Is PF5 Polar or Nonpolar?

Answer: PF5 is a nonpolar molecule because when you consider its horizontal and vertical planes electron pulls balance themselves out to achieve a neutral conformation. 

Although the difference electronegativity difference between phosphorus (2.19) and Fluorine (3.98) is large enough to create polar covalent bonds within the structure, the way these bonds are arranged around the central phosphorus cancels out these inequalities. If you slice the molecule in one direction/plane you will see a linear structure similar to that of CO2 (see why CO2 is nonpolar in this article). If you slice the molecule now in the other orthogonal plane/direction you will see a trigonal planar structure similar to that of BF3 (see why BF3 is nonpolar in this article). Since both of these constituent structures are nonpolar, the sum of their parts is also nonpolar.

Another possible question regarding this structure may be the apparent violation of the octet rule on the central Phosphorus atom. When you count up all of the electrons, it seems that the central phosphorus atom shares ten electrons. This kind of configuration can work under the theory of expanded octets which explains this violation by having some electrons participate in bonding via the d subshell found in the third energy level. This means that elements without a third subshell (i.e. all the elements with less protons than Neon) cannot have expanded octets. Although other molecules with expanded octets are rare, they do exist especially as the number of electrons in an element increases.

PF5 Ball and Stick Structure. Created with MolView.

How does PF5 actually behave in nature?

Due to the presence of many extremely electronegative fluorine atoms, the structure is electron-deficient and acts as a Lewis acid. PF5 will as a result of these characteristics will readily undergo hydrolysis even though this is an atypical property for nonpolar molecules.

Is PH3 Polar or Nonpolar?

Answer: PH3 is polar due to the presence of a lone pair of electrons with electron-electron repulsion causing an overall "bent" structure. This results in a dipole moment throughout the molecule. 

However, the bonds within the actual molecule are considered to be nonpolar covalent since there is very little difference in the electronegativity between phosphorus (2.19) and hydrogen (2.20). Another reason why the lone pair creates a region of negative charge is because it does not have a corresponding proton to balance out the negative charge as the other bonds do. This essential +1 positive charge "balancer" encompasses the function of hydrogen within the other bonds.

PH3 has a similar structure to NH3 (ammonia) which makes sense since phosphorus and nitrogen are in the same group (pnictogens). You can read more about the Lewis Structure or Polarity of NH3 by clicking on the linked articles.

PH3 Ball and Stick Model. Created with MolView.

What state is PH3 normally found in?

PH3 is normally a colorless gas at standard temperature and pressure. The weak dipole interactions result in a boiling point of -87˚C which thereby makes this compound suitable as a "cryogenic liquid" (similar to the use of liquid nitrogen however at relatively less extreme temperatures). PH3 is said to have a very distinctive odor and can be flammable because of spontaneous formation of P2H4 within regions of PH3 buildup which can occur in certain places since PH3 is heavier than the atmosphere. Applications for PH3 include in certain Organic Chemistry reactions and as a pesticide for farm fields (agriculture).

How many valence electrons are in an atom of Iron

Answer: A neutral atom of Iron has two valence electrons located in the fourth energy level. 

Properties of Iron. Source

As mentioned above, Iron contains two valence electrons located in the fourth energy level. Iron is technically part of Group 8 in the Periodic Table but it is typically just grouped in with many of the other "transition metals." A Bohr model for Iron can be viewed below which confirms the presence of two electrons within the valence shell:

Bohr Model of Iron with different orbital shells labelled. Source

The reason for the low number of valence electrons in the fourth shell is due to the filling up of the d-shell in the third energy level before more electrons are placed into the fourth energy level (in either the p, d or f sublevels). Iron's entire valence shell consists of two electrons in the s subshell, the same number as many other elements in the fourth row including Potassium, Calcium and Zinc. 

Iron Orbital Notation. Source

Iron as a transition metal with extra electrons in the d-orbital of the third energy level oftentimes participates in metallic bonding with other iron atoms. Metallic bonding a property in many other transition metals because the large number of electrons in the third energy level shield the positive nucleus from the two outer valence electrons. This makes them very mobile between all of the different atoms within the structure and makes these metals excellent conductors of electricity.

Metallic Bonding in an Iron Compound. Source

Iron was one of the few elements known in its pure form to the ancient world. Due to the ease with which Iron corrodes, it was originally a rare choice for tools and weapons. However, as the technology and knowledge associated with Iron metallurgy progressed, its use picked up considerably in all of the ancient civilizations. The forged items were utilized for a wide variety of applications including agriculture, construction and warfare. 

Sources:

https://pubchem.ncbi.nlm.nih.gov/compound/Iron 

Is BF3 Polar or Nonpolar?

Answer: BF3 is nonpolar because all of the fluorine atoms are arranged in a trigonal planar fashion around the molecule, thereby cancelling out each other's pull for electrons. 

Although the difference between Boron's electronegativity (2.04) and Fluorine's (3.98) is great enough to make the individual bonds polar covalent, the symmetrical arrangement of atoms around the central Boron atom cancels out these possible dipole moments. This results in an overall structure that is generally nonpolar in character. 

You may have observed that this structure for BF3 seems to violate the octate rule specifically for the central Boron atom which only has six electrons in its valence shell. These are generally called incomplete octets and are formed due to the low electronegativity of Boron. Since double-bonding one of the fluorine's to complete the octet would leave the fluorine with a formal charge of +1, it becomes quickly apparent the infeasibility of this structure since fluorine is the most electronegative element and would not simply lose an electron. Therefore, it is simply assumed that the structure with the incomplete octet is a more stable configuration.

However, when these kinds of elements are handled in real life they are often unstable due to the incomplete octet. BF3 for example will try to form an octet on the central atom by converting to BF4-.  Other elements that may at times form incomplete octets include Beryllium and Aluminum. 

BF3 Ball and Stick Model. Created with MolView.

How does BF3 behave in the real world?

Typically this compound is highly reactive, being able to corrode metals including stainless steel. It is utilized as a catalyst in a wide variety of organic chemistry reactions. BF3 typically behaves as an acid since the presence of fluorines produces an "electron-deficient" structure. This character is evident in many of the different organic reactions which utilize BF3.

Electronegativity Chart: https://i1.wp.com/chemistry.com.pk/wp-content/uploads/2018/09/electronegativity-chart.jpg?ssl=1