Question

Refer to the periodic table of the elements (Figure 3.5) to help you answer Questions \(2,3,\) and \(4 .\) 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 b) 92 electrons c) 146 neutrons

Step-by-step solution

Identify the Element

The element with 92 protons can be identified by looking at the atomic number on the periodic table. The atomic number is equal to the number of protons in an atom, which directly identifies the element as Uranium. Thus, the element with atomic number 92 is Uranium (U).

Calculate the Number of Electrons

For a neutral atom, the number of electrons is equal to the number of protons. Since the atom has 92 protons, it also has 92 electrons.

Calculate the Number of Neutrons

The mass number of an atom is the sum of its protons and neutrons. Given that the mass number is 238 and the number of protons is 92, the number of neutrons can be found by subtracting the number of protons from the mass number: \[ \text{Number of neutrons} = 238 - 92 = 146 \]. So, there are 146 neutrons in the atom.

Key concepts

Atomic Number

The atomic number of an element is a fundamental property that is crucial for identifying elements. This number equals the number of protons found in the nucleus of an atom. Every element has a unique atomic number.

On the periodic table, elements are arranged in order of increasing atomic number. So, by knowing the atomic number, you can easily identify the element. For example, if we know an element has an atomic number of 92, we can look at the periodic table and identify it as Uranium.

When using the periodic table, the atomic number is usually found above the symbol of the element, giving you quick information about the composition of the atom.

Neutrons

Neutrons are subatomic particles found in the nucleus of an atom alongside protons. Unlike protons, neutrons have no electrical charge. They play a vital role in adding mass to the atom while also stabilizing it.

To determine the number of neutrons in an atom, we use the formula: \[ \text{Number of neutrons} = \text{Mass number} - \text{Atomic number} \] The mass number is the sum of protons and neutrons.

For instance, with Uranium, when given a mass number of 238 and an atomic number of 92, the calculation would be: * Subtract the atomic number from the mass number: 238 - 92 * The result is 146 neutrons.

Neutrons ensure the stability of the nucleus. An imbalance in the number of neutrons can lead to radioactive isotopes.

Electrons

Electrons are negatively charged subatomic particles that orbit the nucleus of an atom. In a neutral atom, the number of electrons is equal to the number of protons, rendering the atom charge-neutral.

For example, Uranium, which has 92 protons, will also have 92 electrons in its neutral state. These electrons are arranged in various energy levels around the nucleus.

• The first energy levels are filled up first as they have lower energy.
• As electrons fill closer to the nucleus, the atom becomes more stable.

Understanding electron arrangement is important for explaining how elements interact with each other. Electrons are responsible for the chemical properties and reactivity of an atom. By considering electron configurations, chemists can predict how elements will bond.