How do covalent bonds contribute to molecular geometry?

Covalent bonds determine molecular geometry by dictating the shape and arrangement of atoms in a molecule.

Covalent bonds are formed when two atoms share a pair of electrons. This type of bond is common in many molecules, including water (H2O), methane (CH4), and carbon dioxide (CO2). The geometry of these molecules is determined by the number of covalent bonds and the arrangement of these bonds around the central atom.

The Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of molecules based on the number of valence electron pairs surrounding an atom. According to this theory, electron pairs will arrange themselves to be as far apart as possible to minimise repulsion. This results in specific geometric shapes for molecules.

For example, in a water molecule, the oxygen atom forms two covalent bonds with two hydrogen atoms and has two lone pairs of electrons. According to the VSEPR theory, these four pairs of electrons will arrange themselves in a tetrahedral shape to minimise repulsion. However, because we only see the atoms and not the lone pairs, the shape of the water molecule appears bent or V-shaped.

In methane, the carbon atom forms four covalent bonds with four hydrogen atoms. There are no lone pairs of electrons, so the electron pairs form a perfect tetrahedral shape. This is why methane is a tetrahedral molecule.

In carbon dioxide, the carbon atom forms two double covalent bonds with two oxygen atoms. There are no lone pairs of electrons, so the molecule is linear.

In summary, the number and arrangement of covalent bonds in a molecule determine its geometry. The VSEPR theory helps us understand and predict these shapes by considering the repulsion between electron pairs.