The Chemistry of Life: The Nature of Matter Essential Question: What are the parts of the atom? HW: Atoms worksheet

Matter is Made of Atoms Atom— smallest unit of matter that cannot be broken down by chemical means Made up of subatomic particles protons neutrons electrons

Elements Are the Simplest Pure Substances Elements—substance made of only one kind of atom Elements are represented by a one- or two-letter symbol.

Elements The number of protons in an atom of an element is the element's atomic number. Is also the number of electrons Atomic weight (mass) is equal to the number of protons and neutrons

Isotopes Atoms of an element that contain a different number of neutrons Identified by their mass numbers http://www.uwm.edu/Dept/EHSRM/RAD/Figure_1.jpg

Elements and Isotopes Radioactive Isotopes Their nuclei are unstable and break down at a constant rate over time, releasing energy Although the radiation these isotopes give off can be dangerous, they have important scientific and practical uses.

Elements and Isotopes Radioactive isotopes can be used: to determine the ages of rocks and fossils. to treat cancer. to kill bacteria that cause food to spoil. as labels or “tracers” to follow the movement of substances within an organism. BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003

Atoms Can Bond Together Compounds linked together by chemical bonds Covalent Non-polar Polar Ionic Hydrogen Van der Waals interactions Bond Strength

Covalent Bonding Valence electrons are shared by atoms Sharing electrons means that the moving electrons actually travel in the orbitals of both atoms.

Ionic Bonding High electronegativity difference strips valence electrons away from another atom Electron transfer creates ions (charged atoms) Cation (positive ion) Anion (negative ion) Na+ http://www.sacbee.com/static/weblogs/health-and-fitness/Salt%2520Shaker.jpg Cl– BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003