Question

Assume that the number of protons in a neutral atom is 92 and its atomic mass is 238.03. (Hint: Refer to the periodic table in Figure 1.5 to answer this question.) a. What is the name of the element? b. How many electrons does it have? c. Given its atomic mass, how many neutrons must it have?

Short answer

The element is uranium. It has 92 electrons and approximately 146 neutrons.

Step-by-step solution

Determine the Element Name

In a neutral atom, the number of protons in the nucleus equals the atomic number. The atomic number 92 corresponds to the element uranium in the periodic table.

Calculate the Number of Electrons

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

Calculate the Number of Neutrons

The atomic mass is given as 238.03. To approximate the number of neutrons, subtract the atomic number (number of protons) from the atomic mass (rounded to the nearest whole number): \[238 - 92 = 146.\]Thus, the element has approximately 146 neutrons.

Key concepts

Periodic Table

The periodic table is a crucial tool in chemistry that organizes all known elements based on their atomic number, which is the number of protons in an atom's nucleus. Each element on the table is unique and is defined by the number of protons it has. This means that no two different elements can have the same number of protons. The periodic table is structured such that elements with similar properties fall under the same column or group. For example, uranium, which is the element of focus in this discussion, resides within these organized columns based on its properties.

• Atomic Number: This number is key to identifying an element on the periodic table.
• Element Symbol: Each element is represented by a unique one- or two-letter symbol.

Periodic trends, such as reactivity and electronegativity, can also be observed using the table. Therefore, understanding how to navigate the periodic table is essential for anyone studying chemistry.

Protons

Protons are subatomic particles found within the nucleus of an atom. They are positively charged and, along with neutrons, make up the atomic nucleus. The number of protons in an atom is referred to as its atomic number, and it dictates the identity of the element. For instance, an atom with 92 protons is uranium.

• Charge: Positively charged, resistant to change once in an atomic nucleus.
• Mass: Each proton has a mass of approximately 1 atomic mass unit (amu), which contributes to an element's atomic weight.

The balance of protons in the nucleus and electrons orbiting around it maintains the general electrical neutrality of an atom. Increasing the number of protons will create a different element altogether, which is why protons are an essential defining characteristic in atomic structure.

Electrons

Electrons are negatively charged particles that move in orbitals surrounding the atom's nucleus. These orbitals have differing energy levels, and the arrangement of electrons within these orbitals determines how an atom reacts chemically.

• Charge: Electrons have a negative charge that balances the positive charge of protons in a neutral atom.
• Mass: Electrons have negligible mass compared to protons and neutrons.

In a neutral atom, the number of electrons equals the number of protons. Therefore, for uranium with 92 protons, it also has 92 electrons. The behavior of electrons within their orbitals is crucial in forming chemical bonds and reactions.

Neutrons

Neutrons, along with protons, are found in the atomic nucleus and have no electrical charge. They are neutral particles that play a crucial role in the atomic mass and stability of an atom. For instance, uranium has a calculated 146 neutrons when you subtract its atomic number from its atomic mass.

• Charge: Neutrons have no charge, which makes them neutral and contributes to the stability of the nucleus.
• Mass: Each neutron has a mass very similar to a proton, slightly more than 1 amu.

Neutrons help to bind protons within the nucleus due to nuclear forces, which counterbalance the repulsion between the positively charged protons. The number of neutrons can vary in atoms of the same element, leading to different isotopes. Isotopes are atoms of the same element that have the same number of protons but differ in the number of neutrons.