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 ?

MoleculesMolecules 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.

Elements that are molecules: Br I N Cl H O F

AcidsAcids 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. 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

Acids - name to formula

Name to formula: 1st: change hydro___ ic back to -ide or

-ic acid back to -ate or -ous back to -ite2nd: find the name on the ion sheet and its

charge, 3rd: add enough H+1 to make neutral

Remember write formula without charges!

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 OctetAny 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 StructuresResonance 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 MoleculesWhat 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, NCl3H2O