Chapter 3 – Elements Combine to Form Compounds

Ion Charge or Combining Capacity Revisited The number of bonds an atom wants to form –Determined by the number of e - in the outer shell that an element wants to donate or borrow. Example: –Ca = +2 –Na = +1 –Cl = -1

Metals vs. Nonmetals Metals have positive (+) charges. –Therefore, they want to donate an e - from their outer shells. Most non-metals have negative (–) charges. –Therefore, they want to accept an e - into their outer shells.

Ionic Compounds Atoms gain or lose electrons and form ions. The charges of the ions are attracted to the opposite charge; therefore a compound is produced. Example: Na and Cl combine to form NaCl NOTE: In covalent compounds, atoms combine by sharing electrons to form molecules. Example: C and O share electrons to form CO

Ionic Bonds Lead to the formation of crystal lattices. All the ions are attracted to all other ions in the crystal, although nearest ions have the greatest attraction. Repeating pattern of negative and positive charges. Think in terms of ratios. NaCl is a ratio of one sodium to one chlorine, but many NaCl will form a crystal lattice.

Two Representations of Crystal Lattices

Rules for Naming Ionic Chemical Compounds 1.Write the name of the metal element 1 st 2.Write the name of the non-metallic element 2 nd (is farther right on the Periodic Table) 3.Change the ending of the non-metallic element to “ide” Example: CaCl 2 Calcium chloride

Chemical Formulas of Ionic Compounds Formulas contain symbols to identify each ion in an ionic compound, as well as the relative numbers of ions in the compound. Example:NaCl – 1 sodium:1chlorine CaF 2 – 1 calcium:2 fluorines Note: Relative numbers of each ion is a subscript to the right of the symbol

Rules for Writing Ionic Chemical Formulas 1.Write the symbol of the metal 1 st 2.Write the symbol of the non-metal 2 nd 3.Write in the ion charges of both symbols as superscripts to the top right of each symbol (found on the Periodic Table) 4.Drop the +/- signs and cross the ion charges and write as subscripts (to the bottom right of the symbol). The number 1 is never written. 5.Reduce, if necessary

Example of a Metal & Non-metal Combining 1.Calcium chloride (write the symbols) 2.CaCl (superscript combining capacities) 3.Ca 2+ Cl 1- 4.Ca 2+ Cl 1- (drop the +/- signs and cross combining capacities) 5. CaCl 2

Compounds Containing Multivalent Metals Notice that some metallic elements have more than 1 ion charge. We need to use Roman Numerals to indicate which combining capacity is used.Roman Numerals E.g. Copper (II) chloride = Cu +2 E.g. Copper (I) chloride = Cu +1

Naming Note: Multivalent Metal Use the Roman Numeral equal to the ionic charge to indicate which combining capacity was used E.g. CuCl 2 Cu 1+ or Cu 2+ Copper (II) chloride E.g. Fe 2 O 3 Fe 3+ or Fe 2+ Iron (III) oxide You need to reverse cross to find combining capacities.

Reactions involving Polyatomic Ions (Radicals) E.g. Ammonium sulfide Ammonium = NH 4 1+ (1+ is the ion charge) (given on the back of the Periodic Table) When NH 4 1+ S 2- combine, the NH 4 stays together So, NH 4 1+ S 2- You need to put brackets around NH 4 so you can separate the digits (NH 4 ) 2 S

Naming Note: Polyatomic Ions Write the metal name first. Write the name of the polyatomic ion; do not change using “ide”. Example: Sodium combines with cyanide NaCN Sodium cyanide

Radicals & Roman Numerals Copper sulfate Copper (II) sulfate 1.Cu SO 4 2.Cu 2+ SO Cu 2+ SO Cu 2 (SO 4 ) 2  the 2’s reduce 5.Cu(SO 4 )  brackets can be dropped

Types of Chemical Reactions Exothermic – energy is released from the reaction Example: Atomic blast Memory Tip: –Exo – starts with the letters “ex” similar to exit

Types of Chemical Reactions Endothermic – energy is absorbed in order for the reaction to occur Example: cooking eggs Memory Tip: –Endo – starts with the letters “en” similar to enter