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Ecap

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About Ecap

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  1. I don't think a magnetic field is really made of anything. A magnetic field surrounds a magnet. The magnetic fields were "mapped" by observing the behavior of charges placed into the field.
  2. A covalent bond is when two atoms share electrons. CH4 An ionic bond occurs when there is a complete electron exchange: Na+Cl- Ionic bonds are much stronger then covalent bonds.
  3. Hello There are a couple different "types" of intermolecular forces which have very specific effects on the general 'nature' of a substance, particularly how that substances "phase" (solid, liquid, gas) is effected by temperature changes. The strongest intermolecular force is the "ion". An ion occurs when electrons are transferred from one atom to another. This typically occurs between an atom which is a strong electron donator and an atom which is higly electronegative. What does this mean exactly? Take, for example, two atoms on opposite sides of the period table: Lets take NA (sodium) and CL (Chlorine). NA has 11 protons in its nucleus (core), and each of these protons is exerting a positive force which keeps the negatively charged electrons "trapped" in orbits around its nucleus. These 11 electrons, which all carry identical negative charges, are simultaneously drawn toward the positively charged core and repulsed by the other negatively charged electrons. This results in electrons circling the nucleus in a manner which minimizes electron-electron repulsion: the electrons occupy different "layers" and "shells". Think about this: since the protons are exerting a positive pull outward, any electrons which occur between the nucleus and the outer-shell electrons will "absorb" some of the positive pull so to speak, shielding the valence (outer-shell) electrons from the magnetism. Na happens to only have a single electron in its outermost shell, so this electron is weakly held. Therefore, it is easy to give up, and if it is given up, the sodium ion reaches a very stable Na+ form. This is known as "ionizing". Now look at chlorine. Chlorine is in the same "row" as sodium, therefore it has the same outer layer. However, chlorine has 17 protons, therefore the amount of magnetism exerted from the core on to the electrons is much greater. Since the bulk of its electrons all occur in the outer shell, they don't serve to "shield" eachother from the inner pull. Furthermore, if chlorine gains a single electron, its outer shell achieves "noble gas configuration" - a highly stable state where all of the valence shells are filled. (note that sodium can reach this same configuration by giving up an electron). That is why, when these atoms encounter one another, they "ionize" - sodium gives up an electron to chlorine, forming Na+ Cl- ---> table salt!! This intermolecular force is the most powerful, and this is why salt melts at 900 degrees celsius (or something like that). The next signifigant intermolecular force is known as "hydrogen bonding". This occurs when you have covalent bonds between hydrogen and sulfur, oxygen, or nitrogen. "Covalent" is not the same as ionizing. As I described above, ionizing involves the exchange of electrons. Covalent, rather, involves the sharing of electrons. Covalency still obeys the same rules, however - atoms will share bonds in such a way as to achieve the "noble gas configuration". Hydrogen bonding is strong but not nearly as strong as ionizing. H-bonds account for waters high boiling point. Next down the ladder is "dipole". Dipole simply means "Di"=2 "Pole"=poles of a magnet. This is used to describe any atomic bond, outside of hydrogen bonds, which exhibits polarity. Lets say, for example, you have a carbon atom, which is only moderatly electonegative. (Note: electronegativity relates to the magnitude of the positive nuclear charge, electron shielding effect, and relative atom size, as described earlier). If the carbon atom bonds with a fluorine atom, which is higly electronegative, you would describe the covalent bond as a "dipole". These are less strong then hydrogen bonds. Finally, the weakest force is known as london dispersion forces. These are present in all molecules to some extent, but are the only force operating in things which don't have H-bonds, ions, or dipoles. London dispersion forces describe the natural tendency for electrons to create a net positive or negative charged based on their cycling repulsion. Simply stated- because electrons repulse eachother, at any given time within a molecule a "chain reaction" can occur where "A" repulses "b" to the right, which causes "B" to repulse "C" to the right, which causes "C" to repulse "D" to the right, and so on until you have a negative charge at one end and a positive charge at the other. These forces are very weak and fluctuate. Finally, how do these forces effect phases and energy? Well, imagine I have a cup of water. All of the H20 molecules are H-bonding within themselves and with eachother. These electromagnetic forces keep them together. Also, the compacted air molecules of our Earth atmosphere are constantly pushing "down" on the water molecules, with a magnitude of pressure sufficient to keep them trapped in the liquid phase. If I start to heat the molecules up, I am in fact supplying them with "energy", and the atoms start the vibrate and move around. If I continue to heat them up to a "boil", that means that the motion energy of the molecules pushing up EQUALS the magnitude of the atmospheric pressure pushing down. Vapor pressure = atmospheric pressure, bubbles form, and the gaseous H20 escapes into the atmosphere. As far as energy, the basic rule is this: You have to put energy into a system in order to break strong bonds (ie. H-bonds) and replace those with weaker bonds (ie. dipoles). This is known as an "endothermic" reaction. If you have weaker bonds creating stronger bonds, that would be an exothermic reaction, and heat is "lost" to the environment. anyways hope that was helpful.
  4. The solubility should decrease with increased temperature
  5. Hello, What you are describing is a common "titration" problem, wherebye you use a recorded volume of an acid at a known concentration (this is called a "standardized solution") to measure the concentration of an unknown base. A "pH" value gives you an idea of the concentration of hydrogen ions in a solution. The scale runs from 1-14 and increases with basicity. So 1 is very highly acidic, 14 is highly basic, and 7 describes a neutral substance. the pH 9 value tells you that you have a basic solution. When you add a strong acid (like HCL) to a basic solution it will lower the pH as it neutralizes the base. The equation is (since the base is uknown I'll just refer to it as X, followed by 'OH' to indicate basicity): HCL + XOH ---> XCL + H20 Acids and bases come together to form water. Next, you know that the HCL you used is of the concentration 1 mol / mL. This is refered to as "molarity", and the equation is given by: Molarity = moles / volume First convert mL to L (0.16 mL = .00016 L), 1 = x/(.00016), (so x, or "number of moles", is .00016). Since it took x moles of acid to "neutralize" the alkilinity to a pH of 7 (which is nuetral) you know that you have "used up" all of the present base. Therefore the amount # of moles of base is is equal to the # moles of acid. Now that you know how many moles of base there were, you can use the molarity equation to solve for concentration base. Use the volume of the "polluted water" that you picked up, which was 5ml (= .005 L) So Molarity base = (# moles base)/(volume base) = (.00016 mole / .005L ) = 0.032 n / L
  6. This is an odd question, but hear me out. "We could be an atom to an atom to an atom, we could be in a grain of sand." My friend made this philosophical observation when we were hanging out earlier. I said that we couldn't, and we argued about it. First I asked him if he thought that we would be made out of the same "fundamental stuff" He said why not, and I made some observations. Quantum particles(?) compose larger particles, particles compose atoms, atoms compose molecules and compounds, and so on and so forth all the way up to biological systems like us. To this he quickly agreed. So then I made the statement that the universe must progress in regular ways. To this he agreed as well. Then I described a situation where a scientist was performing experiments on very small pieces of matter. The scientist was splitting the pieces and observing the byproducts. Would you ever expect a scientist to, upon splitting a particle, observe a new universe? Of course you wouldn't. It doesn't make sense. Its not reasonable. Its like trying to describe to someone mathematics through the language of biology. You can't do it. You can only describe biological in the language of mathematics. He insisted that I was wrong, but his only real counter-point was: "Why couldnt it?" So how do you apply "sciency" logic in your social situations? Do you avoid it? I find people seem to be repulsed by talking about "science".
  7. Ecap

    Hello!

    I stumbled upon this forum. This is great! Over the last year or so I have really taken an interest in chemistry... There are a couple concepts I am a bit confused about. Despite having scored good grades in my classes, I have to admit that my knowledge is pretty limited to "bookish" chemistry - in other words - completing problem sets!! I am curious about orbital hybridization. I know the orbitals based on the periodic table, and can predict the hybridization of an atom within a molecule based on the lewis dot structure. However, I'm not sure how or why hybridization occurs. In class it was described as the "promoting" of an electron to a free orbital within a valence shell, usually a p orbital. What does this mean, exactly? Do the repulsions of simultaneously-orbiting electrons force other electrons into different "orbital shapes" (ie., s, p, d, f ) to minimize electromagnetic interference? Is this 'electron promotion' really as regular as classroom hybridization would have me believe? Also, what happens when you start forming compounds with elements in the "d" block? I notice strange things with manganese. KMno4-1, MNO2, all these variations occur (unlike Na, which produces highly predictable +1 ions). Anyways, just bantering...
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