Chemistry Chemical Bonds

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

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

Objectives Describe how an ionic, covalent and metallic bonds forms Relate the properties of ionic compounds to the structure of crystal lattices Compare polar and non polar bonds, and demonstrate how polar bonds affect polarity of a molecule Describe the structure and strength of bonds in metals & relate their properties to their structure

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

Networks / Crystal Lattices - 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

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: Cl2 Polar - bonded atoms that do not share e-’s equally - different atoms bonded H ex. H – N – H: NH3

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