Chapter 6

Chemical Bonds

6.1 Ionic BondingStable electron configuration – when the

highest occupied energy level of an atom is filled with electrons, it is stable and not likely to react

Ex. = Noble Gases

(He = 2 v.e., others = 8 v.e.) “8 is great”Nature always strives for stability (8 v.e.)Need to be able to see the electron

configuration

Electron Dot DiagramA model to show the valence electrons for

any elementDeveloped by G.N. Lewis in 1916Only shows Symbol & valence electrons

Ex. H He

Li Be B

C N

O F Ne

Ionic BondsElements that have unfilled outer energy

levels (incomplete sets of v.e.) tend to react with other elements

Some elements achieve a stable electron configuration through transfer of electrons between atoms

Ex. Na + Cl → Na+ Cl -

Formation of Ions

When an atom gains or loses an electron, the # of protons & electrons is no longer =

The charge on the atom is not balanced and the atom is not neutral

An atom that has a + or – electric charge is called an ion

We show this by placing a plus or minus sign by the symbol

IonsAnion = is an ion which has gained an

electron (Cl- in the last slide) “a negative ion” = anion

(anion = has one extra electron)Name it by the root & -ide (ex. Chloride)Cation = is an ion which has lost an

electron (Na+ in the last slide)

(cation = has one fewer electron)Name it by element only (ex. Sodium ion)

Bonds

Chemical Bond = force that holds atoms or ions together as a unit

Ionic bond = force that holds cations & anions together when electrons are transferred from one atom to another

Covalent bond = chemical bond where 2 atoms share a pair of electrons

Ionization Energy It takes more energy to remove an electron from

Fluorine than from a metal in Group 1 Easiest to remove from the bottom of Group 1 Ionization energy generally increases as you

move up the P.T. Generally Increases

& toward nonmetals

Generally

Increases

Ionic CompoundsCompounds with Ionic bonds are Ionic

CompoundsChemical Formulas show the ratio of the

atoms or ions of elements in the compound (subscript # tells how many)

If there is only 1, subscript is not neededNaCl = 1 Na (Sodium ion) &

1 Cl (Chloride ion)? How many of each in MgCl2, CO2, Al2S3

Crystal Lattices

Chemical formula tells you the ratio of ions in a compound but not how they are arranged

Solid particles in a lattice structure are called crystals (they have flat sides naturally)

Properties of Ionic CompoundsHigh melting point (ex: NaCl = 801°C) In solid state = poor conductor, but in

melted state = good conductor of electricity

Crystals shatter when struck by a hammer

Properties of an ionic compound can be explained by the strong attractions among ions within a crystalline lattice

Cave of Crystals – in Mexico

6.2 Covalent BondingCovalent Bonding

= sharing electrons (“cooperating”)Nonmetals form covalent bondsEx. = H2

Electron Dot Diagram Structural Formula

H H H HDiatomic molecules (2 atoms) –gens & -inesMolecule = neutral group of atoms joined

by 1 or more covalent bonds

Multiple Covalent BondsMore than 1 pair of electrons can be

sharedRepresented by a long dash between the

element symbols

Ex. N N shows a triple bond between Nitrogen atoms

Ex. H H shows single & double bonds

C C

H H

Unequal Sharing of Electrons

In general elements on the right side of the P.T. have a greater attraction for electrons than elements on the left

(except Noble Gases)Element w/ strongest attraction =

Fluorine

Polar Covalent BondsA covalent bond where the electrons are

not shared equally is called a polar covalent bond

The atom with the greater attraction for electrons has a partial negative charge & the other atom has a partial positive charge

Type of atoms & shape (arrangement) determine if the molecule is polar or nonpolar

Attraction is stronger b/t polar molecules

6.3 Naming Compounds & Formulas

Binary Ionic Compounds – easiest b/c we use the name of the cation & then the anion with –ide on the end of the root name

NaCl = Sodium Chlor ide = Sodium ChlorideCaO = ?Calcium + Ox + ide = ?Calcium Oxide

Common Anions (P. 171 chart)

F = Fluorine = Fluor + ideCl = Chlorine = Chlor + ideBr = Bromine = Brom + ide I = Iodine = Iod + ideO = Oxygen = Ox + ideS = Sulfur = Sulf + ideN = Nitrogen = Nitr + ideP = Phosphorus = Phosph + ide

Some Metal Cations (p. 172)

Copper(I) = Cu+

Copper(II) = Cu+2

Iron(II) = Fe+2

Iron(III) = Fe+3

Lead(II) = Pb+2

Lead(IV) = Pb+4

Notice the Roman Numerals in parentheses

Chromium(II) = Cr+2

Chromium(III) = Cr+3

Titanium(II) = Ti+2

Titanium(III) = Ti+3

Titanium(IV) = Ti+4

Mercury(II) = Hg+2

= tells you what the oxidation # is for that isotope of the element

Some Polyatomic Ions (p. 173)

Ammonium NH4+

Hydroxide OH-

Nitrate NO3-

Sulfate SO4-2

Carbonate CO3-2

Phosphate PO4-3

Chromate CrO4-2

Silicate SiO3-2

Acetate C2H3O2-

Peroxide O2-2

Permanganate MnO4-

Hydrogen Sulfate HSO4-

Hydrogen Carbonate HCO3

-

Hydrogen Phosphate HPO4

-2

Dichromate Cr2O7-2

Hypochlorite OCl-

Prefixes for Naming Compounds

1 = mono2 = di3 = tri4 = tetra5 = penta

6 = hexa7 = hepta8 = octa9 = nona10 = deca

If a formula gives you prefixes, use those numbers regardless of balancing

Writing the Formula If you know the name, you can write the

formula1st write symbol for the cation2nd write symbol for the anion3rd add subscripts to show the ratio of the

ions in the compound (total charges must = 0 “neutral”)H+1 O-2 looks like H2O for it to be

balanced or neutral It takes 2 H+1 to balance or neutralize 1 O-2

Write the Formula Calcium Oxide Copper (I) Sulfide Sodium Sulfate Sodium Hydroxide Lithium Oxide Iron (III) Oxide Nitrogen Dioxide Dinitrogen Tetraoxide Sodium Pentoxide Diphosphorus Tetrafluoride

Write the FormulaCalcium OxideCopper (I) SulfideSodium SulfateSodium HydroxideLithium Oxide Iron (III) OxideNitrogen DioxideDinitrogen

TetraoxideSodium PentoxideDiphosphorus

Tetrafluoride

CaOCu2SNa2SO4

NaOHLi2OFe2O3

NO2

N2O4

NaO5

P2F4

6.4 Metallic BondsMetallic bond = the attraction b/t a metal

cation & the shared electrons that surround it

In a metal = valence electrons are free to move around the atoms

This is why metals are malleable & ductileMetals w/ less v.e. are not as strong as

those with more v.e. (ex. Sodium can be cut with a butter knife, but Tungsten is harder and has a higher melting pt.)

Alloys

Alloys = mixture of 2 or more elements where at least 1 is a metal & they have the characteristic properties of a metal

Gold = 24kt = 100% pure (soft, bends)

18kt = 75%

14kt = 58%

12kt = 50% (stronger)

Other Alloys

Bronze = alloy of copper & tinboth are soft metals but are harder and

stronger when put together in an alloyUsed for propellers on ships and statues

Brass = alloy of copper & zincbrass is softer & can be shaped easierUsed for instruments (French Horn, bells)

Other Alloys (cont’d)Steel = alloy of Iron & small amt of CarbonCarbon bonds with Iron and makes it

stronger than iron aloneStainless Steel has Chromium and very

little Carbon in the alloy with IronSteel wires used as bridge cables have S,

Mn, P, Si, and C mixed with Fe to allow the cables to resist breaking when they are pulled.

Steel wires used as bridge cables have S, Mn, P, Si, and C mixed with Fe to allow the cables to resist breaking when they are pulled.

Study for your TEST

Friday, March 21, on Ch. 6

Ch. 7 when we come back from Spring Break

We will have vocabulary quiz for Ch. 7 on Thursday, April 3

TESTFriday, 3/21

Know your chemical names and formulas

This sign appeared at Louisville Waterfront Park

It was posted on the large water fountain in the park