Question

Assume that the number of protons in a neutral atom is 92 and its mass number is 238 . a. What is the name of the element? b. How many electrons does it have? C. How many neutrons does it have?

Short answer

a. Uranium (U) b. 92 c. 146

Step-by-step solution

Identifying the Element by Atomic Number

The atomic number of an element is equal to the number of protons in the nucleus. Here, the atomic number given is 92. By consulting the periodic table, we find that the element with atomic number 92 is Uranium (U). Hence, the first question is answered: The element is Uranium.

Determining 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 are balanced by the negative charges of electrons. Here, since the atom has 92 protons, it also has 92 electrons.

Calculating the Number of Neutrons

The mass number of an atom is the sum of the number of protons and neutrons in its nucleus. Given that the mass number is 238 and the atomic number (number of protons) is 92, we can calculate the number of neutrons with the formula: \[ \text{Number of neutrons} = \text{Mass number} - \text{Number of protons} = 238 - 92 = 146. \] Thus, the atom has 146 neutrons.

Key concepts

Atomic Number

The atomic number of an element is a fundamental property that defines its identity. This number represents the total count of protons found in an atom's nucleus. Each element on the periodic table has a distinct atomic number, making this a unique fingerprint for elements.
For example, in the exercise, the atom has an atomic number of 92. Looking this up on the periodic table, we find that this signifies the element Uranium.
Knowing the atomic number is crucial because:

• It tells you the number of protons in the nucleus.
• It helps in identifying the element on the periodic table.
• It determines the chemical properties of the element.

In this case, Uranium is defined by having exactly 92 protons in its nucleus. Without this specific atomic number, it could not be Uranium or express the characteristics of Uranium.

Mass Number

The mass number of an atom is another crucial concept. It is not displayed on the periodic table but is essential for understanding the composition of an atom.
The mass number is calculated as the combined total number of protons and neutrons in an atom's nucleus. In the Uranium example provided, the mass number is 238.
Here's why the mass number is important:

• It helps in calculating the number of neutrons, given the atomic number.
• It influences the atomic weight of an element.
• It is vital for understanding isotopes, which are atoms with the same number of protons but different numbers of neutrons.

By subtracting the atomic number (92) from the mass number (238), we find that Uranium has 146 neutrons. This calculation is fundamental when studying atomic structures.

Protons, Neutrons, and Electrons

Understanding protons, neutrons, and electrons is essential for grasping atomic structure. These are the three primary subatomic particles that make up an atom.

• Protons: Positively charged particles found in the nucleus. They define the atomic number and thus the element's identity.
• Neutrons: Neutral particles also in the nucleus. They add mass to the atom and influence isotopic characteristics.
• Electrons: Negatively charged particles orbiting the nucleus. They balance the protons' charge in neutral atoms.

In Uranium's case, it has:

• 92 protons, establishing its place as Uranium on the periodic table.
• 92 electrons, ensuring the atom remains electrically neutral.
• 146 neutrons, adding to the atomic mass and participating in isotopic variation.

Understanding these particles helps explain why elements behave the way they do chemically.

Periodic Table

The periodic table is a critical tool in chemistry and the study of atomic structure. It organizes all known elements in a manner that highlights their properties and relationships.
Elements are arranged in order of increasing atomic number, helping to quickly identify them based on their proton counts. Uranium, for example, can be found by locating the element with atomic number 92.
The periodic table is useful because:

• It provides quick access to information about each element, including atomic number and symbol.
• It shows trends in element properties, such as electronegativity, atomic radius, and ionization energy.
• It helps predict how elements might react chemically based on their position and group.

Using the table, students can identify not only the element's location but also the characteristics that define it. This organization simplifies the study and application of chemical elements.