IONIC BONDS Chapter 4 Section 1

Octet Rule: Atoms “want” 8 valence electrons to be stable Review Octet Rule: Atoms “want” 8 valence electrons to be stable some atoms have “extra” valence electrons some atoms “need” more valence electrons

Review Shortcut to know the number of valence electrons...1’s digit of group number Group 1  1 valence electron Group 2  2 valence electrons Group 13  3 valence electrons Group 14  4 valence electrons Group 15  5 valence electrons Group 16  6 valence electrons Group 17  7 valence electrons Group 18  8 valence electrons

Ion – atom or group of atoms that has become electrically charged Ions Ion – atom or group of atoms that has become electrically charged Atoms become ions by… losing an electron more protons than electrons  becomes positive gaining an electron more electrons than protons  becomes negative

Charges The charge of an ion depends on how many electrons it gains or loses. Ex) Chlorine (7 valence electrons) will gain one electron to have a full outer shell. This means it has 18 negative charges (electrons) to 17 positive charges (protons), giving it an overall charge of -1. Try: Sulfur Potassium S2- K1+

Charges You can predict an ion’s charge based on the element’s location in the periodic table: Group 17 elements will gain 1 electron  charge = -1 Group 16 elements will gain 2 electrons  charge = -2 Group 15 elements will gain 3 electrons  charge = -3 Group 1 elements will lose 1 electron  charge = +1 Group 2 elements will lose 2 electrons  charge = +2 Group 13 elements will lose 3 electrons  charge = +3 Group 14 can be -4 or +4 (gain or lose 4 electrons)

Ionic Bonds formed by ions who’s opposing charges attract. Example: Sodium Chloride (NaCl) “Table Salt” Sodium (Na) has an extra electron (1 valence electron) Chlorine (Cl) needs one more (7 valence electrons) If Na transfers its electron to Cl… both become more stable as ions. Chlorine  negative ion (Cl-) Sodium  positive ion (Na+) opposite charges attract and bond the atoms like magnets.

Neutral Compounds – Ionic compounds are electrically neutral. IONIC BONDS Neutral Compounds – Ionic compounds are electrically neutral. Ions bond so that the charges balance. ex) It takes 1 sodium ion (Na+) to balance out 1 chloride ion (Cl-)  NaCl (sodium chloride) ex) It takes 1 calcium ion (Ca2+) to balance out 2 chloride ions (Cl-)  CaCl2 (calcium chloride)

Polyatomic Ions – ions made of more than one atom a group of atoms that act as one ion Example: Carbonate (CO32-) One Carbon ion (+4) Three Oxygen ions (-2) + (-2) + (-2) = (-6) Overall charge (+4) + (-6) = (-2) Common polyatomic ions on p.115

Naming Compounds usually the name of a metal (ex: sodium) the name of the positive ion comes first usually the name of a metal (ex: sodium) sometimes a positive polyatomic ion (ex: ammonium) the name of the negative ion comes second if an element, the end changes to “-ide” (ex: oxide) if polyatomic, the name is unchanged (ex: carbonate) Al2S3 Na2CO3 aluminum sulfide sodium carbonate

Try These (use p.115 for help) Name the following: NaCl CaCl2 LiNO3 MgCl2 NH4F sodium chloride calcium chloride lithium nitrate magnesium chloride ammonium fluoride

Try These (use p.115 for help) Give the correct formula: Remember to form a neutral compound! potassium bicarbonate sodium sulfate calcium fluoride lithium sulfide aluminum oxide KHCO3 Na2SO4 CaF2 Li2S Al2O3

Properties of Ionic Compounds Crystal Shape Atoms form organized, alternating, 3-D pattern High Melting Point Solids at room temp. Electrical Conductivity conduct electricity well in solution (or when melted)