• Metabolism refers to all the chemical reactions that occur in an organism.
• Atoms, which are the fundamental units of matter, are involved in these reactions.
Atoms join together to form compounds.
• Much of the body is composed of organic compounds, such as proteins, lipids, and carbohydrates.
• These compounds are involved in many chemical reactions that help organisms maintain homeostasis.

• Atoms consist of 3 kinds of particles:
1) protons
2) neutrons
3) electrons
• The core of the atom, called the nucleus, I made up of protons and neutrons.
• The region around the nucleus that electrons may occupy at any time is called the electron cloud.

• Electrons are negatively charged, so the electron cloud has a negative charge.
• Protons are positively charged and neutron have no charge, so the nucleus has a positive charge.
• Since protons and neutrons have opposite charges they attract one another

• Element—a pure substance made of only one kind of atom
• Periodic table p.1046-1047
• Elements differ in the number of protons their atoms contain.
• The number of neutrons in an atom is often but not always equal to the number of protons in the atom.
• Atoms of an element that contain different numbers of neutrons are called isotopes.

• For example, three isotopes of carbon, C, are carbon-12, carbon-13, carbon-14. Each contains six protons, but carbon-13 contains 7 neutrons, and carbon-14 contains 8 neutrons.
• Nuclear medicine uses radioisotopes to treat certain diseases. Isotopes are atoms of the same element that have different numbers of neutrons. A radioisotope is an isotope that has an unstable nucleus and undergoes radioactive decay.

• Atoms join with other atoms to form stable substances.
• A force that joins atoms is called a chemical bond.
• Compound--a substance made of the joined atoms of 2 or more different
• elements
Ex. When sodium atoms, Na, bond with chlorine atoms, Cl, the compound sodium chloride (table salt) forms

• A compound is represented by a chemical formula that identifies the elements in the compound and their proportions.
• Ex.: The formula for sodium chloride, NaCl, shows that there is I one sodium atom for every chloride atom in the compound.

• Covalent Bonds—these form when 2 or more atoms share electrons to form a molecule
• Molecule--A group of atoms held together by covalent bonds
Ex. : a water molecule, H
2
O, CO
2,
,
O
2
*The arrangement of electrons determines how atoms bond together.

• Electrons are grouped into different levels which have different levels of energy.
• The levels closest to the nucleus have less energy than the levels farther from the nucleus. Each level can hold a limited number of electrons.
• An atom is stable when its outer level is full. If it is not full, an atom will react readily with atoms that can provide electrons to fill its outer level.

• Hydrogen Bonds—molecules with an unequal distribution of electrical charge, such as water molecules are called polar molecules. This attraction between two water molecules is an example of a hydrogen bond—a weak chemical attraction between polar molecules.

• Ionic Bonds—sometimes atoms or molecules gain or lose electrons. An aom or molecule that has gained or lost one or more electrons is called an ion. Ions have an electrical charge because they contain an unequal number of electrons and protons.
• An atom that has lost electrons is positively charged, whereas an atom that has gained electrons is negatively charged

• Ions of opposite charge may interact to form an ionic bond
Ex.: Na + forms an ionic bond with Cl to form an ionic bond

• Water in living things:
• Storage of heat:
• Cohesion-
• Adhesion-

Solutions:
Polarity: polarnonpolar-

• Acids-
• Bases-

•
•
•
•
• Carbon compounds:
• -Carbohydrates-
-Lipids-
-Proteins-
-Nucleic Acids-

• Energy for life processes:
• Energy in Chemical reactions:
• Activation Energy:

• Enzymes:
• Enzyme specificity-

• Factors that affect enzyme specificity: