|
CHEMICAL BONDING Chapter 5 BASIC IDEA - all elements want to be like the noble gases and have their outermost shell filled with electrons. To achieve this goal atoms will (1) share electrons (covalent bonding), (2) give away electrons (ionic bonding), or (3) take electrons (ionic bonding). Covalent
Bonding H · + · H ------> H ··H or H—H or H2 hydrogen gas By sharing their electrons, the Hydrogen atoms have the s shell filled. They ‘feel’ like the noble gas, helium. A single bond means 2 electrons are shared H -- H A double bond means 4 electrons are shared
H H A triple bond means 6 electrons are shared. H-C º C-H Valence electrons - electrons available for bonding +1 Column I of chart has
1 electron H Br H has one electron on outermost level or shell. Br has 7 electrons on outermost level or shell H Br = H-B Ionic BondingAtoms either gives away or takes electrons - no sharing. NaCl Sodium (Na) has 1 electron on the outermost shell. Chlorine (Cl) has 7 electrons on the outermost shell. If Na gives away 1 electron, it will feel like the noble gas, Neon. If chlorine accepts the electron, it will have 8 on its outermost shell and feel like the noble gas Argon (Ar). Na Cl -----> Na+1 Cl-1 Na+ Cl- Na is short one negative charge. Cl got it. Positive ions are called
cations. CaCl2 -----> Ca+2 Cl-1
Ca gives away 2 electrons. ION SIZESMetals - The ion has a smaller diameter than the atom of a given metal. Sodium atom Sodium ion Nonmetals - The ion has a larger diameter than the atom of a given nonmetal.
Chloride atom Chloride ion
IONS MUST HAVE 1. A metal and a non
metal Nomenclature The metal is written
first. NaCl hydride, carbide, fluoride, iodide, nitride, oxide, phosphide sulfide. COVALENT BONDING If an atom can't give away its electron easily and another atom can't accept it, the two atoms will share their electrons. Elements or compounds would like to have 8 electrons. The electrons involved in bonding are called valence electrons. The periodic chart gives us an idea of how the elements will react with each other. Chemical FormulaH2O
2 hydrogens at +1 (+1) (2) = +2 H is special NH3
1 nitrogen at -3
(-3) (1) = -3 carbon tetrachloride CCl4
carbon C = +4
(+4) (1) = +4 CO2
C = +4 (+4) (1) = +4 We have been working with oxidation numbers. Oxidation number or oxidation state is used to tell us the positive or negative character of an atom. When electrons are removed or shifted away during a reaction, the atom is assigned a positive oxidation number. This also works for the ionic compounds Al2O3 Means we have 2 aluminum atoms and 3 oxygen atoms
Al is +3 on
chart (+3) (2) = +6 Na+1 Mg+2 When electrons are
gained, the element is given a negative oxidation number. Cl-1
The algebraic sum of the positive oxidation number and the negative oxidation number of the atoms and ions present in a compound must always be zero. MgO CaBr2 Polar vs Non Polar Covalent BondingSome atoms will have a greater strength for pulling electrons to itself than other atoms. Sometimes in sharing (covalent) electrons one of the atoms has a greater pull on the electrons. Electrons have a negative charge. So the atoms that can pull the electrons strongly have a greater electronegativity value.
Electronegativity Values
H Li Be B C N
O F Na Mg Al Si
P S Cl K
Ca Br If the difference
between two electronegativity values is If the difference is zero we have non polar covalent If the difference
is greater than zero and less than Do MgO NaCl CH4 ELEMENTS AND OXIDATION NUMBERS Pages 127 - 136 Look at the chart for
most of the numbers.
H +1
F -1 Radicals - Ions Page 135 ( ) Everything inside the brackets stays together and acts as an "element" - ion. (NH4)+1 Ammonium ion (OH)-1 Hydroxide ion H(OH) - water (NO3)-1 Nitrate (CO3)-2 Carbonate (SO4)-2 Sulfate (PO4)-3 Phosphate NomenclatureDo the element on the left first Mg(SO4) Magnesium sulfate
Sometimes you can have two elements come together in more than one ratio. NO N2O N2O3 nitrogen monoxide dinitrogen monoxide dinitrogen trioxide
1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 ennea- 10 deca- We will work primarily
with just one or two values. For example oxygen will be nitrogen +5 or -3
Let's see what the formulas of the following would be.
What would the formula be for sodium carbonate? Na(CO)3 Na+1 (CO3)-2
Na2(CO3) Na2+1(CO3)1-2 (NH4)(OH) Is it balanced: Ca (NO3) Na (NO3) Na (SO4) Ca (PO4) Al (SO4)
Multiple Valences for Metals Fe Iron +2, +3 Ferrous +2 Ferric +3 Cu Copper +1, +2 Cuprous +1 Cupric +2 Hg Mercury +1, +2 Mercurous +1 Mercuric +2 Sn Tin +2, +4 Stannous +2 Stannic +4 Pb Lead +2, +4 Lead II Lead IV Write the formulas using the appropriate subscripts: Stannic chloride Find the oxidation state of Mn in the compound KMnO4 . Given K = +1 O = -2 BALANCING EQUATIONS Pages 160 - 162
No quick, easy way. Requirements: pencil + eraser + patience The number of atoms on the left side of the equation has to equal the number of atoms on the right side of the equation.
Left Right
When balancing equations LEAVE THE SUBSCRIPTS ALONE, work with the coefficients. 1. In Al2(SO4)3 a) the number of atoms of Al is _____. b) the number of atoms of S in the formula is _____. c) the number of atoms of oxygen in the formula is ______. 2. Balance the following equations: [*H2O can also be written as H(OH)] (a) ____H2 + ____ N2 -------> ____NH3 (b) ____C3H6 + ___O2 --------> ____ CO2 + ____ H2O (c) ____ Na + ____ HCl ------> ____ Na Cl + ____ H2 (d) ____ Na + ____ H2O -------> ____ NaOH + ____ H2 (e) ____HCl + ____ NaOH -------> ____NaCl + ____ H2O* (f) ____ HCl + ____Ca(OH)2 -------> ____CaCl2 + ____H2O* (g) ____H2(SO4) + ____Na(OH) ------> _____Na2(SO4) + ____H2O* (h) ____H2(SO4) + ___ Ca(OH)2 -------> ____ Ca(SO4) + ___H2O* (i) ____Al + ___H(NO3) -------> ____ Al(NO3)3 + ____ H2 (j) ____ Fe + ____ H2(SO4) -------> ____ Fe(SO4) + ____ H2 |
|
Wednesday, March 21, 2007 01:28:03 PM |