Chapter 1: The Chemistry of Life

1.1 Atoms, Molecules, & Compounds Chemistry= study of the composition, structure, properties, and reactions of a substance. Matter= Anything that has mass & occupies space (pretty much everything you see & even the stuff you can’t see – air) Mass= The quantity of matter an object has

Atoms Basic unit of matter Smallest individual units of elements that retain the properties of that element Composed of protons (+)- positive charge neutrons (0)- neutral charge electrons (-)- negative charge

Atoms Protons and neutrons are located in a central area called the nucleus. Electrons move about the nucleus. All atoms have an equal # of electrons and protons. (They are neutral)

Structure of Atoms: Bohr Model Electron Shells- “Clouds” where electrons are found orbiting the nucleus Each shell (other than first) holds 8 electrons 1st shell: 2 electrons 2nd shell: 8 electrons 3rd shell: 8 electrons ex: Hydrogen (1), Carbon (6), Oxygen (8), Chlorine (17) Any unfilled outer shell will cause the atom to be reactive. Filled outer shells means the atom is stable.

Elements CARBON-C OXYGEN-O HYDROGEN-H NITROGEN-N A pure substance that contains only one type of atom About 96% of the mass of all kinds of living things is composed of a combination of just 4 elements… CARBON-C OXYGEN-O HYDROGEN-H NITROGEN-N

Isotopes Atoms of the same element that have different number of neutrons Mass number (Atomic mass) = number of protons plus neutrons in nucleus of atom NOT the same as Atomic Weight (on Periodic Table) Useful in biological research: we know how long they take to decay, so can be used to determine the age of objects.

Isotopes Examples: carbon-12, carbon-13, carbon-14 Carbon – 12 # protons # neutrons

Periodic Table Developed as a way to organize elements Elements are found in order of atomic number (# of protons) Atomic weight (# of protons + # of neutrons) get bigger as you go across and down Periods of elements = rows As you go across a row, elements get smaller in size BUT greater in mass Groups of elements = columns Elements in the same group have similar properties and will bond in similar ways

Information on the Periodic Table 2 He Helium 4 Atomic Number Chemical Symbol Element Name Atomic Mass ***Element Song***

Compounds A substance formed by the bonding of two or more elements in definite proportions Fundamental Units of Chemistry Physical & Chemical properties of compound are DIFFERENT from each element alone

Compounds Chemical formula = composition of the compound Shows the number of atoms of each element in a molecule Examples: H2O, NaCl, CO2

Chemical Bonds The forces that hold together the atoms that make up compounds Result from the attraction, sharing, or transfer of valence shell electrons from one atom to another Two types of chemical bonds: Ionic Bonds Covalent bonds

Ionic Bonds A TRANSFER of electrons takes place ALWAYS between a metal and a nonmetal Results in ions, or a charged “atom” (+ or -) Ions of opposite charge attract strongly form an ionic bond

**Atoms want their outermost shell to be full** Ionic Bonds Example: NaCl Remember Rule= 2-8-8! The number of electrons in outer energy shell determines the chemical properties of an atom. **Atoms want their outermost shell to be full**

Ionic Bonds When sodium chloride (NaCl) is formed, one electron from sodium is transferred to chlorine.

Ionic Bonding Examples: Calcium Fluoride Lithium Nitride Magnesium Oxide

Covalent bonds involves SHARING of electrons single covalent bond = share one electron double covalent bond = share two electrons…etc. result of covalent bond- a molecule, the smallest unit of a compound Example: Methane (CH4)

Covalent bonds In a double bond, 2 atoms share 2 pairs of electrons (4 electrons)

Covalent bonds In a triple bond, 2 atoms share 3 pairs of electrons (6 e-)

Structure of the 4 elements that make up most of the mass of living things: