Chemical Bonding & Equations

• These notes cover Chemical Bonding & Chemical Equations including Molecular and Ionic Compounds, Chemical Formulas, Naming Compounds, Molecular Geometry, and Reaction Types.

Molecular and Ionic Compounds

• Compounds classify based on bonds holding atoms together

Molecular Compounds

• Atoms share electrons
• Forms covalent bonds

Ionic Compounds

• Atoms charged (ions)
• Difference in charge holds them together
• Transfer of electrons occurs, don't share electrons
• Typically a metal and nonmetal

Molecular Compounds

• Involve shared electrons, such as in methane
• Table salt is an example

Formulas

• Indicate number & type of atoms in molecule using a chemical formula
• Chemical formulas notation, for example: C3H6O, 3 Carbon atoms, 6 Hydrogen atoms, and 1 Oxygen atom

Chemical Unit

• Chemical formulas indicate the simplest structural unit
• Sodium oxide, an ionic compound, written as Na2O
• A metal combined with a nonmetal, resulting in an ionic compound

Aluminum Sulfate

• Consists of two aluminum atoms with 3 sulfate groups
• Contains 3 sulfur atoms and 12 oxygen atoms (4x3)

Thumb Rule:

• Nonmetal + Nonmetal = Molecular (Covalent) compound (electrons shared)
• Metal + Nonmetal = Ionic compound (electrons transferred)

Ionic Formulas

• Charges sum to zero
• Cations (positive ions) written first
• Anions (negative ions) follow

Magnesium Chloride Example

• Mg+2 Cl-1 becomes MgCl2

Naming Ionic Compounds

• Positive ions are named first or the cation
• If a transition metal has multiple oxidation states, charge written as a Roman numeral
• Negative ion (anion) named second
• Binary compounds names end in "-ide"

Chemical Naming Beginnings

• Naming starts with metal
• May start with transition metal
• Or start with Hydrogen for acids
• Molecular compounds are also an option
• For NaCl (ionic), no prefix used
• Molecular compounds get prefixes, like for CO2
• For acids, start with Hydrogen (HCl -> acid)

Molecular Compounds Naming

• If only one atom of the first element, no prefix is used
• If more than one atom of the first element, a prefix is added
• If two elements, binary, end in -ide
• The 2nd element always has a prefix

Numerical Prefixes

• 1 = mono-
• 2 = di-
• 3 = tri-
• 4 = tetra-
• 5 = penta-
• 6 = hexa-
• 7 = hepta-
• 8 = octa-
• 9 = nona-
• 10 = deca-

Molecular examples

• CO2 is carbon Dioxides
• CO equals carbon Monoxide
• P4S10 equals tetraphosphorus decasulfide
• N2O5 equals dinitrogen pentaoxide

Molecular Compound Formulas

• Less electronegative element written first
• If 1st element has one atom, no written subscript
• Subscripts should include proper atom numbers

Chemical Nomenclature Order

• Carbon typically leads

Chemical Example:

• Diarsenic pentabromide is As2B5

Polyatomic Ions

• Are charged groups of covalently bonded atoms
• List must be memorized

Ions for Memorization

• NH4+ which is Ammonium
• PO43- which is Phosphate
• OH- which is Hydroxide
• CO32- which is Carbonate
• SO42- which is Sulfate
• NO3-1 which is Nitrate

Polyatomic Compound Formulas

• Charges sum to zero
• Cation is first, anions next
• If more than one polyatomic ion, put in parenthesis

Lithium/Calcium/Aluminum Examples

• Lithium hydroxide equals Li+1 OH-1 = LiOH
• Calcium nitrate gives Ca+2 NO3-1 = Ca(NO3)2
• Aluminum phosphate equals Al+3 PO4-3 = AlPO4

Polyatomic Names

• Mention cation name first before identifying the anion

Memorize these Acids

• HF, or Hydrofluoric acid
• HCl, or Hydrochloric acid
• HBr, or Hydrobromic acid
• HI, which is Hydroiodic acid
• HNO3, or Nitric acid
• H2SO4, or Sulfuric acid
• H3PO4, or Phosphoric acid
• H2CO3, or Carbonic acid

Acid Formulas

• Begin with 'H'
• Charges add to zero

Naming acids

• If binary, use hydro-_____-ic acid
• If not binary, use _____ic acid

Molecular compounds can be drawn using Lewis structure

• Determine number of valence electrons
• Arrange atoms in molecule
• Attach with bonds (one bond contains 2 electrons)
• Distribute non-bonding pairs

Multiple Bonds

• Valence electrons of elements

Octet Rule

• Chlorine can share an additional electron to fulfill the octet rule
• If atoms can share an additional electron to fulfill the octet rule,
• single bonds are formed
• Non bonding pair possible

Writing Lewis Structures

• Sum valence electrons of all atoms in polyatomic ion, or molecule
• If its anion, add one electron for each negative charge
• If its cation, subtract one electron for each positive charge
• Central atom is typically least electronegative element, that isnt Hydrogen
• Outer atoms connected with single bonds

Octet Rule

• Fill octets of outer atoms so can keep track of the electrons
• Central atom in structures needs full octet
• If you run out of electrons before the central atom, then form multiple bonds

Examples

• Some examples include NF3, SBr2, and CCl4
• Multiple covalent bonds exist within Nitrogen

Limiting octet rule and the periodic table:

• The first two periods are best to follow the octet rule.

Resonance Structures

• If more than one Lewis structure, is the average.

VSEPR

• Valence shell electron pair repulsion determines structure
• Molecule determined by minimizing electron pair repulsions

Molecular Geometry Prediction

• Needs the Lewis Structure drawing
• Determine number of electron pairs around central atom counting multiple bonds as one group.
• Arrange the electron pairs accordingly

Electronic and molecule shape

• Depends on pair placement

Number of electron domains affect electron and molecular geometry.

Polarity

• Bond polar if difference in electronegativity
• Uneven charge creates dipole moment

Bonds

• Covalent bonds have H:F characteristics
• Cl is more electronegative
• Nonpolar bonds will share electrons evenly such as with F:F

Molecule Considerations

• Shape of molecule affects polarity
• Bond and overall dipole must be considered for polarity determination
• Two lone pairs indicates Polarity

Balanced/Unbalanced

• Polar is not balanced
• Nonpolar is equal/balanced

Chapter 4: Chemical Equations and Calculations

Moles and Mass, Atoms.

• Need to master use of moles, calculations, molar mass and mass of atoms.

Conversions

• Conversion factor to solve these problems needs be memorized/understood

Mass and Atoms

• One mole 6.02 x 10^23 particles which are related to the molar mass and mass of one mole with atomic mass in grams.
• One mole can equal 6.02 x l0^23 particles with molar mass grams.

Chemical Reactions

• Can often visually see a chemical reaction through evidence like release of gas,
• Solution, if becomes a solid called precipitate, heat or color change.
• Acid base mixed can visually show end result.

Reaction Types

• The common patterns that you are expected to identify are combinations, decompositions, single/double replacement, Recognizing patterns, and balancing them aids understanding.
• Combination reaction A + B = AB, while decomposition is reverse such AB = A + B.

Reactions

• Single replacement one atom replace another in to form new element.
• Double replacement changes partners form two new products.

Precipitate

• Reactions between aqueous solutions of ionic compounds yield ionic compound not soluble in water so then precipitation occurs with insoluble

Solubility of Ionic Compounds:

• Depends on temperature.

Types of Reactions

• Gas form directly results from exchange of ions
• Other reactions such acids and bases or hydrocarbons involve transfer ion from one reactant to another = H20

Redox Reactions

• Result from transfer one/more electrons from 1 reactant to another.
• Writing:
• Can symbolically put chemical reactions with chemical formulas

Writing equations

• Use conservation of mass
• Total atoms each side matched also need get to a balanced result with product as indicated.
• It Is NOT Balanced result

Reaction balancing with chemical equation

• To properly conduct chemical reaction, balance the following equations — O2 + PCl3 -> POCl3 — P4+ N2O -> P4O + N2 — F2 + H2O -> HF + O2 — H3PO4 + Ca(OH)2 -> Ca3(PO4)2 + H2O

Mass Conversion

• The mass must also be converted for proper balancing
• Then ratio from respective balance equation applied after convert to achieve desired result
• Use the balanced result to the specific example convert and solve.