Atomic Structure and Bonding

ionic bonding

how it works: metals give up electrons to non metals, strong non directional coulomb forces

example: nacl

large bond energy (600 - 1500 kj/mol)

properties: high melting point, hard but brittle, electrical insulator, often transparent

why do ionic solids cleave?

after shear is applied, same charge atoms face each other causing the solid to split instead of deforming

covalent bonding

how it works: adjacent atoms share valence electrons, bonds are strong and directional, they point at specific neighboring atoms, fixed bond angles

ex. diamonds, silicon

properties: very strong, directional, hard, usually insulating, set crystal geometry

metallic bonding

how it works: valence electrons are delocalized into a sea of shared electrons. strong, non directional bond

examples: copper, iron, aluminum

properties: ductile, tough, conductive (electricity/heat), opaque, reflective

secondary bonds

van der waals: weak forces between molecules caused by dipole interactions. very weak

hydrogen bonding: H with O, N, F. stronger than van der waals

depth of bond energy curve

deeper well means higher boiling point

width of bond energy curve

wider well means smaller elastic modulus (more flexible)

bond type melting temp

covalent > ionic > metallic > secondary

bond type elastic modulus

covalent > ionic > metallic > secondary

bond type conductivity

metallic : conductor

covalent, ionic, secondary : insulator

bond type ductility

metallic: ductile

secondary: soft

ionic, covalent: brittle

where is each bond type common

ionic: ceramics, salts

covalent: diamond, silicon, polymers

metallic: metals and alloys

secondary: between polymer chains

rank by melting temperature: tungsten, solid argon, diamond

diamond (covalent) > tungsten (metallic) > argon (van der waals)

why is alumina not conductive when copper is?

alumina is covalent

copper is metallic

why do polymers have low boiling points despite having strong covalent bonds?

individual polymer chains are held together with van der waals forces, which are easy to break apart