front 1 Purpose of Experiment 12 | back 1 become familiar with: 1. Lewis structures 2. principles of the VSEPR model 3. the three-dimensional structures of covalent molecules |
front 2 chemical bond | back 2 when atoms or ions are strongly attached to one another |
front 3 Three types of chemical bonds | back 3 1. ionic 2. covalent 3. metallic |
front 4 Ionic bond | back 4 - electrostatic forces btwn ions of opposite charge - formed by transfer of one or more electrons - from atom of low ionization energy to atom of high ionization energy usu metals with nonmetals (except noble gases) |
front 5 Covalent bond | back 5 sharing of electrons between two atoms More familiar exs= bonds among nonmetallic elements |
front 6 Metallic bonds | back 6 found in metals like gold, iron, magnesium each atom is bonded to several neighboring atoms give rise to high electrical and thermal conductivity b/c in m bonds electrons are relatively free to move throughout the 3D shapes of mc's |
front 7 Which electrons are involved in bonding | back 7 valence electrons (reside in incomplete outer shell of an atom) |
front 8 creator of Lewis Dot structure | back 8 G.N. Lewis, American chemist |
front 9 Lewis symbol consists of: | back 9 chemical abbreviation for the element and a dot for each valence electron each side accommodates up to two electrons |
front 10 What can atoms do to achieve noble gas config? | back 10 gain, lose, or share electrons |
front 11 octet rule | back 11 atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons octet of electrons= full s and p subshells |
front 12 Properties of ionic substances (most substances do not have these characteristics) | back 12 usually brittle high melting point crystalline solids w/ well-formed faces - characteristics result from electrostatic forces that maintain ions in a rigid, well-defined, 3D arrangement |
front 13 Example of how H2 forms a bond | back 13 - the nuclei and electrons cause electron density to concentrate btwn the nuclei - the shared pair of electrons acts as a kind of "glue" holding the atoms together |
front 14 single bond double bond | back 14 sharing of one pair of electrons sharing of two pairs of electrons - triple bond is the sharing of three pairs of electrons |
front 15 Steps for drawing Lewis dot structures | back 15 1. Sum the number of valence e- a. add electrons for negative charges b. subtract electrons for positive charges 2. Decide the central atom (least electronegative excluding H) 3. Assign leftover electrons to the terminal atoms until all octet 4. Assign any leftover e- to the central atom (if central atom doesn't have octet, create multiple bonds) |
front 16 Why formal charge? | back 16 sometimes can draw several diff Lewis structures that all obey the octet rule formal charge helps decide the structure that is the most reasonable |
front 17 formal charge (of an atom) | back 17 the charge that an atom in a molecule or ion would have if all atoms had the same elcectronegativity |
front 18 equation for formal charge | back 18 (regular valence e-) - (valence e- found in the molecule) * remember to count only one of the two bonded molecules for each bonded atom |
front 19 Most bonds btwn two diff kinds of atoms are usually... | back 19 polar |
front 20 Why are most bonds of two diff atoms usu polar? | back 20 b/c diff atoms have diff electronegativities (so electrons are not shared equally by the two bonded atoms) |