1. Biology Standard 1.1
Recognize that biological organisms are composed primarily of very few elements.
The six most common are C, H, N, O, P, and S.

2. Essential Questions 1. Identify elements by symbol
2. Differentiate between “atom, element, molecular compound ”
3. Why is carbon central to all life?

3. Essential Vocabulary
Matter, atom, element, molecular compound, ion, ionic compound, chemical bond

4. Chemistry
The scientific study of the structure, properties, and reactions of the chemical elements and the compounds they form (matter).
The study of Chemistry is essential to the study of Biology because all living things are made of matter.

5. Learning Check
Why is the study of chemistry essential to understanding biology?
Because all living things are made of matter.

6. Matter Anything that takes up space and has mass.
Matter is composed of substances made of the various elements.
The basic unit of matter is the atom.

7. Element
A substance that cannot be broken down into simpler substances by chemical means.
An element is composed of atoms that have the same atomic number, that is, each atom has the same number of protons in its nucleus as all other atoms of that element.
Today, 118 elements are known .
Elements are identified by a symbol (letter or letters).

8. Six Elements Essential to Living Things
Carbon- C
Hydrogen- H
Oxygen- O
Nitrogen- N
Phosphorus- P
Sulfur- S

9. Learning Check What are the six elements that are essential to life?
C, H, O, N, P, S

10. Chemical Bonds Chemical bonds hold atoms together.
Chemical bonds form by an attraction between two atoms, like magnets sticking together.

11. Molecular Compound
1. A group of atoms that is held together chemically.
2. A group of molecules that can be broken down by means of a chemical reaction.
A molecule of water (H2O)consists of one oxygen atom and 2 hydrogen atoms
Sugar is broken down into carbon dioxide and water by a chemical reaction called cellular respiration.

12. Water Water is the most abundant molecule in living organisms.
Water has special traits that make it important to life.

13. Learning Check What molecule is found most often in living things?
Water

14. An atom or molecule that has a positive or negative charge
Ions
An atom or molecule that has a positive or negative charge
H+ (Hydrogen)
Na+ (Sodium)
Cl- (Chlorine)
OH- (Hydroxide)

15. Na+ and Cl-  NaCl (salt)
Ionic Compounds
Compounds composed of ions whose opposite charges attract to each other.
Na+ and Cl-  NaCl (salt)

16. Water dissociates (separates) and releases hydrogen ions (H+) and hydroxide ions (OH-).

17. Acids are molecules that release hydrogen ions in solutionpH
Acids are molecules that release hydrogen ions in solution
HCl  H+ + Cl-
Bases are molecules that either take up hydrogen ions or release hydroxide ions in solution.
NaOH  Na+ + OH-

18. Concentrations of hydrogen ions or hydroxide ions can be represented using the pH scale.

19. Learning Check
What is the pH number of the strongest acid on the pH scale? 1
What is the pH of the weakest acid? 6

20. Carbon The element that is essential to all living things.
Carbon easily bonds with itself and other atoms; can form 4 chemical bonds.
Carbon is found in many large, complex compounds. These compounds are called organic molecules.