- There are three rules on determining how many significant figures are in a number:
- Non-zero digits are always significant.
- Any zeros between two significant digits are significant.
- A final zero in the decimal portion ONLY is significant.
In science, all numbers are based upon measurements. Since all measurements are uncertain, one must only use those numbers that are meaningful. A common ruler cannot measure something to be 22.407244 cm long. Not all of the digits have meaning (significance) and, therefore, should not be written down. In science, only the numbers that have significance (derived from measurement) are written.
Lewis dot structure gives the idea of completion of octet on every atom that is present in bonded compound. In the compound XeF4 , there are a total of six pairs of electrons in valence shell and two pairs of lone pair of electrons.
According to VSEPR explanation, the six electron pairs form an octahedron with two positions occupied by lone pairs.
Hybridization of orbitals takes place in central atom Xenon. The valence shell of Xe contains two electrons in 5s orbital and six electrons in 5p orbital. In the fifth orbital, there is a place for d orbital and f orbital both of these are empty.
Of the 5s and 5p electrons in outermost orbit of Xe, two of the 5p orbital electrons get excited to vacant 5d orbital resulting in 4 unpaired hybridized electrons, 2 in 5p and 2 in 5d orbitals.
Four fluorine atoms bond with these four electrons. Remaining two pairs of non-hybridized electrons are free on either side of the central atom. Hybridization in XeF4 is d2sp2 because two electrons of p migrate to d orbital and these form sigma bond with F. while the two pairs of unhybridized lone pairs remain in its sigma state. Hence, shape of XeF4 is square planar with two lone pairs in perpendicular plane.
