Final answer:
The tetrahedral electron-pair geometry can lead to different bond angles depending on the number of lone pairs. Without lone pairs, angles are 109.5°. With one or two lone pairs, the angles decrease to around 107° or 104.5°, respectively.
Step-by-step explanation:
The shape and number of electron pairs around a central atom that would result in bond angles of 109.5°, 107°, or less are related to the tetrahedral electron-pair geometry. However, depending on the presence of lone pairs, the molecular structure and the precise angles can vary. If a molecule has a tetrahedral electron-pair geometry and no lone pairs, the bond angles are 109.5°. When lone pairs are present, the bond angles decrease due to increased repulsion. This is why a molecule with a tetrahedral electron-pair geometry and one lone pair will have a trigonal pyramidal molecular structure with bond angles of around 107°. With two lone pairs, the molecular structure becomes bent with even smaller bond angles, close to 104.5° as mentioned in the reference materials.