Chem+Review

//Honors Biology is a pre-requisite for this class, so you will be expected to have a grasp on basic chemistry. You will probably need to review/refresh on these concepts to be able to move forward into Environmental Chemistry.//
 * [[image:http://www.ictscience.com/assets/dynamic/girl_shaking_science_experiment_lg_clr.gif align="left"]]Link to Chapter 3 - Environmental Chemistry**

//Check out the chemistry review if you feel you need some additional chemistry background for this section//

CHEMISTRY REVIEW AND PRIMER!!!
There are 92 naturally occurring elements in nature. These different forms of matter differ uniquely in their physical and chemical properties: carbon (C) and hydrogen (H) differ in their size, reactiveness with other atoms, and other physical and chemical properties. An element is a substance that cannot be broken down to other substances by ordinary chemical means. An element can be combined with another elements in a chemical reaction to make a compound. For instance, hydrogen combines with oxygen to produce water. Scientists use symbols (hydrogen=H, oxygen=O) as a kind of short-hand for describing compounds. For example H2O is short for water, which is comprised of 2 toms of hydrogen and one atom of oxygen.
 * Chemistry **is the science dealing with the composition of matter and the transformations of matter. Matter comes in a variety of forms. We call these different unique types of matter ** elements **. An ** atom ** is the smallest unit of an element that has all of the properties of that element.

ATOMIC STRUCTURE
**3. Scientists recognize various elements by the number of protons in the nucleus.** Scientists use assign the unique number or protons as their **atomic number** ). Each element has a unique number of protons, and every atom of that element has the same number. For example, the atomic number of hydrogen is 1 (1 proton in the nucleus). Other elements and their atomic numbers: carbon (6), nitrogen (7), oxygen (8), uranium (92). You may wonder what holds the protons and neutrons together in the nucleus (you may know that like charges repel each other). The nucleus is held together only by powerful counterbalancing forces, called nuclear forces, which hold the nucleus together, like a glue. However, as you will see later, these nuclear forces may be inadequate in holding the atom together, and then the nucleus can break up ( **fission** ) and **radioactivity** may occur. We'll come back to this later. **8. You can idenitfy every feature of an element's atomic structure by observing the Periodic Table.**
 * 1) ** Matter is composed of different substances that are called //__elements__//. **An element is something that cannot be broken down into other simpler substances, while retaining the unique chemical properties. The smallest indivisible unit of an element is called an **atom** . Atoms of each element have a characteristic structure: which gives each element its unique physical and chemical properties. Atoms are extremely small: 12 grams of carbon (about 1/2 ounce) contains 6.023 x 1023 atoms, each of which is one to several angstroms (10-10 m) long. A 100 million atoms lined up from end to end would equal about 1 inch.[[image:http://www.reprise.com/host/electricity/images/atom_animation.gif width="159" height="155" align="right"]]
 * 2) ** Atoms in turn are composed of //__subatomic particles__// **//. The three particles of interest to us are// **protons** **, neutrons **  **and electrons ** (these are in turn made of smaller components, called **quarks**, but we will not need to discuss them for this class). The proton, which has a positive electrical charge, and the neutron, which has no charge, are concentrated in an area at the center of an atom, called the **nucleus** . These two particles have essentially the same mass. Electrons, which have "very little**"** mass (about 1/1840th of a proton), possess a negative electrical charge and zip around the nucleus in **orbitals** , or **energy levels** (it's more complicated than that, but for the purposes of this class, we need not discuss it in more detail). To put the difference in mass into perspective: Imagine that you could enlarge protons, neutrons and electrons to a size we could see. If the protons and neutrons would be comparable to a gallon of water, then an electron would be about the size of a dime.These subatomic particles are constantly vibrating and bouncing off of one another. This constant vibrational movement and activity is called **Brownian Motion** **.**
 * 4. Atomic weight is another feature describing atoms and elements. **The atomic weight is the number of protons and neutrons in the nucleus. The number of protons is all atoms of a particular element is constant, however, the number of neutrons may vary. For example, in carbon (the most important element for life), carbon ordinarily has 6 protons and 6 neutrons in the nucleus. However, some carbon atoms have 7 neutrons, and others may have 8 neutrons (this carbon atom, carbon-14, or 14C, by the way, is unstable and radioactive). Atoms of an element that have different atomic weights are called **isotopes** . They vary only in the number of neutrons. The atomic weights are often put above and prior to the chemical symbol: 14C and 12C for the radioactive and non radioactive isotopes of carbon, respectively). (YOU ARE ON YOUR OWN NOW TO LOCATE THE BOLD TERMS!!)
 * 5. Electrons are Unpredictable Wierdos. **Electrons are constantly struggling between wanting to be closest to the nucleus and wanting to stay away from each other.For the purpose of this class, we'll look at an old-fashioned model of an atom. In a normal atom, the number of electrons equals the number of protons, therefore the number of positive and negative charges are equal, making the atom **electrically neutral**. For an atom to be neutrual, the electron's negative charge is the same in magnitude as the proton's positive charge. //The simplest (and most abundant) atom in the universe is the hydrogen atom. It has one proton in the nucleus, with one electron circling around it//. Even though this seems simple and stable enough, Hydrogen isn't with its one lonely. Electrons are constantly zipping around the nucleus, but they tend to hang out in specific energy levels, or orbitals (labeled //**k, l, m**// and //**n**// below).
 * //**K-orbital**// can hold upto 2 electrons
 * //**L****-orbital**// hold up to 8
 * //**M-orbital**// can hold 8 (or 18).
 * For the atom pictured below, N-orbital is the **valence shell**, or outermost orbital.
 * 6. Not all atoms are electrically neutral. **Different atoms of the element may vary in the number of electrons they possess. Some atoms may have more (or less) electrons than protons, and thus the entire atom has a net positive or negative charge. Atoms or groups of atoms (molecules, see below) may have one or more net positive or negative charges, and are thus called ions. Ions retain most of the properties of the uncharged atom of the element, but other properties may change.
 * For example, a chlorine atom has an atomic number of 17 (17 protons and 17 electrons). However, most of the atoms found in nature (particularly in water) are charged ions (the chlorine atom receives one electron from another atom, thus becoming more stable in its outer electron shell (this topic of electron shells is more complex than needed here). It becomes a chlorine ion or chloride ion (Cl-, 17 protons and 18 electrons).
 * Similarly sodium (Na, atomic number 11), in order to be more stable, has only one electron in its outer shell. It readily donates its outer electron to another atom (such as chlorine), and thus normally in water, the sodium atom is an ion with a positive charge (Na+, 11 protons, 10 electrons).
 * A molecule may have a net positive or negative charge, and thus be an ion (nitrate, NO3, is composed of one nitrogen and three oxygen atoms covalently bound together as one molecule, and the whole molecule has a net negative charge of -1, or NO3-).
 * Other common molecular and atomic ions are phosphate (PO4-3, 3 negative charges), calcium (Ca+2, 2 positive charges), ammonium (NH4+), sulfate (SO4-2) and hydrogen ions (H+, the simplest ion, consisting of one proton).
 * 7. Each element has its own unique chemical symbol. **
 * An element's **chemical symbol** consists of one or two letters, the first is often the first letter of the name, and is always capitalized. Hydrogen is H, carbon (C), nitrogen (N), oxygen (O), sulfur (S), phosphorus (P), calcium (Ca), chlorine (Cl), uranium (U). Some elements, such as sodium (Na), iron (Fe), silver (Ag), lead (Pb) and gold (Au), are named after their Latin names (such as natrium for sodium, for example).
 * The atomic number is the whole number in the box. The atomic mass is the larger, decimal number. It is a decimal number because the number of neutrons varies from atom to atom, so it is an average of the most common isotopes of the element.



**CHEMICAL REACTIONS and BONDING**
The law of conservation of matter states that matter cannot be created or destroyed, so that means that any atom entering the reaction must exit the reaction, even if its as a part of a different molecule.
 * What atoms want more than anything else is to be stable. ** A stable atom has a valence shell that holds the most electrons it could possibly hold. Atoms achieve this by sharing or transferring electrons with other atoms in a **chemical reaction.** The goal of chemical reactions is to achieve the "perfect number" of valence electrons in their valence shells. Atoms are willing to take on or lose electrons in exchange for having a full valence shell. Because many atoms would be satisfied to have 8 electrons in their //**l, m**// or //**n orbital**//, they are typically said to follow the "**octet rule**" (octet = a set of eight). These chemical reactions are predictable and repeatable. There are also definite clues that a reaction has taken place including:
 * change in physical properties
 * color change
 * gas given off
 * temperature change
 * In a chemical reaction there are reactants and products, and these occur in definate proportions. Reactants** are what undergo a chemical change, and the **products** are the molecules that form as a result of the chemical change. (A good way to remember this is that the arrow always __**p**__oints towards the __**p**__roduct - "p to p")


 * When two or more atoms react and combine to form ions, molecules or compounds. **
 * Molecules** can be made of one element, for example, oxygen gas is O2 (the 2 to the left of the symbol means that two oxygen atoms are bound together in the molecule). If two different types of elements join together, they are called **compounds**. A **compound** is a molecule that is made of two or more atoms of different elements. Scientists use a 'chemical shorthand' (or chemical formula) to indicate these molecules. Water, for example, is a compound written as H2O; this **chemical formula** symbolizes both the elemental composition of the molecule and their relative proportions. Water is composed of 2 atoms of hydrogen and one of oxygen, covalently bound together. NaCl represents sodium chloride, or table salt, consisting of one atom of sodium and one of chlorine.


 * There are four important types of chemical bonds. **
 * 1) The first is **ionic bonding**, the bonding that occurs between sodium and chlorine in table salt. This bonding occurs between two ions, often forming an orderly array of positive and negative ions into a crystal, called a **salt.** This link is due to sodium giving up its one outer electron to chlorine, which needs one electron to fill up its outer shell. Both atoms become electrically charged (ions), and are thus attracted to each other by the electrical charges. The bonds may be weak; this is why interactions with water molecules causes table salt crystals to break apart, or **dissolve**, into the water. Table sugar, or sucrose (C12H22O11), although polar, does dissolve in water, but not as readily as table salt.
 * 2) A second type of bonding involves the sharing of a pair (or multiple pairs) of electrons. A shared pair of electrons is called a **covalent bond**. A carbon atom, for example, needs four electrons to fill its outer shell, it thus can form a total of four covalent bonds with other atoms, including other carbon atoms (//this is the crucial important aspect to the importance of carbon for life: because of its versatility in forming covalent bonds, it forms the large variety of carbon containing molecules found in living things. A second important aspect of carbon is that it is relatively abundant//). After a covalent bond forms, each pair of electrons orbits both of the atoms. In methane (CH4, the simplest hydrocarbon), carbon shares a pair of electrons with each of the hydrogen atoms. Each atom has its outer shell filled with electrons, and thus methane is a relatively stable molecule. Covalent bonds are the strongest of the bonds, and represent energy (when you 'burn' glucose in your cells during respiration, or 'burn' natural gas in heating, the covalent bonds holding glucose and natural gas molecules are broken, releasing heat and light energy).
 * 3) The last two types of bonds are the weakest, compared to ionic and covalent bonds. The third type of bond is **hydrogen bonding**. This is a weak bond that occurs between two molecules. Some molecules are what we call polar (they have slight separation of electrical charges at different parts of the molecule). Water for example, is a polar molecule. These slight charges can be attracted to opposites charges (of other polar molecules, and to ions). The slightly negative region of a water molecule (around the oxygen nucleus, which due to the larger size and greater number of protons in the oxygen nucleus, attracts the shared pair of electrons more strongly than the smaller hydrogen nucleus) can be attracted to the slightly positive regions around the hydrogen nucleus of another water molecule, thus a weak bond forms between the two molecules. These bonds are quite weak, however, by their sheer numbers, can be important. This is why water molecules can be carried to the tops of trees, and small insects can scurry around on the surface of the water. More about this property of water later). Polar molecules are **hydrophilic** ('water-loving'), i.e., they readily react with polar water molecules.
 * 4) The fourth bond is **hydrophobic bonding**. This occurs between a polar molecule (such as water) and a nonpolar molecule (such as oil). A nonpolar molecule has no slight separation of charges in its structure, so it does not interact with water ('water-hating' or hydrophobic). Nonpolar molecules will react often with each other, but not with polar molecules, on the whole, and this bond is quite weak. Hydrophobic bonding is a very important aspect of cell membrane formation, molecular folding and shape, and environmental concerns (such as oil slicks, where the oils and other hydrocarbons do not dissolve in water. This makes it possible to remove the oil in some cases, because it may 'float' on the surface, if it is of the right type).