Question

Determine the number of protons, neutrons, and electrons in each of the following: a. \({ }^{239} \mathrm{Pu}\) b. \({ }^{52} \mathrm{Cr}^{3+}\) C. \({ }^{16} \mathrm{O}^{2-}\) d. \({ }^{40} \mathrm{Ca}^{2+}\)

Short answer

a. Pu: 94 protons, 145 neutrons, 94 electrons; b. Cr3+: 24 protons, 28 neutrons, 21 electrons; c. O2-: 8 protons, 8 neutrons, 10 electrons; d. Ca2+: 20 protons, 20 neutrons, 18 electrons.

Step-by-step solution

- Identify Pu Atomic Number

Check the periodic table to identify the atomic number (Z) of Plutonium (Pu). The atomic number represents the number of protons. For Plutonium, Z = 94.

- Calculate Neutrons in Pu

Using the isotope notation \( ^{239}_{94}Pu \) (mass number = 239, atomic number = 94), subtract the atomic number from the mass number to find the number of neutrons: Neutrons = Mass Number - Atomic Number = 239 - 94 = 145.

- Identify Electrons in Pu

Pu has no charge; the number of electrons equals the number of protons: Electrons = Protons = 94.

- Identify Cr Atomic Number

Check the periodic table to identify the atomic number (Z) of Chromium (Cr). The atomic number represents the number of protons. For Chromium, Z = 24.

- Calculate Neutrons in Cr

Using the isotope notation \( ^{52}_{24}Cr \) (mass number = 52, atomic number = 24), subtract the atomic number from the mass number to find the number of neutrons: Neutrons = Mass Number - Atomic Number = 52 - 24 = 28.

- Identify Electrons in Cr3+

Cr3+ indicates a +3 charge, which means 3 more protons than electrons. Therefore, Electrons = Protons - 3 = 24 - 3 = 21.

- Identify O Atomic Number

Check the periodic table to identify the atomic number (Z) of Oxygen (O). The atomic number represents the number of protons. For Oxygen, Z = 8.

- Calculate Neutrons in O

Using the isotope notation \( ^{16}_{8}O \) (mass number = 16, atomic number = 8), subtract the atomic number from the mass number to find the number of neutrons: Neutrons = Mass Number - Atomic Number = 16 - 8 = 8.

- Identify Electrons in O2-

O2- indicates a -2 charge, which means 2 more electrons than protons. Therefore, Electrons = Protons + 2 = 8 + 2 = 10.

- Identify Ca Atomic Number

Check the periodic table to identify the atomic number (Z) of Calcium (Ca). The atomic number represents the number of protons. For Calcium, Z = 20.

- Calculate Neutrons in Ca

Using the isotope notation \( ^{40}_{20}Ca \) (mass number = 40, atomic number = 20), subtract the atomic number from the mass number to find the number of neutrons: Neutrons = Mass Number - Atomic Number = 40 - 20 = 20.

- Identify Electrons in Ca2+

Ca2+ indicates a +2 charge, which means 2 more protons than electrons. Therefore, Electrons = Protons - 2 = 20 - 2 = 18.

Key concepts

Atomic Number

When exploring the periodic table, one of the essential elements to understand is the atomic number, symbolized by the letter Z. This number is unique for each element and defines its identity by indicating the number of protons in the nucleus of an atom. For instance, in our exercises above, the atomic number guides us to the identification of protons - the Plutonium atom has 94, Chromium has 24, Oxygen has 8, and Calcium has 20 protons.

Understanding the atomic number is crucial as it not only dictates the element's position on the periodic table but is also intrinsically linked to an element's chemical properties. An interesting thing to note is that in a neutral atom, the number of electrons will always equal the atomic number since atoms are electrically neutral overall.

Neutrons Calculation

Moving beyond the atomic number, the calculation of neutrons in an atom plays a vital role in grasping nuclear chemistry. Neutrons can be determined by taking the atom's mass number, typically found as a superscript on the upper left side of the element symbol (for example, (^{239}Pu)), and subtracting the atomic number from it.

The equation looks like this: Neutrons = Mass Number - Atomic Number. For the given atoms in our exercise:

• Plutonium (Pu) has 145 neutrons,
• Chromium (Cr) has 28,
• Oxygen (O) has 8,
• Calcium (Ca) has 20.

The importance of neutrons lies in their ability to define isotopes, as changes in neutron numbers can result in various isotopic forms of an element which may differ in stability and radioactive behavior.

Ion Charge and Electrons

The charge of an ion has a direct impact on the number of electrons present in an atom. Ions are atoms that have gained or lost electrons and possess a net charge. When an atom loses electrons, it becomes positively charged (cation), whereas an atom that gains electrons becomes negatively charged (anion).

For example, Chromium with a 3+ charge ((^{52}_{24}Cr^{3+})) has lost 3 electrons, resulting in a total electron count of 21 (24 protons - 3). Conversely, a charged Oxygen atom with a 2- charge has 10 electrons (8 protons + 2).

To calculate the electrons in an ion, you can use the formula: Electrons = Protons - (Ion Charge). Remember, in this context, a positive ion charge is subtracted, and a negative ion charge is added to the atomic number, as seen in the exercise with Calcium (Ca) having 18 electrons for its 2+ charge. Monitoring the electron count is fundamental in determining an atom's reactivity and predicting how it will interact with other atoms to form compounds.