Chemical Bonds
008: Chemical Bonds Bonding: the way atoms are attracted to each other to form molecules, determines nearly all of the chemical properties we see. And, as we shall see, the number 8 is very important to chemical bonding.
Molecule 2 atoms chemically combined, smallest part of compound Compounds atoms of 2 or more elements chemically combined, new properties not like the elements it is made of Law of Definite Proportions atoms combine in proportions, whole number ratios. H 2 O = 2 H for every O
Atoms combine so that their outer energy level is full Bonds force of attraction that holds atoms together in a molecule Octet Rule - all elements want to be happy!!! 8e- in outer level, like the noble gases When atoms combine, electrons are shared or exchanged
Atoms are electrically neutral (p+ = e-) Ions - Atoms with a charge due to gain or loss of e- Cation - +charge, lost e-, have more p+ than e- Anion - charge, gained e-, fewer p+ than e- Polyatomic ions group of atoms acting together and carrying a charge
8 e- in outer level 1 e- in outer level 7 e- in outer level
Ionic Bonds: transfer e- How can we make Na and Cl happy? Na gives up e- to Cl Chemical Formula = NaCl
The positive and negative ions are attracted to each other
The Lewis dot structure for Chlorine Cl chlorine is in group VIIA so it has 7 valence electrons
The Lewis dot structure for calcium Ca calcium is in group IIA so it has 2 valence electrons
Making calcium chloride Ca + Cl Cl Ca( Cl ) 2
Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become - ions.
Potassium & Fluorine K + and F - KF Potassium fluoride Aluminum oxide Al +3 O -2 Cross multiply (LCM=6) Al 2 O 3 +6-6=0 charge
Give up electrons Acquire electrons He - Ne - Ar - Kr - Xe - Rn - F 4.0 Cl 3.0 Br 2.8 I 2.5 At 2.2 Li 1.0 Na 0.9 K 0.8 Rb 0.8 Cs 0.7 Fr 0.7 H 2.1 Be 1.5 Mg 1.2 Ca 1.0 Sr 1.0 Ba 0.9 Ra 0.9 Ti 1.5 Cr 1.6 Fe 1.8 Ni 1.8 Zn 1.8 As 2.0 CsCl MgO CaF2 NaCl O 3.5
Na + + Cl - = NaCl Ca +2 + O -2 = CaO Ca +2 + Cl - = CaCl 2 Na + + O -2 = Na 2 O Al +3 + S -2 = Al 2 S 3 Ca +2 + N -3 = Ca 3 N 2 You try these! Li + + Br - = LiBr Mg +2 + F - = MgF 2 Al +3 + I - = AlI 3 NH 4+ + PO -3 4 = (NH 4 ) 3 PO 4 Sr +2 + P -3 = Sr 3 P 2 K + + Cl - = Not NH KCl 43 PO 4
METALLIC BONDS e- are shared by all atoms sea of electrons allow current to flow through metal = conductors In sodium, 1 out of the 11 electrons is released so that Na has two filled shells. The extra electrons move around the metal in a sea of negative charge. This negatively charged sea moves around a regular structure of positive Na ions.
Atoms share electrons Polar Covalent result of uneven sharing, ends have slight +/- charges Ex. Water
Single bond: sharing 1 pair of e- Double bond: sharing 2 pairs of e- Triple bond: sharing 3 pairs of e-
He - Ne - Ar - Kr - Xe - Rn - F 4.0 Cl 3.0 Br 2.8 I 2.5 At 2.2 Li 1.0 Na 0.9 K 0.8 Rb 0.8 Cs 0.7 Fr 0.7 H 2.1 Be 1.5 Mg 1.2 Ca 1.0 Sr 1.0 Ba 0.9 Ra 0.9 Ti 1.5 Cr 1.6 Fe 1.8 Ni 1.8 Zn 1.8 As 2.0 SiC C(diamond) H2O C 2.5 H2 Cl2 F2 Si 1.8 Ga 1.6 GaAs Ge 1.8 O 2.0 column IVA Sn 1.8 Pb 1.8 3.5
Lewis dot structure of a compound NH 3 1) How many valence electrons does N have? N is in group VA so it has 5 valence electrons 2) How many valence electrons does H have? H is in group IA so each H has 1 valence electron 3) How many total valence electrons are there in this molecule? (3 x 1) + 5 = 8 You know it had to be 8 because it has NO CHARGE!
Lewis dot structure of a compound NH 3 H N H H
Non-polar: e- are shared equally btwn atoms Bonding between atoms of the same element or atoms close to each other on table Polar: uneven distribution of charge unequal attraction for the shared e-
MOLECULAR ATTRACTIONS Polar molecules are more positively charged on one side and more negative on the other. http://programs.northlandcollege.edu/biology/biology1111/animation s/hydrogenbonds.html
Tendency of an atom to attract a pair of e- to itself when bonded Ionic bonds: atoms differ greatly Covalent bonds: atoms similar Polar covalent: moderate difference Increases from left to right & decreases from top to bottom
Ranges from 0.7 to 4.0, Large values: tendency to acquire electrons. Smaller electronegativity Larger electronegativity
http://www.chem.iastate.edu/group/greenbowe/sect ions/projectfolder/flashfiles/reaction/bonding1.swf Metallic Ionic Covalent Polar Nonpolar Hydrogen
Combining ability of an atom: how many e- it will gain or lose written as a superscript (top right) Oxygen: O -2 gains 2 e- The sum of oxidation numbers in a compound must be zero H +1 & O -2 = H 2 O each O needs 2 H atoms
Write symbol of element w/ + oxidation# Write symbol of element w/ - oxidation # Add subscripts so that sum of oxidation #s is zero cross multiply Use (parenthesis) around the +1 polyatomic ions (NH 4 ) 2
Write name of cation or + polyatomic ion if it has multiple oxidation numbers, write the charge as a Roman Numeral Fe 2+ would be iron (II) ion and Fe 3+ would be iron (III) ion Write name of polyatomic ion, if it is an anion, write the root name and change the ending to ide
Naming the ions Names of main-group monatomic ions are straightforward. A cation takes the name of the element plus the word "ion." Na Sr Ba Na + sodium ion Sr 2+ strontium ion Ba 2+ barium ion
For anions, the element name has its ending replaced with ide. N O Cl N 3- nitride ion O 2- oxide ion Cl - chloride ion
Example calcium chloride calcium is Ca 2+ and chlorine is Cl - in order to balance charges there needs to be two negative charges to balance the 2+ on the calcium +2-1
Common polyatomic ion names Formula NH + 4 CO 2-3 PO 3-4 SO 2-4 OH - NO - 3 Name Ammonium ion Carbonate ion Phosphate ion Sulfate ion Hydroxide ion Nitrate ion
Anions + Cations = ionic compound name F- Fluoride ion CO 3 2- PO 4 3- SO 4 2- OH - NO 3 - Cl - O 2- S 2- Carbonate ion Phosphate ion Sulfate ion Hydroxide ion Nitrate ion Chloride ion Oxide ion Sulfide ion NH 4+ Na + Ca 2+ Fe 3+ Ag + Al 3+ Ammonium ion Sodium ion Calcium ion Iron(III) ion Silver ion Aluminum ion Ammonium fluoride Iron phosphate Silver oxide Note: Ag has a charge of +1 and oxide has a charge of 2 so the chemical formula of silver oxide must be Ag 2 O
What is the correct name for the ionic compound Na SO? 2 4 A. disodium sulfate B. sodium sulfoxide C. sodium sulfate D. sodium sulfide
Covalent compounds CO 2 Carbon Dioxide H 2 O Dihydrogen Monoxide
Carbon tetrachloride is A. CCl 4 B. CClO 4 C. C 2 Cl 4 D. CCl 5 TETRA = 4
POLYATOMIC IONS (-1 CHARGE) H 2 PO 4 C 2 H 3 O 2 HSO 3 HCO 3 NO 2 NO 3 CN OH MnO 4 ClO ClO 2 ClO 3 ClO 4 DiHydrogen phosphate Acetate Hydrogen Sulfite Hydrogen Carbonate Nitrite Nitrate Cyanide Hydroxide Permanganate Hypochlorite Chlorite Chlorate Perchlorate
POLYATOMIC IONS (-2 CHARGE) HPO 4 C 2 O 4 SO 3 SO 4 CO 3 CrO 4 Cr 2 O 7 SiO 3 Hydrogen Phosphate Oxalate Sulfite Sulfate Carbonate Chromate Dichromate Silicate
POLYATOMIC IONS (-3 CHARGE) PO 3 PO 4 Phosphite Phosphate
Rule 1 If two identical elements combine then the name doesn t change This happens with the following elements: 1) H 2 2) N 2 3) O 2 4) F 2 5) Cl 2 6) Br 2 These elements always go around in pairs (diatomic molecules). For example, hydrogen looks like this
Rule 2 When two elements join and one is a halogen, oxygen or sulphur the name ends with ide e.g. Magnesium + oxygen magnesium oxide 1) Sodium + chlorine 2) Magnesium + fluorine 3) Lithium + iodine 4) Chlorine + copper 5) Oxygen + iron 6) KBr 7) LiCl 8) CaO 9) MgS 10)KF
Rule 3 When three or more elements combine and two of them are hydrogen and oxygen the name ends with hydroxide e.g. Sodium + hydrogen + oxygen Sodium hydroxide 1) Potassium + hydrogen + oxygen 2) Lithium + hydrogen + oxygen 3) Calcium + hydrogen + oxygen 4) Mg(OH) 2
Rule 4 When three or more elements combine and one of them is oxygen the ending is ate e.g. Copper + sulphur + oxygen Copper sulphate 1) Calcium + carbon + oxygen 2) Potassium + carbon + oxygen 3) Calcium + sulphur + oxygen 4) Magnesium + chlorine + oxygen 5) Calcium + oxygen + nitrogen 6) AgNO 3 7) H 2 SO 4 8) K 2 CO 3
Covalent formulas Ionic formulas H 2 O Water NaCl Sodium chloride CO 2 NH 3 H 2 O 2 Carbon dioxide Ammonia Hydrogen Oxygen CaCl 2 MgO HCl H 2 SO 4 HNO 3 Calcium chloride Magnesium oxide Hydrochloric acid Sulphuric acid Nitric acid N 2 Nitrogen NaOH Sodium hydroxide SO 2 Sulphur dioxide Ca(OH) 2 CaCO 3 Calcium hydroxide Calcium carbonate Al 2 O 3 Aluminium oxide Fe 2 O 3 Iron oxide
Even though all atoms want the same number of electrons as the Noble Gases, some want to get or give them more than others. The magnitude of this attraction for electrons is called Electronegativity. The more electronegative an atom is, the more it wants the electrons. Some atoms want to gain electrons so bad, they take them altogether to form negative ions. Some want to lose them so bad that they become positive ions.
HCl The Chlorine wants the electrons more than the Hydrogen. Thus we have +δ HCl -δ. NaCl Since Na is a metal it gives up its electron to form Na + and Cl takes the electron completely to form Cl -. Cl 2 (Cl Cl) The Chlorine molecules want the electrons equally so they form a non-polar molecule with NO partial or full charges. H 2 O Water is a bent molecule. The lone pair of electrons from the Lewis structure distorts its shape and it becomes a very polar molecule... :O:H.... O::C::O H CO 2 Carbon Dioxide is a linear molecule. It has no lone pairs of electrons from the Lewis structure. The two oxygen atoms pull equally and make it a non-polar molecule.
Binary Compounds have two types of atoms (not diatomic which has only two atoms). Metals (Groups I, II, and III) and Non-Metals Metal Sodium + Non-Metal ide Chlorine Sodium Chloride NaCl Metals (Transition Metals) and Non-Metals Metal Iron +Roman Numeral ( ) III + Non-Metal ide Bromine Iron (III) Bromide FeBr 3 Compare with Iron (II) Bromide FeBr 2
Metals (Transition Metals) and Non-Metals Older System Metal (Latin) Ferrous + ous or ic + Non-Metal ide Bromine Ferrous Bromide FeBr 2 Compare with Ferric Bromide FeBr 3 Non-Metals and Non-Metals Use Prefixes such as mono, di, tri, tetra, penta, hexa, hepta, etc. CO 2 Carbon dioxide CO Carbon monoxide PCl 3 Phosphorus trichloride CCl 4 Carbon tetrachloride N 2 O 5 Dinitrogen pentoxide CS 2 Carbon disulfide
Name the following. CaF 2 K 2 S CoI 2 SnF 2 SnF 4 OF 2 CuI 2 CuI SO 2 SrS LiBr Calcium Flouride Potassium Sulfide Cobalt (II) Iodide or Cobaltous Iodide Tin (II) Flouride or Stannous Flouride Tin (IV) Flouride or Stannic Flouride Oxygen diflouride Copper (II) Iodide or Cupric Iodide Copper (I) Iodide or Cuprous Iodide Sulfur dioxide Strontium Sulfide Lithium Bromide
Ammonium... NH + 4 Nitrate NO - 3 Permanganate. MnO -. 4 Chlorate ClO - 3 Hydroxide. OH - Cyanide. CN - Sulfate... SO 2-4 Carbonate. CO 2-3 Chromate.. CrO 2-4 Acetate.. C 2 H 3 O - 2 Phosphate. PO 3-4