The atomic bond is one of the three main chemical bond types. These include the ionic bond and the metal bond. A bond is formed when one or more shared pairs of electrons are formed between atoms with each other. At least one atom achieves the noble gas configuration, e.g. the well-known full valence shell with eight electrons.
A distinction is made between polar and non-polar atomic bonds, which differ in their different strengths of attraction of the common pair of electrons from one of the two atoms. We will explain more about this in the following paragraphs.
How is an atomic bond formed?
Atoms always want to reach an energetically stable state. They do this by fully occupying their outer electron shell. In the case of the main group elements, this stable state is almost always achieved by a figure-eight shell.
In order to reach an energetically stable state, atoms can either lose or gain electrons. This means that they form ions or share electron pairs with other atoms. The shared pair of electrons then causes the binding forces between the molecules. Two different types of binding can arise:
atomic bonds
Non-polar atomic bond
polar atomic bond
Examples:
hydrogen molecule,
oxygen molecule
Examples:
water molecule
hydrogen chloride molecule
Non-polar atomic bond
Atoms with the same electronegativity attract the shared pairs of electrons equally. This creates a non-polar atomic bond.
polar atomic bond
When the atoms have different electronegativity, the shared electron pairs are more attracted to the atom that has higher electronegativity. This creates a polar atomic bond.
The atoms of the seventh main group of the periodic table are missing an electron so that they have a full eight-shell, which is also known as an octet. To achieve this state, they can form a shared pair of electrons with other atoms. The bond that is formed is also called an electron pair bond (also called an atomic bond).
So if only one electron is missing for the stable state, atoms can use a shared pair of electrons. However, several shared electron pairs are also possible. More on that in the next section.
Where are metallic bonds found?
In the last section we explained that both one and several shared electron pairs are possible. Now two examples:
Molecules with an electron pair bond
halogens
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When atoms of the same element combine with each other, non-polar atomic bonds are formed, for example the chlorine molecule: Two chlorine atoms have the same electronegativity and therefore use a pair of electrons equally. Each chlorine atom contributes an electron.
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Polar atomic bonds form between different elements, eg in the case of the hydrogen chloride molecule: the chlorine atom and hydrogen atom each contribute an electron for the common pair of electrons. However, the chlorine atom has a higher electronegativity than the hydrogen atom and therefore attracts the electron pair more strongly. It is shifted towards chlorine. Now the atomic bond is polar.
Molecules with multiple electron pair bonds
oxygen
Oxygen has six outer electrons. For a full eight-shell, it would have to absorb two more electrons. If it absorbs two, an oxygen ion O2- is formed.
However, as soon as two oxygen atoms combine with each other by forming two shared electron pairs for the atomic bond, they can also achieve a full eight-shell. Since there are now two shared pairs of electrons, this is called a double bond.
When oxygen bonds with other elements, such as hydrogen, the oxygen also forms two atomic bonds, each with a hydrogen atom. These bonding pairs of electrons are attracted towards the oxygen atom because the electronegativity of oxygen is higher than that of hydrogen. Polar atomic bonds are formed.
The most important thing about the atomic bond at a glance!
What is an atomic bond?
- A bond between atoms by aiming for a full valence shell with eight electrons
- Polar atomic bonds are formed between different elements
- Non-polar atomic bonds form between the same elements.
How is an atomic bond formed?
- To achieve the full eight-shell, pairs of electrons are formed between the atoms