Characteristics of Ionically Bonded Substances

A substance that is ionically bonded is called an ionic compound. All ionic compounds share certain properties, such as high melting and boiling points. This is because the strong bonds between ions in an ionic compound prevent the ions from moving much without a large amount of energy. Because of the aforementioned high boiling point, ionic compounds are almost never found as a gas at room temperature. Ionic compounds contain charged particles, so they are able to conduct electricity. However, because ionic solids are in fixed locations, they are usually not good conductors of electricity. When ions can move, as in a liquid, salts are good conductors of electricity. If a solid salt is dissolved in water, it would then be a good conductor of electricity because its ions are no longer tightly packed together and are now able to move. There are some exceptions, though. There are a few ionic compounds who have an unusually open lattice structure, so ions can move past each other. These solids are good conductors of electricity. Most ionic compounds are hard and brittle. These qualities can be associated with the layered pattern of the cations and anions in salts. When a force is applied to the salt and a layer shifts, the cations of one layer are lined up with the cations of the next layer (the same happens with the anions). This causes them to repel each other and the layers to split apart. That is why all salts break along what is called a cleavage plane, or a line extending throughout the crystal. The ions in the salt form reoccurring patterns because each ion is held in place by attractive forces, which are stronger than the repulsive ones. These repeating units form the crystal lattice, and are the reason for the crystal shape found in most salts. The smallest repeating unit found in the crystal is called a unit cell. The shape of the crystal structure depends on the ratio of each element in the compound.

Salt Formation, Explained

I will now explain the earlier posted process. Before the process can occur, two materials are needed, these being sodium metal and chlorine gas. Energy must be contributed to sublime the sodium. Energy is also required to take away an electron from an atom of the sodium gas. As chlorine is already a gas, no phase transition is needed. Energy is needed to separate the two Cl atoms bonded together in the gas, so that each individual atom can react with the sodium. All of the steps so far have been endothermic, they require energy. The next steps will all release energy, so they are called exothermic. After the Cl2 is separated, an electron is added to a Cl atom to form an anion. In the last step, the Cl anions and the Na cations come together due to the attractive forces of each. In the case of sodium chloride, a large amount of energy is released from this last step. This is the lattice energy.

Salt Formation, The Process

Salt formation is an important part of ionic bonding. I will now explain the steps of salt formation using sodium chloride as an example.

(Process courtesy of Holt Chemistry textbook)

A "^" followed by either a "+" or an "-" signifies a superscripted "+" or "-", while a stand-alone "+" means "and".

0. Starting: Na(s) and Cl2(g)
1. Energy must be added to the sodium to make it a gas: Na(s) + energy ---> Na(g)
2. More energy must be added to remove an electron from each sodium atom:
Na(g) + energy ---> Na^+(g) + e^-
3. Energy must be added to break up Cl2 molecules to produce Cl atoms: 1/2 Cl2(g) + energy ---> Cl(g)
4. Some energy is released as an electron is added to each Cl atom to form a Cl^- ion:
CL(g) + e^- ---> Cl^-(g) + energy
5. Much more energy is released as Na^+ and Cl^- ions come together to form an ionic crystal:
Na^+(g) + Cl^-(g) ---> NaCl(s) + energy = Lattice Forms

NaCl Crystal Structure

here is a webpage showing the NaCl lattice from different viewpoints

Ionic Bonding, In-Depth

Ionic Bonding requires the removal of an electron from one atom and the subsequent transfer of that electron to another atom. When an electron is removed from an atom, that atom is now positively charged. When another atom receives that electron, that atom is negatively charged. The attraction between these opposing forces is what makes the ionic bond. For example, Na has one valence electron. It gives up that one valence electron to form a stable Na+ cation. Cl has seven valence electrons. It is easier for it to gain one electron than lose seven, so it gains the one valence electron that Na lost. The Cl is now a Cl- anion. This particular combination of elements is called Sodium Chloride, or table salt. Salt is the term used to describe many ionic compounds. All salts that are ionic compounds are neutrally charged. The cations and anions in salts are present in a simple, whole-number ratio. (For example, NaCl is 1:1, sodium to chloride) The attractions between anions and cations do not stop with a single one of each in a salt, each attracts several of the opposite. As a result of this, many ions are packed tightly together in a crystalline structure. Moving an electron from an atom requires energy (ionization energy) and energy is also needed to transfer an electron to an atom (electron affinity). However, some elements readily accept extra electrons. For these elements, when an electron is added, energy is released. Be that as it may, the energy released is less than the energy required to remove an electron from the other atom. The rest of the energy needed to form an ionic bond comes from the process of salt formation. Actually, the salt formation process will produce more than enough energy so that the overall process actually releases energy.

Ionic Bonding

Ionic Bonding is another concept that can be challenging. Ionic bonds tend to form between metals and non-metals. Unlike covalent bonding, ionic bonding involves the removal of electrons from one atom and the consequent attachment of those electrons to another atom, resulting in the formation of attracting positive and negative ions. The element that loses the electrons is the atom that started with the least amount of electrons. This is because it is easier to lose a small number of electrons than it is to gain a large number of electrons. The atom that then gains the electrons is the one that has the most starting electrons, because it is easier to gain a small number of electrons than it is to lose a large number of them. The atom that lost electrons now has a positive charge, and is called a cation. The atom that gained electrons now has a negative charge and is called an anion.