Finding Species with the Same Number of Electrons

The question asks us to identify the species among the given options that has the same number of electrons as \({}_{17}^{35}Cl\). To solve this, we need to determine the number of electrons in \({}_{17}^{35}Cl\) and then calculate the number of electrons for each of the given species.

Calculating Electrons in \({}_{17}^{35}Cl\)

The notation \({}_{Z}^{A}X\) represents an element X with atomic number Z (number of protons) and mass number A (number of protons + neutrons). In a neutral atom, the number of electrons is equal to the number of protons.

• For \({}_{17}^{35}Cl\):
• Atomic number (Z) = 17
• Number of protons = 17
• Since \({}_{17}^{35}Cl\) is a neutral atom (no charge indicated), the number of electrons = number of protons = 17.

So, \({}_{17}^{35}Cl\) has 17 electrons.

Calculating Electrons in the Given Options

Now, let's calculate the number of electrons for each species in the options. For ions (charged species), the number of electrons is adjusted based on the charge:

• Positive charge (e.g., \(\text{X}^+\)) means the species has lost electrons. Number of electrons = Atomic number - Charge.
• Negative charge (e.g., \(\text{X}^-\) or \(\text{X}^{2-}\)) means the species has gained electrons. Number of electrons = Atomic number + Magnitude of charge.

Option 1: \({}_{16}^{32}S\)

• Atomic number (Z) = 16
• Neutral atom.
• Number of electrons = 16.

Option 2: \({}_{16}^{34}S^+\)

• Atomic number (Z) = 16
• Charge = +1 (lost 1 electron).
• Number of electrons = 16 - 1 = 15.

Option 3: \({}_{18}^{40}Ar^+\)

• Atomic number (Z) = 18
• Charge = +1 (lost 1 electron).
• Number of electrons = 18 - 1 = 17.

Option 4: \({}_{16}^{35}S\)**^2-

• Atomic number (Z) = 16
• Charge = 2- (gained 2 electrons).
• Number of electrons = 16 + 2 = 18.

Comparison of Electron Counts

Let's summarize the number of electrons for each species:

Comparing the number of electrons, we find that \({}_{18}^{40}Ar^+\) has 17 electrons, which is the same number of electrons as \({}_{17}^{35}Cl\).

Conclusion

The species that has the same number of electrons as \({}_{17}^{35}Cl\) is \({}_{18}^{40}Ar^+\).

Revision Table: Understanding Electron Calculation

Additional Information: Isoelectronic Species

Species that have the same number of electrons are called isoelectronic species. Identifying isoelectronic species is a common concept in chemistry. For example, \({}_{17}^{35}Cl\) and \({}_{18}^{40}Ar^+\) are isoelectronic because both have 17 electrons. Isoelectronic species often exhibit similar chemical and physical properties, particularly regarding their size and ionization energy, due to having the same electron configuration, although their nuclear charge (number of protons) is different.

• The mass number (A) does not directly affect the number of electrons in an atom or ion; it relates to the number of neutrons. Isotopes of an element have the same atomic number (same number of protons and electrons in a neutral atom) but different mass numbers (different number of neutrons).
• The charge determines whether electrons have been gained or lost compared to the neutral atom.