Objectives  Explain why atoms form bonds  Define chemical bond & name three types of chemical bonds  Compare and contrast the advantages and disadvantages of varying molecular models

Lewis Dot Diagrams/Lewis Structures  diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.  Comes in handy when dealing with reactions and chemical bonds.  Lone electrons are where other elements can bond and create molecules.

Drawing Lewis Dot Diagrams  First you need to identify the number of valence electrons  Find the V.E. from writing out the shorthand configuration  Or based upon the group that it’s in find the number of V.E. from that.  Second, place the elements valence electrons around the chemical symbol

Quick Check!  Draw out the Lewis Dot Diagrams for the following elements  Iodine  Hydrogen  Calcium  Indium

Bonding Atoms  Why do atoms bond? - each atom wants a full outermost energy level - gain, lose, and share valence electrons to achieve the duet or octet rule aka: “being happy” - gives each atom an electron configuration similar to that of a noble gas ex. Group 18: He, Ne, Ar

Chemical Bonds  Chemical Bonds - attractive force that holds atoms or ions together - 3 types ionic, covalent, metallic - determines the structure of compound - structure affects properties - melting/boiling pts, conductivity etc.

Chemical Structure/Models  Chemical Structure/Molecular Models - arrangement of bonded atoms or ions - bond length: the average distance between the nuclei of two bonded atoms - bond angles: the angle formed by two bonds to the same atom

Ionic Bonds / Ionic Compounds  Definition - bond formed by the attraction between oppositely charged ions cation: positive: lost e-’s anion: negative: gained e-’s - oppositely charged ions attract each other and form an ionic bond ex. Na + + Cl - = NaCl - electrons are transferred from one atom to another - negative ions attract more positive ions, and soon a network is formed

Ionic Bonding: The Formation of Sodium Chloride Cl 1s 2 2s 2 2p 6 3s 2 3p 5 Na 1s 2 2s 2 2p 6 3s 1 Cl - 1s 2 2s 2 2p 6 3s 2 3p 6 Na + 1s 2 2s 2 2p 6

Networks / Crystal Lattices  Networks - repeating pattern of multiple ions ex. NaCl - every Na ion is next to 6 Cl ions - strong attraction between ions creates a rigid framework, or lattice structure: aka: crystals ex, cubes, hexagons, tetragons

Properties of Ionic Compounds  Structure affects properties - strong attractions between ions: strong bonds - high melting/boiling pt - shatter when struck (think of it as one unit) - conductivity solid: ions are so close together, fixed positions, (can’t move) NO conductivity liquid: ions are freely moving due to a broken lattice structure Good conductivity

How many Atoms? AND

Ca + F_________________H + Br_________________ B + P_________________Al + O_________________ Sr + N_________________K + N_________________ B + I_________________Li + Se_________________ Without drawing a diagram, decide how many atoms of each element there are. Then write the formula.

Covalent Bonds  Definition - chemical bond in which two atoms share a pair of valence electrons - can be a single, double, or triple bond single, 2e-’s (-); double, 4e-’s (=); triple, 6e-’s( ) - always formed between nonmetals - mostly low melting/boiling points  2 types of bonds - polar - non polar

Covalent Bond Cont.  Non Polar - bonded atoms that share e - ’s equally - same atoms bonded ex. Cl – Cl: Cl 2  Polar - bonded atoms that do not share e - ’s equally - different atoms bonded H ex. H – N – H: NH 3

Covalent Bonds Cont.  Special Diatomic Atoms  Bonded to each other (there are 7!) H 2 N 2 O 2 F 2 Cl 2 Br 2 I 2

Metallic Bonds  Definition - a bond formed by the attraction between positively charged metal ion (cation) and the shared electrons that surround it (sea of electrons) ex. Cu  Properties - Conductivity: Good: electrons can move freely - Malleable: lattice structure is flexible

Predicting Bond Type