Question

Molecular Structure and Physical Properties

Consider the following statements and determine which are true and which are false.

true/false  SeF₄ has a see-saw structure.
true/false  KrF₄ is a polar molecule.
true/false  NO₃^- has three resonance Lewis structures.
true/false  Bond angles for IF₆⁺ are 90 °.
true/false  Selenium tetrafluoride (SeF₄) is a non-polar molecule.
true/false  The formal oxidation state of an atom in a molecule (or molecular ion) can be calculated as:
(the number of valence electrons on a free atom) minus (half the number of electrons in bonds to that atom) minus (the number of unshared electrons assigned to the atom in the molecule)

Answer 1

SeF4 has a see-saw structure = True ,because its an SP3D see-saw ,Its shape is in the gaseous phase which is similar to that of SF4 having a non-symmetrical see-saw shape that would make the molecule polar.

KrF4 is a polar molecule = False, because Although the four bonds of the krypton tetrafluoride (KrF4) are polar, it has a symmetrical square planar structure and the bond polarity is cancelled by the symmetry making it non-polar.

NO3- has three resonance Lewis structures = True ,The nitrate ion can be viewed as if it resonates between THREE different structures. Each of these structures is known as resonance structure. In actuality, the ion behaves as if it were a blend of the 3 resonance structures giving a single resonance hybrid.

Bond angles for IF6+ are 90 ° = True ,because it is an SP3D2 octahedral, square bipyramid ,[IF6]- has an octahedral geometry, consisting of the six fluorine atoms attached to central iodine atom. Its shape is a square based ‘base-to-base’ pyramid with a F-I-F bond angle of the exactly 90degrees.

Silane (SiH4) is a non-polar molecule = True,The molecular geometry of SiH₄ is the tetrahedral with symmetric charge distribution around the central atom.
Therefore this molecule is non-polar.

The formal oxidation state of an atom in a molecule (or molecular ion) can be calculated as:
(the number of valence electrons on a free atom) minus (half the number of electrons in bonds to that atom) minus (the number of unshared electrons assigned to the atom in the molecule)=True,because the FORMAL CHARGE is a concept used to determine the most probable Lewis structure.
The formal charge of an atom in a Lewis formula is hypothetical charge you obtain by assuming that bonding electrons which are equally shared between bonded atoms and the electrons of each lone pair (nonbonding pair) belong completely to one atom.

Formal Charge = G - B - N.E
G = Group number of the element in the periodic table or the number of valence electrons on the free atom.
B = Number of bonds of the element in the molecule which is also equal to half the number of electrons in bonds to that atom.
N.E = Number of nonbonding (unshared) electrons of the element in the molecule.