Question

How many protons, neutrons, and electrons are in each of the following atoms or ions? a. \({ }_{12}^{24} \mathrm{Mg}\) b. \({ }_{12}^{24} \mathrm{Mg}^{2+}\) c. \({ }_{27}^{59} \mathrm{Co}^{2+}\) d. \({ }_{27}^{59} \mathrm{Co}^{3+}\) e. \({ }_{27}^{59} \mathrm{Co}\) f. \({ }_{34}^{74} \mathrm{Se}\) g. \({ }_{34} \mathrm{Se}^{2}\). h. \(\frac{63}{28} \mathrm{Ni}\) i. \(\frac{59}{28} \mathrm{Ni}^{2+}\)

Short answer

a. 12 protons, 12 neutrons, 12 electrons b. 12 protons, 12 neutrons, 10 electrons c. 27 protons, 32 neutrons, 25 electrons d. 27 protons, 32 neutrons, 24 electrons e. 27 protons, 32 neutrons, 27 electrons f. 34 protons, 40 neutrons, 34 electrons g. Invalid input (missing mass number) h. 28 protons, 35 neutrons, 28 electrons i. 28 protons, 31 neutrons, 26 electrons

Step-by-step solution

a. \({ }_{12}^{24}\mathrm{Mg}\)

Z = 12 (from the atomic symbol). So, there are 12 protons. A = 24. So, the number of neutrons is A - Z = 24 - 12 = 12 neutrons. Since it is a neutral atom, the number of electrons equals the number of protons, which is 12 electrons.

b. \({ }_{12}^{24}\mathrm{Mg}^{2+}\)

Z = 12. So, there are 12 protons. A = 24. So, the number of neutrons is A - Z = 24 - 12 = 12 neutrons. Since it is a 2+ ion, it has lost 2 electrons. Therefore, the number of electrons is 12 - 2 = 10 electrons.

c. \({ }_{27}^{59}\mathrm{Co}^{2+}\)

Z = 27. So, there are 27 protons. A = 59. So, the number of neutrons is A - Z = 59 - 27 = 32 neutrons. Since it is a 2+ ion, it has lost 2 electrons. Therefore, the number of electrons is 27 - 2 = 25 electrons.

d. \({ }_{27}^{59}\mathrm{Co}^{3+}\)

Z = 27. So, there are 27 protons. A = 59. So, the number of neutrons is A - Z = 59 - 27 = 32 neutrons. Since it is a 3+ ion, it has lost 3 electrons. Therefore, the number of electrons is 27 - 3 = 24 electrons.

e. \({ }_{27}^{59}\mathrm{Co}\)

Z = 27. So, there are 27 protons. A = 59. So, the number of neutrons is A - Z = 59 - 27 = 32 neutrons. As it is a neutral atom, the number of electrons equals the number of protons, which is 27 electrons.

f. \({ }_{34}^{74}\mathrm{Se}\)

Z = 34. So, there are 34 protons. A = 74. So, the number of neutrons is A - Z = 74 - 34 = 40 neutrons. As it is a neutral atom, the number of electrons equals the number of protons, which is 34 electrons.

g. \({ }_{34}\mathrm{Se}^{2}\)

The given symbol is missing the mass number. We are not able to find the number of neutrons without it.

h. \(\frac{63}{28}\mathrm{Ni}\)

Z = 28. So, there are 28 protons. A = 63. So, the number of neutrons is A - Z = 63 - 28 = 35 neutrons. As it is a neutral atom, the number of electrons equals the number of protons, which is 28 electrons.

i. \(\frac{59}{28}\mathrm{Ni}^{2+}\)

Z = 28. So, there are 28 protons. A = 59. So, the number of neutrons is A - Z = 59 - 28 = 31 neutrons. Since it is a 2+ ion, it has lost 2 electrons. Therefore, the number of electrons is 28 - 2 = 26 electrons.

Key concepts

Proton Count

The proton count in an atom is an important aspect of atomic structure, as it determines the identity of the element itself. Protons are positively charged particles found in the nucleus of an atom. Each element is defined by its number of protons, which is also known as its atomic number (Z).
For instance:

• Magnesium (Mg) has 12 protons.
• Cobalt (Co) contains 27 protons.
• Selenium (Se) possesses 34 protons.
• Nickel (Ni) has 28 protons.

The proton count remains constant for each specific element in the periodic table, whether the atom is neutral or forms an ion, as ion formation only involves electrons.

Neutron Count

Neutrons are neutral particles that reside in the nucleus alongside protons. Unlike protons, the number of neutrons can vary even within a single element, leading to different isotopes. To find the neutron count of an atom, you subtract the atomic number from the mass number (A), which is the total number of protons and neutrons in the atom. The formula for finding the neutron count is: \[\text{Neutron count} = A - Z\]Some examples are:

• Magnesium: 24 (mass number) - 12 (atomic number) = 12 neutrons.
• Cobalt: 59 - 27 = 32 neutrons.
• Selenium: 74 - 34 = 40 neutrons.
• Nickel: 63 - 28 = 35 neutrons.

Neutrons serve the important function of adding mass and stability to the nucleus but do not affect the charge.

Electron Count

Electrons are negatively charged particles that orbit the nucleus of an atom. In a neutral atom, the number of electrons equals the number of protons. For ions, electron count changes depending on the charge of the ion:

• If the ion is positively charged (cation), it has lost electrons. Subtract the charge number from the atomic number to find the electron count.
• If the ion is negatively charged (anion), it has gained electrons. Add the charge number to the atomic number to determine the electron count.

Examples include:

• Neutral Magnesium has 12 electrons, while \( \mathrm{Mg}^{2+} \) has 10 electrons after losing 2.
• Neutral Cobalt has 27 electrons; \( \mathrm{Co}^{2+} \) and \( \mathrm{Co}^{3+} \) have 25 and 24 electrons, respectively.
• Neutral Nickel contains 28 electrons, whereas \( \mathrm{Ni}^{2+} \) has 26 electrons.

Electron count helps determine the atom's or ion's charge and its chemical reactivity.

Atomic Number

The atomic number (Z) is a fundamental property of an element and represents the number of protons in an atom. It is a unique identifier for all elements in the periodic table. The atomic number not only dictates the element's identity but also determines its position in the periodic table.

For example:

• Magnesium has an atomic number of 12.
• Cobalt has an atomic number of 27.
• Nickel has an atomic number of 28.
• Selenium has an atomic number of 34.

The consistency of the atomic number makes it a reliable way to identify elements, regardless of how many neutrons or electrons are present.

Mass Number

The mass number (A) is the total count of protons and neutrons in an atom’s nucleus. It gives an approximate mass of the atom and is especially useful in distinguishing different isotopes of an element, which have the same number of protons but differing neutron counts.

To calculate the mass number:\[A = \text{Number of Protons (Z)} + \text{Number of Neutrons}\]Consider the following:

• Magnesium: Sum of 12 protons and 12 neutrons results in a mass number of 24.
• Cobalt: Comprising 27 protons and 32 neutrons gives a mass number of 59.
• Nickel: With 28 protons and 35 neutrons, the mass number is 63.

The mass number is crucial for calculating the atomic mass and is often used in nuclear chemistry to understand isotopic variations.