Chemical Bonding & Electronegativity

Atoms bond to lower their vibrational energy (complete an octet)

}}Electronegativity is the tendency of an atom’s nucleus to attract electrons in a covalent bond}}

VSEPR--- Valence Shell Electron Pair Repulsion

==Dipoles== have partial charges

“Like dissolves like”

Types of Bonds

Covalent

• shared electrons
• ^^polar---^^ charge is shared unevenly (creates dipoles)
• ^^nonpolar---^^ charge is shared evenly
• low melting point, non-conductor, particles are called molecules
• Ex: H2O

Ionic

• transferred electrons
• 2 ions with opposite charges (Electrostatic Attractions)
• high melting point, conductor when melted/dissolved (non-conductor when solid), particles are called formula units
• Ex: NaCl

Metallic

• delocalized electron “sea”
• metallic properties stay (conductivity, luster, malleability, high melting point)

Octet Rule

• Hydrogen--- 2 electrons stabilize
• Beryllium--- 4 electrons stabilize
• Boron & Aluminum--- 6 electrons stabilize
• Elements larger than aluminum can share >8 electrons (empty d-orbital)
• C, Si, & O can double/triple bond

Intramolecular forces

London Dispersion Forces

• ]]caused by momentary polarization of electron clouds]]
• instantaneous dipole induces a dipole on a nearby molecule
• short-range, between ^^nonpolar^^ molecules

Dipole-Dipole Forces

• ]]positive dipole aligns with negative dipole]]
• increased strength with increased polarity
• molecules must be close together and ^^polar^^

LDF + dipole-diple = ^^van der Waals^^

Hydrogen Bonding

• hydrogen covalently bonds to a negative element with a lone pair
• other element must be oxygen, nitrogen, or fluorine
• causes surface tension

Bond Strength

metallic

⬇

ionic & covalent

⬇

hydrogen

⬇

dipole-dipole

⬇

LDF

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