Ionic Compounds & Covalent Bonding

Forming Chemical Bonds Chemical Bond: the force that holds atoms together. May form by the attraction between a positive nucleus and negative electrons, which result in positive and negative ions. This is because of valence electrons, which are the electrons in the outer shell of the electron cloud that are involved in bonding. 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 (maximum amount allowed)

Formation of Ions Ion: an atom with a charge (gain or loss of electrons). Cation – positive ion (lost electrons) Anion – negative ion (gained electrons) Atoms gain or lose valence electrons to obtain a complete outer energy shell. (lose to get to 0 / gain to get to 8) Group 1: +1 (loses its 1 valence electron to have zero) Group 2: +2 (loses its 2 valence electrons to have zero) Group 13: +3 (loses its 3 valance electrons to have zero) Group 15: -3 (gains 3 valence electrons to have eight) Group 16: -2 (gains 2 valence electrons to have eight) Group 17: -1 (gains 1 valence electron to have eight)

Ionic Compounds Contain Ions (basically you are adding positives and negatives and balancing to equal 0) Net charge of a compound must be ZERO. Total positive charge = Total negative charge If the positive ion does not equal negative ion, *subscripts* are used to help balance total charges. Symbols, Charges, Switch and Reduce. Example: Sodium, Na, group 1, will lose 1 valence electron (electrons are negative, gives it a +1 charge) Chlorine is group 17, will gain 1 more electron to get to 18 and be like a noble gas, giving it -1 charge (gains 1 negative electron). Together, +1 and -1 are 0, so the compound for Sodium and chlorine is NaCl, named Sodium chloride.

More examples of ionic compounds A compound with Calcium and chlorine forms like this: Calcium is group 2, so loses 2 electrons, +2 charge Chlorine, group 17, gains 1 electron, -1 charge. Symbols: Ca+2 Cl-1 Symbols, charges, switch, reduce (by switch, we mean switch the charges to the opposite atom, make it a subscript, drop the charge) Ca+2 Cl-1 So the formula is Ca1Cl2. There should be 2 Chlorines with 1 Calcium to make this compound neutral. You can drop the ‘1’ as a subscript. CaCl2 Calcium chloride

Properties of Ionic Compounds and hints for naming/writing: Ionic Compounds (Ionic Bonding): Bonding between positive & negative ions. The *metal (groups 1,2, Al and B in 13, and the transition metals) will LOSE ELECTRONS TO BECOME POSITIVE. The *nonmetals (groups 15, 16, 17) will GAIN ELECTRONS TO BECOME NEGATIVE (group 14 shares) Positive ions transfer their electrons to negative ions. Between a metal cation and a non-metal anion. Most called salts, or oxides if the non-metal is oxygen. Strong attractive forces that result in crystal lattice structures. High melting points, high boiling points, hard-rigid-brittle solids.

Binary Compounds with Polyatomic ions Compounds containing more than 2 elements Polyatomic ions (PAI) These are groups of atoms covalently bonded but have one charge, and as a group behave as one substance, example: sulfate ion is SO4-2. In this PAI, there is one Sulfur, 4 Oxygens, together they have a charge of -2. If you remember from your Lewis structures and studies of valence electrons, this means there are 2 extra electrons in the bonding process.

Binary with Polyatomic Ions, cont’d The PAI acts as one unit, and then can bond with a metal or oppositely charged ion to form an ionic bond. The bonding between the atoms IN the PAI is covalent, the bonding between the PAI (polyatomic ion) is *ionic Example: Sodium sulfate, a product found in soaps and shampoos, is Na2SO4 You have a chart with polyatomic ions, *learn it!

Types of Compounds Covalent Compounds (Covalent Bonding) Bonding in which valence electrons are shared. Between only non-metals A molecule is formed when two or more atoms bond covalently. Most elements when found uncombined in nature are monatomic, which means there is one individual atom. A few exceptions include atoms that must exist diatomically, these molecules contain 2 atoms. These are bound covalently, and include: Hydrogen H2 Nitrogen N2 Oxygen O2 Fluorine F2 Chlorine Cl2 Bromine Br2 Iodine I2

Metallic Bonding Transition metals, groups 3-12, or the d block, form metallic bonds with each other, which are strong lattice structures where the positive nuclei are rigid and the electrons travel in the spaces between: They do not share valence electrons with neighboring atoms nor do they lose electrons to form ions when bonding with other transition metals. The outer energy levels of the metals atoms overlap. Electron Sea Model: all metal atoms in a metallic solid contribute their valence electrons to a sea of electrons (called delocalized electrons- because they are free to move and form a metal cation). Metallic Bond: the attraction of a metallic cation for delocalized electrons.

Metallic compound properties Properties: physical properties of metals can be explained by metallic bonding. High Melting Point High Boiling Point Malleable Ductile (they can be drawn into wires) Durable Conductors of heat and electricity

Metallic compounds cont’d Alloy: a mixture of elements that has metallic properties. Alloy’s properties are different than the individual metals in the alloy. Examples include: stainless steel, brass, and bronze which are all mixtures of different transition metals