Final answer:
Silicon tetrachloride forms covalent bonds because silicon requires four additional electrons to reach an octet, which is achieved by sharing electrons with four chlorine atoms in a tetrahedral structure.
Step-by-step explanation:
Silicon tetrachloride (SiCl4) forms a covalent bond because silicon, a group 14 element, requires four additional electrons to achieve an octet in its valence shell. When silicon bonds with four chlorine atoms in SiCl4, each chlorine atom shares one valence electron, leading to the formation of four covalent bonds, ensuring that the octet configuration is achieved for silicon. This is in line with the general tendency of nonmetals like silicon to share electrons rather than transfer them, differentiating covalent bonds from ionic bonds.
Since silicon atoms do not readily form double or triple bonds like carbon, they usually form single covalent bonds. The SiCl4 molecule assumes a tetrahedral structure as per VSEPR (Valence Shell Electron Pair Repulsion) rules, which also suggests the presence of strong directional covalent bonding.
These covalent bonds contribute to SiCl4 being a nonpolar, low-boiling liquid. Silicon halides such as SiCl4, however, are sensitive to water and react to form compounds like orthosilicic acid (Si(OH)4).