• metals: lose valence electrons – formform cation cation (+ ion)

• non-metals: gain electrons –form anionanion (- ion)

Ionic Bond

• occurs between:

metalmetal element & non-metal non-metal elementelement

• involves involves transfer of electrons transfer of electrons between between metal & non-metal elements to form metal & non-metal elements to form ionsions

• # electrons# electrons lost lost by by cation(s)cation(s)

= # electrons = # electrons gainedgained by by anion(s)anion(s)

Metals are Losers!Metals are Losers!

• Na atom configuration: 2-8-1

• Na loses 1 electron → Na+1 ion–Na+1 configuration is 2-8

• same as Ne configuration (2-8)

Na metal Na metal

elements from what group _?_ will easily taketake the one valence electron from Na??

what group has 7 valence electrons so only need one more?

group 1 elements will easily give up their one valence electron to the elements in group 17

Non-metals are Winners!Non-metals are Winners!

• Cl configuration: 2-8-7• Cl gains 1 electron → Cl-1 ion

–Cl-1 has the configuration 2-8-8 • same as Ar configuration (2-8-8)

ClCl22 (g) (g)

electron electron transferredtransferred from Na to Cl from Na to Cl

http://images.google.com/imgres?imgurl=http://cougar.slvhs.slv.k12.ca.us/~pboomer/chemlectures/bonding/metallic.jpg&imgrefurl=http://cougar.slvhs.slv.k12.ca.us/~pboomer/chemlectures/bonding/bonding.html&h=363&w=504&sz=113&tbnid=HNZqIdFN6nEJ:&tbnh=92&tbnw=

Structure of Ionic Compounds

• oppositely charged ions are attracted to each other by strong electrostatic interactions (+/-)

• (+/-) ions form crystal lattice – regular 3-D pattern or array – ions held in fixed positions (solid state)

• Unit Cell = smallest repetitive unit in lattice

lattice structure lattice structure

NaCl has its own NaCl has its own unique propertiesunique properties

The more Na and ClThe more Na and Cl22, the , the larger the resulting crystal oflarger the resulting crystal of NaCl will beNaCl will be

different representations different representations of a crystal latticeof a crystal lattice

Lewis Diagrams for Ionic Compounds

Lewis structure for NaCl shows ions:Lewis structure for NaCl shows ions:

[[NaNa]]+1+1[ [ ClCl ]]-1-1••••

•• ••

•• ••

••••

remember: Lewis diagrams show remember: Lewis diagrams show valencevalence electrons! electrons!

Predicting Ionic Compounds

• What is the ionic compound formed from What is the ionic compound formed from calcium and iodine?calcium and iodine?

• calcium: metal with 2 valence electrons calcium: metal with 2 valence electrons - loses both electrons - loses both electrons [[CaCa]]+2+2

• iodine: non-metal with 7 valence electrons iodine: non-metal with 7 valence electrons - gains 1 electron - gains 1 electron [[ I I ]]-1-1

• how many iodine ions are needed to make a how many iodine ions are needed to make a neutral compound?neutral compound? 22

••

•••• •

•

Lewis Diagram of calcium iodide (CaI2)

[[CaCa]]+2+2[:[:II:]:]-1-1[:[:II:]:]-1-1 or or [:[:II:]:]-1-1[[CaCa]]+2+2[:[:II:]:]-1-1

note: total charge MUST add up to zero note: total charge MUST add up to zero

since compounds are neutral since compounds are neutral

········

········

····

····

····

····

Properties of Ionic Compounds

• high melting points

• low vapor pressures

• tend to be hard and brittle

• solids do not conduct electricity

• molten (liquid) states do conduct electricity

• aqueous solutions do conduct electricity

#1:transfer of e- from metal to non-metal atoms: IONS form

#2:electrostatic attraction between +/- ions leads to ionic bond