Why are the water molecule bonds at an angle and not straight like the CO2?
The reason for the water molecule (H2O) bonds being at an angle instead of straight, like in carbon dioxide (CO2), is due to the arrangement of the electron pairs surrounding the oxygen atom.
To understand this, let's consider the electron configuration of oxygen. Oxygen has six valence electrons, two of which participate in the covalent bond with the two hydrogen atoms, while the remaining four electrons are in two lone pairs surrounding the oxygen atom.
In a water molecule, the two hydrogen atoms are connected to the oxygen atom via covalent bonds. Each hydrogen atom contributes one electron, and the oxygen atom contributes two electrons, resulting in a total of eight electrons in the water molecule.
In order to achieve a stable electron arrangement, the water molecule adopts a bent or V-shaped structure. The repulsion between the two lone pairs of electrons on the oxygen atom causes them to move away from each other, pushing the hydrogen atoms closer together. This arrangement minimizes the repulsion between the electron pairs and maximizes the stability of the molecule.
On the other hand, in carbon dioxide, each oxygen atom is connected to the carbon atom via double bonds. Carbon has four valence electrons, while each oxygen contributes two electrons, totaling 16 electrons. Due to the linear arrangement of the atoms, the carbon-oxygen double bonds and the carbon-oxygen bond angle in CO2 are 180 degrees.
In summary, the different arrangements of the electron pairs surrounding the central atom dictate the bond angles in molecules. In the case of water, the presence of two lone pairs on the oxygen atom leads to a bent structure, resulting in a bond angle of approximately 104.5 degrees. In carbon dioxide, the absence of lone pairs and the linear arrangement of the atoms result in a bond angle of 180 degrees.