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Chemistry

A lovely illustration of my teacher and a classmate performing a chemical reaction involving fire.

Electron Orbitals

An atom is composed of a nucleus containing positively charged protons and uncharged neutrons. The overall charge of an atom, however, is zero because an atom consists of as many negatively charged electrons as positively charged protons. These electrons orbit the nucleus in different clouds. There are four types of clouds: the S cloud, the P cloud, the D cloud, and the F cloud.

The S Cloud

The first electron cloud is the S cloud. Hydrogen and helium, the first two elements on the periodic table, have their electrons located in an S cloud. The S cloud is spherical in shape, with the electron(s) at the same distance from the nucleus no matter where they are. The S cloud can hold only two electrons. When the S cloud contains two electrons, it is full, and any other electrons would be in another cloud--the P cloud.

The P Cloud

The P cloud is shaped like two cones coming together at the vertices. When an electron is located in the P cloud, it has more energy than an electron in an S cloud, because it is most probably that the electron will be farther than the nucleus at any given moment. The noble gases, at the far right of the periodic table, have a stable electron configuration because all of the electron clouds, ending with the P cloud, are full. Atoms form ions in order to have the electron configuration of a noble gas. (The P shell is full when it contains six electrons.) For example, the electron configuration of a sodium (Na) atom is 1s22s2p63s1. However, when sodium ionizes, it forms Na1+. This is because it loses the electron in the 3s cloud, and it then has the electron configuration of neon. A chlorine atom has an electron configuration of 1s22s2p63s2p5. When it ionizes, it has a charge of 1-, because it adds an electron to its 3p cloud, thus giving it the configuration of argon. Since the charges are equal and opposite, the sodium and chloride ions form an ionic bond and create NaCl... what you would call table salt. Since both Na and Cl have stable electron configurations, two highly reactive, dangerous elements form a common, stable compound.

The S shell and the P shell put together only hold 8 electrons. What happens when a period contains more than 8 elements?

The D Cloud

Periods 4-7 contain transition elements. These are the common metals you're used to hearing.... iron, silver, gold, nickel, zinc... those types of things. One thing that these elements have in common? The D cloud! The D cloud is shaped like a P cloud, except that the orbitals more closely resemble flattened triangles. As there are three P clouds, there are five D clouds, each holding up to two electrons. This exaplains how a period can consist of 18 elements. However, what about the lanthanide and actinide series? Don't they cause the periods to be even longer? What happens then?

The F Cloud

The lanthanide and actanide series have electrons added to an F shell, which I really don't know much about. The F shell holds up to 14 electrons.

Naming Compounds

You won't get too far in Chemistry without knowing how to name an element based on its chemical formula, and vice versa. The first thing you need to learn about is one of my favorite things in Chemistry--electronegativity. Don't worry, it's not as scary as it sounds. Electronegativity is a ranking, on a scale of 0 to 4, of how strongly electrons in a bond are attracted to the nucleus of an atom. (Note: I'll be adding the electronegativities of the elements to the periodic table section of this page.) The greater an atom's electronegativity, the more strongly attracted to the nucleus an electron is. To determine the name of a compound, you must first know whether its bonds are ionic or covalent. Ionic bonds are the result of a transfer of electrons, and covalent bonds are the result of the sharing of electrons. To determine whether a bond is ionic or covalent, we must compare the electronegativities of the elements involved. If the difference between the electonegativities of the elements is greater than 1.67, the bond is ionic. If the difference between the electronegativities of the elements is below 1.67, the bond is covalent. Let's see a few examples:

Let's bond sodium and chlorine. If we look up the electronegativities of these elements, we will see that the electronegativity of sodium (Na) is 0.93, and the electronegativity of chlorine (Cl) is 3.16. Before you do anything, notice that chlorine's electronegativity is close to 4, and is therefore very high. Because of this, you know that the electrons in a bond are going to be closely attracted to chlorine. Also, notice that sodium's electronegativity is close to 0, and is therefore very low. The electrons in a bond will tend to stray from sodium. When we subtract 0.93 from 3.16, we get 2.23. This number is greater than our critical value of 1.67, so we know that the compound formed when sodium and chlorine combine is ionic.

Let's try something else. This time, we'll bond carbon and oxygen. The electronegativity of carbon is 2.55 and the electronegativity of oxygen is 3.44. Wow! Those electronegativities are pretty close! If we subtract 2.55 from 3.44, we get 0.89. This is far below our critical value of 1.67, so we know that the compound formed when carbon and oxygen combine is covalent.

Naming Ionic Compounds

Once you've determined that your compound is ionic, it's really very simple to name it. Generally, an ionic compound consists of a metal and a nonmetal. Simply state the name of the metal first, and add a suffix of "ide" to the end of the nonmetal. For example, sodium and chlorine would form sodium chloride. Lithium and bromine would form lithium bromide. Follow this pattern for all ionic compounds consisting of two elements.

Naming Covalent Compounds

This is more complicated than naming ionic compounds. To name these, first you must look at the chemical formula. We can't name covalent compounds in the same way as ionic compounds, because covalent compounds can combine in different ratios. For example, when carbon and oxygen combine, we can't call the resulting compound "carbon oxide." This is because carbon and oxygen can combine to form different compounds. C and O can combine to form CO2, a common gas that is a product of respiration. C and O can also form CO, a deadly poison. How do we differentiate between these compounds? We use prefixes. CO2 is called "carbon dioxide" while CO is called "carbon monoxide." The prefix "di" in "carbon dioxide" indicated the presence of two atoms of oxygen, as the prefix "mono" in "carbon monoxide" indicates that there is only one atom of oxygen.

Polyatomic Ions

Sometimes, a group of covalently bonded elements can form an ionic bond. These are called polyatomic ions. Two examples are sulfate (SO4) and nitrite (NO2). These groups of elements behave like ions in a compound. For example, sodium reacts with sulfate ions to form sodium sulfate. The chemical formula for this would be Na2(SO4). Similarly, silver would react with nitrite ions to form silver nitrite, AgNO2.

Polyvalent Atoms

Some atoms can do weird things. Let's look at an example--copper. Yes, our good friend Cu can be really weird. I mentioned sulfate ions above. Let's combine copper with sulfate to make copper sulfate.... okay, sulfate ions have a charge of 2-, that's easy enough... so let's look at copper. Oh no! It says that copper can have a charge of 1+ or 2+! What do we do?! Hmmm... well, if we use the 1+ charge, we get Cu2SO4, but if we use the 2+ charge, we get CuSO4. So they've gotta be different. Look again. Were you supposed to find out the formula for copper sulfate? Or did it say copper (I) sulfate? Or copper (II) sulfate? In these cases, the roman numeral in parentheses refers to the positive charge of the copper ions. (In other words, CuSO4 is copper (II) sulfate, whereas Cu2SO4 is copper (I) sulfate.) This, however, isn't the only way these compounds can be named. There's also a Latin (*groan*) way to do it. Actually, I prefer the Latin way, even though I openly despise Latin. It really isn't too important to know the Latin names for elements to figure out what they're talking about, since they're usually really close. (ie: copper ---> cuprum) If they're not, check the periodic table and see if the symbols are close. (ie: If you're wondering what "argentum" is, check the periodic table, and you'll find the symbols "Ar" and "Ag." Well, is this argon or silver, then? Here's an easy way to figure it out. "Ar" actually makes sense as the symbol for "argon." "Ag," however, makes absolutely no sense for a symbol for silver... wait a minute, unless the Latin word for silver is "argentum"!) Anyway, the valence of the atom in the compound is shown using special suffixes. The suffix -ic is used for the higher valence, while the suffix -ous is used for the lower valence. (Note: if the atom has more than two positive valences, these suffixes are meaningless and cannot be used. Use the other method instead.) This can easily be remembered if you know that "ic" comes before "ous" if you put them in alphabetical order, so "ic" is higher up than "ous." So, copper (I) sulfate is the same thing as cuprous sulfate, and copper (II) sulfate is the same thing as cupric sulfate. You can use either method, but make sure you don't just leave it as "copper sulfate," or else everyone else will be as confused as you were before you started reading this. :)

Greater Effective Nuclear Charges

Greater effective nuclear charges are probably my most favorite topic in all of chemistry. Actually, understanding greater effective nuclear charges can help you to cut down on a lot of memorization---especially regarding atomic radii. Simply, the GENC is a comparison between the ratios of protons to electrons of different elements and/or ions. Kind of. Let's use fluorine and chlorine for an example. Fluorine has 9 protons and 9 electrons, while chlorine has 17 protons and 17 electrons. Both will gain an electron to from -1 ions. When chlorine gains its electron, it will have 18 electrons and 17 protons---leaving the ion with 94.4% of the net positive charge it used to have. The fluoride ion, however, goes from haivng 9 electrons to 10, leaving it with a net positive charge of only 90% of what it used to have. Because the chloride ion has a higher proportion of protons to electrons, it has a greater effective nuclear charge, and will hold its extra electron closer to the nucleus than the fluoride ion will.

The Periodic Table of Elements

Okay, so this isn't a periodic table. This is a list of elements, and some of their basic properties and uses. I know that I started this a long time ago and that I'm still not finished, but I am working on it again. Feel free to suggest any interesting info you know about these elements.

  1. hydrogen
  2. helium
  3. lithium
  4. beryllium
  5. boron
  6. carbon
  7. nitrogen
  8. oxygen
  9. fluorine
  10. neon
  11. sodium
  12. magnesium
  13. aluminum
  14. silicon
  15. phosphorus
  16. sulfur
  17. chlorine
  18. argon
  19. potassium
  20. calcium
  21. scandium
  22. titanium
  23. vanadium
  24. chromium
  25. manganese
  26. iron
  27. cobalt
  28. nickel
  29. copper
  30. zinc
  31. gallium
  32. germanium
  33. arsenic
  34. selenium
  35. bromine
  36. krypton
  37. rubidium
  38. strontium
  39. yttrium
  40. zirconium
  41. niobium
  42. molybdenum
  43. technetium
  44. ruthenium
  45. rhodium
  46. palladium
  47. silver
  48. cadmium
  49. indium
  50. tin
  51. antimony
  52. tellurium
  53. iodine
  54. xenon
  55. cesium
  56. barium
  57. lanthanum
  58. cerium
  59. praseodymium
  60. neodymium
  61. promethium
  62. samarium
  63. europium
  64. gadolinium
  65. terbium
  66. dysprosium
  67. holmium
  68. erbium
  69. thulium
  70. ytterbium
  71. lutetium
  72. hafnium
  73. tantalum
  74. tungsten
  75. rhenium
  76. osmium
  77. iridium
  78. platinum
  79. gold
  80. mercury
  81. thallium
  82. lead
  83. bismuth
  84. polonium
  85. astatine
  86. radon
  87. francium
  88. radium
  89. actinium
  90. thorium
  91. protactinium
  92. uranium
  93. neptunium
  94. plutonium
  95. americium
  96. curium
  97. berklium
  98. californium
  99. einsteinium
  100. fermium
  101. mendeleevium
  102. nobelium
  103. lawrencium
  104. rutherfordium
  105. dubnium
  106. seaborgium
  107. bohrium
  108. hassium
  109. meitnerium
  110. ununnilium
  111. unununium

Stupid Things My Chem Lab Group Has Done

AP Chemistry Mistakes

Organic Lab Mistakes... New!

Don't worry, we'll do more stupid things, and I'll put them up here...

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