HONORS CHEMISTRYUnit C: Chemical Bonding, Formulas, Reactions & Equations

CHAPTER SIX: CHEMICAL BONDING

IONIC & COVALENT BONDSuCHEMICAL BONDS are formed from a

mutual attraction between the nuclei and valence electrons of different atoms

uThe force of attraction binds atoms/ions together

u IONIC and COVALENT bonding are the two most general bonding types

BOND CHARACTERuIONIC BONDING results from the

electrical attraction between cations and anions (IONS)

uCOVALENT BONDING results from the sharing of electron pairs between atoms (ATOMS)

BOND CHARACTER

IONIC BONDINGuBond types are almost never PURELY

ionic or covalentuBond character is based on 100%

scaleuGreater than 50% ionic is IONICuElectronegativity difference (END)

greater than 1.7

COVALENT BONDINGuBond types are almost never PURELY

ionic or covalentuBond character is based on 100%

scaleuGreater than 50% covalent is

COVALENTuElectronegativity difference (END) of

1.7 or less (0.0 -1.7)

COVALENT BONDINGuCovalent bonds can be classified as POLAR

COVALENT or NON-POLAR COVALENTuPOLAR COVALENT bonds are “shared unevenly”

and have END values 0.2 – 1.7uNON-POLAR COVALENT bonds are “shared

evenly” and have END values 0.0 – 0.2

COVALENT BONDING & COMPOUNDS

uMOLECULES are groups of neutral atoms held together by covalent bonds

uMOLECULAR COMPOUNDS are chemicals whose simplest unit is a molecule

uMOLECULAR FORMULAS show the type and number of atoms combined in a single molecule

COVALENT BONDING & COMPOUNDS

uDIATOMIC MOLECULES are molecules containing only 2 atoms (usually the same element)

uMAGNIFICENT SEVEN: H2, N2, O2, F2, Cl2, Br2, I2

COVALENT BOND FORMATION

uCovalent bonds form because of the attractive forces between nuclei (+) and valence electrons (-) of two or more atoms

uElectrons repel each other & nuclei repel each other

uThe bond settles at the point where attraction and repulsion balance out (lowest PE)

COVALENT BOND FORMATION

COVALENT BOND CHARACTERISTICS

uShared electron pairsuOverlap of valence electron orbitalsuResults in a molecule with a decreased PE &

increased stability

COVALENT BOND CHARACTERISTICS

uBOND ENERGY is the energy is required to break a covalent bond

uBOND LENGTH is the distance between bonded atoms

uBOND LENGTH & BOND ENERGY depend on the sizes and EN of the atoms and number of bonded electron pairs

ELECTRON DOTS & LEWIS STRUCTURES

uELECTRON DOT NOTATION uses dots to show the valence electrons for an atom

uLEWIS STRUCTURES use element symbols, electron dots, and bond lines to show the structure of a molecule

uThe OCTET RULE (rule of 8) is usually followed, but many exceptions exist

RESONANCE STRUCTURESuRESONANCE STRUCTURES are representations of

molecules that have multiple possible structuresuRESONANCE is bonding in a molecule that can be

correctly represented multiple waysuDrawn as 2 or more structures, but the reality is a

single hybriduDouble arrow indicates resonance

IONIC BONDINGuIONIC COMPOUNDS are composed of cations

and anionsuThe ions combine so that the sum of the charges is

equal to zerouMost exist as crystalline solids (salts)uForm 3-D network of many, many ions in a lattice

patternuElectrons transferred, not shared

IONIC BONDINGuA FORMULA UNIT is the simplest collection of ions

for which an ionic compound formula can be written

uExpressed using whole numbers in the most reduced form

uCation is listed 1st , Anion is listed 2nd

uCharges must sum to zero, but are not included in the formula unit

IONIC BONDING

IONIC BONDINGuIonic bonds minimized PE, resulting in an orderly

arrangement of ions as CRYSTAL LATTICEuAttraction exists between cations & anions, but

repulsion exists between like charged ions

IONIC BONDINGuLATTICE ENERGY describes the strength of an ionic

bonduIon sizes affect the number of surrounding ions

and crystal structureuIons of greater charge (2+/-, 3+/-) have a greater

attractive force

IONIC vs. MOLECULAR BONDING

uMolecular and ionic bonds are very stronguIonic bonds have a stronger force of attraction

among formula unitsuMolecules bond less strongly between each other

(intermolecular bonds)uIonic compounds are generally solid, hard, brittle,

and only conductive in an (aq) state

POLYATOMIC IONSuPOLYATOMIC IONS are a group of covalently

bonded atoms with an overall chargeuVery common in biology, chemistry, and industryu8 MUST KNOW POLYATOMIC IONS: (see board)

METALLIC BONDINGuMETALLIC BONDING results from the attraction

between metal atoms and their “delocalized” electrons

uMetals have few valence electrons, and many vacant orbitals

uThe overlap of vacant orbitals allows electrons to be mobile in a metal sample

METALLIC BONDING

METALLIC PROPERTIESuMALLEABILITY is the ability of a substance to be

hammered into thin sheets (Al, Au, Pb, Sn, etc.)uDUCTILITY is the ability of a substance to be drawn

into a wire (Cu, Al, Fe, Ag, Au, etc.)

METALLIC PROPERTIESuMetals are CONDUCTIVE (heat & electricity)uMetals can be polished to reflect light (LUSTER)

MOLECULAR GEOMETRYuProperties of molecules depend on the elements

and the shape of the moleculeuBond polarity and molecular polarity are

important characteristics of moleculesuThe shape can be predicted by the molecular

formula and VSEPR Theory

VSEPR THEORYuValence Shell Electron Pair Repulsion (VSEPR)uVSEPR THEORY states that repulsion between sets

of valence shell electron pairs around atoms causes the pairs to be oriented as far apart as possible

uUses all 3-D space and focuses on the internal atom(s)

VSEPR THEORY

VSEPR THEORYuBONDING PAIRS are the electrons involved in the

covalent bondsuNONBONDING PAIRS are “lone” pairs that are

unshareduBoth electron pair types repel others and

compete for spaceuNONBONDING PAIRS repel stronger than bonding

pairs

HYBRIDIZATIONuHYBRIDIZATION is the

“blending” of the different energy s & p orbitals to produce hybrid orbitals of averaged and equal energy

uEvidence for HYBRIDIZATION is seen in the fact that all bonding regions around an atom appear uniform

HYBRIDIZATION

INTERMOLECULAR FORCESu INTERMOLECULAR FORCES (IMF)

are the forces of attraction between molecules

uVary in strength, but generally weaker than covalent bonds (intramolecular – “within”)

u IMFs: Dipole-Dipole Interactions, Hydrogen Bonding, Dispersion Forces

INTERMOLECULAR FORCES

MOLECULAR POLARITYuPOLAR MOLECULES have a strong IMFuPolar molecules act as DIPOLES which are equal

and opposite partial chargesuBOND POLARITY and MOLECULAR GEOMETRY

determine molecular polarityuMolecules are generally POLAR or NON-POLAR

MOLECULAR POLARITY

HYDROGEN BONDINGuHYDROGEN BONDING is an IMF where an H atom

bonded to an N, O, F atom in a molecule is attracted to the non-bonding electrons of an electronegative atom in a nearby molecule

uSmall size of H atoms and partial positive charge allows for hydrogen bonding

uRepresented by dotted lines

HYDROGEN BONDING

DISPERSION FORCESuDISPERSION FORCES are the attractions that result

form the constant motion of electronsuCreates instantaneous and weak dipolesuActs on all atoms and molecules – including

Noble Gases and Non-Polar MoleculesuDISPERSION FORCES are stronger for higher

electron or mass atoms and molecules

DISPERSION FORCES