Transcript Chapter 8 Ionic Bonding

Chapter 8
Ionic Bonding
Ionic Compounds/ Chemical Bnds
 Chem Bond: force that holds 2 atoms
together.
 Arises from attraction of positive nucleus
and neg. e’s
 Or from attraction of positive ions and
neg.ions
 Review valence e’s and dot structures
Formation of + ions (cations)
 When atom loses one or more valence e’s
to have octet.
 Atom will become ion and become +.
 1e lost→+1 ion, 2e’s lost →+2 ion, 3e’s lost
→+ 3 ion
 Then ion will have e config. of noble gas.
– Na+ has config. of [Ne] from [Ne]3s1
– Mg+2 has config. of [Ne] from [Ne]3s2
Formation of Negative Ions (Anions)
 On right side of P.T. nonmetals will not lose
e’s, but gain e’s.
 F atom has config. of [He]2s22p5, gains 1e
to be [He] 2s22p6 or [Ne].
 S atom has config. of [Ne]3s23p4, gains 2e
to be [Ne]3s23p6 or [Ar].
 These ions(+ or -) do not become those
noble gases; their e’s are just in same
places and have same stability.
Result?
 Then + ions (cations) attract – ions (anions).
Not just one attracting one other, but large
numbers of each come together to form a
crystal-lattice. See p217
 Greater the attractions between +and –
ions, the higher the m.pt., b.pt., and
hardness. (Requires more energy to break
strong bonds.)
Names & formulas for Ionic Cpds.
 Simplest ratio of ions (formula) is called a
formula unit.
 NaCl, MgBr2, KI are technically formula
units, not molecules.
Oxidation Number of Ions
 Sometimes called charge or oxidation state.
 Both interchangeable.
 Many transition metals have multiple ox.
Numbers.
 Gr I is +1, Gr II is +2.
To write correct formula
 Write ions with charges, put + 1st, then –ion.
 Check to see if charges add up to zero.
– If so, write as is.
– If not, cross charge numbers (not sign).
– Multiply up and check for adding up to zero.
– CHARGE OF COMPOUND must be ZERO.
 Examples: sodium sulfide, aluminum
chloride, magnesium oxide, calcium iodide.
P. 224-226.
 If polyatomic ion, same idea.
 Transparency, 8-5
Metallic Bonds and Properties of
Metals
 Metals are not ionic, but have some similar
characteristics.
 Why? Because ionic cpds. Have + and –
particles and metals have + and – regions
as well.
 Metals’ structure sometimes is referred to as
a “sea of electrons” or delocalized e’s.
 This means there are + nuclei lined up and
e’s from those metal atoms flow in and out
around those nuclei.
 See p. 228 or draw on board.
 This “sea” causes a number of specific
metallic properties.
– High m.pt., and b.pt.
– Malleable, ductile, lustrous
Metal alloys
 A mixture of elements with metallic
properties.
 Steel is Fe and other elements.
 2 types alloys
– Substitutional: some atoms are replaced by
other metal atoms. (brass- copper & zinc)
– Interstitial: has small holes filled by other small
atoms. (carbon steel)