Question

Uranium-235 is the isotope of uranium commonly used in nuclear power plants. How many (a) protons are in its nucleus? (b) neutrons are in its nucleus? (c) electrons are in a uranium atom?

Short answer

Answer: The uranium-235 isotope has 92 protons, 143 neutrons, and 92 electrons in a neutral atom.

Step-by-step solution

(Step 1: Understand the problem and notations)

We need to know the number of protons, neutrons, and electrons in the uranium-235 isotope. The symbol for uranium is U, and "uranium-235" means that it's an isotope of uranium with a mass number (A) of 235. The atomic number (Z) of uranium is 92, which represents the number of protons in the nucleus. The mass number (A) is the sum of the number of protons and neutrons. So, we can write it as: U-235 (uranium-235).

(Step 2: Calculate the number of protons)

The atomic number (Z) of uranium is 92. The number of protons in the nucleus of an atom is equal to the atomic number of the element, which is the number used to define the element. So, there are: Protons = Atomic number (Z) = 92 That means there are 92 protons in the nucleus of uranium-235.

(Step 3: Calculate the number of neutrons)

The mass number (A) of uranium-235 is 235, which is the sum of the number of protons and neutrons. We already know there are 92 protons in the nucleus. So, we can calculate the number of neutrons as: Neutrons = Mass number (A) - Atomic number (Z) = 235 - 92 Neutrons = 143 There are 143 neutrons in the nucleus of uranium-235.

(Step 4: Calculate the number of electrons)

In a neutral atom, the number of electrons is equal to the number of protons, because the positive charges of protons and the negative charges of electrons balance each other. In this case, uranium-235 is a neutral atom, so the number of electrons will be equal to the number of protons: Electrons = Protons = 92 There are 92 electrons in a neutral uranium-235 atom. The answers to the given questions are: (a) There are 92 protons in the nucleus of uranium-235. (b) There are 143 neutrons in the nucleus of uranium-235. (c) There are 92 electrons in a neutral uranium-235 atom.

Key concepts

Atomic Number

The atomic number is a fundamental characteristic of an element, serving as a unique identifier on the periodic table of elements. It is denoted by the symbol 'Z' and defines the number of protons in an atom's nucleus.

For example, the atomic number of uranium is 92, which is a constant for all atoms of uranium irrespective of the isotope. It is this quantity of protons that determines the chemical properties of the element and its placement on the periodic table. When students are asked to find the number of protons in uranium-235, they can directly reference the element's atomic number to arrive at the answer of 92 protons.

Neutrons in Nucleus

Understanding the concept of neutrons in the nucleus is critical when discussing isotopes. Neutrons, along with protons, make up the nucleus of an atom. The number of neutrons is variable in different isotopes of the same element, which results in differing mass numbers (denoted as 'A').

For uranium-235, we start with the mass number of 235 and subtract the atomic number, which represents the amount of protons, to find the number of neutrons. Mathematically, this is demonstrated by the equation:
Neutrons = Mass number (A) - Atomic number (Z) = 235 - 92 = 143.

This simple subtraction provides the neutron count, which is essential for identifying isotopes and their properties. In this case, uranium-235 contains 143 neutrons.

Atomic Structure

Atomic structure refers to the configuration of an atom, encompassing the nucleus (comprised of protons and neutrons) and the surrounding electron cloud. Electrons are negatively charged particles that orbit the nucleus at various energy levels or shells.

In a neutral atom, the number of electrons equals the number of protons, resulting in a balanced charge. The structure of uranium-235, like other atoms, follows this principle. As it has 92 protons, it also has 92 electrons when in a neutral state. This structure is important to grasp as it informs us on the reactivity and bonding nature of elements. Uranium's large and complex electron cloud explains its use in nuclear power and weaponry, showcasing the importance of its atomic structure.