Is H2O2 Polar or Nonpolar?

Answer: H2O2 (Hydrogen Peroxide) is a polar molecule due to the unequal distribution of charge throughout the structure caused by lone pair electron-electron repulsion causing "bent" angles within the overall molecule.

The dipole nature of this molecule is increased by the large electronegativity difference between oxygen (3.44) and hydrogen (2.20). This qualifies the bonds as polar covalent and creates partial charges as strong as those in water (H2O). Both oxygen molecules have two lone pairs which increases the amount of negative charge that appears around the center of this molecule. This is why H2O2 is liquid that has a slightly higher boiling point than water of 150˚C and is slightly more viscous (i.e. imagine that is is slightly harder to "swim" through this substance than water although you would never attempt to do this due to the reactive nature of H2O2). This property is also increased as a result of hydrogen peroxide's polar nature.

Another interesting fact relates to the spatial geometry of the molecule. While the oxygen's keep the hydrogens (since these are more positive and opposite partial charges attract) at a distance of approximately 100 pm, the two oxygens maintain of a distance of 150 pm, approx. 1.5 times that of the distance b/t oxygen and hydrogen. This distance again reinforces the true magnitude of negative charge within the center of this molecule.

H2O2 Ball and Stick Model
H2O2 Ball and Stick Model. Created with MolView.
How is hydrogen peroxide utilized in the real world?

H2O2 is commonly utilized for bleaching, disinfecting specific surfaces, and laundering. This is b/c H2O2 commonly reacts with and tags organic molecules, allowing them to be easily removed in wastewater treatment processes. This is also why it is very effective at destroying a wide range of pathogens including bacteria and viruses. However, approx. 60% of all hydrogen peroxide utilized goes to bleaching different items in industrial processes.

Is SiCl4 Polar or Nonpolar?

Answer: SiCl4 (Silicon Tetrachloride) is a nonpolar molecule because all of the four chlorine molecules are equally spaced around the central silicon atom in a tetrahedral structure. 

As the electronegativity difference between chlorine (3.16) and silicon (1.90) is quite high, the bonds within the molecule are polar covalent. However, since the molecules on the outside are all the same these charges eventually cancel out when considering the polarity of the entire molecule. 

However the nature of the polar covalent and the large number of halides on the molecule does create partial charges within the molecule. In this scenario the chlorine receives a partial negative charge and the silicon gets a partial positive charge. As a result SiCl4 is a liquid with a boiling point of approximately 60˚C (this video details how to create SiCl4 in a chemistry lab although this is NOT recommended as the substance is toxic). This effect is similar to that for SiF4 (learn more about this molecule in this article). 

SiCl4 Ball and Stick Model
SiCl4 Ball and Stick Model. Created with MolView.
How is SiCl4 utilized in the real world?

Oftentimes SiCl4 is utilized as an intermediate in order to extract the Silicon. Therefore, it is unsurprising that it finds many uses in advanced technological applications including fiber optic cables and solar cells for solar panels.

Is BeF2 Polar or Nonpolar?

Answer: BeF2 (Beryllium Fluoride) is a nonpolar molecule because all of the constituent atoms are arranged linearly around the central atom. 

The bonds in BeF2 would be considered polar covalent due to the great electronegativity difference between fluorine (3.98 i.e. the most electronegative element on the whole periodic table) and beryllium (1.57). The large electronegativity difference is also the cause for beryllium having an incomplete octet both because it lacks extra electrons in its valence shell for bonding and because it doesn't have a high enough electronegativity to form these bonds to complete its octet. This situation is very similar to that of BF3 which is discussed in more detail in this article

BeF2 Ball and Stick Model
BeF2 Ball and Stick Model. Created with MolView.
In fact, this great electronegativity difference gives BeF2 many of the properties of polar molecules. Due to the pull of fluorine on the shared electrons, the central beryllium atom becomes electron-deficient (gains partial positive charge). These partial positive and negative charges allow BeF2 to dissolve readily in water. Furthermore, the partial charges are so strong that at standard temperature and pressure BeF2 is found as a solid (picture below). This quartz structure becomes so strong that is has a melting point of 554˚C and a boiling point of over 1000˚C.

Example of BeF2 quartz. Source
When considering these realities, it is safe to qualify the original statement as BeF2's structure in a gaseous state which occurs very rarely in nature. Typically BeF2 is found in its solid form and thereby exhibits characteristics typically associated with polar molecules. As with any field, chemistry has exceptions and outliers that don't fit the rigid molds and descriptions we try to define. BeF2 is a molecule that certainly would qualify in this respect.

Creating a Symmetrical Drawer in Scratch

Welcome back! In this tutorial we will be creating a "symmetrical drawer" in Scratch. You will still control a single pen point but whenever you draw three other points forming a rectangle around the origin (0,0), also known as the center of the stage, will also draw. This application will permit the creation of more complex symmetrical shapes than the simpler drawing application we created in the last post. As a reminder, you can extend this series of lessons by creating your own home-made digital stylus (tutorial located here).

Thank you to kenny2scratch for suggesting this tutorial idea. 

Objective: Learn how to program with multiple sprites and utilize "slider" variables effectively. In addition to this, we are strengthening the skills from the previous lesson's objective.

Final Product: 

Graphical Template: (the "see inside" button will pull up the programming interface)

As a reminder, you will need to install the pen extension in order to complete this tutorial:

Extension addition button
Select the "Extension addition" button
pen extension selection Scratch
Select the pen extension.

Sprite "Draw1"

Draw1 Sprite

Sprite "Draw2"

Draw2 Sprite

Sprite "Draw3"

Draw3 Sprite

Sprite "Draw4"

Draw4 Sprite

Tips: In order to duplicate a script into another sprite, grab the stack of blocks and place it onto the sprite to where you want to code to be copied. 

Troubleshooting: Make sure that the correct scripts are in the correct sprites!

Extension: See what other variables with the pen could be controlled by a slider in a similar manner to the color feature. What is the shortest range of numbers that will allow you to scroll through the entire color scale? How could be get the stylus indicators to show the color we are drawing with rather than show a random scale?

Completed Program: Link

Creating a Drawing Application in Scratch

This tutorial is based on a legacy tutorial from Scratch 2.0. (Scratch 101: Creating a Paint Program Part 1 and Part 2). If you are interested in adding a hardware component to this lesson, check out the this tutorial on how to make a capacitative stylus.

Objective: Learn how to utilize the "pen" extension within Scratch to create an interactive whiteboard utilizing loops, conditionals and sensing.

Final Product:

Graphical Template: (the "see inside" button will pull up the programming interface).

You will also need to add in the paint extension (see the following two step process):

Extension addition button
Select the "Extension addition" button
pen extension selection Scratch
Select the pen extension.
Paintbrush Scripts Scratch
Painting Scripts in Scratch (creates the paintbrush)
Once you have the first script programmed, you can give your project a try to see whether you are able to write on the screen. Then you can add in some more advanced features with the scripts below.

Some more advanced pen features (eraser, thickness, etc.)
Notice that the first script still contains your paintbrush with a few minor reset additions at the top of the script. The other two scripts add in five buttons to your program: e, p, c, d, 1 | These function in the following ways:

e: switches to "eraser" mode

p: switches to "painting mode"

c: erases everything on your screen

s: changes pen saturation by ten (i.e. color change)

1: increases pen size by one (i.e. makes your strokes thicker)

Extension: Test out some of the other features within the pen extension and see how they affect your painting program!

Integrating with the Stylus: This tutorial fits in well with the stylus tutorial. Once you have completed the steps detailed in the paragraph below, you will have programmed a painting application for your digital stylus.

If you have a Scratch account, you can save your project by clicking the remix button on the top bar. Once you have saved the project to your own account you can share it to your profile by clicking the "share" button.

On your touchscreen device navigate to the following link: replacing "YourScratchUserNameHere" with your scratch username. Click on the shared painting application. Press the Green Flag and enjoy the use of your self-made digital stylus in your own self-made painting application!

Completed Program: Link

How to Make a Digital Stylus with Common Household Items

Please note that this tutorial is an expanded version of a tutorial available on CNET. If you wish to learn about a related software topic, check out this tutorial on programming a drawing/painting application in Scratch.

Materials for the Stylus
Materials for the Stylus
In order to complete this tutorial you will need a pen (one you can open and remove the ink from), a cotton swab (a.k.a. q-tip), scissors, tape and a small sheet of aluminum foil.

This design is best for capacitative touch screens that rely on the transfer of electric charge in order to operate. Many Apple and Samsung touchscreen products rely on capacitative technologies and will work with this DIY stylus. Aluminum foil allows the stylus to transfer the electric charge typically found in our fingers to the tip of the stylus.

Professional Stylus
Example of a store-bought electric stylus for capacitative touch screens. 
Step 1: Remove the ink from the pen (technique may vary based on your selected pen).

Pen taken apart for DIY Stylus
Step 1 Results. 
Step 2: Reattach the pen tip if it was removed (or other pieces of the pen removed during Step 1). A secure pen tip is required for the next steps.

Reattached pen tip w/ ink removed
Step 2 Results.
Step 3: Cut the cotton swap at a sharp angle (i.e. diagonally) into two unequal lengths (approx. a 1/3 - 2/3 split along the length of the cotton swab).

Cotton Swab Cut
Step 3 Results.
Step 4: Insert the longer section of the cotton swab into the pen tip.

Cotton Swab inserted into Pen
Step 4 Results.
Step 4 Insert Close-Up
Step 4 Close-Up.
Step 5: Secure the cotton swab with a piece of tape.

Cotton Swab Insert + Tape
Step 5 Results.
Step 6: Cut the necessary length of aluminum foil (enough to wrap around the handle and base of the pen three to six times).

Aluminum Foil Cut
Step 6 Results.
Step 7: Wrap the aluminum foil around the handle and base of the pen. Keep approx. one to two centimeters of the cotton swab in front of the start of the aluminum foil. Fasten the aluminum foil with a piece of tape.

Stylus Wrapped w/ Aluminum Foil
Step 7 Results.
Stylus Close-Up
Stylus Close-Up.
Step 8: Moisten the tip of the stylus (cotton swab) gently with a couple drops of water.

Moisten Stylus
Step 8 Results.
Step 9: Enjoy the use of your digital stylus on capacitative touch screens! Feel free to check out the demo with the stylus built in this tutorial below.

The Lewis Dot Structure for H2S

Lewis Dot Structure for H2S
Created by MakeTheBrainHappy.
This is the Lewis Dot Structure for H2S (hydrogen sulfide). The rules for drawing lewis structures permit the replacement of the bond lines with two electrons. As we have previously discussed, hydrogen only requires two electrons to fill up its valence shell because it only has a 1s shell as the very first element in the periodic table. Sulfur in this case shares the second required valence electron to fill hydrogen's octet. On the flip side, hydrogen shares its one electron which combined with sulfurs two lone pairs fill sulfur's valence shell with an octet.

Within the structure of the molecule it can be easily calculated that all of the formal structures are neutral based on the amount of electrons required to fill their valence electron. However in a similar manner as the H2O molecule, the presence of two lone pair electrons creates a dipole moment and similar "bent" structure. Although the resulting intermolecular forces are not considered hydrogen bonds due to the relatively lower electronegativity difference between hydrogen and sulfur than between hydrogen and oxygen, they still qualify this molecule with the designation of "polar."

H2S Gas by Concentration (Appearance)
H2S color at various concentrations. Source
Due to the weaker nature of these dipole interactions, H2S has a much lower melting point of -82˚C and boiling point of -60˚C. Nevertheless, H2S is extremely flammable and corrosive due to its polar nature.

H2S Probe
H2S probe. Source
In the absence of oxygen some bacteria are able to produce H2S as a byproduct of the decomposition of organic materials. H2S is considered a hazard to human health and therefore is monitored utilizing a probe as shown in the image above. H2S is most typically found at facilities producing crude oil or handling waste. It tends to accumulate in poor ventilated low lying spaces due to H2S having a molecular mass greater than that of the atmosphere. This increases the risk because higher levels of H2S damage the human body more than lower levels.

It smells like "rotten eggs" and can therefore be detected by humans.

Sulfur Cycle
The Sulfur Cycle. Source
Sulfur plays a key role in the "sulfur cycle" within earths atmosphere both in the process of decomposition by bacteria, within the material spewed from a volcano and from the products created by oil and natural gas manufacturing. Different kinds of bacteria either utilize H2S as a fuel source or release it into the environment as a byproduct of energy processing. Oftentimes H2S is lethal to many animals (not just humans) and in fact it has been implicated in numerous mass extinctions of life, most notably the Permian extinction event 252 million years ago.

Is Benzene Polar or Nonpolar?

Answer: Benzene is a nonpolar molecule due to the presence of a large number of nonpolar carbon-hydrogen bonds spaced out in equal proportion around the molecule ring. 

Benzene's carbon ring displays resonance with either the structure as shown in the image below or with its single-double bonds switching places while maintaining their equidistant spacing. In a sense on average each space within the ring between two carbon atoms contains 1.5 bonds; however this is typically drawn as two resonance structures because the molecule will spend half of its time in one form and half of its time in the other form.

The symmetrical nature of benzene has been verified through x-ray crystallography. This definitely showed that the bondlengths between the carbons were constant as were the angles between the different atoms.  The molecule is considered to be "planar" because it doesn't have a 3D (z-axis) distinct shape. Furthermore, the theory of 1.5 bonds was also given a boost due to the distance between the carbons being shorter than a single bond (weaker attraction) but not as short as a double bond (stronger attraction).

Benzene Ball and Stick Model
Benzene Ball and Stick Model (one of two resonance structures). Created with MolView.
How is benzene utilized in the real world?

Oftentimes benzene is the constituent/starter carbon compound from which more complex carbon rings and compounds are built in order to carry out a wide variety of specific applications. However, benzene's most famous use is in gasoline in order to support the efficient operation of car engines. Due to health and environmental concerns, the percentage of benzene is typically limited to 1% in the U.S. and .62% in the European. In fact, benzene's largest contribution may have been its own name which translates to the word gasoline in many European languages. For example, Benzin in German stands for gasoline. 

Is OH Polar or Nonpolar?

Answer: OH (hydroxide) is a polar molecule due to the great electronegativity difference between oxygen and hydrogen.  

This electronegativity difference between oxygen (3.44) and hydrogen (2.20) qualifies this bond as polar covalent and therefore leads to the dipole. Due to the great strength of these dipoles, hydrogen bonds would be formed between these molecules with a strength closer to that of HF than H2O due to the presence of the extra lone pair electrons on the oxygen. OH is typically a base due to its affinity for hydrogen atoms (i.e. more positive charge) to balance out the extreme nature of the oxygen's negative charge; it is also found as a constituent of strong bases such as NaOH. These salts often aid in the formation of basic solutions by disassociating with Na+ and OH- ions.  

OH is related to H2O and only requires the addition of a single hydrogen to convert from one form to another. You can learn more about the closely related lewis structure of H2O or the polarity of H2O at the hyperlinked pages, respectively. 

OH Ball and Stick Model
OH Ball and Stick Model. Created with Avagadro
How is -OH utilized in organic chemistry?

In the context of these applications -OH is considered to be a catalyst of reactions by reacting with "positively charged" structures such as electron-deficient core "central" atoms within a complex organic molecule. These so-called hydroxyl groups can either stably be attached to the molecule or simply remove a hydrogen/other positive element during a reaction. One of the most famous hydroxyl groups in all of Biology appears at the 2nd carbon of the ribose/deoxyribose sugar constituting RNA and DNA, respectively. The presence of an OH group in ribose but not in deoxyribose explains the wide range of structural and functional differences between RNA and DNA (such as the single-stranded vs. double stranded nature and the capability of RNA to become a ribozyme).

Is SF6 Ionic or Covalent?

Answer: SF6 (or sulfur hexafluoride) is a covalent compound because both sulfur and fluorine are nonmetal elements. This means that in their natural forms either S2 or F2 they are found as nonmetals. 

Furthermore, SF6 is in a gaseous state of standard temperature and pressure which contributes to the view that the compound contains covalent "sharing electron" bonds. The molecule due to the saturation of fluorines is electron-deficient and therefore readily undergoes many different kinds reactions. Since the structure is symmetrical in both the vertical and horizontal directions, all of the different charges along the molecule cancel out and it is determined to be nonpolar. SF6 therefore has poor solubility in water and high solubility in less polar/more nonpolar compounds.

As you would expect SF6 does not disassociated into ions when placed in water as many ionic compounds are bound to do (think about how NaCl splits into Na+ and Cl- ions when it enters water (H2O)). These properties are similar to other molecules saturated with fluorines including SF2 and SiF4 (learn about their polarities by clicking on the hyperlinks). SF6 exists because an expanded octet allowing for the d subshell to engage in bonding with different elements, thereby permitting the sulfur to have more than eight valence electrons.

SF6 Ball and Stick Structure
SF6 Ball and Stick Molecular Structure. Created with MolView.
How is SF6 commonly utilized in the world?

SF6 is commonly utilized as a tracer in the medical field and other varied applications. The reasons for this are twofold: SF6 can be easily detected at very low concentrations and SF6 exists at negligible concentrations within the atmosphere. This makes it ideal for tracing the movement of gaseous compounds through different spaces.

Is CN Polar or Nonpolar?

Answer: CN is a polar molecule because of the unequal distribution of charge between the carbon and nitrogen because of their large electronegativity difference. 

Electronegativity is defined on a one to four scale as the relative amount an element attracts electrons (i.e. how strong the element's pull on its valence electrons is). When you compare carbon's electronegativity (2.55) with nitrogens (3.04) you can see that there is a pretty large difference. Since nitrogen has a higher electronegativity value, it attracts the electrons more and therefore has a partial negative charge. This leaves carbon with a partial positive charge. The reason why nitrogen is more electronegative than carbon is because nitrogen has a large nucleus with more protons (positive charge) pulling on its valence electrons with the same amount of shielding (two electrons in the first orbital).

The lewis dot structure for CN is similar to that of HCN if you are interested in learning more about this kind of molecule.

CN Ball and Stick Model
CN Ball and Stick Model. Created with Avagadro.
What is CN utilized for in the real world?

Since CN and CN compounds are typically very poisonous, it finds usage in dissolving mining sediment, pest control and other industrial processes. Due to its reactivity, there are a large number of tests able to detect for the presence of cyanide including Prussian blue and copper/aromatic amine chemical detection mechanisms.

Is I2 Polar or Nonpolar?

Answer: I2 (iodine) is a nonpolar molecule because of its linear structure and the identical electronegativity of both molecules.

Due to the large number of electrons present in the molecule, temporary forces known as London Dispersion Forces (due to the distribution of electrons within the molecule) exist and enable the molecule to take a solid form at standard temperature and pressure. In fact, these temporary dipoles are so strong that this molecule has a higher melting point and boiling point than water at 114˚C and 184˚C respectively. Due to its status as a halogen with a large number of electrons, I2 has the capability of undergoing many different kinds of chemical reactions. 

This is similar to the reason why H2 is a nonpolar molecule. Read more concerning H2 specifically in this article about whether H2 is polar or nonpolar

I2 Ball and Stick Model
I2 Ball and Stick Model. Created with MolView.
What is the importance of I2 (iodine) in biological systems?

I2 is very important in the creation of thyroid hormones. An iodine deficiency often results in cognitive disabilities and other negative effects. This is why iodized salt is commonly sold around the world to ensure that no one's diet iodine-deficient.

Is CH2F2 Polar or Nonpolar?

Answer: CH2F2 is a polar molecule because of the pull of electrons towards the fluorine dipoles (i.e. the partial negative charge) and the resulting partial positive charges on the hydrogen ends of the tetrahedron. 

Although we have discussed many cases of tetrahedral molecules that are nonpolar, in all of these cases the four molecules around the central carbon or silicon atom have been the same element. This example likens back more to CH3Br which was slightly polar due to the presence of the Br molecule and the overall combined pull of electrons. However in this example CH2F2 has a far stronger dipole due to the much larger relative polarity of fluorine (3.98) to carbon (2.55) and hydrogen (2.20).

However the polarity does not rival the strength of smaller hydrogen bonding capable molecules. Due to these set of facts, the molecule forms a gas at standard temperature and pressure with a boiling point of -51˚C.

CH2F2 Ball and Stick Model
CH2F2 Ball and Stick Model. Created with MolView.
How is CH2F2 utilized in the real world?

The molecule is commonly utilized in refrigeration and air conditioning systems. It's relative size in number of electrons yet polar character allow it to serve as an excellent insulator to prevent the transfer of heat between two mediums. Although the compound does not seem to damage the ozone layer, it keeps greenhouse gases trapped on earth at a rate of 675 times than of carbon dioxide.

Is SiF4 Polar or Nonpolar?

Answer: SiF4 is a nonpolar molecule because the fluorine's are arranged around the central silicon atom in a tetrahedral molecule with all of the regions of negative charge cancelling each other out. 

Although the bonds within the molecule are polar covalent due to the great difference in electronegativity between fluorine (3.98) and silicon (1.90), the arrangement of the molecule disperses that charge within it pretty equally so that no negative dipoles are created in the process. Due to the presence of many fluorine's pulling electrons away from the center of the molecule, the structure as a whole is determined to be "electron-deficient" when compared to other molecules. This means it tends to pull in other charges and typically forms Hexafluorosilicic acid naturally, combining with two extra hydrogen atoms.

The way SiF4 is configured is very similar to the way methane's four hydrogen's encapsulate its central carbon. In fact, both silicon and carbon are part of the same group (Group 14 also known as the "carbon group") and therefore have very similar bonding properties, being capable of forming four bonds which is rare among elements with such a low atomic number. Feel free to learn more about either the Lewis Dot Structure for CH4 or the Polarity of CH4.

SiF4 Ball and Stick Model
SiF4 Ball and Stick Model. Created with MolView.
Where is SiF4 found in nature?

Volcanic fumes typically produce several tonnes of SiF4 during eruption. 

Is SF2 Polar or Nonpolar?

Answer: SF2 is a polar molecule due to the presence of lone pair electrons on sulfur which force the molecule to adopt a bent configuration due to electron-electron propulsion. 

Due to the difference in electronegativity between Fluorine (3.98) and Sulfur (2.58), the molecule has a weaker dipole moment because some negative charge is being pulled towards the fluorine ends causing a little bit more of an even distribution of charge within the molecule. Although this author attempted to locate verifiable information about the boiling and freezing point of this molecule, this was not readily available due to the inherent instability present within the molecule. Due to the opposing regions of negative charge (one due to electronegativity and another due to lone pair electrons), the molecule is extremely unstable and readily "decomposes" into the molecule S2F4. In this new structure two SF2 molecules combine and form a double bond in between them.

S2F4 has a melting point of -98˚C and a boiling point of 39˚C. However, these numbers are probably not representative of those for SF2 because of the much larger structure (i.e. the newly formed molecule has many more electrons) and because the region of negative charge due to lone pairs has been essentially removed/cancelled away by the double bond.

For a reference point, the structure of SF2 is similar to that of H2O in terms of its configuration due to the same kind of electron-electron repulsion. Feel free to check out the Lewis Dot Structure of H2O and information related to its polarity.

SF2 Ball and Stick Model
SF2 Ball and Stick Model. Created with MolView.
What else is interesting about this compound? 

The bonding angle for SF2 is approximately 98˚ which is less than that of water (H2O) which has a bonding angle of 104.5˚. This is most likely also a result of the more negative fluorine dipoles which themselves are repelled from the lone pair electrons by negative-negative charge repulsion. This is as opposed to water where the partial positive hydrogen poles are more attracted to the negative lone pair electron region.

Is CH3Br Polar or Nonpolar?

Answer: CH3Br is a slightly polar molecule due to the slightly negative dipole present on the Br molecule since it is the most electronegative element in the entire structure. 

When you compare the electronegativity of hydrogen (2.20), carbon (2.55) and bromine (2.96), it seems as though the bonds between them are all nonpolar covalent which would thereby indicate a nonpolar molecule. The polar dipole is actually created by the sum of the differences between the different molecules. The small difference between carbon and hydrogen creates a very small electron pull towards the center of the molecule. The slightly larger difference between Bromine and Carbon then pulls these electrons towards the Bromine, creating a slightly negative dipole. The sum of these effects create partially positive dipoles on the hydrogen atoms.

As a result of the very slight polar charge, the molecule has a weaker dipole moments and therefore a low boiling point of 4˚C. This means that it is typically found as a gas at standard temperature and pressure even though it is much much larger than a molecule like H2O in terms of molar mass.

CH3Br has a tetrahedral structure similar to CH4 (methane). The difference is that one of the hydrogens has been replaced by Bromine (a much larger halide). Feel free to learn more about either the Lewis Dot Structure of CH4 or whether CH4 is polar or nonpolar.

CH3Br Ball and Stick Model
CH3Br Ball and Stick Model. Created with MolView. 
How is this chemical utilized in the real world?

For a good portion of the twentieth century this chemical was synthetically created as a pesticide. It was widely utilized in agriculture throughout Australia, China, New Zealand and the United States. However, after the compound was shown to deplete the ozone level, it was gradually phased out from use and replaced by alternative pesticides. The molecule has more of a tendency to deplete the ozone level since the large difference in element size makes it far easier to undergo a chemical reaction with light energy stimulus. Furthermore, the pesticide has been shown to have dangerous effects on human health.

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
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
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
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:

Iron Bohr Model
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
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.

Iron Metallic Bonding
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. 


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
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: