What force holds ionic structures together? (A) Gravity, (B) magnetism, (C) electrostatic attraction, (D) covalent bonds, or (E) metallic bonds.
This question deals with ionic structures and ionic bonds, which are formed between oppositely charged ions. One way these structures might result is through the transfer of electrons between atoms. Atoms can lose or gain electrons. This behavior can often be explained by the octet rule of thumb, which tells us that an atom will tend to react to achieve eight electrons in its outer shell. When electrons are lost, positively charged ions are formed, which we can refer to as cations. And when electrons are gained, negatively charged ions are formed, which we can refer to as anions.
We can represent charged ions by using square brackets and indicating the charge of the ion on the outside of the brackets. These oppositely charged ions are now attracted to each other. And as more and more ions are held together by their attraction in all directions, the structure that is formed is called an ionic lattice, which is a giant three-dimensional structure that is composed of oppositely charged ions.
With this information in mind, let’s look at the answer choices. Answer choice (A) gravity is the noncontact force which pulls all objects towards each other and is directly related to mass. One example of this is gravity holds celestial bodies in orbits around one another, such as the Moon in orbit around our planet Earth due to the Earth’s gravitational force. Since all objects with mass have gravity, ions in ionic structures are exerting a very small force of gravity on each other. However, this is not the force that explains why ionic structures hold together in the formation that they do. We can eliminate answer choice (A).
Answer choice (B) magnetism is the noncontact force caused by magnetic fields. It is the force that causes opposite poles of magnets to be attracted to each other and the same poles to repel. While in ionic structures there is attraction, it occurs between oppositely charged particles and is not caused by magnetic fields. We can eliminate answer choice (B).
Answer choice (C) electrostatic attraction is the attractive force that occurs between positive and negative charges. This type of attraction describes exactly what is occurring in ionic structures where positively charged ions and negatively charged ions are held together by their strong attraction to each other in all directions. Answer choice (C) electrostatic attraction describes the force holding ionic structures together. Let’s rule out answer choices (D) and (E) just to be sure.
Answer choice (D) covalent bonds occur when two nonmetal atoms share one or more pairs of electrons. Since there are no ions involved in covalent bonds, there are no oppositely charged particles to form ionic bonds and, thus, ionic structures. Instead, covalent bonds often form structures such as molecules. We can eliminate answer choice (D).
Finally, answer choice (E) metallic bonds occur due to the strong electrostatic attraction that exists between positively charged metal cations and delocalized electrons. While this interaction does feature the attraction of oppositely charged particles and the formation of a lattice structure, the lattice is composed of metal cations and delocalized electrons, not oppositely charged ions as we would expect to see in an ionic structure. We can eliminate answer choice (E).
Therefore, we have confirmed the force that holds ionic structures together is answer choice (C) electrostatic attraction.