Question

An isotope known as iodine-131 has 53 protons. How many neutrons does it have? A) 78 C) 68 B) 53 D) 184

Short answer

Iodine-131 has 78 neutrons.

Step-by-step solution

Understand the Definition of an Isotope

An isotope is defined by its number of protons and neutrons. The total of these particles gives the isotope its atomic mass number. For iodine-131, the atomic mass number is 131.

Determine the Number of Protons

The number of protons in iodine-131 is given as 53. This is a constant for iodine atoms and it defines the element.

Use Atomic Mass Number to Find Neutrons

To find the number of neutrons in an isotope, use the formula: \[ \text{Number of neutrons} = \text{Atomic mass number} - \text{Number of protons} \]Substituting the known values for iodine-131:\[ \text{Number of neutrons} = 131 - 53 \]

Calculate the Number of Neutrons

Perform the subtraction: \[ 131 - 53 = 78 \]Therefore, iodine-131 has 78 neutrons.

Key concepts

Atomic Mass Number

In chemistry, understanding isotopes starts with the concept of the atomic mass number. This number combines all the particles within an atom's nucleus: protons and neutrons. The atomic mass number is crucial because it gives us insight into the weight and stability of an element's isotope.
For instance, iodine-131 is an isotope where the '131' represents its atomic mass number. This tells us that the sum of its protons and neutrons equals 131.

• This number can vary for different isotopes of the same element due to the different number of neutrons.
• The atomic mass number helps differentiate between isotopes, as the protons typically remain constant for a given element.
• It's also essential for calculating the number of neutrons, one of the building blocks of an isotope's identity.

Understanding the atomic mass number is vital for grasping the more complex characteristics of isotopes.

Neutron Calculation

Calculating the number of neutrons in an isotope is a straightforward yet essential concept in chemistry. Neutrons play a crucial role in the stability of an element and often vary among isotopes, even when the number of protons stays the same.

To calculate them, we use a simple formula:

• Number of neutrons = Atomic mass number - Number of protons.

Let's break it down using the iodine-131 isotope as an example:

• For iodine-131, we know its atomic mass number is 131.
• It has 53 protons.
• By plugging these into the formula: \[ ext{Number of neutrons} = 131 - 53 \]
• We find that iodine-131 has 78 neutrons.

This easy calculation is invaluable for understanding how isotopes differ and why certain isotopes are preferred in scientific and medical applications.

Protons in Elements

Protons are fundamental to defining what element an atom is. The number of protons in an atom is constant for every element on the periodic table, and this is known as the atomic number.
The atomic number distinguishes one element from another.

• For iodine, regardless of its isotope form, it always has 53 protons.
• This is not just a random number; it is what makes iodine distinctly iodine.

Having a stable number of protons is essential in chemical reactions and bonding, as it determines how elements interact with each other.
It is also noteworthy that while protons remain constant across isotopes, the neutron count may change, leading to different isotopes like iodine-131. This consistency in proton count is what keeps the identity of the element intact, no matter which isotope is under consideration.