Is C2H2 Polar or Nonpolar?

Answer: C2H2 (acetylene) is nonpolar because of the nonpolar covalent bonds being arranged in a linear structure around the two central carbon atoms. 

The bonds are considered to be nonpolar covalent (as all C-H bonds are incidentally) due to the low electronegativity difference between carbon (2.55) and hydrogen (2.20). This generally distributes charge around the molecule pretty evenly. Furthermore, the molecule has a linear structure due to the relatively rigid triple bond between the two carbons (this is because there are multiple kinds of bonds involved which present rotation, specifically the combination between sigma and pi bonds). A triple bond contains one sigma bond and two pi bonds.

The kind of linear structure present in C2H2 is similar to the kind of bond formed by H2 (i.e. a linear covalent bond) or that formed by CO2. Overall the presence of many nonpolar bonds makes the whole molecule nonpolar. It is one of the simpliest unsaturated hydrocarbons (saturation => hydrocarbon molecule with only single bonds | unsaturated => hydrocarbon molecule has at least one double or triple bond).

C2H2 Ball and Stick Model
C2H2 Ball and Stick Model. Created with MolView.
How is this molecule found in nature?

Due to its relatively low number of total electrons and nonpolar character, the molecule is found as a gas due to the presence of quite limited London Dispersion Forces and very weak intramolecular forces. However, the molecule is unstable in its pure form and thereby difficult to find in nature. Nevertheless, scientists have identified multiple types of bacteria that are able to digest C2H2 as a food source. Within different research fields acetylene (C2H2) is generally utilized as a chemical building block and as a fuel source since it can participate in a wide variety of reactions. [1]


Creating a Simple Calculator in Scratch

Hello and Welcome to Scratch 101! In this tutorial we will be creating a simple four-function calculator! These four functions are addition (+), subtraction (-), multiplication (*) and division. Furthermore, these kinds of calculators will typically include a number pad with the values zero through nine.

Objective: To understand the mathematical operations within Scratch and how to combine these with user input/conditional statements. 

Four Function Calculator
Example of a Four Function Calculator.
It would not be difficult to expand these principles to a project involving a scientific calculator since Scratch contains many of these advanced functions as well.

Graphic Template: The graphic template is located here although the only customization is the new background image. 

Calculator Scratch Script

Consider: What other functions would you wish to include in this list? What if you wanted to increase that you could work with? How would be do more than one operation at a time (i.e. without having to restart the program every time)? How could you represent a running list of operations continuously? How would you build in PEMDAS (Order of Operations) into expressions with multiple operations. Think about all of these question in the context of the list data type. 

Wrap Up: If you are interested in more mathematics projects, feel free to consider the Fibonacci and Factorial projects in the 2.0. series. Furthermore, you could create quadratic, cubic or quartic equation solvers in Scratch or learn about your own mathematical concept and convert it to a programming exercise. Leveraging computer science with statistics specifically is an excellent endeavor because random number generators are great with sampling. 

Final Project: Link

Is CS2 Polar or Nonpolar?

Answer: CS2 is a nonpolar molecule because of its linear structure which balances out all of the charges.

Since the difference between the electronegativity of sulfur (2.55) is quite small when compared to carbon (2.55), the bonds are nonpolar covalent leading to few charge differences within the actual molecule. Without a permanent pull of electrons one way or the other the molecule lacks a mechanism to create dipole-dipole interactions. Furthermore, the molecule has a linear structure which means that any possible small charges are also cancelled out across the molecule. The two sulfur atoms are symmetrical to each other, leading to them cancelling out any average charge and again removing the possibility of strong dipole-dipole interactions. 

This is a similar mechanism to how CO2 is polar. Feel free to also check out our article about the Lewis Dot Structure for CO2 to learn more about CS2's more important counterpart. Oxygen and Sulfur have similar bonding patterns because they are both Chalcogens, having six valence electrons and being able to form two possible bonds (i.e. two single bonds or one double bond). 

CS2 Ball and Stick Model
CS2 Ball and Stick Model. Created with MolView.
How is CS2 different from CO2?

At standard temperature and pressure (STP) CO2 is a gas because of its nonpolar nature. CS2 on the other hand is a liquid at standard temperature and pressure although its melting point of 45˚C [1] isn't to much greater than the 25˚C standard at STP. CS2 is a liquid because of temporary charge interactions formed by London Dispersion Forces (i.e. the random movement of electrons). This is due to the larger number of electrons within CS2, specifically within the sulfur atoms when compared to the oxygen atoms within CO2. CS2 has a few niche uses within certain refining protocols as a solvent or intermediate molecule.


Is H2O Polar or Nonpolar?

Answer: H2O (water) is a polar molecule because charge is not equally distributed around the molecule. 

As mentioned previously when discussing the Lewis Dot Structure for H2O, the oxygen molecule contains four free electrons organized into two lone pairs. As a result, these create regions of negative charge within the molecule. Electron-electron repulsion (since they have the same charge) forces the molecule into a "bent" structure where the hydrogens are only approximately 104.5˚ apart. Furthermore, due to the great electronegativity difference between hydrogen and oxygen (2.20 and 3.44, respectively), the oxygen generally pulls hydrogen's electron towards itself increasing the partial positive charge on each of the hydrogen atoms. These partial positive charges are typically represented by a lowercase greek letter delta (δ).

Due to the "bent" confirmation of the water molecule, dipole-dipole interactions among H2O molecules are especially strong, leading chemists to term these kinds of intermolecular forces "hydrogen bonds." Hydrogen bonds can only form between HF, H2O and NH3 molecules due to the large electronegativity difference between these most electronegative elements (F, O, and N) and hydrogen. In large part this is what gives water many of its essential qualities such as a high melting and boiling point.

H2O Ball and Stick Model
H2O Ball and Stick Model. Created with MolView.
Water as a "universal solvent"

H2O, since it has high polarity, is very good at dissolving other polar and ionic substances. For example, NaCl (or table salt) will dissolve into aqueous ions within solution (Na+ and Cl-) as will all other ionic salts. However, H2O is not a great solvent for nonpolar substances (such as those with a lot of C-H hydrocarbon bonds) which will separate from water based on their density. Those which are less dense than water (less than 1 mg/mL) will float above and those that are more dense will float below. This is a generalization of the typical "oil and water" effect whereby nonpolar and polar solvents separate into distinct layers over time (shown below).

Image of the Oil and Water Effect. Source
Water as a solid, liquid and gas

One of most important qualities of water which drives its behavior is the existence of water in all three states of matter in the natural environment. Water vapor is constantly in the atmosphere driving weather patterns. Liquid water serves as a critical resource for life on earth and constitutes a majority of the surface of the planet. Solid water is most prevalent at the Arctic ice caps trapping a large amount of greenhouse gases.

Water in all three of its natural states (solid, liquid, gas). Source
To learn more about the relationship between these states, check out the article about the Lewis Dot Structure for H2O.

Is CH4 Polar or Nonpolar?

Answer: CH4 is nonpolar because all of the nonpolar covalent bonds are spaced within a tetrahedral structure around the molecule. This distributes electron charge equally around the central carbon atom.

CH4 contains nonpolar covalent bonds because the electronegativity difference between hydrogen (2.20) and carbon (2.55) is lower than .5. Regardless of these nonpolar covalent bonds, CH4 is nonpolar because charge is equally distributed (the same reason that CCl4 is nonpolar). Due to the relatively small size of the molecule, CH4 does not have enough electrons to create strong charges due to temporary random displacement (i.e. London Dispersion Forces). This is why methane is a gas at standard temperature and pressure.

If you are interested in learning more, feel free to check out this article on CH4's Lewis Dot Structure.

CH4 Ball and Stick Model
CH4 Ball and Stick Structure. Created with MolView.
When was methane first discovered?

Methane was first discovered in 1776 by the Italian physicist Alessandro Volta [1]. However, the utilization of the term methane to describe CH4 only appears to have begun ninety years later. Early scientists examining the compound were attempting to understand its flammable properties. As a result, methane has many prominent uses in modern technologies as a fuel source.


The Sprite and the Stage in Scratch

In addition to motion, the Sprite has many built in commands.
Say and Think Blocks w/ Translated Effects
Examples of built-in commands with their effects on sprite behavior (think and say).
Changing Sprite Size (Format: Before, Change, After)

Change Size Block with Effects (Before and After)
Effect of changing sprite size. 
Size changed based on percentage (%).

Set Sprite Size and Effects
Effect of changing sprite size by percentage.
Changing Effects (Format: Before, Change, After)

Four Graphic Effects (Color, Fisheye, Whirl, Pixelate)
Graphic effects built into the Scratch editor including color, fisheye, whirl and pixelate.
Graphic Effects Part 2 (mosaic, brightness, ghost and clear)
Four more built-in graphic effects (mosaic, brightness, ghost, and clear)
Let’s combine the effects!

Combined Graphic Effects Before and After
Combined Graphic Effects (Ghost, Pixelate, Fisheye, Brightness, Whirl, Color)
A Vanishing Act (Format: Before, Change, After)

Effects of show/hide blocks on sprite
Show/Hide Blocks with Effects
Layers (Format: Before, Change, After)

Example of Layers in Scratch
Back and Front Layers (see how the Apples are stacked on each other)
Costumes and Backdrops (drawing and creating Sprites)

Graphical Painting Interface
Graphical Painting Interface within Scratch 

Short Activities: 

Write a story told by the Scratch Cat that utilizes five speaking blocks.

Create a program where one of the effects is being continuously changed (remember the forever loop).

Imagine the stage being a rectangle. As you move closer to the edges (WASD controls), have one or more effects become more pronounced (i.e. more extreme; of greater value). 

Longer Activity (Simon Memory Skill Game)

Simon Memory Skill Game Interface
Simon Memory Skill Game Interface w/ Four Sprites
Simon Memory Skill Painting Costume for each block
Graphics Interface for Simon Memory Skill Block (i.e. needs two color settings per sprite)

Draw and structure the graphics for the Simon “Memory Skill” Game (see example to the right and below)

Repeat the setup to the left for all four sprites (the four cubes)

Code a script to switch between the two costumes based on key commands for one of the four sprites. 

Change this script to create a specific sequence of costumes changes (i.e. the order in which they light up)

Random Block
Random Number Generator
Implement the random number generator to create random sequences/patterns for the sequence of sprites "lighting up".  

This activity was taken from a Scratch 2.0 lesson idea: Creating "Simon" - a Memory Skill Game

Appendix: Learn about the difference between the bitmap and vector editors:

Is CCl4 Polar or Nonpolar?

Answer: CCl4 (carbon tetrachloride) is nonpolar because charge is equally distributed around the molecule in a tetrahedral structure.

Even though the bonds between carbon and chlorine are polar covalent due to the electronegativity difference (2.55 vs. 3.16, respectively), the differences in electron-push-pull is cancelled out by the different chlorine molecules being in a tetrahedral 3D structure around the carbon atom. Since the molecules are equally spaced out, there is no point where enough negative charge would accumulate to create a dipole moment on the molecule (i.e. induce polarity).

This is similar logic for why CH4 is nonpolar with a similar Lewis Dot Structure ( Since the molecule is nonpolar, it is insoluble in water and does not form an aqueous solution. You would expect to see a "water and oil" effect with CCl4 in the bottom layer (since it is denser) and water on the upper layer.

CCl4 Molecule Ball and Stick Model. Created with Molview.
How is CCl4 utilized today? 

At standard temperature and pressure CCl4 is a colorless liquid; it used to be utilized in many varied applications including firefighting and refrigeration. However, due to safety concerns and toxicity to certain organ systems, specifically the central nervous system and liver, carbon tetrachloride has been phased out from all large-scale uses. Therefore, it is unlikely that CCl4 as a pure liquid will be utilized for any specific applications in your daily life at this point in time. [1]


The Odyssey Book 12 Practice Multiple Choice [National Mythology Exam 2020 Section Practice]

According to the bibliography for the National Mythology Exam 2020, the Odyssey section will include questions relating to Book 12: the sea trials (near the end of the flashback narrative of Odysseus's wanderings). Here are some practice multiple choice for that section:

1.) On whose island do Odysseus and his men arrive at the beginning of Book 12?
A.) Calypso
B.) King Pelias
C.) Agamemnon
D.) Circe

2.) Who destroyed Odysseus's ship in Book 12?
A.) Zeus
B.) Charybdis
C.) Scylla
D.) The Cyclops

3.) Where are Odysseus and his men headed?
A.) Mainland Greece
B.) Troy
C.) Ithaca
D.) Crete

The next four questions relate to the following passage: 

"But why should I tell thee this tale? For it was but yesterday that I told it in thy hall to thyself and to thy noble wife. It is an irksome thing, me seems, to tell again a plain-told tale." - The Odyssey

4.) Who is the speaker?
A.) Odysseus
B.) Circe
C.) Telemachus
D.) Eurylochus

5.) Who is the direct audience ("thyself and thy noble wife")?
A.) The King and Queen of the Phaeacians
B.) The King and Queen of the Minoans
C.) The King and Queen of the Ithacan people
D.) The King and Queen of the Athenians

6.) What is "this tale" related to considering this quote is from the very end of Book 12?
A.) The Sirens
B.) Helios Island
C.) Calypso's Island
D.) The Argonauts

7.) What is the narrative technique being employed in Book 12 as a whole?
A.) Frameshift
B.) Flashback
C.) Cause-Effect
D.) Compare and Contrast

8.) When they went by the sirens, Odysseus's men stuffed their ears with
A.) Nothing
B.) Wax
C.) Wool
D.) Wheat

The next two questions relate to the following passage: 

"Rash man, lo, now again thy heart is set on the deeds of war and on toil. Wilt thou not yield even to the immortal gods?" - The Odyssey

9.) Who is the speaker?
A.) Circe
B.) Odysseus
C.) Helios
D.) Zeus

10.) Which of the following characters is immortal?
A.) Eurylochus
B.) Charybdis
C.) Odysseus
D.) Jason

Answer Key (highlight the text): 1.) D 2.) A 3.) C 4.) A 5.) D 6.) C 7.) B 8.) B 9.) A 10.) B

Is NH3 Polar or Nonpolar?

Answer: NH3 (ammonia) is a polar molecule because partial charges are not dispersed equally around the molecule with a region of negative charge near the top (i.e. the lone pair electrons) and a region of relative positive charge by the hydrogen atoms. 

There is certainly a large electronegativity difference between N (3.04) and H (2.20) causing these polar covalent bonds. This in turn results in an unequal dispersion of electrons and therefore electric charge within the molecule. Since the structure is "bent" as a result of lone pair electron-electron repulsion, these polar covalent bonds cause a strong partial charge. In fact, the partial charge is much stronger than typical dipole interactions and is one of only three bond types that are permitted the capability of "hydrogen bonding." The other two types of bonds include -OH and -FH molecules (either those with these groups attached or in their natural forms: NH3, H2O and FH).

However, between the different hydrogen bond types NH3 is the weakest, H2O is relatively strong and FH is the strongest dipole interaction because of the increasing differences in electronegativity. As a result, NH3 is a colorless gas at room temperature as opposed to H2O which is a liquid (water) at room temperature.

To learn more about why NH3 is polar, read more about the lewis structure for NH3.

NH3 Molecule Ball and Stick
NH3 Molecule Ball and Stick Diagram. Created with Avagadro.
What are the most common uses of ammonia (NH3)?

The two most common uses are as fertilizer and in cleaning products. The former accounts for nearly 88% of ammonia usage in the United States [1]. Ammonia acts in a similar fashion to water in both cases; however, it has the effect of increasing output for certain agricultural crops.


Is BrF5 Polar or Nonpolar?

Answer: BrF5 is a polar molecule because negative charge is not distributed equally around the molecule. 

Since bromine (Br) is a halogen, it has seven valence electrons. Within its structure it share's five of these with covalently bonded fluorine (F) atoms, leaving two electrons to form a lone pair at the top of the molecule. Since the lone pair is a region with associated with more negative charge since it is not balanced by any atom's positively charged nucleus, the molecule is polar.

From an electronegativity perspective, BrF5 is contains many polar covalent bonds since the difference between bromine's electronegativity (2.96) and fluorine's (3.98) is greater than .5 (even though both are halogens). In general, bromine's electronegativity is less than fluorine's because Br has more layers of electrons shielding the nucleus and decreasing its pull on average over its valence electrons. Fluorine does not have as many layers of internal electrons that could contribute to this shielding effect so it has a much larger electronegativity (in fact the highest of any element on the periodic table!).

BrF5 Structure Ball and Stick Model
BrF5 Structure Ball and Stick Model. Created with MolView.
Is BrF5 reactive? 

In fact, due to the presence of highly electronegative halogens, this molecule will spontaneously react with many organic substances and water (H2O). Per studies in the 1950s and 60s, BrF5 was found to be an extremely effective oxidizer (i.e. removing electron's from molecules) as a result of the presence of many halogens [1]. However, this led to many difficulties in handling and performing research experiments with this substance in a safe and effective manner.


Is H2 Polar or Nonpolar?

Answer: H2 is a nonpolar molecule because electrons are dispersed equally throughout this linear molecule.

Although temporary imbalances may occur with small London Dispersion forces, the fact that H2 only has two electrons makes these rare occurrences and inconsequential when considering intermolecular forces.

Considering the question from the angle of electronegativity (of 2.20), one sees that the two hydrogens have the same electronegativity and therefore have the same pull on the electrons, causing the molecule to be nonpolar.

H2 Molecule Ball and Stick
H2 Molecule Ball and Stick Model. Created with Avagadro.

Does this mean that H2 is not reactive?

Since hydrogen does not have a full valence shell, it will form bonds easily with many different elements (ex. H2O and HF). When diatomic hydrogen comes in contact with other elements, it may react quite violently in order to form a bond with the new element. These kinds of reactions are the reason for the Hindenburg Disaster of 1937 which underscored the fact that helium cannot simply be replaced by hydrogen (H2) even thought the latter is a cheaper and more widely available resource. Helium is much stabler element because it has a full valence shell as a noble gas. On the flip side, the reactivity of H2 has allowed it to become a principle component on some fuel systems [1].

Various uses of hydrogen flowchart
Various uses of hydrogen. Source

Exploring the Music Instrument Digital Interface in Scratch

Welcome back to Scratch 101! In addition to uploading sounds, Scratchers can create their own tunes utilizing the Music Instrument Digital Interface (learn more about MIDI).

You will need to load this feature in as an extension in Scratch 3.0. It is built into Scratch 1.4 and 2.0.

Scratch Editor Screenshot highlighting Extension Button

Scratch Extension Page Music Highlighted

Once you load in the music extension, all of the necessary blocks will appear in their own tab. Scratch allows you to set your tune to twenty-one different instruments (ex. block below) or create music with a combination of instruments for temporary notes.

Set Instrument Block
Different instruments for the Scratch MIDI system
Different Instruments for the Scratch MIDI System
Different instruments for the Scratch MIDI system for temporary notes.
You can also include rests and set a tempo. The latter sets how quickly the music flows, a lower number means that the music is slower while a higher number means the music goes faster.

Rest and Tempo Blocks
Blocks for rests and tempo setting.

With these tools you can create music ranging from simple to complex depending on your skill level and how much time you have spent with the MIDI. Here is a simple version of Beethoven's piece Ode to Joy:

Ode to Joy Scratch MIDI
Ode to Joy Scratch MIDI
You probably have two questions when seeing this script:

1.) Why is there Green Flag clicked with an empty forever script?

This essentially helps to ensure that the code runs continuously and that the song does not experience any hiccups when moving from fragment to fragment...

2.) Why are the notes broken up into fragments separated by broadcasting messages?

This is done to minimize the number of errors the MIDI makes when translating the song. It is more difficult for the compiler to play one hundred notes than ten notes. Therefore the logical way to play one hundred notes is to break it up into groups of ten. Of course when this code was created the approximate breakup between the groups was very rough; therefore, each segment has a slightly different number of notes.

Sound Output (watch video):

Of course this is only the surface of creating music with Scratch and those more practiced can produce far more polished pieces.

Here are some examples of more advanced songs (some of them have even been featured on the Scratch homepage!):

Tetris by SAPotter
Hedwig's Theme by SA Potter
Snowdin Town - Undertale by WolfCat67
Flight of the Bumblebee by WolfCat67

Now it is your turn to try and create some music in the Scratch MIDI Editor! Let's see what you come up with! 

Tip: If you are running an especially complex MIDI script, consider switching over the phosphorus player. This javascript compiled version optimizes the Scratch GUI interface and makes it easier to run complex code. Overall when listening to your music (given that it has some complexity) you will hear an enhanced quality and tone. You can also try a newer version called forkphorus specifically for Scratch 3.0...

Phosphorus Interface
Phosphorus Interface Picture.
Conclusion: The goal of this project was to gain familiarity with the Scratch MIDI Interface and inspire creativity through musical exploration.

Completed Project: Share your work with those around you!

Does the Lewis Dot Structure for O2 Contain a Triple Bond?

Answer: The lewis dot structure for O2 does not contain a triple bond because this would break the octet rule.

By the octet rule, if their were a triple bond between two oxygens each would share six electrons and thereby be left with three lone pairs in their valence shells. This would add up to a total of nine electrons which is greater than eight. This would from a conceptual standpoint place to much negative charge in the region between the two oxygen atoms and would thereby be electronically unfavorable. This would in turn lead to a triple bond being an unstable confirmation.

The correct configuration with a double bond is shown as a ball and stick model below. To see the full Lewis Dot Structure and learn more about the O2 molecule, feel free to read this article about the Lewis Dot Structure for O2.

O2 Ball and Stick Model
O2 Ball and Stick Model. Created with Avagadro.

Creating an Aim-Game / Tower Defense Game in Scratch

Welcome back to Scratch 101! In this lesson, we will be creating an "aim-game", i.e. a precursor script to a more fully developed tower defense game.

Objective: Understand how the flow of control allows for the interaction between different sprites. Furthermore, this will strengthen student's understanding of both direction and cloning. 

Tower Defense Games
Screenshots from various tower defense games. 
To quote an article from the Loop, "Tower Defense, is a game system which, like all great game systems, is simple to learn but hard to master. Almost without exception, it involves a horde of lumbering creatures who enter from one location and are trying to make a trip to the opposite side of your screen. If enough of them are successful, you lose the game. To thwart their plans, you build “towers” to block their paths as best you can. The towers don’t just get in their way, however; they shoot, pummel or otherwise attack the passing creeps. If you’re quick on your feet and a bit of a strategist, you can prevent the oncoming hordes from successfully making it from point A to point B. And that’s what it’s all about."

This tutorial modifies this structure by creating a target that neither moves nor interacts with the user. Rather, this game simply tests "aim" towards a static structure. You can see more of the logistics within the video sample of the completed project below.

Final Product:

Graphic Template: Please find the necessary costumes/backgrounds in this project. Hit the "remix" button to move this to your personal account (the projects are named "precision shot").


Place these sequences within the "Turrent" sprite

Turrent Sprite Code
Script to connect the "turrent" the mouse and provide "turrent" functionality to the user. 

Place these sequences within the "shot" sprite

Scratch Code Cloning Shot Sprite
Sprite script to execute "turrent" functionality utilizing cloning (primarily).

Place these sequences within the "target" sprite

Scratch Code Target Sprite
Sprite to execute "target" random movement and functionality.

Consider: At the end of my video, the "target" sprite become to small to hit. How would I change the movement of the sprite towards my target (i.e. the "shot") in order to avoid this from happening in the future? During the second half of my video, I just started moving the cursor onto the target (kind of removing the necessity of having any skill). What code would you add in order to make sure that the person could only change the direction of the turrent within a limited (circular) radius around the turrent?

Wrap Up: This lesson focused on the interaction between sprites and clones to create a simpler version of more famous tower defense games. If you wish to continue with this concept, see what other game elements you can build into the project. 

Completed Project: Attached is the final version of the project.