Chapter 6 Sections 1,2 and 3

Key Terms  Only a few atoms exist as isolated atoms – Noble Gases  Molecule  Smallest electrically neutral unit of a substance that still has the properties of the substance.  Made up of two or more atoms that behave as a unit.  Some are diatomic (appear as pairs)  Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2

Molecular Compounds  Atoms of different elements combine chemically  Compounds composed of molecules are called molecular compounds.  Some general characteristics:  Low melting and boiling points  Most are liquids or gases  Composed of two or more non-metals

Ionic Compounds  Ions – atoms or groups of atoms that have positive or negative charges (that means the # of p + does not equal the # of e - )  Metallic elements tend to form cations (positive charges)  The protons outnumber the electrons  The charge is usually written after the symbol and to the upper right (Na + )  Cations are named the same as the element.  Ions behave very differently than the atoms they came from.

 Anions  Non-metals usually form anions.  Negative (electrons outnumber the protons).  Happens when elements gain electrons  The name of a typical monatomic anion (1 atom that is negative) ends in –ide Example: Cl - = chloride

 Compounds composed of cations and anions are called ionic compounds.  Usually made of metals with non-metals  Ionic compounds are electrically neutral  Usually solids at room temperature and melt at extremely high temperatures.

Chemical Formulas  Shows the kinds and number of atoms in the smallest representative unit of the substance.  Use elemental symbols  Subscripts show haw many of each atom are present.  Example: oxygen = O 2

Molecular Formula  Chemical formula for a molecular compound.  Tells nothing about structure or arrangement of atoms.  Example = carbon dioxide = CO 2 One carbon atom and two oxygen atoms tightly bound to each other.

Formula Unit  Used for ionic compounds  Ionic compounds are not molecules  It is the lowest whole number ration of ions in a compound.  Example: NaCl (sodium chloride or table salt) is made of one sodium ion and one chloride ion. Thus, the ratio is 1:1 (sodium = +1 charge and chloride = -1 charge)  Example #2: MgCl 2 (magnesium chloride) is made of one magnesium cation (+2 charge) and two chloride anions (-1 each) thus the ratio is 1:2

Laws  Law of multiple proportions  If two or more compounds made of the same elements exist they are a whole ratio of each others composition.  Law of definite proportions  Samples of the same compound have the elements present in the same ratio.

Monatomic Ions  Ions consisting of only one atom  Table 6.2 (p143)  Can be predicted from group on the periodic table. 1A2A3A4A5A6A7A8A Li + Be +2 N -3 O -2 F-F- Na + Mg +2 Al +3 P -3 S -2 Cl - K+K+ Ca +2 As -3 Se -2 Br - Rb + Sr +2 I-I- Cs + Ba +2

Transition Metals  Most can have multiple charges  Exceptions = Silver (Ag + ), Zinc (Zn +2 ) and Cadmium (Cd +2 )  Roman Numeral is used to show the charge on the cation  Example: Copper (I) = Cu +1 Roman Numeral is the charge!

Table 6.3 Page 144 FormulaStock NameClassical Name Cu + Copper (I)Cuprous ion Cu +2 Copper (II)Cupric ion Fe +2 Iron (II)Ferrous ion Fe +3 Iron (III)Ferric ion Pb +2 Lead (II)Plumbous ion Pb +4 Lead (IV)Plumbic ion Sn +2 Tin (II)Stannous ion Sn +4 Tin (IV)Stannic ion

Polyatomic Ions  Tightly bound groups of atoms that behave as a unit and carry a charge.  Change the prefix and suffix to show a change in the number of oxygen present.  Exceptions = Cyanide, Hydroxide and ammonium  Practice with the common ion sheet