2Octet Rule An octet means 8 valence electrons. is associated with the stability of the noble gases.Exception:Helium (He) is stable with 2 valence electrons.valence electronsHeNe 2,Ar 2, 8,Kr 2, 8, 18,Electron level arrangement
8Learning Check A. The number of valence electrons in aluminum is 1) 1e ) 2e-. 3) 3e-.B. The change in electrons for octet requires a1) loss of 3e ) gain of 3e ) a gain of 5e-.C. The ionic charge of aluminum is1) ) ) 3+.D. The symbol for the aluminum ion is1) Al3+. 2) Al3-. 3) Al+.
9Formation of Negative Ions In ionic compounds, nonmetalsachieve an octet arrangement.gain electrons.form negatively charged ions with 3-, 2-, or 1- charges.
14Ionic Compounds Ionic compounds consist of positive and negative ions. have attractions called ionic bonds between positively and negatively charged ions.have high melting and boiling points.are solid at room temperature.
16Ionic Formulas An ionic formula consists of positively and negatively charged ions.is neutral.has charge balance.total positive charge = total negative chargeThe symbol of the metal is written first followed by the symbol of the nonmetal, e.g. NaCl.
20Formula from Ionic Charges Write the ionic formula of the compound with Ba2+ and Cl.Write the symbols of the ions.Ba2+ ClBalance the charges.Ba2+ Cl two Cl- needed ClWrite the ionic formula using a subscript 2 for two chloride ions that give charge balance.BaCl2
21Lets try it out!Select the correct formula for each of the following ionic compounds.A. Na+ and S2-1) NaS 2) Na2S 3) NaS2B. Al3+ and Cl-1) AlCl3 2) AlCl 3) Al3ClC. Mg2+ and N3-1) MgN 2) Mg2N3 3) Mg3N2
26Examples of Ionic Compounds with Two Elements Formula Ions Namecation anionNaCl Na+ Cl- sodium chlorideK2S K S2- potassium sulfideMgO Mg2+ O2- magnesium oxideCaI2 Ca2+ I- calcium iodideAl2O3 Al O2- aluminum oxide
27Learning CheckWrite the formulas and names for compounds of the following ions:Br− S2− N3−Na+Al3+
33Polyatomic Ions A polyatomic ion is a group of atoms. has an overall ionic charge.Some examples of polyatomic ions areNH4+ ammonium OH− hydroxideNO3− nitrate NO2− nitriteCO32− carbonate PO43− phosphateHCO3− hydrogen carbonate(bicarbonate)
36Naming Compounds with Polyatomic Ions The positive ion is named first followed by the name of the polyatomic ion.NaNO3 sodium nitrateK2SO4 potassium sulfateFe(HCO3)3 iron(III) bicarbonateor iron(III) hydrogen carbonate(NH4)3PO3 ammonium phosphite
37Writing Formulas with Polyatomic Ions The formula of an ionic compoundcontaining a polyatomic ion must have a charge balance that equals zero (0).Na+ and NO3− NaNO3with two or more polyatomic ions has the polyatomic ions in parentheses.Mg2+ and 2NO3− Mg(NO3)2subscript 2 for charge balance
39Covalent Bonds Covalent bonds form when atoms share electrons to complete octets.between two nonmetal atoms.between nonmetal atoms from Groups 4A(14), 5A(15), 6A(16), and 7A(17).
40Hydrogen Molecule A hydrogen molecule is stable with two electrons (like helium).has a shared pair of electrons.
41Forming Octets in Molecules In a fluorine, F2,, molecule, each F atomshares one electron.attains an octet.
42Naming Covalent Compounds To name covalent compoundsSTEP 1: Name the first nonmetal as an element.STEP 2: Name the second nonmetal with an ide ending.STEP 3: Use prefixes to indicate the number of atoms (subscript) of each element.Table4.12
43Naming Covalent Compounds What is the name of SO3?1. The first nonmetal is S sulfur.2. The second nonmetal is O named oxide.3. The subscript 3 of O is shown as the prefix tri.SO3 sulfur trioxideThe subscript 1 (for S) or mono is understood.
49Electronegativity The electronegativity value indicates the attraction of an atom for shared electrons.increases from left to right going across a period on the periodic table.is high for the nonmetals with fluorine as the highest.is low for the metals.
51Nonpolar Covalent Bonds A nonpolar covalent bondoccurs between nonmetals.is an equal or almost equal sharing of electrons.has almost no electronegativity difference (0.0 to 0.4).Examples:ElectronegativityAtoms Difference Type of BondN-N = Nonpolar covalentCl-Br = Nonpolar covalentH-Si = Nonpolar covalent
52Polar Covalent Bonds A polar covalent bond occurs between nonmetal atoms.is an unequal sharing of electrons.has a moderate electronegativity difference (0.5 to 1.7).Examples:ElectronegativityAtoms Difference Type of BondO-Cl = 0.5 Polar covalentCl-C = 0.5 Polar covalentO-S = 1.0 Polar covalent
54Ionic Bonds An ionic bond occurs between metal and nonmetal ions. is a result of electron transfer.has a large electronegativity difference (1.8 or more).Examples:ElectronegativityAtoms Difference Type of BondCl-K – 0.8 = IonicN-Na 3.0 – = IonicS-Cs 2.5 – 0.7 = Ionic
55nonpolar covalent (NP), polar covalent (P), or ionic (I). A. K-N Use the electronegativity (see Figure 4.6) difference (Δ) to identify the type of bond between the following asnonpolar covalent (NP), polar covalent (P), orionic (I).A. K-NΔEN = 2.2 ionic (I)B. N-OΔEN = 0.5 polar covalent (P)C. Cl-ClΔEN = 0.0 nonpolar covalent (NP)D. H-ClΔEN = 0.9 polar covalent (P)EN: K=0.8, N=3.0