What are the Two Types of Chemical bonds?
Types of chemical bonds can divide into the main two types. They are,
- Ionic bond.
- Covalent bond.
If you are new to the subject, “Chemical bonds”, please have a look at our most informative article about “What is a chemical bond” with explanations.
By these two types of chemical bonds, there are two ways in which atoms can obtain noble gas configurations:
- By outright transfer of electrons from one atom to another to form what is called ionic bonding.
- By the sharing of electrons between pairs of atoms with each atom “considering” that it “owns” all the shared electrons; this is called covalent bonding.
Under the main two types of chemical bonds, firstly, let’s have a look at what ionic bonding is.
Ionic bonding is a type of chemical bond which involves the outright transfer of electrons from one atom to another. The bonding consists of electrostatic attraction between the positive and negative ions formed by this transfer of electrons.
We have selected three examples of ionic bonds to give you a wide informative knowledge about this main type of chemical bond,
Note: For a better understanding of these two types of chemical bonds, you should have a basic knowledge about electron configuration. Therefore, you can have a look at “Electron Configuration and the Periodic Table” before coming into chemical bonds.
Sodium and Chlorine combine to form the compound, sodium chloride
The sodium atom, with electronic configuration (2, 8, 1) tends to lose one electron to become like neon (2, 8); the chlorine atom, with electronic configuration (2, 8, 7) tends to gain an electron to become like argon (2, 8, 8). Hence one electron transferred from a sodium atom to a chlorine atom. When the neutral sodium atom loses one electron, it becomes positively charged: we call it a positive ion. When the neutral chlorine atom gains an electron, it becomes negatively charged: it is a negative ion which we call the chloride ion. Schematically:
There is a strong electrostatic attraction between the positive and negative ions, and this is what holds the ions together in ionic bonding. Sodium chloride is, therefore, NaCl (i.e. one sodium atom per chlorine atom, since that is the way to balance charges). We occasionally write it as Na+Cl– to stress the ionic nature of the bonding.
Crystals of Sodium chloride
Crystals of sodium chloride consist of sodium ions and chloride ions packed in an orderly fashion. The electrostatic attraction between pairs of oppositely charged ions extends throughout the whole crystal. This shows in the figure below.
There are no separate molecules of NaCl. Just an extremely large array of positive and negative ions held tightly together.
So, for further clarifications of ionic bonding which is one of the main types of chemical bonds lets look at example 02.
Magnesium and Oxygen combine to form “magnesium oxide“
Magnesium, with electronic configuration (2, 8, 2), loses two electrons to become like neon (2, 8), while oxygen (2, 6) gains two electrons also to become like neon.
By losing two electrons, the neutral magnesium atom becomes the doubly charged positive ion, Mg+2. Similarly, by gaining two electrons, the neutral oxygen atom becomes the doubly charged negative ion, O2-, called the oxide ion.
Since each magnesium atom loses two electrons and each oxygen atom gains two electrons, the compound formed will consist of one oxygen atom per magnesium atom. Its formula is MgO, which we may write as Mg2+O2- to emphasize the ionic bonding. Again there are no discrete molecules of MgO. Just an infinite lattice of positive and negative ions very tightly bound together by electrostatic attraction.
So, let’s have a look at a different kind of example too.
Calcium and Fluorine combine to form calcium fluoride
Each calcium atom, with electronic configuration (2, 8, 8, 2), loses two electrons to become like argon (2, 8, 8), while each fluorine atom (2, 7) gains one electron to become like neon (2, 8). Hence two fluorine atoms must combine with one calcium atom to form the ionic compound, CaF2.
If we wish to emphasize the ionic nature of the bonding, we may write the formula as Ca2+(F–)2.
Summary of Ionic Bonds
There are two main types of chemical bonds, and an ionic bond is one of them. In ionic compounds, there are no discrete molecules. These substances consist of arrays of positive and negative ions with the attraction between pairs of oppositely charged ions extending throughout the whole crystal. For such ionic compounds, the formula (e.g. NaCl, MgO, CaF2, etc.) specify the ratios in which the atoms (or ions) are present, rather than the composition of discrete molecules.
Properties of Ionic substances because of chemical bonds
Because the strong electrostatic attraction between neighboring oppositely charged ions can extend indefinitely in all directions, ionic substances are all solids at room temperature and have very high melting and boiling points.
When ionic substances do melt, the orderly arrangement of ion breaks up, and the ions can move about relatively freely. Hence molten ionic substances are good conductors of electricity, because there are ions present and because these are free to move towards oppositely charged electrodes.
Similarly, when ionic substances dissolved in water, the crystals completely break up, and the solutions consist of individual ions moving randomly about through the water. Hence solutions of ionic substances conduct electricity, again because the ions can move towards oppositely charged electrodes. This flow of ions constitutes the flow of electricity.
By using the above three examples, we covered up all parts of ionic bonds.
Secondly, its time to discuss widely another interesting type of bond which comes under the main two types of chemical bonds, called Covalent bonds.
Covalent bonding is a type of chemical bond which forms between pairs of atoms by the atoms sharing electrons.
Again the nature of this type of chemical bond is best explained by considering specific examples as follows.
Two chlorine atoms combine to form a chlorine molecule.
A chlorine atom, with electronic configuration (2, 8, 7), tends to gain one electron to acquire the configuration of argon (2, 8, 8). Two chlorine atoms can combine to form a chlorine molecule, Cl2. Two atoms share a pair of electrons, with atom contributing one electron to the shared pair and with each atom considering that it “owns” the shared pair and thus counting both members of the pair to determine whether it has a noble gas configuration.
Cl (2, 8, 7) + Cl (2, 8, 7) -> Cl (2, 8, 6) + shared pair + Cl (2, 8, 6)
This shared pair of electrons occupies a volume of space (orbital) which encompasses both atoms. These electrons move around both nuclei, and in so doing hold the atoms together, i.e. form a chemical bond. This illustrated in the figure below. The rest of the electrons (the unsaturated ones) remain in orbitals that surround one nucleus only.
Each chlorine atom in the chlorine molecules now considers that it has the configuration (2, 8, 8) and is therefore satisfied. This bonding results from sharing pairs of electrons is called covalent bonding. Each pair of shared electrons is a covalent bond. These types of chemical bonds denote by a dash. So, molecular chlorine has the structure,
A common way of describing covalent bonding is to use the electron-dot diagrams, which are symbols or formula of elements or compounds with the outer energy level electrons shown as dots. The electron-dot formula for the chlorine atom is,
(the completely filled first and second main levels- the 2,8- ignored and just the seven electrons in the incomplete third level showed.) We then denote the pairing up of electrons by drawing.
Which can then write as,
A dash equals one bonding pair of electrons or one covalent bond.
So, for further clarifications of covalent bonding which is one of the main types of chemical bonds lets look at example 02.
Hydrogen and Chlorine combine to form the gaseous compound, hydrogen chloride
The hydrogen atom, with only one electron, needs to gain another electron to become like helium. Chlorine (2, 8, 7) also needs to gain one electron to become like argon (2, 8, 8). Hence a covalent bond is formed by each atom contributing one electron to a pair that is shared by both atoms. So, in this way, both atoms consider that they own the pair and they have achieved the desired noble gas configuration. In electron dot form:
Hydrogen and Oxygen combine to form water
Oxygen (2, 6) needs to gain two electrons to become like neon (2, 8) while hydrogen needs to gain one electron to become like helium. Hence covalent bonds are formed between one oxygen atom and two hydrogen atoms.
So, In this way, each hydrogen atom and the oxygen atom consider that they have achieved the noble gas configuration (because each atom counts both electrons in the shared pair).
Multiple covalent chemical bonds
Sometimes, to attain noble gas configurations, pairs of atoms must share more than one pair of electrons.
Examples for Multiple covalent chemical bonds
To form carbon dioxide, carbon (2, 4) which needs to gain four more electrons and oxygen (2, 6) which needs to gain two more electrons, pair up their electrons as follows:
Between the carbon atom and each oxygen atom, there are two shared pairs of electrons. So, In this way, carbon considers that it too has eight outer electrons. Because there are two shared pairs of electrons between carbon and each oxygen atom, we call these double bonds.
Similarly, for ethene, C2H4, there is a double bond between the carbon atoms (and single bonds between each carbon atom and the hydrogen atoms):
Nitrogen (2, 5) needs to gain three electrons to become like neon (2, 8). Hence to form nitrogen molecules, pairs of atoms must share three pairs of electrons to form what we call a triple bond.
Similarly, in hydrogen cyanide, HCN, a triple bond form between N and C to satisfy the bonding drives to all three atoms:
and Ethyne (acetylene) as well.
Properties of Covalent substances because of chemical bonds
Covalent substances consist of discrete molecules, in contrast to ionic substances which are infinite arrays of ions. While the bonding forces holding atoms together within covalent molecules are very strong, the forces between molecules-the intermolecular forces-are by comparison rather weak. This means that covalent substances are often gases (N2, SO2, NH3) or liquids (H2O, CCl4, H2SO4). If they are solids (I2, H3BO3), they have relatively low melting and boiling points.
Since the molecules making up these covalent substances are electrically neutral, covalent substances do not conduct electricity either in the liquid state or in solution (unless the compound such as hydrogen chloride (HCl) or sulfuric acid reacts with the solvent, water, to form ions when it dissolves).
So, Have a look at this video too.
Types of Chemical bonds Summary
There are two main types of chemical bonds in chemistry. They are ionic bonds and covalent bonds. The differences between these two bonds depend on how they share electrons to gain the noble gas configuration when making molecules. They differ from their chemical and physical properties as well.
Chemical bonds act as the foundation of chemistry.