Unit 4 - Bonding and Compounds - Chapters 5 and 12

Unit 4 - Bonding and Compounds - Chapters 5 and 12 • Chemical formula - a combination of symbols that represents the composition of a compound • Only noble gases exist as isolated atoms • Compounds are comprised of molecules and ionic compounds • 2 or more atoms that act as 1 unit • diatomic - 2 atoms • triatomic - 3 atoms • polyatomic - generally more than 3 atoms

Ionic Compounds • Ionic compounds composed of particles called ions. • Ions - atoms or groups of atoms that have a positive (lose e-) or negative (gain e-) charge • Metallic elements - (lose e-) called cations • Nonmetallic elements - (gain e-) called anions • When ions combine, compound is neutral

Naming Ionic compounds • Example NaCl - its name is ? • Metallic element listed 1st - retains its name • Nonmetallic element listed 2nd - name changed to 1st syllable of element with -ide suffix • CaS name? LiBr? • sodium sulfide? calcium chloride?

Naming Ionic compounds (con’t) • Polyatomic ions (usually negative except NH4+1) • tightly bound groups of atoms that behave as a single unit that have that charge • listed on the ion sheet • CaSO4 ? Li2C2O4 ? • aluminum nitrate ? magnesium phosphate ?

Molecules Molecules are made from only nonmetals, so we recognize them by a nonmetal listed 1st. Nonmetals all want to gain electrons!!! Molecules are NOT made from ions. They have to share... the nonmetals can share in many ways. Both CO and CO2 exist... can’t just say carbon oxide!!! not unique... so we have to use prefixes to tell how many of each atom. Naming is similar 1st element keeps name, 2nd element root +ide. • nitrogen dioxide • dibrominetetraflouride • trisulfurpentaoxide • O2Cl • N3F6 • Se2O5 Elements that are molecules: Br I N Cl H O F

Acids Acids produce hydrogen ions when dissolved in solution. H+1 is the hydrogen ion (a proton !). Acids all have Hydrogen listed 1st. Only the hydrogens listed 1st are dissolved in water. • HCl • H2SO4 • HNO3 • HC2H3O2 • H3PO4 • hydrochloric acid • sulfuric acid • nitric acid • acetic acid • phosphoric acid Most Common Acids (know these). Notice they have different numbers of hydrogens

Acids - 3 types of naming • Formula to name: • from the ion sheet, if the negative ion has no oxygen (ends with -ide) use root (usually 1st syllable) • -ide hydro_____ic acid • if it has oxygen, then it ends either -ate or -ite • -ate _____ic acid • -ite _____ous acid HBr HNO3 HNO2 H2CrO4

Acids - name to formula • Name to formula: • 1st: change hydro___ ic back to -ide or • -ic acid back to -ate or -ous back to -ite • 2nd: find the name on the ion sheet and its charge, • 3rd: add enough H+1 to make neutral • Remember write formula without charges! hydroiodic acid sulfuric acid oxalic acid nitrous acid

Nomenclature Summary • H 1st - Acid, 3 types of naming H+1 and Nonmetal-x • -ide hydro______ic acid • -ate ______ic acid • -ite ______ous acid • Nonmetal 1st - Molecule (not ions!!!) • Use prefixes (memorize them!) • 1st element keeps its name, 2nd element ending is -ide • If use mono , only on the second atom • Metal 1st - Ionic compound - use ion sheets • Metal is positive ion, the rest is the negative ion • Make the compound neutral

Chemical Bonding -Chapter 12 • Chemical Bond? • a force that holds atoms together and function as 1 unit. • Chemical Bonding depends on attraction for electrons(electronegativity). Differences between atoms in electronegativity determine the type of bonding. • Ionic Bonding occurs between metals and nonmetals. • Metals lose e- & Nonmetals gain e- • Each ion becomes like a noble gas (filled outer shell - octet) • Ionic bond is an electrostatic force (+) attracts (-)

Ionic bonding examples - electron dot structures Electrons filling shells Lewis dot structures

Electronegativities of elements

Covalent Bonding • Covalent Bonding occurs between 2 or more nonmetals to form molecules or polyatomic ions. • Nonmetals all want electrons - what do they do? • -need to share electrons to achieve octets • Polar Covalent bonds - share electrons but not evenly! • more polar N-S bond or O-S bond?

Lewis Structures • Valence electrons for • H F O C • Simplest molecule H2 - lets do Lewis dot structure • What about F2 ?

Covalent Bonding Continued • Bonding pairs of electrons • Nonbonding pairs of electrons (lone pairs)

Exceptions to Octet • Any odd number of valence electrons • examples NO and NO2 • Boron - valence electrons? • many times only makes 3 bonds (6 total electrons) • BF3 • 3rd period - sulfur and phosphorus most common • they can expand their octet - 5 or 6 pairs • PCl5 or SF6

Resonance Structures • Resonance occurs when more than one equivalent Lewis dot structure can drawn for a molecule or polyatomic ion. • CO2 • NO • NO3-1 • How do you recognize resonance, usually same atom attached to central atom with at least one double bond

What do molecules look like? Molecular shapes! • Use Lewis structures to predict shapes... How? • VSEPR - valence shell electron pair repulsion - This Model is based on 1000’s of known molecular structures and gives us a rationale for predicting structures • Electron pairs repel each other --> as far apart as possible • Bonding pairs and non-bonding pairs repel each other • CH4 is not planar!!! the hydrogens can get further away in 3D

Polarity of Molecules • What determines polarity in a covalent bond? • electronegativity differences!! • C-H polar bond? • N-O polar bond? • Br-Br polar bond? • Which way does it point? • Which is most polar C-N, C-O or C-F? • Which is most polar O-F, S-F or Se-F? • Polarity of Molecules - the molecule has a permanent dipole, it is polar.

Molecules with polar bonds can be non-polar overall... Symmetry is key!!! • CO2, N2, HF, HCCH • SO3, SO2, • CH4, CF4, CH2F2 • NH3, NCl3 • H2O

Unit 4 - Bonding and Compounds - Chapters 5 and 12