Bonding

Bonding: electrical attraction between atoms’ nuclei and valence e- Why bond? More stability

Ionic vs. Covalent Bonding Ionic bonds Between metal and nonmetal only e- are transferred Joined by electrostatic forces Very strong Another name is salt Most crystalline solids at room temp Conduct electric current in molten state or in solution (electrolyte) Movement of ions = flow of electricity

Covalent bonding Many molecules are gases and liquids Have weaker bonds e- are shared Occurs b/t 2 nonmetals

Chapter 6 Ionic Compounds Section 3 Ionic Bonding and Ionic Compounds Chapter 6 Ionic Compounds Most ionic compounds exist as crystalline solids. (minimize their potential energy) A crystal of any ionic compound is a 3-D network of (+) and (-) ions mutually attracted to each other.

NaCl and CsCl Crystal Lattices Section 3 Ionic Bonding and Ionic Compounds Chapter 6 NaCl and CsCl Crystal Lattices

Electron-Dot Notation Chapter 6 Electron-Dot Notation To keep track of valence electrons, it is helpful to use electron-dot notation. Electron-dot notation is an electron-configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the element’s symbol. The inner-shell electrons are not shown.

Drawing Lewis Structures Count # valence e- of all atoms in compound; this is the number of e- you may work with Most atoms like 8 e- surrounding them, except H (only 2 e-) Space atoms out symmetrically with H’s on outside Central atom is least EN atom, except if C is involved and NEVER H Put 1 pair of e- in between each atom (shared pairs) Put remaining e- around atoms (lone or unshared pairs)

Never make a multiple bond if you don’t have to Polyatomic Ions: If there are not enough e- to put around as lone pairs, make a lone pair another shared pair (double and triple bonds) Never make a multiple bond if you don’t have to Polyatomic Ions: Do same thing as before, but Add # e- if it’s a negative charge Subtract # e- if it’s a positive charge Put ion in brackets with charge on outside

Resonance Structure that occurs when it is possible to draw 2 or more valid e- dot structures Double-headed arrows used to connect structures EX: O3 SO2

Exceptions to Octet Rule Cannot be satisfied in molecules whose total # is odd # Some molecules have more or fewer than 8 e- Atoms that have more than 8 e- usually bonded to highly EN atoms, like the halogens bonding involves e- in d and f orbitals EX BF3 SF6 PCl5

VSEPR [Valence Shell Electron Pair Repulsion] Repulsion b/t e- prs causes molecular shapes to adjust so that valence-electron prs stay as far apart as possible Determines geometry of molecules See lab for shapes to know

Electronegativity and Polarity Electronegativity (EN): how attractive an atom is to shared pair of e-; greater difference, more ionic and the more polar

Trends in EN on Per. Table As you go across period left to right, atoms have same # E levels and same # shielding e-. Increased nuclear charge = increased attraction of valence e- to nucleus Therefore, EN increases As you go down group, add more E levels and e-. Increased shielding balances increased nuclear charge, which means less e- attraction to nucleus Therefore, EN decreases EXCEPTIONS: high values in d-block because d-orbitals shielded differently than s and p

Molecular Polarity Polar bonds often make molecules entirely polar Molecules can be nonpolar but have polar bonds When polar bonds cancel each other out Ex: CO2

Metallic Bonding The unique characteristics of metallic bonding gives metals their characteristic properties: electrical conductivity thermal conductivity malleability ductility shiny appearance

In a metal, the vacant orbitals in the atoms’ outer energy levels overlap. This overlapping of orbitals allows the outer electrons of the atoms to roam freely throughout the entire metal. The electrons are delocalized, which means that they do not belong to any one atom but move freely about the metal’s network of empty atomic orbitals. These mobile electrons form a sea of electrons around the metal atoms, which are packed together in a crystal lattice.

The chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons is called metallic bonding.