1. Unit 2 Ecological Biochemistry
Unit 2A: Basic Chemistry

2. Atoms are the Basic Units of Matter
Atoms are incredibly small. Placed side by side, 100 million atoms would make a row only about 1 centimeter long—about the width of your little finger!

3. What are Atoms made of?
Atoms are made of particles called protons, neutrons, and electrons.
Protons have a positive (+) charge
Electrons have a negative (-) charge
Neutrons are neutral (no charge)
Atoms normally have equal numbers of electrons and protons, making them neutral

4. Elements Elements are pure substances made of only one type of atom
Elements are listed in the periodic table of elements
They are arranged in order of their atomic numbers
An atom is the smallest unit of an element that has the properties of that element

5. Atomic Number and Mass Number
The atomic number of an element is the number of protons (typically the same as the number of electrons)
The mass number of an element is the number of protons plus the number of neutrons

7. Element
Symbol
Atomic Number
Mass Number
Number of Protons
Numbers of Neutrons
Number of Electrons
Helium He 2 4
Magnesium Mg 12
Zinc Zn 30 65 35
Bromine Br 80 45
Aluminum Al 13 14

8. Important Elements for Biology
The five most abundant elements in living things are:
Hydrogen – 10%
Oxygen – 65%
Nitrogen – 4%
Carbon – 19%
Phosphorus – 1% H H

9. Molecules, Compounds, and Chemical Formulas
A molecule is made when 2 or more of any atom are joined together (Ex: O2, H2O)
A compound is a substance formed by the combination of two or more different elements (Ex: H2O, C6H12O6)
All compounds are molecules, but not all molecules are compounds
Chemical Formula- written shorthand showing the composition of a compound

10. Chemical Formulas
Coefficient: tells how many molecules of that substance (the large number BEFORE the formula)
Subscript: goes with the element symbol preceding the number; tells how many atoms of that element within one molecule of the substance (small number WITHIN the formula).

11. 6

12. Example 2: 6CO2 What is the coefficient? _______
What is carbon’s subscript? ________
What is oxygen’s subscript? ________
How many molecules of this compound are represented by this formula? _________
How many atoms TOTAL are present in this molecule?
______

13. Chemical Bonds
The atoms in compounds are held together by chemical bonds.
Making bonds involves the electrons that surround each nucleus.
The electrons that are available to form bonds are called valence electrons.

14. This type of drawing is called a Bohr model
Valence Electrons
The electrons of an atom are spread out in different layers around the nucleus to make an “electron cloud”
These layers are called energy levels
2 electrons go in the first energy level
8 electrons can go in the second energy level and beyond (octet rule)
This type of drawing is called a Bohr model

15. Valence Electrons (cont.)
If there are not 8 electrons for the outer level, these empty spots are called vacancies and some electrons are thus unpaired
The unpaired electrons in the outer layer are the valence electrons
The valence electrons can pair with those from other atoms to “fill” the vacancy
This creates a molecule

16. Bohr Model vs. Lewis Dot Structure
Lewis Dot Structure: shows just the valence electrons in the outer energy level
Bohr Model: shows all of the electrons in their energy levels

17. Reactive vs. Stable
The reactivity of an atom is determined by the number of vacancies in its outer energy level
If there are vacancies, the atom is reactive/unstable
If there are no vacancies, the atom is nonreactive/stable
If the vacancies are filled due to bonding, the molecule is stable

18. The main types of chemical bonds are
1. ionic bonds
2. covalent bonds
There are other types of bonds and interactions but they are not as strong as these two types

19. 1. Ionic Bonds
An ionic bond is formed when one or more electrons are transferred from one atom to another.
An atom that loses electrons becomes positively charged.
An atom that gains electrons has a negative charge.
These positively and negatively charged atoms are known as ions.
These oppositely charged ions have a strong attraction for each other, forming an ionic bond.

20. 2. Covalent Bonds
When electrons are shared by atoms instead of transferred.
The moving electrons travel about the nuclei of both atoms, forming a covalent bond.

21. A covalent bond can be a…
Single Covalent Bond: atoms share 2 electrons (1 pair)
Double Covalent Bond: atoms share 4 electrons (2 pairs)
Triple Covalent Bond: atoms share 6 electrons (3 pairs)

22. HONC
This is the number of bonds each of these can form!
H O N C
Bonds between the most important biological atoms will be covalent
The number of bonds each can make is important for the compounds that will be created using these atoms
Hydrogen -can form 1 single bond
Oxygen- can form 2 single bonds or one double bond
Nitrogen- can form 3 single bonds or 1 double bond and 1 single bond
Carbon- can form 4 single bonds or 2 double bonds, or 1 double bond and 2 single bonds (no quadruple bond!)

23. Structural formulas Show you the types of elements in the molecule
the number of atoms of each element AND
the arrangement of atoms and location of covalent bonds. Shows the two dimensional shape of the molecule.

24. Chemical Reactions
Chemical Reactions: process that changes or transforms one set of chemicals into another set of chemicals. Involves changes to the chemical bonds that join atoms in compounds.
Reactants: elements or compounds that enter into a chemical reaction
Products: elements or compounds produced by a chemical reaction
HINT: Reactants react to produce products!
Bonds of the reactants are broken and new bonds form in the products

25. Chemical Equations
What process is this equation for?
Chemical Equation: a mathematical representation of a chemical reaction. It shows the numbers and types of compounds involved.
6O C6H12O  CO H2O ___

26. Balancing Chemical Equations
The Law of Conservation of Matter: matter (atoms and elements) in a chemical reaction cannot be created or destroyed. Only the arrangement of the atoms is changed, NOT the number or types.
Therefore both sides of a chemical equation must be “balanced” (have the same number of atoms).

27. Are these equations balanced?
C + 2H2 --> CH4
Na2SO4 + CaCl2 --> CaSO4 + NaCl
C2H6 + O2 --> CO2 + H2O
2Al2O3 --> 4Al + 3O2