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