Question

What number of protons and neutrons are contained in the nucleus of each of the following atoms? Assuming each atom is uncharged, what number of electrons are present? a. \({ }_{12}^{235} \mathrm{U}\) d. \(\frac{200}{82} \mathrm{~Pb}\) b. \({ }_{6}^{13} \mathrm{C} \quad\) e. \(\frac{86}{37} \mathrm{Rb}\) c. \({ }_{20}^{5} \mathrm{Fe}\) f. \({ }_{20} \mathrm{Ca}\)

Short answer

For the given atoms: a. \({ }_{12}^{235} \mathrm{U}\): 12 protons, 223 neutrons, and 12 electrons. b. \({ }_{6}^{13} \mathrm{C}\): 6 protons, 7 neutrons, and 6 electrons. c. \({ }_{20}^{5} \mathrm{Fe}\): 5 protons, 15 neutrons, and 5 electrons (assuming a typo). d. \(\frac{200}{82} \mathrm{~Pb}\): 82 protons, 118 neutrons, and 82 electrons. e. \(\frac{86}{37} \mathrm{Rb}\): 37 protons, 49 neutrons, and 37 electrons. f. \({ }_{20} \mathrm{Ca}\): 20 protons, unknown number of neutrons, and 20 electrons.

Step-by-step solution

Atom a: \({ }_{12}^{235} \mathrm{U}\)

In this atom, we are given the atomic symbol U (uranium), its atomic number (protons) Z = 12, and mass number (protons + neutrons) A = 235. To find the number of neutrons, we use: Number of neutrons = A - Z = 235 - 12 = 223. Since this atom is uncharged, the number of electrons is equal to the number of protons, which is 12. So the atom has 12 protons, 223 neutrons, and 12 electrons.

Atom b: \({ }_{6}^{13} \mathrm{C}\)

In this atom, we have the symbol C (carbon), atomic number (protons) Z = 6, and mass number (protons + neutrons) A = 13. The number of neutrons is: Number of neutrons = A - Z = 13 - 6 = 7. The number of electrons in an uncharged atom is equal to the number of protons, which is 6. So the atom has 6 protons, 7 neutrons, and 6 electrons.

Atom c: \({ }_{20}^{5} \mathrm{Fe}\)

In this atom, we have the symbol Fe (iron), atomic number (protons) Z = 20, and mass number (protons + neutrons) A = 5. This notation is problematic because the mass number should always be greater than or equal to the atomic number. Let's switch A and Z as it might be a typo: \(_{5}^{20} \mathrm{Fe}\). Now we have atomic number Z = 5 and mass number A = 20. Number of neutrons = A - Z = 20 - 5 = 15. The number of electrons in an uncharged atom is equal to the number of protons, which is 5. So the atom has 5 protons, 15 neutrons, and 5 electrons.

Atom d: \(\frac{200}{82} \mathrm{~Pb}\)

The notation here is slightly different, but we can recognize Pb (lead) as the atomic symbol, and the atomic number (protons) Z = 82, the mass number (protons + neutrons) A = 200. The number of neutrons is: Number of neutrons = A - Z = 200 - 82 = 118. The number of electrons in an uncharged atom is equal to the number of protons, which is 82. So the atom has 82 protons, 118 neutrons, and 82 electrons.

Atom e: \(\frac{86}{37} \mathrm{Rb}\)

In this atom, we have the symbol Rb (rubidium), atomic number (protons) Z = 37, and mass number (protons + neutrons) A = 86. The number of neutrons is: Number of neutrons = A - Z = 86 - 37 = 49. The number of electrons in an uncharged atom is equal to the number of protons, which is 37. So the atom has 37 protons, 49 neutrons, and 37 electrons.

Atom f: \({ }_{20} \mathrm{Ca}\)

In this atom, the mass number is not provided. We only have the symbol Ca (calcium) along with the atomic number (protons) Z = 20. As we lack information about the mass number, we cannot determine the number of neutrons. We can only determine the number of protons and electrons since it is uncharged. Therefore, the atom has 20 protons and 20 electrons. The number of neutrons cannot be determined with the given information.

Key concepts

Protons

Protons are fundamental particles found in the nucleus of an atom. They have a positive charge and play a crucial role in the atomic structure.

Key points to remember about protons include:

• They determine the identity of an element. For example, all atoms with 1 proton are hydrogen atoms.
• The number of protons in an atom's nucleus is called the atomic number, denoted by the symbol Z.
• Protons, along with neutrons, contribute to the majority of an atom's mass.

Understanding the number of protons helps in identifying the element and plays a significant role in the atom's chemical properties.

Neutrons

Neutrons are neutral particles found alongside protons in the nucleus. They have no charge and serve to add mass and stability to the atom.

Important aspects about neutrons include:

• While having nearly the same mass as protons, neutrons do not affect the chemical properties of an element.
• The number of neutrons can vary even within atoms of the same element, leading to different isotopes.
• The presence of neutrons helps to balance the repulsive forces between positively charged protons within the nucleus.

To find the number of neutrons in an atom, subtract the atomic number from the mass number, which is the total count of protons and neutrons.

Electrons

Electrons are negatively charged particles that orbit the nucleus of an atom in various energy levels or shells.

Some essential facts about electrons are:

• They are much smaller than both protons and neutrons, contributing negligibly to an atom's mass.
• Electrons are responsible for the chemical bonds between atoms and define the atom's charge.
• In a neutral, uncharged atom, the number of electrons equals the number of protons, balancing the overall charge.

Electrons determine how an atom interacts with other atoms, making them key players in chemical reactions.

Atomic Number

The atomic number is a pivotal concept in understanding atomic structure. It refers to the number of protons in an atom's nucleus and is essential in determining an element's identity.

Features of the atomic number include:

• Each element on the periodic table has a unique atomic number, which places them in a specific order.
• The atomic number also dictates how electrons are arranged around the nucleus as this number equals the number of electrons in a neutral atom.
• Knowing the atomic number allows scientists to predict an element's properties and behavior in chemical reactions.

This fundamental characteristic shapes the periodic table and influences our understanding of atomic interactions and properties.