Chemical Bonding Chemistry Unit 6

How do atoms make compounds? EQ How do atoms make compounds?

Review- Oxidation numbers Write the Lewis Dot Diagram and give the oxidation number of the following. S O Ca Na P Al

Bonding Chemical bond- hold two or more atoms held together to make each have 8 valence electrons Who they bond with is determined by their oxidation number Atoms gain, lose, or share electrons to get 8 valence electrons (Octet Rule)

Compounds are always neutral IMPORTANT Compounds are always neutral For ex-NaCl Na = oxidation #= 1+ Cl = oxidation # = 1- Total charge on NaCl = 0= neutral For ex- CaF2 Ca= oxidation # = 2+ F = oxidation # = 1- F2 = 2- Total charge = 0 = neutral

Types of bonds Ionic- cation (metal) and anion (nonmetal) bond based on oxidation number; metal loses electrons, nonmetal gains electrons Covalent- nonmetal and nonmetal share electrons Metallic- two metals share electrons

The number of electrons an atom has gained, lost or shared Oxidation number The number of electrons an atom has gained, lost or shared STABLE Tells about To become

Group Number Oxidation number Oxidation numbers of elements can be found by GROUP #s on the periodic table. Group Number Oxidation number Group # 1 1+ Group # 2 2+ Group # 13 3+ Group # 14 4+ Group # 15 3- Group # 16 2- Group # 17 ( halogens) 1- Group # 18 ( Noble Gases)

Ones and Twos When do chemical bonds form? Who is more reactive: alkali metals or alkaline earth metals? Give the number of valence electrons for oxygen, sulfur, arsenic, phosphorous, and bromine. Why does calcium form a +2 ion instead of a +3 ion?

Is a compound made up of 2 elements Binary Compound Is a compound made up of 2 elements Na Cl For ex- NaCl is made up of 2 elements

Review- Write the answers in your notebook Which of the following compounds are Binary Compounds? KCl H2SO4 CO2 KI PO4 P2O5 CaSO4

Types of Bonds Purpose- to make atoms more stable How e- are distributed determines the type of bond Ionic- electrical attraction b/t cation & anions Covalent- sharing of e- pairs b/t two atoms

Vocab Cations- positive ions Anions- negative ions Electronegativity- the ability of an atom to attract electrons; used to estimate if the bond is ionic or covalent Diatomic- two of the same (the gases)

Ionic Bonding & Ionic Compounds Chap 8

Basics of Ionic Bonds Bonding of metal + nonmetal WS- Types of Chemical bonds Transfer of electrons Metal loses e- (cation) nonmetal gains e- (anion) Ionic charges cancel in the bonding

Formula unit- the smallest formula for an ionic compound Ex: table salt is composed of lots of atoms, but the formula is written NaCl The ratio of ions in the formula unit depends upon the oxidation numbers on the atoms

Characteristics of Ionic Bonds Lattice energy- the energy required to form an ionic compound (bond energy is specific to breaking a bond) Negative values indicate that energy is released Positive values indicate that energy is absorbed

Properties of Ionic vs. Molecular Compounds *very strong bond b/c very strong attractive force High melting point (do not vaporize at room temp) High boiling point Hard & brittle crystal lattice: ordered repetition of pos & neg charges Good conductors (if they can dissolve in water) Made of metal & nonmetal *Strong bond, but weak attractive force Low melting point (most are gaseous at room temp) Low boiling point Usually a gas at room temp, soft solids, some liquids Poor conductors Made of nonmetals

Polyatomic Ions Polyatomic Ion- a charged group of covalently bonded atoms; covalently bonded, yet behaves like an ion Pg 224 Table 8-6

Summary Answer the EQ- share your answer with the person next to you AFTER you write (that means write THEN talk)

Molecular Compounds Chap 9

Molecule- neutral group of atoms covalently bonded together Molecular compound- many molecules bonded together Electrons are shared b/t atoms in a covalent bond so they all have 8 valence electrons

Lewis structures- demonstrate covalent bonding Draw the elements symbol Draw the number of valence electrons

Practice- Lewis Structures Pg 244 #1-5 Pg 247 #12

Ionic or Covalent? If two of the same atom are bonded together, then it is completely covalent Nonpolar covalent- bonding e are shared equally; 0-5% ionic character or 0-0.3 EN difference Polar covalent- uneven sharing of e; 5-50% ionic character or 0.3-1.7 EN difference

Naming Molecular Compounds (prefix)1st element + (prefix) root 2nd element Ex. P2O5 diphosphorous pentoxide

# of Atoms Prefix 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca

Ionic or Covalent? EN values < 1.7 is a covalent bond b/c the bond has 50% or less ionic characteristics The bond is ionic if the EN difference is > 1.7 Anions attract e- Cations give away e-

Practice Pg 249 # 13-17

Compare and contrast ionic and covalent bonds Ionic bonds __________ ___________ Covalent bonds ________ _________

Naming Acids Oxyacids- contain hydrogen and an oxyanion (PI with oxygen in it) Replace –ate with –ic Replace –ite with –ous Ex. HNO3 nitrate  nitric acid Binary Acids- contains H and one other element Hydro + element + ic Ex. HCl = hydrochloric acid

Practice- Naming Acids Pg 250 # 18-22

Know the symbols for partial negative charge on the covalent bond (δ-) and partial positive charge (δ+) Know how to tell the bond type based upon EN values