What is Chemistry? Study of composition, structure, and properties of matter Chemicals are the substances that make up everything on Earth Inorganic Chemistry studies every kind of substance that does not require a living organism to exist Organic chemistry is only substances that can be made by living organisms and must have a carbon (C) backbone

What is an Atom? Resembles a solar system Largely emptiness Building blocks of matter Smallest unit of matter Radioactive decay transforms original atom to another atom Smallest particle of an element that keeps all properties of that element

Mass vs. Weight Mass = quantity of matter of an object Weight = force of gravity on an object

Elements in Living Things Elements = pure substances that cannot be broken down The four most abundant elements in living things are carbon, hydrogen, oxygen, and nitrogen or C, H, O, & N, respectively

Parts of an Atom and Charge Nucleus Made up of protons (+) and neutrons (neutral) Makes up most of the mass of an atom The # of protons = atomic number # protons + # neutrons = atomic mass number Electrons (e ‾ ) make up most of the volume of an atom; have a negative charge

Compounds and Molecules Compound = 2 or more elements chemically combined Chemical combination is accomplished by bonding Covalent Bond = sharing of 2 or more pairs of e‾ Ionic Bond = transfer of e‾ ; based on electrical charge Molecule = simplest part of a substance that can exist in a free state Ion = atom/molecule with an electrical charge; if an element has lost e‾, the atom is positively charged, while if an elements has gained an e‾, then it is electrically charged

More about Bonding A chemical bond is the energy required to hold atoms together (union of atoms) Bonds are created by the activity of electrons Bonds broken release energy Bonds formed store energy Electrons farther away from the nucleus have the greatest potential energy (stored energy); kinetic is energy of motion

Types of Chemical Bonds Nonpolar covalent Polar covalentIonic Electrons are shared equally Electrons are shared unequally Electrons are transferred No difference in electronegativity Increasing difference of electronegativity

The Four Types of Bonds Covalent – sharing electrons Ionic – transferring electrons Hydrogen – weak bonds between molecules Polar molecules, such as water and DNA The H⁺ of one molecule bonds with the O¯ of another water molecule (H₂O) van der Waals forces – weak attractions between nonpolar molecules

Electronegativity The force that an atom exerts on its electrons

Water, water everywhere! – that aqueous molecule that is one of the most crucial compounds of life. Mickey Mouse ――› Water: is neutral; however, it is polar because there are uneven charges. The area where O is has a somewhat (-) charge & ‹―― where the 2 H atoms bind O have a slightly (+) charge――› is the universal solvent – Consider an ionic compound (cmpd) like NaCl: the (+) end of a water molec attracts the (-) end of the Cl ‾ and the (-) end of water attracts the (+) end of Na+, so NaCl breaks apart (dissociates) Honors Biology: Chapter 3 – Biochemistry