Problem 145 - Introductory Chemistry Atoms First

Question

What do \(\mathrm{F}^{-}, \mathrm{O}^{2-}, \mathrm{Na}^{+}\), and \(\mathrm{Mg}^{2+}\) all have in common?

Step-by-Step Solution

Answer

All the ions, \(\mathrm{F^{-}}\), \(\mathrm{O^{2-}}\), \(\mathrm{Na^{+}}\), and \(\mathrm{Mg^{2+}}\), have a complete octet in their outer electron shell, making them more stable than their neutral counterparts.

Step 1: Write the electron configurations for the neutral atoms

Using the periodic table, we can write the electron configurations for the neutral atoms: fluorine (F), oxygen (O), sodium (Na), and magnesium (Mg). - Fluorine (F): \( 1s^2 2s^2 2p^5 \) - Oxygen (O): \( 1s^2 2s^2 2p^4 \) - Sodium (Na): \( 1s^2 2s^2 2p^6 3s^1 \) - Magnesium (Mg): \( 1s^2 2s^2 2p^6 3s^2 \)

Step 2: Determine the electron configurations of the ions

Now, we need to find the electron configurations for the given ions by adding or removing electrons from the neutral atoms, based on their charges. - \(\mathrm{F^{-}}\): Add 1 electron to complete the outer shell: \( 1sg^2 2s^2 2p^6 \) - \(\mathrm{O^{2-}}\): Add 2 electrons to complete the outer shell: \( 1s^2 2s^2 2p^6 \) - \(\mathrm{Na^{+}}\): Remove 1 electron from the outer shell: \( 1s^2 2s^2 2p^6 \) - \(\mathrm{Mg^{2+}}\): Remove 2 electrons from the outer shell: \( 1s^2 2s^2 2p^6 \)

Step 3: Identify the common property among the ions

As we can see from their electron configurations, all these ions now have a complete octet in their outer shell (2s and 2p orbitals are fully occupied).

Step 4: Conclusion

Therefore, the property that \(\mathrm{F^{-}}\), \(\mathrm{O^{2-}}\), \(\mathrm{Na^{+}}\), and \(\mathrm{Mg^{2+}}\) have in common is that they all have a complete octet in their outer electron shell, which makes them more stable than their neutral counterparts.

Key Concepts

Octet Rule

The octet rule is a fundamental principle in chemistry that helps to explain the formation of ions and chemical bonds. The rule states that atoms are most stable when they have eight electrons in their outer shell, similar to the electron configuration of noble gases.

• Atoms will often gain, lose, or share electrons to achieve a full octet.
• This configuration is energetically favorable and results in greater chemical stability.

For example, in the case of the ions \( \mathrm{F}^{-}, \mathrm{O}^{2-}, \mathrm{Na}^{+}, \text{and} \mathrm{Mg}^{2+} \), each ion achieves a complete octet by either acquiring or losing electrons. This is why ions tend to form in predictable ways based on the desire to achieve eight valence electrons.

Neutral Atoms

Neutral atoms have an equal number of protons and electrons, resulting in no net charge. In their natural state, atoms like fluorine (F), oxygen (O), sodium (Na), and magnesium (Mg) begin as neutral.

• Each atom's electron configuration is determined by the number of electrons present.
• For example, fluorine has nine electrons, resulting in a configuration of \( 1s^2 2s^2 2p^5 \).

These electron configurations guide how neutral atoms make the transition to ions. When gaining or losing electrons, the atom shifts from a neutral state to a charged ion.

Ion Formation

Ion formation occurs when neutral atoms gain or lose electrons, resulting in a net positive or negative charge. This process is essential for achieving the octet rule.

• Fluorine and oxygen typically gain electrons, forming negatively charged anions \( \mathrm{F}^{-} \) and \( \mathrm{O}^{2-} \).
• Sodium and magnesium lose electrons, resulting in positively charged cations \( \mathrm{Na}^{+} \) and \( \mathrm{Mg}^{2+} \).

By adjusting the number of electrons, these atoms achieve configurations resembling noble gases. This transformation provides them stability and is often referred to as the ionic state, fulfilling the octet rule.

Stability of Ions

The stability of ions is largely due to their electron arrangement, which often results in a filled outer shell. Ions with a complete octet, such as \( \mathrm{F}^{-} \) and \( \mathrm{Na}^{+} \), demonstrate greater stability compared to their neutral atom forms.

• This stability makes ions less reactive and more energetically favorable.
• For instance, \( \mathrm{O}^{2-} \) and \( \mathrm{Mg}^{2+} \) achieve increased stability through the electron removal that realizes a full octet structure.

This enhanced stability is the driving force behind ion formation, giving them a tendency to form ionic compounds and interact in particular ways with other ions.