Chemistry

=Chemistry - in Biology=

Everything - whether a rock, a frog, or a tree - is made up of **elements**.
 * //Why do we learn chemistry before biology?//**

Luckily no. In the back cover of your book there are approximately 118 elements listed in the periodic table. Of those that occur on Earth, only about 25 are essential to live.
 * //Do we learn all of chemistry before biology?//**

No. There are four in particular that are very important to us. See the first four listed in Table 6.1 pg 142. The remaining 21 elements are still very important for all organisms but we will focus on these four.
 * //So do we need to memorize everything about all 25?//**

All atoms, have the same basic atomic structure. The core of every atom contains a **nucleus**. In the nucleus, is where the **protons** (+ charge) and **neutrons** (no charge) are found.
 * Atoms and Atomic Structure-** see Fig 6.2 p143
 * Electrons** ( -- charge) are found in regions called energy levels.

1st level (closest to the nucleus) holds : **2** 2nd level (just beyond the 1st level) holds: **8** 3rd level (just beyond the 2nd level) holds: **18**
 * Maximum # of electrons for each energy level**:

For the purposes of our discussion, we do not need to know everything about atomic structure.

That being said we will assume two things: The **atomic number** for an element (just above the symbol in the table) **= the # of electrons** It also tells you the # of protons, but we don't need that information right now.
 * Assumption #1:**

Atoms "desire" to have full outer energy levels (FYI - atoms are not alive, can't desire). Atoms with full outer energy levels are stable. Atoms with unfilled outer energy levels are unstable.
 * Assumption #2:**

Very few atoms in the periodic table exist having full/stable outer energy levels. //So how do atoms of various elements solve this problem and fill their energy levels?//
 * Bonding -** pg 145
 * Covalent bonds**
 * Ionic bonds**

Before beginning this section on bonds, read pg 148 A common point of confusion is understanding shorthand notation in chemistry
 * Writing Chemical Equations**

Write-out the chemical equation: 2H2 + O2 -> 2H2O

__First explain the difference between the two below:__ an **atom** a **molecule**

__Second:__ Where is the coefficient(s)? Where are the subscripts?

__Third__: Know that coefficients and subscripts of one (1) are never written but are implied. Know that to calculate, the number of atoms of a molecule = coefficient x subscripts

Examples H2 - each atom of H has 1 electron in its outer energy level (atomic # = 1) If each one had 2 electrons, its outer energy level full and it could be stable. The solution: Each H atom shares an electron between them and the force that holds them together (positively charged nucleus attracts the electrons from each H) is called a covalent bond
 * Covalent bonds** - a bond created when negatively charged electrons are shared between two atoms.

H2O - the oxygen molecule has 6 electrons in its outer energy level (2 in the 1st, 6 in the second) because its atomic number is 8. Therefore oxygen needs two electrons to be stable or have a full outer energy level. H has one electron. Therefore one covalent bond is made between H and oxygen and a second covalent bond is made between another H and oxygen.

Day 2
 * Ionic bonds -**