Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Understanding the composition of an atom, particularly the number of neutrons present, is vital in comprehending its stability and characteristics.

1. Atomic Mass and Protons: Helium, symbolized as He on the periodic table, possesses an atomic mass of 4 atomic mass units (u) and contains two protons in its nucleus. Protons, being positively charged particles, define an element’s identity. In the case of helium, the presence of two protons signifies its position as the second element in the periodic table.

2. Determining Neutrons: The atomic mass of an element includes the combined mass of its protons and neutrons. To find the number of neutrons in a helium atom, we use the formula:

Number of neutrons = Atomic mass number – Number of protons
In this instance:
Atomic mass number (A) = 4 u
Number of protons (Z) = 2

3. Calculation: By substituting these values into the formula, we calculate the number of neutrons:

Number of neutrons = Atomic mass number – Number of protons
Number of neutrons = 4 – 2
Number of neutrons = 2

4. Result: Hence, a helium atom, with an atomic mass of 4 u and two protons within its nucleus, contains 2 neutrons. These neutrons, along with the protons, contribute to the overall mass of the atom while also contributing to the stability of the nucleus.

Understanding the specific quantities of protons, neutrons, and electrons within an atom is pivotal in elucidating its properties, behavior in chemical reactions, and overall role in the formation of matter in our universe.