20 Most Recent Scientific Explorer My First Chemistry Kit Questions & Answers

v havent any idea like pentaatomic molecules

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• milk
• blood
• rain
• water

Just because something's invisible doesn't mean it's weightless. So, no, air is not weightless. As a matter of fact, all gases have mass, and therefore they have weight. Air, a combination of gases, is fairly heavy. Good thing, too, ?the weight of the air around us and the force it exerts on our bodies pushes on us, and that is what keeps us from exploding. The pressure inside our bodies, in turn, keeps the air pressure from squishing us flat. Air weighs about .07 pounds per cubic foot. And believe it or not, each square inch of our bodies is under about 14.7 pounds of air pressure.

Hi, ibmpl,

I think I know what you are referring to! Sorry for the delay in responding to your question. Apparently, by mu you mean millimicron. Perhaps because of a limitiation in the formula editor for posting your message, you were not able to write the Greek symbol for micron. The "m" in front of the above symbol represents one-millionth of a micron, that is, 10^-6 micron.

The symbol IU is much easier to write in this forum, and means "International Unit." Unfortunately, the IU is not really a standardized international unit that can apply to any substance equally. It is not a part of the SI system (metric system of units), that is based on units of ten from the exceeding small to the exceedingly large, and which is firmly standardized across all chemical substances.

For example, 1 IU means something different depending on the substance. Here is a revealing list of well known substances and their different definitions for 1 IU:

• 1 IU for Insulin = 45.5 micrograms pure crystalline insulin.
• 1 IU for Vitamin A = 0.3 microgram of retinol or 0.6 microgram beta-carotene.
• 1 IU for Vitamin C = 50 micrograms of L-ascorbic acid.
• 1 IU for Vitamin D = 0.025 microgram cholecalciferol.
• 1 IU for Vitamin E = 0.667 microgram d-alpha-tocopherol.

The reason for this range of values for the IU is its being based on a measured biological effect for each of these substances. That is, 1 IU has a different magnitude of physiological effect depending on the substance (often a drug, hormone, vitamin, or medicine).

Now, what I am going to say might be a disappointment to you: You cannot relate the millimicron to the IU no matter what substance you are describing. The reason is they are in different categories of measure. The millimicron is a metric system of LENGTH. The IU is based on measures of MASS. To convert one to the other they need to be in the same category of measure, length to length, or mass to mass. One COULD convert quantity of length to a quantity of mass, but only if you first convert either length to mass, or mass to length; but that would require the very inconvenient use of additional data, such as surface area and density of the substance of interest - a consequence too impractical for common use.

An exothermic reaction gives off heat as it proceeds. Common examples are the burning of coal or oil. An endothermic reaction absorbs heat from the surroundings and thus cools them. Common examples are the evaporation of liquid (sweat) and baking a loaf of bread (heat is absorbed)

The connection is Planck's Constant, which expresses the proportionality or ratio between the energy of a photon and its frequency. E = hf where h is Planck's Constant (actually frequency is usually represented by the Greek letter nu, but that will not reproduce here) 5.84 x 10^3 x 10^ -29 = 6.626 x 10^ -34 x f f = 8.814 x 10^7 Hz or 88.14 MHz which is about Ch 6 in the VHF TV spectrum

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Not sure making C4 should be outlined here.

19.0If you want three digits after the decimal point then it's 18.980

1. A scientist must be curious about the world 2. A scientist is logical and systematic 3. A scientist is open-minded and free of bias 4. A scientist is intellectually honest 5. A scientist works hard and is persistent 6. A scientist does not jump to conclusions 7. A scientist is a creative and critical thinker 8. A scientist is rational 9. A scientist is willing to suspend judgment until he is sure of his results 10. A scientist tries new approaches to arrive at solutions

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The electron-dot structure (also known as the "Lewis dot structure") for N is shown below: The red dots represent electrons that comprise the atom's 5 valence electrons. Recall that the valence (outermost) electrons are those that are involved in chemical reactions of bonding. The rule you should apply to drawing this electron dot structure is to first draw (or imagine) a rectangle around the atom's symbol, letting the rectangle represent the atom's core electrons (not shown), those within the atom's inner (s) shell. Then place one electron on each side. That leaves the remaining electron to be placed on one of the already occupied sides to give the electron pair.

It doesn't matter what side you place this 5th electron, because the final result is the pattern shown above, 3 single dots and one pair of dots, which neatly reveals the bonding power* of N (3) - and the existence of the one electron pair, which predicts special types of reactivity you will probably appreciate in more advanced topics of this element's behavior.

*The single electrons are more reactive than the electron pair, and will readily form bonds with other atoms, such as H. This allows you to predict that N and H atoms will combine to form NH3.

How do you know there are 5 valence electrons? For the answer, refer to the following partial image of the Periodic Table of the Elements I drew using Word and SnagIT software:

Notice the number-letter labels above each column ("group") of elements, for example "5A." The letter A indicates the groups of "representative" elements, the most common elements studied in general chemistry courses. The numbers before the "A" represents the number of valence electrons surrounding each element's atoms. For example, hydrogen has one valence electron, nitrogen has 5 valence electrons, and oxygen has 6 valence electrons.

Using the rules described above for drawing electron-dot structures, how many single dots and double dots should be drawn around H? Around O? Can you predict the bonding power of each of these atoms? What molecular compounds do you predict would be formed from the reaction of H and H? What molecular compound do you predict would form between combining H atoms and O?

Hints:
Reactions tend to occur that cause the single electrons (dots) to pair up. This occurs because paired electrons are much more stable than single electrons. A strong driving force for a reaction is the going from a less stable state to a more stable state. Hydrogen atoms from H2 molecules (diatomic molecules). H and O atoms combine to form dihydrogen oxide, also known as water!

Summary:

• A very simple set of rules allows you to predict the electron dot structures of the representative elements.
• The electron dot structures are very useful, because they can allow you to predict the bonding power of each representative element.
• They are also useful in guiding your prediction of the compositions of molecules that can form during reactions between their atoms (that is, how many of each element in the molecule).
• In more advanced topics you will also be able to use electron-dot structures to predict the shapes (or geometry) of molecules, including bond angles!
• So, learning the skill of drawing electron-dot structures is very important to mastering chemistry!

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