• Higher Level Class• Monday, May 5• 7:00 pm• Class 3’s classroom• 4th period d-block elements!!

Bonding56-58, 62-70, 165-168, 358-360

• chemical bond: strong electronic attraction between atoms– decreases the P.E. of an atom,

makes it more stable– only the valence electrons are

involved!

• Bond type depends on electronegativity (electron affinity)– very different electronegativities: io

nic•one metal, one non-metal

– both very high: covalent•two non-metals

– both low: metallic•one or more metals

Ionic Bonds

• metal (low electroneg.) + non-metal (high electroneg.)

•Array of positively and negatively charged ions– held together by electrostatic attraction– ions are isoelectronic to noble gases–

have the same electron structure as a noble gas

• metal loses e- = cation– group 1 (+1) and group 2 (+2)– transition metals (+2 most

common)

• non-metal gains e- = anion– groups 17, 16, 15…

sodium and chlorine

• sodium transfers its electron to chlorine

Na Cl

• Polyatomic ions: most covalently bonded, but have an overall electronic charge

Naming Ionic Compounds

• anion ending …ide– Cr(OH)3

– CuF2

– Ca2+ PO43-

• chromium(III) hydroxi

de• copper(II) fluoride• Ca3(PO4)2

– calcium phosphate

Crystal Lattice (Array)

• structure of an ionic bond• each anion is surrounded by

cations and vice versa

Properties of Ionic Compounds• hard•brittle (break easily)• solid• high melting/boiling points• do not conduct electricity as solids• conduct electricity when dissolved in

water (aq) or molten (melted into a liquid) - electrolyte

• more soluble in water than in other solvents

Covalent Bonding

• two non-metals• atoms share some valence

electrons (not transfer)• single covalent bond: shares one

pair of electrons• double: 2 pairs of e-

• triple: 3 pairs of e-

• usually each atom donates (gives) one of each pair of electrons

• dative covalent bond: sometimes one atom donates both electrons

F FElectron PairElectron Pair

Shared by both atomsShared by both atomsEach e- donate by each atomEach e- donate by each atom

• number of bonds formed depends on the number of e- required to fill the valence shell– noble gases = full valence, rarely

form compounds

• octet rule: usually, atoms want 8 valence e- (H, He need 2)

• Ex: C has 4 valence e-– needs 4 more to form a full octet– C forms 4 bonds

• Ex: F has 7 valence e-– needs 1 more to form a full octet– F needs one e-

• Nitrogen?

Bonding between C and F

F

F

F

F C

structural hybrid Lewisformula diagram diagram =e- pair F e- C e- =covalent bond

F

F

F

F CF

F

F

F C

Double Bond

• sharing two pairs of electrons• bonds more strongly than a single

bond

• structural hybrid Lewis

CO O CO OCO O

Triple Bond

• Strongest

NN NN NN

Drawing molecule diagrams

1. Decide how many bonds each atom makes.

2. The central atom is the one that makes the most bonds.

3. Draw with single bonds4. Calculate remaining electrons5. Use remaining electrons

• HCN (hydrogen cyanide) – C=4, N=3, H=1

• HCO2- (methanoate ion)

– H=1, C=4, O=2

Draw structural, hybrid and Lewis structures

• HF

• NH3

• CH4

• CF4

• NO2-

• CHCl3

• NH4+

• H2CO

• SeF2

Length and Strength of Bonds

single double triple

longest shortest

lowest energy highest energy

• covalent bonds holding atoms together in a molecule = strong

• forces between molecules = weaker– covalent molecules are easily separa

ted from one another– soft solids– do not conduct electricity– more soluble in non-polar solvents t

han in water– low melting/boiling points (liquid or

gas at r.t.p.)

– sometimes, a solid lattice is held together with covalent bonds

• covalent network (giant covalent structures): very hard, very high melting/boiling points