Unit 2

Types of Chemical Bonds, Intramolecular Force and Potential Energy, Structure of Ionic Solids, Structure of Metals and Alloys, Lewis Diagrams, Resonance and Formal Charge, VSEPR and Hybridization

metallic bonding

sea of electrons act as a buffer between repelling cations, between atoms with similar electronegativities

properties of metallic bonds

• good conductors

• high MP and BP

• malleable

nonpolar covalent bonding

equal/almost equal sharing of electrons, between atoms with similar high electronegativities (same element or C to H)

polar covalent bonding

unequal sharing of electrons, creates dipoles (partial negative/positive poles), between atoms of different high electronegativities

where do the electrons localize closer to in a polar covalent molecule

the atom with higher electronegativity

properties of covalent bonds

• poor conductors

• when in networks, high MP and BP

• when left as molecules, low MP and BP

• soft or brittle

ionic bonding

transfer electrons, between atoms with very different electronegativities, attraction between cations and anions

where do the electrons transfer to in an ionic bond

the atom with the higher electronegativity (nonmetal)

properties of ionic bonds

• poor conductors when solid

• good conductors when liquid

• form networks - high MP and BP

• brittle

delocalized electrons

electrons that can move around freely

localized electrons

“fixed” electrons restricted to a certain region

intramolecular force

attraction in a bond

bond energy/enthalpy

energy released when a bond forms/energy needed to break a bond, refers to covalent bonds

potential energy diagrams

relationship between potential energy (y) and bond length (x)

low potential energy means

more attraction (bond)

what creates higher attraction

smaller molecules, more bonds (double/triple bonds)

lattice energy

amount of energy needed to separate 1 mole of an ionic compound

always mention this when talking about lattice energy

coulomb’s law

coulomb’s law

attraction between two particles is based on high charge and low distance

which component of attraction is more important

charge

higher lattice energy

higher MP and BP

rxns to form ionic compounds typically

endothermic

rxns to form ionic compounds from gaseous ions are

exothermic because they need to come together to stabilize

lattice structure based on

minimized repulsions and maximized attraction (alternating cation-anion pattern)

alloy

replacing 1 metal atom with another metal atom, usually stronger than metals

types of alloys

substitutional and interstitial

substitutional alloy

consists of 2 metal atoms withe similar atomic radii and chemical properties

properties of substitutional alloys

malleable, stronger, retain many metallic properties

interstitial alloys

add smaller atoms to metal atoms, more disruptive effect on metallic bonding

interstitial element

non-metal that covalently bonds to the metal atoms

properties of interstitial alloys

less malleable, significantly stronger

properties of alloys in general

poor conductors, stronger and harder

general process of drawing lewis structures

1. count valence electrons

2. determine central atom

3. LP around terminal atoms

4. LP on central atom (if applicable)

5. double/triple bonds (if applicable)

6. brackets (if applicable)

7. resonance (if applicable)

how many electrons will fill Be’s valence shell?

4

how many electrons will fill B’s valence shell?

6

which atoms can form an expanded octet

period 3 and under (most commonly C, N, O, P, and S)

which atoms can’t form multiple bonds

F and Cl

resonance structures

show all possible lewis structures of a molecule

what happens in a bond orbital-wise

s & p orbitals overlap

sigma bond

s orbitals overlap

pi bond

p orbitals overlap

how many sigma/pi bonds in a single bond

1 sigma

how many sigma/pi bonds in a double bond

1 sigma, 1 pi

how many sigma/pi bonds in a triple bond

1 sigma, 2 pi

hybridization

combines s & p orbitals into a hybrid orbital for bonding, only occurs for the central atom

domain

regions of electrons; bonds and lone pairs

hybridization for 2 domains

sp

hybridization for 3 domains

sp²

hybridization for 4 domains

sp³

formal charge

tells you which structure is correct

formal charge equation

F.C. = #VE - #NBE - 1/2#BE

sum of the formal charges must equal

the charge of the molecule

in a neutral molecule, formal charges of all atoms must optimally be

close to 0

if the formal charge of all atoms cannot be 0, which atom should get the negative charge?

the most electronegative atom

VSEPR theory

molecules arrange to minimize repulsion between electron pairs (will space out as much as possible)

2 domains

linear

linear

linear bond angle

180

3 domains, 0 lone pairs

trigonal planar

trigonal planar

trigonal planar bond angle

120

3 domains, 1 lone pair

bent

bent

bent (1 LP) bond angle

<120

4 domains, 0 lone pairs

tetrahedral

tetrahedral

tetrahedral bond angle

109.5

4 domains, 1 lone pair

trigonal pyramidal

trigonal pyramidal

trigonal pyramidal

<109.5

4 domains, 2 lone pairs

bent

bent

bent (2 LP) bond angle

<109.5

5 domains, 0 lone pairs

trigonal bipyramidal

trigonal bipyramidal

trigonal bipyramidal bond angle

90, 120

5 domains, 1 lone pair

see saw

see saw

see saw bond angle

<90, <120

5 domains, 2 lone pairs

t shape

t shape

t shape bond angle

<90

5 domains, 3 lone pairs

linear

linear

6 domains, 0 lone pairs

octahedral

octahedral

octahedral bond angle

90, 90

6 domains, 1 lone pair

square pyramidal

square pyramidal

square pyramidal bond angle

90, <90

6 domains, 2 lone pairs

square planar

square planar

square planar bond angle

90

how to find electron geometry

same as molecular geometries with same number of domains and 0 LP

why are the bond angles with lone pairs slightly smaller

LP need more space to move around

nonpolar molecules

symmetrical, even distribution of partial negative/positive charges

polar molecules

asymmetrical, dipole moment

dipole moment

uneven distribution of charges

bond order

number of bonds / number of domains