Ionic bonding occurs when positive ions (cations) and negative ions (anions) are attracted to each other through electrostatic forces within an ionic crystal lattice. Covalent bonding, on the other hand, are established by the sharing of outer electrons between two atoms. These resulting ionic or covalent bonds are typically quite robust and require a significant amount of energy to break. Another type of chemical bonding is metallic bonding.
Ionic Bonding Chemical bonding
When an atom loses one or more electrons, it becomes a positive ion. This is a common occurrence in metal atoms, which tend to lose electrons and transform into positive ions. Conversely, when an atom gains one or more electrons, it becomes a negative ion. This process is typical for non-metal atoms, as they often gain electrons and turn into negative ions. As mentioned previously, cations and anions interaction form ionic bonds or sometimes called electrovalent bond to have the configuration of noble gas.
From Figure 1, we can see that sodium has one electron in its outer shell. Meanwhile, chlorine lacks of an electron in its outer shell to have the configuration of noble gas. This conditions causes the electron from sodium transferred to chlorine. As the result, sodium formed positive ion with charge +1 and chlorine form negative ion with charge -1. Interaction between those two ions called ionic bonding.
We employ dots and crosses in diagrams to represent the electronic arrangement of chloride and sodium ions. This method assists us in tracing the origin of electrons. It’s important to note that the transferred electron is no different from the others; these diagrams are referred to as dot-and-cross diagrams. Please note that this dot-and-cross diagrams only shows the outer electron shells. To make it clearer, let’s see the example below,
From the picture above, we can see that ‘x’ indicates the electrons in the outer shell of magnesium atom while ‘dot’ insicates the electrons in the outer shell of oxygen atom. Because of the electron transfer, oxygen has more electrons which are written by ‘x’, means those electrons are from magnesium. The ion’s charge typically written in the top right-hand corner. From Figure 2, we know that magnesium has charge +2 while oxygen has charge -2.
There are three types of covalent bonding, including single covalent bonds, muliple covalent bonds, and co-ordinate bonding. Let’s find out one by one!
Single Covalent Bonds
Single covalent bonds occurs when two non-metal atoms combine by sharing one or more pair electrons. A single covalent bond is symbolized by a single line connecting the atoms, for example Cl─Cl. The picture below will make us more understand about that.
Figure 3 shows chlorine has 7 electron in its outer shell. To distinguish the electrons from each chlorine, electrons in the first chlorine written by ‘x’ while electrons from the second chlorine written by ‘dot’. It is differenet from the ionic bonds. Instead of transfer electrons, the pair of electrons are used together. Other examples of single covalent bondings provides by the figures below,
In certain situations, the electrons surrounding a central atom may not possess the electron arrangement typical of noble gases, which is often referred to as an octet of electrons. For instance:
Boron trifluoride has only 6 electrons around Boron atom. We call this electron deficient.
Phosphorus(V) chloride has 10 electrons around phosphor atom. We call this expanded octet. Other examples of expanded octet are sulfur hexafluoride and sulfur dioxide.
Multiple Covalent Bonds
Some atoms bond together by sharing two pair of electrons which we call double covalent bonds. Double lines between the two atoms symbolises this double covalent bond, for example O=O.
From figure 4, we know that oxygen needs two electrons to reach octet. When two oxygens combine, each oxygen shares one pair of electron. So, there are two pair of electrons that being used together.
Some atoms can also bond together by sharing three pairs of electorns or we call that triple covalent bond. The figure above is the example for this. Each nitrogen atom needs three electron to reach octet so that when two nitrogen atoms join together, they share three pair of electrons. Just like the picture above, thre lines between the two atoms represents triple covalent bond.
The last type of covalent bonding we will discuss is co-ordinate bonding. In this case, an atom share a pair of electron to be used together with another atom.
From Figure 6, we can see that ammonia share a pair of electron to be used together with hydrogen ion (proton). The arrow indicates coordinate bond. the head of the arrow points to the atom that needs the electrons.
Source: Chemistry Cambridge As and A Level 3rd Edition