)
17
35
17
17
18
Argon (Ar)
18
40
18
18
22
Potassium (K)
19
39
19
19
20
Calcium (Ca)
20
40
20
20
20
Scandium (Sc)
21
45
21
21
24
Titanium (Ti)
22
48
22
22
26
Vanadium (V)
23
51
23
23
28
Chromium (Cr)
24
52
24
24
28
Manganese (Mn)
25
55
25
25
30
Iron (Fe)
26
56
26
26
30
Cobalt (Co)
27
59
27
27
32
Nickel (Ni)
28
59
28
28
31
Copper (Cu)
29
64
29
29
35
Zinc (Zn)
30
65
30
30
35
FAQ
Who discovered the atomic number (Z)?
The atomic number (Z) was first introduced by the English physicist Henry Moseley based on the number of electrons present in an atom.
The symbol Z comes from German Zahl which literally means ‘’number’’.
In the modern scientific world today, Z is generally defined as the number of protons present in an atomic element.
As a neutral (uncharged) atom has an equal number of protons and electrons so the atomic number (Z) = number of protons = number of electrons.
What is mass number (A)?
The mass number (A) is defined as the total number of protons and neutrons present in the nucleus of an atom. It is calculated by taking the relative atomic mass (Ar) of an element from the Periodic Table and rounding it off to the nearest whole number value.
How to find the number of neutrons of an atom from its mass number (A)?
The number of neutrons present in an atom = mass number (A) – atomic number (Z).
For example, Bromine has elemental notation 35 80Br. Its atomic number (Z) = 35 while its mass number (A) = 80. Number of neutrons = 80-35= 45.
So, an atom of bromine has 45 neutrons present in its nucleus.
How do find the number of protons and electrons when an ion has a positive or negative charge?
Ions have the same number of protons as their constituent atomic elements.
In case of positive charge: Number of electrons = atomic number – the magnitude of the charge
In case of negative charge: Number of electrons = atomic number + magnitude of charge.
How many protons, neutrons, and electrons are present in krypton, represented by 36 83.8Kr ?
Number of protons = atomic number = 36.
Number of electrons = number of protons= atomic number =36.
Number of neutrons = Mass number – atomic number
The superscript having decimal points is the relative atomic mass of krypton which is the average mass of all the isotopes of Kr elements.
8 rounded off to the nearest whole number is 84 so the mass number of Kr = 84.
Number of neutrons = 84-36= 48.
How many total protons, neutrons, and electrons are present in a water (H2O) molecule?
H2O is a compound made up of two atoms of hydrogen and one atom of oxygen.
Hydrogen has 1 proton, 0 neutrons, and 1 electron.
2 hydrogen atoms mean 2 protons, 0 neutrons, and 2 electrons.
Oxygen has 8 protons, 8 neutrons, and 8 electrons.
So, the H2O molecule has a total of 2+ 8 = 10 protons, 0 + 8 = 8 neutrons, and 2 + 8 = 10 electrons.
Summary
An atom consists of sub-atomic particles. Protons are positively charged particles while neutrons are neutral particles.
Both protons and neutrons are present in the nucleus of an atom.
Electrons are negatively charged particles that rotate around the nucleus in specific energy levels.
A proton and an electron have an equal but opposite charge.
The atomic number (Z) of an element represents the total number of protons present in an atom of that element.
A number of protons of an atom = Number of electrons = Atomic number (Z).
Mass number (A) represents the total protons and neutrons present in the nucleus of an atom.
The number of neutrons = mass number (A) – atomic number (Z).
Both atomic and mass numbers can be determined from the Periodic Table.
Ions are electrons deficient or electron-rich species.
The number of protons and neutrons present in an atom and its ion stays the same while the number of electrons differs based on the magnitude of charge present.
Isotopes are different forms of an element that have the same atomic number, but their mass number differs.
So, two or more isotopes of an element have the same number of protons and electrons but a different number of neutrons.
Ammara Waheed is a highly qualified and experienced chemist, whose passion for Chemistry is evident in her writing. With a Bachelor of Science (Hons.) and Master of Philosophy (M. Phil) in Physical and Analytical Chemistry from Government College University (GCU) Lahore, Pakistan, with a hands-on laboratory experience in the Pakistan Council of Scientific and Industrial Research (PCSIR), Ammara has a solid educational foundation in her field. She comes from a distinguished research background and she documents her research endeavors for reputable journals such as Wiley and Elsevier. Her deep knowledge and expertise in the field of Chemistry make her a trusted and reliable authority in her profession. Let's connect - https://www.researchgate.net/profile/Ammara-Waheed
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The mass number of an element is its relative atomic mass (Ar) rounded off to the nearest whole number value. Therefore, one should always keep in mind that we use the mass number and not the relative atomic mass of an element to calculate the number of neutrons present in it. 
