In this video, we will draw dot and cross diagram of oxygen molecule. From there, we will determine the structural formula of oxygen.
Knowing how to write accurate structural formula is particularly important when students deal with Organic Chemistry.
Covalent bond is formed when electrons are shared between non-metals. After bonding, each atom attains the noble gas electronic configuration. Elements and compounds with covalent bonds are called molecules. A molecule is a group of two or more atoms held together by covalent bonds.
Before drawing the dot and cross diagram of oxygen (O₂), we first need to determine the number of electrons in each atom.
We can find the number of electrons from the periodic table. The number at the top of each element is the atomic number, which tells us the number of protons. In an atom, the number of protons and electrons is the same. Therefore, this number also represents the number of electrons.
Electron arrangement of oxygen:
- Oxygen has 8 electrons.
- 2 electrons are in the first shell.
- 6 electrons are in the second shell (outermost shell).
Since oxygen needs 2 more electrons to achieve a stable noble gas (octet) configuration, and there are two oxygen atoms in an oxygen molecule (O₂), each oxygen atom will share 2 electrons with the other.
Drawing the dot and cross diagram:
- Each oxygen atom shares 2 of its valence electrons with the other oxygen atom.
- This results in 4 electrons being shared between the two oxygen atoms.
- The inner shells are not involved in bonding.
After drawing the diagram, we should check whether each atom has achieved a noble gas electronic configuration:
- Both oxygen atoms now have 8 electrons in their outermost shell ✓
Both atoms have achieved a stable electronic configuration.
Note for exams: If the question asks you to draw only the outermost electrons, you can omit the inner shells. Only show the valence electrons involved in bonding.
Converting to structural formula: From the dot and cross diagram, we can see that 4 electrons are shared between the two oxygen atoms. Since 4 electrons are shared, this means 2 bonds are formed. Therefore, oxygen gas contains a double bond between the two oxygen atoms (O=O).
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