Determine the number of protons and the number of electrons in each ion. b. Se^2-

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Identify the atomic number of selenium (Se) from the periodic table. The atomic number represents the number of protons in a neutral atom of selenium.

Understand that the atomic number of selenium is also the number of protons in the Se ion, as the number of protons does not change during ion formation.

Recognize that the '2-' in Se2- indicates a charge of -2, meaning the ion has two more electrons than protons.

Calculate the number of electrons in the Se2- ion by adding two electrons to the number of protons (which is equal to the atomic number of selenium).

Summarize the findings: The number of protons in Se2- is equal to the atomic number of selenium, and the number of electrons is the atomic number plus two.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Atomic Structure

Atoms consist of protons, neutrons, and electrons. Protons are positively charged particles found in the nucleus, while electrons are negatively charged and orbit the nucleus. The number of protons defines the element, and in a neutral atom, the number of electrons equals the number of protons.

Ions

Ions are atoms or molecules that have gained or lost one or more electrons, resulting in a net charge. Cations are positively charged ions formed by losing electrons, while anions are negatively charged ions formed by gaining electrons. The charge of the ion indicates the difference between the number of protons and electrons.

Charge Calculation

To determine the number of protons and electrons in an ion, one must consider its charge. For example, in the case of Se2-, the '2-' indicates that the ion has gained two extra electrons compared to its neutral state. Therefore, the number of electrons is the atomic number of selenium plus two, while the number of protons remains equal to the atomic number.

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