Atomic Stability Atoms tend to be most stable when they have an electron configuration with a full (or sometimes half-full) valence level (shell). Evidence: look at the reactivity of noble gas elements and the reactivity of atoms in compounds. Reactive atoms show a tendency to gain or lose or share electrons until they become “stable”. This activity results in chemical bonds! Atoms tend to be most stable when they have an electron configuration with a full (or sometimes half-full) valence level (shell). Evidence: look at the reactivity of noble gas elements and the reactivity of atoms in compounds. Reactive atoms show a tendency to gain or lose or share electrons until they become “stable”. This activity results in chemical bonds!

Bonding  Two or more atoms join together to form a stable group.  There are several types of forces (BONDS) which hold the atoms together in these groups.  IONIC (ionic compounds)  COVALENT (molecular compounds)  Chemical Bonds Chemical Bonds  METALLIC (pure elements or homogeneous mixtures)  WEAK INTERMOLECULAR (ie.: the forces that hold water molecules together)

Differences in properties  Ionic Compounds  High melting point  Conduct electricity when molten or dissolved in water  Ionic Compounds  High melting point  Conduct electricity when molten or dissolved in water  Molecular Compounds  Low melting point  Does NOT conduct electricity when molten or dissolved in water.

Ionic Compounds -compounds of two or more elements involving atoms in the form of ions  What is an Ion?  An ion is an atom (or a group of atoms) which has “lost” or “gained” one or more electrons, thus obtaining a “net” positive or negative charge.

Cations vs. Anions  Cations - ions formed when e - are lost from an atom/group of atoms  Positive Ions ( + )  Usually formed from metal elements  (exceptions: Hydrogen and some polyatomic ions)  Cations - ions formed when e - are lost from an atom/group of atoms  Positive Ions ( + )  Usually formed from metal elements  (exceptions: Hydrogen and some polyatomic ions)  Anions - ions formed when e - are gained by an atom/group of atoms  Negative Ions ( - )  Usually formed from nonmetal elements  (exceptions: some polyatomic ions)

Ions in Water A Matter of Ions

Ions vs. Molecules lose or gain e - sharing of e - (between atoms)

Valence Electrons  Valence Electrons are the electrons in the Outermost Energy Shell.  The number of valence electrons matches the group number for the representative elements (s & p).  Transition (d) and Inner-transition (f) elements typically have “2” valence electrons.  However, some of their “outer ‘d’” electrons may participate in bonding. This is used to explain unusual/unexpected bonding patterns.  Valence Electrons are the electrons in the Outermost Energy Shell.  The number of valence electrons matches the group number for the representative elements (s & p).  Transition (d) and Inner-transition (f) elements typically have “2” valence electrons.  However, some of their “outer ‘d’” electrons may participate in bonding. This is used to explain unusual/unexpected bonding patterns.

Electron dot structures for selected representatives and noble-gas elements. EDS show the number of valence electrons as dots around the symbol. Electron Dot Structures for Representative Elements

Octet Rule  Atoms will typically gain or lose electrons and attain the same electron configuration as a Noble Gas.  Noble Gases have 8 valence electrons (except Helium)  What actually happens is dependent on the elements involved in the reaction!  Metal & Nonmetal = Ionic Bond (eg.: NaCl)  Nonmetal & Nonmetal = Covalent Bond (eg.: H 2 O)  Atoms will typically gain or lose electrons and attain the same electron configuration as a Noble Gas.  Noble Gases have 8 valence electrons (except Helium)  What actually happens is dependent on the elements involved in the reaction!  Metal & Nonmetal = Ionic Bond (eg.: NaCl)  Nonmetal & Nonmetal = Covalent Bond (eg.: H 2 O)

Predicting Ionic Charges Periodic table in which the metallic elements that exhibit a fixed ionic charge are highlighted.

Monatomic Ions vs. Polyatomic Ions  Monatomic IONS are comprised of only ONE element.  Ex. Na +, Cl -, Al 3+, O 2-, etc.  Polyatomic IONS are comprised of two or more elements/atoms. Thus, a group of atoms together have an unequal total of p + vs. e -.  NH 4 +, NO 3 -, SO 4 2-, CO 3 2-, etc.  These ions typically use covalent bonds to hold the group of atoms together - more on this later:-)!  Monatomic IONS are comprised of only ONE element.  Ex. Na +, Cl -, Al 3+, O 2-, etc.  Polyatomic IONS are comprised of two or more elements/atoms. Thus, a group of atoms together have an unequal total of p + vs. e -.  NH 4 +, NO 3 -, SO 4 2-, CO 3 2-, etc.  These ions typically use covalent bonds to hold the group of atoms together - more on this later:-)!

Polyatomic Ions!

Ionic Compounds Ionic Compounds are typically Crystalline in form. ← (a) fluorite and ← (b) ruby. table salt ‹

Ionic compounds occur when cations and anions bond together. 3D  These ions join together because of electrostatic attractions between charged IONS. This “joining” occurs in 3D, thus, crystalline in form.  Remember, cations are usually metallic elements (or “ammonium”) and anions are usually nonmetallic elements (or MnO 4 -, CrO 4 -2, Cr 2 O 7 -2, MoO 4 -2 ).

Which part of the ionic compound is responsible for the typical physical properties? Copper (II) oxide is black, whereas copper (I) oxide is reddish brown. Iron (II) chloride is green, whereas iron (III) chloride is bright yellow.

(a,b) Two-dimensional cross section and a three- dimensional view of sodium chloride. (c) sodium chloride crystals Sodium chloride

Why is the formula for table salt, sodium chloride, NaCl? → Cross section of the structure of the ionic solid NaCl.

Reactions of Ionic Compounds (an important example)  Tooth Enamel Demineralization Ca 10 (PO 4 ) 6 (OH) 2 + 8H + 10Ca HPO H 2 O vs. Ca 10 (PO 4 ) 6 F 2 + 2OH - + 2H + Ca 10 (PO 4 ) 6 F 2 + 2H 2 O Mouth bacteria metabolize sucrose and produce lactic acid, so…  Tooth Enamel Demineralization Ca 10 (PO 4 ) 6 (OH) 2 + 8H + 10Ca HPO H 2 O vs. Ca 10 (PO 4 ) 6 F 2 + 2OH - + 2H + Ca 10 (PO 4 ) 6 F 2 + 2H 2 O Mouth bacteria metabolize sucrose and produce lactic acid, so…

Predicting formulas using the Periodic Table and valence electrons  Metal atoms LOSE valence electrons to form cations  Nonmetal atoms GAIN valence electrons to form anions  Na (1 v.e - ) --> Na + (looks like neon)  Cl (7 v.e - ) --> Cl - (looks like argon)

Naming Ionic Compounds Nomenclature of ionic compounds.

Formation of ionic compounds Loss of an electron from a sodium atom leaves it with one more proton than electrons, so it has a net electrical charge of +1.

Tests for Ionic Compounds  Flame Tests  Ex: Ba, Na, K  Precipitation Tests  Ex. Pb(NO 3 ) 2 + KI  Flame Tests  Ex: Ba, Na, K  Precipitation Tests  Ex. Pb(NO 3 ) 2 + KI