Pure magnesium's formula would just be Mg because all elements except for 7 nonmetals are just left alone when they are by themselves in a formula. The 7 diatomic elements( means they have to have two of them without another element attached to it aka. a subscript two after it when it's by itself) are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine. An easy way to remember the diatomic seven is that when looking at a periodic table if you trace over them from nitrogen over to fluorine and down to iodine all of those elements are diatomic + hydrogen.
And your unbalanced and balanced equations are correct.
(sorry I went on a tangent with the diatomic rules hopefully it will help you in the future though)
The shape of XeO₂F₂ is Trigonal bi-pyramidal see-saw tetrahedron (see attached pictures)
- As you said the hybridization of Xe here is sp³d so its geometry has to be Trigonal bi-pyramidal in which F atom located on axial positions but for the final shape we exclude lone pair on Xe to give
see-saw shape (see second picture)
- Remember that we have 5 pairs (4 bond pairs + 1 lone pair) and we have to place lone pair at equatorial position.
Tc is Technetium, and it has an atomic number of 43. Its atomic configuration is [Kr] 5s(1) 4d(5) [I'm on my phone so I can't do numbers on shoulders, pretend that 1 and 5 are on the s and d's shoulder]
The outside most ring is the 4d(5), and the d orbital can hold ten electrons.
Valence electrons are electrons, in you could say the outside ring that isn't filled, the extra ones. In this case, there are 5.