Question

Which of the following statements are true regarding an ionic bond between aluminum and nitrogen in an AlN formula unit? (a) Aluminum and nitride ions bond by covalent attraction. (b) Aluminum atoms lose electrons and nitrogen atoms gain electrons. (c) The ionic radius of an aluminum ion is less than its atomic radius. (d) Breaking an ionic bond between aluminum and nitrogen releases energy.

Short answer

Statements (b) and (c) are true.

Step-by-step solution

Understand Ionic Bonding

An ionic bond is formed when one atom donates electrons to another atom, resulting in oppositely charged ions that attract each other. In the case of AlN, aluminum (Al) atoms lose electrons and nitrogen (N) atoms gain those electrons, forming aluminum cations ( ext{Al}^{3+}) and nitride anions ( ext{N}^{3-}).

Analyze Statement (a)

Statement (a) suggests a covalent attraction, which is incorrect for ionic bonds. Ionic bonds, like in AlN, involve electrostatic attraction between ions, not shared electrons. Therefore, statement (a) is false.

Analyze Statement (b)

Statement (b) is about electron transfer in ionic bonding. Aluminum loses three electrons to form ext{Al}^{3+} cations, and nitrogen gains these electrons to form ext{N}^{3-} anions. This correctly describes the formation of ionic bonds in AlN, making this statement true.

Analyze Statement (c)

For metals like aluminum, forming cations by losing electrons results in a decrease in atomic size, as there are fewer electron shells and less electron-electron repulsion. Thus, the ionic radius of ext{Al}^{3+} is indeed smaller than the atomic radius of neutral aluminum, making this statement true.

Analyze Statement (d)

Breaking an ionic bond requires energy input to overcome the electrostatic attraction between ions; it does not release energy. Usually, energy is released when forming bonds, not breaking them. Therefore, statement (d) is false.

Key concepts

Electron Transfer

In the world of chemistry, electron transfer is a key process in the formation of ionic bonds. When atoms interact, they may transfer electrons to achieve a more stable electronic configuration. In an ionic bond, one atom donates one or more electrons to another atom, resulting in the creation of ions. These ions bear opposite charges and attract each other to form a stable compound.

For example, let's look at aluminum (Al) and nitrogen (N) when they form aluminum nitride (AlN). Aluminum atoms tend to lose three electrons, forming Al^{3+} ions. Meanwhile, nitrogen atoms gain these electrons, becoming N^{3-} ions. The transfer of electrons from aluminum to nitrogen is the crux of how they bond ionically.

The importance of understanding this electron movement is not only about forming compounds. It also helps predict the charge on the resulting ions and the structure of the compounds they form.

Atomic and Ionic Radius

The size of an atom or ion, referred to as its radius, changes depending on whether it is in its atomic or ionic form. Atomic radius is the size of a neutral atom, while ionic radius describes the size of an ion.

• Atomic Radius: This is typically larger for a neutral atom because it includes all its natural electron shells.
• Ionic Radius: This can be smaller or larger depending on whether an atom has lost or gained electrons to become an ion.

When aluminum forms an Al^{3+} ion, it loses three electrons. This reduces its size because there are fewer electron shells and less electron-electron repulsion, resulting in a smaller ionic radius compared to its atomic radius.
On the other hand, if an atom gains electrons, like nitrogen forming N^{3-} , its ionic radius increases due to added electron-electron repulsion, causing the electron cloud to expand.

Energy in Bond Formation and Breaking

Understanding energy dynamics in bond formation and breaking is crucial in chemistry. The process of forming or breaking bonds involves changes in energy.

• Bond Formation: When a bond forms, energy is released. This release happens because the atoms achieve a more stable state. For example, when aluminum and nitrogen form an ionic bond to create AlN, energy is released.
• Bond Breaking: Contrary to formation, breaking a bond requires an input of energy. This input is needed to overcome the attractive forces holding the ions together. For instance, breaking the Al-N ionic bond would require energy to separate the Al^{3+} and N^{3-} ions.

This knowledge is vital as it helps in understanding reaction spontaneity and energy requirements. Energy changes in these processes are a fundamental part of thermodynamics in chemistry.