To determine the bond angles and molecular geometry of CH3SH (methanethiol), we first need to look at the molecular structure.
CH3SH has a central sulfur atom (S) bonded to three hydrogen atoms (H) and one methyl group (CH3). This gives it a total of four regions of electron density around the sulfur atom, which suggests using VSEPR (Valence Shell Electron Pair Repulsion) theory.
According to VSEPR theory, four regions of electron density will arrange themselves in a tetrahedral geometry to minimize repulsion. However, because sulfur has larger atomic size and can also form lone pairs, we have to account for the lone pair present on the sulfur atom. In CH3SH, sulfur has one lone pair, which will alter the geometry.
With that lone pair and the three hydrogen atoms, the molecular geometry of CH3SH becomes trigonal pyramidal. The presence of the lone pair pushes the hydrogen atoms slightly closer together.
The ideal bond angle in a tetrahedral arrangement is 109.5 degrees. However, the actual bond angles in CH3SH are slightly less than this, approximately 107 degrees, due to the repulsion exerted by the lone pair of electrons.
In summary, CH3SH has a molecular geometry that is trigonal pyramidal with bond angles that are approximately 107 degrees.