Bonding in chemistry is a fascinating topic. You can make predictions about the type of bonding in a species using general rules. For instance, covalent bonds happen between two non-metals while ionic bonds occur between a metal and a non-metal. But, this is not always the case. A better way to tell the bonding in a species is by its properties. Let's recap the different types of bonding: covalent, ionic, and metallic. Then, we'll explore their characteristic properties. This will give us a better understanding of bonding and elemental properties in chemistry.
Chemistry has three primary types of bonding: covalent, ionic, and metallic. We have detailed articles on each of these bonding types, but for now, let's do a quick recap to refresh our memory before we delve into their properties.
When atoms share a pair of valence electrons to achieve a full outer shell, a covalent bond forms. Non-metals usually form covalent bonds to fulfill their electron needs. This happens when the valence electron orbitals of two atoms overlap, causing a pair of electrons to form and be shared between the two atoms. In some cases, atoms can create multiple covalent bonds, or even double or triple bonds. For instance, ammonia has a nitrogen atom that forms single covalent bonds with three hydrogen atoms. Meanwhile, the cyanide ion has a carbon atom that forms a triple covalent bond with a nitrogen atom.
An ionic bond is the strong electrostatic attraction between oppositely charged ions. These ions are formed through the transfer of electrons, where one atom donates an electron to another atom. This creates two ions with full outer shells of electrons, which are then attracted to each other by strong electrostatic forces. A great example of ionic bonding is sodium chloride, where sodium donates an electron to chlorine, forming positive sodium ions and negative chloride ions that are attracted to each other by strong electrostatic attraction.
Covalent bonding and ionic bonding are two sides of the same coin that exist on a spectrum. Non-polar covalent bonds share an electron pair equally, while ionic bonds completely transfer an electron from one atom to another. Polar covalent bonds are between the two; the electron pair is shared unequally between the two species involved. The determining factor of whether a compound bonds covalently or ionically is the elements' electronegativities, which is their ability to attract a shared pair of electrons. Elements with a large difference in electronegativity form ionic bonds, while elements with a small difference or no difference in electronegativity form covalent bonds. Elements with a medium difference in electronegativity lie somewhere in the middle, forming polar covalent bonds. For more information on this, check out Polar and Non-Polar Covalent Bonds.
When it comes to bonding between two metals, they use something called metallic bonding. Metallic bonding is a type of chemical bonding found within metals, which consists of an array of positive metal ions in a sea of delocalized electrons. To achieve a full outer shell, each metal atom gives up its valence electrons and becomes a positive metal ion. These valence electrons form a sea of delocalization that surrounds the metal ions, and the whole structure is held together by electrostatic attraction between the positive ions and negative electrons. Sodium is a typical example of metallic bonding, where each sodium atom loses its outer shell electron to form a positive sodium ion, and the electrons form a sea of delocalization that surrounds these metal ions.
Bonding and Properties
We've seen how metals and non-metals bond both with themselves and with each other. Let's now turn our attention to how this bonding affects their properties.
Covalent bonds can form two different types of structures: covalent-network solids or simple covalent molecules. Covalent-network solids are formed when hundreds or thousands of atoms are joined together by multiple covalent bonds, forming a giant lattice that stretches in all directions. They don't form molecules, and the covalent bonds holding the structure together are very strong, requiring a lot of energy to overcome. As a result, covalent-network solids have very high melting and boiling points, and they are also hard and strong.
On the other hand, simple covalent molecules consist of just a handful of atoms bound together by covalent bonds. The molecules are held together by weak intermolecular forces, and they have low melting and boiling points. This is because you don't need to overcome the covalent bonds within the molecule in order to melt the substance, but rather, you need to overcome the weak intermolecular forces between the molecules. Simple covalent molecules are usually gaseous at room temperature. Both covalent-network solids and simple covalent molecules are usually poor conductors of electricity because there aren't any charged particles free to move and carry a charge within the structures. Covalent network solids are also insoluble in water due to the strong covalent bonds holding the structure together.
Ionic bonding and covalent bonding may exist on the same spectrum, but they show very different properties. Ionic compounds form giant lattices of alternating positive and negative ions that stretch in all directions, creating a crystal structure. The electrostatic attraction between the ions is very strong, giving ionic compounds high melting and boiling points. These compounds are also hard and brittle, with the lattice easily breaking apart if jolted.
In solid-state, ionic compounds are poor conductors of heat and electricity. The charged ions are held firmly in place by the strong electrostatic attraction and cannot move around. However, when molten or aqueous, the ions are not held firmly in place and can move around, carrying charges. Because of this, molten and aqueous ionic compounds are good conductors of electricity. Most ionic compounds are highly soluble in water and some are even soluble in organic liquids.
Metals form giant lattices and are held together by strong electrostatic attraction between positive metal ions and a sea of delocalized electrons. Because of this, metals have medium to high melting and boiling points. However, unlike ionic compounds, metals are often malleable and ductile, allowing them to be shaped and drawn into wires.
The sea of delocalized electrons also makes metals good conductors of heat and electricity. The electrons are free to move around the array of positive metal ions, carrying charges. Metals are also insoluble in water. The bonding of metals contributes to their shiny, lustrous appearance. When light shines on a metal, some of the delocalized electrons on the outside of the structure are excited. As they return to their ground state, they release energy as light, giving off a lustrous gleam.
Looking at a species' properties is often a useful indication of its type of bonding. This is particularly handy when looking at species that stray from the familiar trends.
For example, beryllium chloride, BeCl2, consists of beryllium and chlorine atoms. Beryllium is a metal, and chlorine is a non-metal. Because of that, you might expect them to bond ionically. However, they actually bond covalently, forming a simple covalent molecule. We can infer this when we look at the molecule's properties: beryllium chloride has low melting and boiling points. Here's a table that compares the different types of bonding, and the structures and properties associated with them.
If we knew an element's position on the periodic table, could we predict how it bonds? In fact, we often can. Bonding shows periodicity. Periodicity is the repetition of properties after a certain interval. On the periodic table, we see trends that repeat with every new period.
Here's the periodic table.
We know that metals, found on the left-hand side of the periodic table, bond using metallic bonding. As you move across to the right-hand side of the periodic table, you encounter the non-metals. We know that these tend to bond using covalent bonding. Moving down a column in the periodic table, known as a group, you encounter elements with very similar properties. This happens because the elements in the same group bond in similar ways. In fact, electron configuration and location on the periodic table are good indicators of an element's bonding.
In the image above, there's a brown diagonal line snaking its way down the right-hand side of the periodic table. It starts at boron and ends at tellurium. These elements are the metalloids. They bridge the gap between metals and non-metals in the periodic table, and their properties are a mixture of the two. For example, metalloids are typically shiny, much like metals, but brittle, much like non-metals. They're also fairly good conductors of electricity and can form alloys with other metals. That's it! By now, you should be able to explain the differences between the three types of bonding, and compare the properties they give a species.
The three types of bonding in chemistry are covalent, ionic, and metallic bonding. Covalent bonds are formed when atomic orbitals overlap, creating a shared pair of electrons. They are very strong and require a lot of energy to overcome. Covalent network solids have high melting and boiling points and are hard and strong, whereas simple covalent molecules have low melting and boiling points and are gases at room temperature. Both are poor conductors of heat and electricity. Ionic bonds are formed when one atom donates electrons to another. The resulting ions are electrostatically attracted to each other. Ionic bonds are also very strong and require a lot of energy to overcome. Ionic compounds form hard, brittle lattices with high melting and boiling points. They are poor conductors as solids, but good conductors when molten or aqueous. Metallic bonds are formed when metal atoms delocalize their outer shell electrons to form an array of positive metal ions in a sea of delocalization. Metallic bonds are fairly strong and require a moderate amount of energy to overcome. Metals are malleable, ductile, and have medium-high melting and boiling points. They are good conductors of heat and electricity in all states.
What are the types of bonding and their properties?
The three types of bonding in chemistry are covalent, ionic, and metallic. Covalent bonds are strong and result in either giant covalent macromolecules, which are hard, strong and have high melting and boiling points, or simple covalent molecules, which have low melting and boiling points. Ionic bonds are also strong and result in hard, brittle ionic lattices that can conduct electricity when molten or aqueous. Metal bonds are weaker and result in malleable, ductile metal lattices that conduct electricity in all states.
What determines the bonding properties of an element?
An element's bonding properties are affected by its electron configuration and number of valence electrons.
What periodic trends affect bonding?
Periodic trends such as electronegativity, electron affinity, and ionization enthalpy affect bonding. These influence how easily an element can gain or lose an electron, and how well it attracts shared electrons in a covalent bond. An element's number of outer shell electrons also affects its bonding.
What are the physical and chemical properties of ionic bonds?
Ionic bonds are hard and strong and result in hard, brittle ionic lattices with high melting and boiling points.
What are the physical and chemical properties of covalent bonds?
Covalent bonds are strong. They either result in giant, insoluble macromolecules with high melting and boiling points, or simple covalent molecules with low melting and boiling points. Both giant macromolecules and simple covalent molecules are poor conductors.
