C H E M I S T R Y

Levels of Organization As things get more complex, things tend to get more disorganized Natural events tend to increase disorder Entropy- disorder Living things are highly organized They use energy to maintain their organization Living things need a continuous input of energy Atoms Molecules Organelles Cells Tissues Organs Organ Systems Organisms Unicellular Multicellular

Elements A substance that cannot be broken down into simpler chemical substance (90 natural elements) Of all the elements, only about 25% are essential to living organisms ALL LIVING THINGS CONTAIN CARBON!! Each element is identified by a 1 or 2 letter symbol H, He, Li, Mg

Atoms Elements are made up of atoms Structure Electron Energy Levels The smallest particle of an element that has the characteristics of that element Structure Nucleus made up of protons (+) and neutrons (neutral) Surrounding the nucleus are electrons (-) Electron Energy Levels The 1st level can hold up to 2 electrons, the 2nd level can hold up to 8 electrons Atomic Number The number of protons Atomic weight The weight of the nucleus (protons + neutrons)

Isotopes and Ions Isotope Ion An atom of the same element that have different numbers of neutrons Ex. Carbon-14- used for radioactive dating because isotopes are usually unstable and break apart easily to give off radiation Radiation is also used in medical practices Radioactive cobalt is used for cancer patients Radioactive iodine is used for seeing the functioning of the thyroid gland Ion an atom that gains or loses an electron either positively or negatively charged ex. Na+, Cl-

Bonds Covalent bond- sharing of electrons Ex. H2O, CH4, CO2 Most compounds in organisms have covalent bonds Ionic bond- form through the loss or gain of electrons Ex. NaCl- Na loses an electron, Cl gains one Ionic bonds are not seen as frequently in living organisms, but are important in nerve impulses, muscle contractions, etc.

Why do atoms bond? They combine to become more stable They do this by having their outermost energy level filled

What happens when atoms bond? Molecule- a group of atoms held together by covalent bonds and having no overall charge Ex. H2O Compound- a substance that is composed of atoms of 2 or more different elements that are chemically combined Ex. NaCl, CO2 Mixture- a combination of substances in which the individual components retain their own properties Solution- a mixture in which 1 or more substance are distributed evenly in another substance

COHN The four most abundant elements in the body Carbon- 18.5% Oxygen- 65% Hydrogen- 9.5% Nitrogen- 3.3% Trace elements- very small amount of these elements in the body We get them from food

Role of Carbon A carbon atom has 4 available electrons for bonding Makes covalent bonds When each atom shares 2 electrons, a double bond is formed Ex. CO2

Role of Carbon, cont. Carbon can form straight chains, branched chains, rings, etc. Isomers- molecules with the same chemical formula but different structure Diamonds and Graphite are completely made of carbon Diamonds are the hardest substance on Earth Graphite can be broken easily They can do different things because their structures are so different DNA backbone is partially made of carbon Carbon Cycle- when organisms die, CO2 is emitted Photosynthesis and Respiration

Without Carbon… THERE WOULD BE NO LIFE!!!