Yes, elements with more than 8 valence electrons can exist. While the octet rule is a useful guideline for understanding the stability of elements, it is not a strict rule that applies to all elements.
Elements beyond the second period (row) of the periodic table, such as elements in the third period and beyond, can have expanded valence shells that can accommodate more than 8 electrons. This is because these elements have access to the d orbitals in addition to the s and p orbitals.
For example, elements in the third period (periodic table rows) can have up to 8 valence electrons in their s and p orbitals, but they can also utilize the d orbitals to accommodate additional electrons. This allows for elements such as sulfur (S), with 16 electrons, and chlorine (Cl), with 17 electrons, to exist with more than 8 valence electrons.
Elements in the fourth and subsequent periods can have even larger valence shells due to the availability of the f orbitals in addition to the s, p, and d orbitals. This allows for the possibility of elements with more than 8 valence electrons in these periods as well.
It's important to note that while many elements can have expanded valence shells, the stability and reactivity of these elements can vary. Elements tend to achieve a stable electron configuration by gaining, losing, or sharing electrons to achieve a filled valence shell, and this can influence their chemical behavior.