Science Guyz Chapter 1

Electronegativity

tendency of atom to attract electrons density towards itself causing unequal distribution in electrons

Ionic bonds

Electronegativty difference exceeds 1.7: attraction between oppositely charged ions

Covalent bonds

Electronegativity difference of 0 - 0.5: equal electron sharing

Polar covalent bond

in between 0.5 and 1.7: one atom pulls more strongly creating induction

Induction

tendancy of atoms to pull toward itself: represented by dipole arrow

Increasing electronegativity

towards right side and up

homolytic cleavage

breaks a non-polar covalent bond, with each atom retaining one electron, forming radicals

non metal + nonmetal doesn’t necessarily mean always covalent and non metal + metal doesn’t necessarily always mean ionic

Heterolytic cleavage

Breaks polar covalent bond

more electronegative atoms retains both electrons: formin an anion

curved arrows

depict electron movement

arrow shows the direction of electron flow

from source to destination

double headed arrow

shows an electron pair moving

single headed arrow

shows a single electron moving

formal charge

valence electrons - dots - lines

valence electrons of ions depend on charge

Lewis Structure Format

1. Sum up total valence electrons

2. Determine Central Atom (Usually Most Electropositive or in organic molecules always carbon)

3. Add valence electrons of central atom to central atom

4. Connect atoms via covalent bonds ( try to give each atom full octet)

5. Minimize formal charge

Exceptions to Octet Rule

Hyrogen only needs two e- for outer shell and still be stable with 0 e-

Boron only needs 6e- for stability

Beryllium only needs 4e- for stability

Non metals in period 3 or higher can have more than 8 electrons

formal charge can be negative

kekule structures

Like Lewis structures but omit lone pairs

Constitutional Isomers

Compounds with same molecular formula but differ in connectivity

have different physical properties

electrons are organized according to their energy level (n=1,n=2,etc) and sub-level (s,p,d,f)

atomic orbitals

atomic orbital

region of space in atoms where electrons are most likely to be found

degenerate orbitals

same energy level. Ex: 3 p orbitals

Shading of Orbitals represents phases. Shaded is + and not shaded is -

aufbau princple

lower energy Orbitals are filled first

Pauli Exclusion principle

each orbiatle can have 2 electrons. Must have opposite signs

Hunds Rule

Degenerate orbitals must be filled individually before spin-pairing

What happens when atomic orbitals combine according to molecular orbital (MO) theory?

• The number of orbitals is conserved.

• Two atomic orbitals combine to form two molecular orbitals:

  • Bonding MO: lower energy

  • Antibonding MO: higher energy

• Antibonding MOs have misaligned phases/shading, creating a node (a region of destructive interference).

Highest Occupied Molecular Orbital (HOMO)

highest energy molecular orbital where electrons can be found

Lowest Unoccupied Molecular Orbital

Lowest energy molecular orbital where electrons can not be found

Why doesn’t helium exist as an diatomic like H2

Its anti-bonding orbital is filled

valence bond theory

covalent bond forms when:

two atoms reach an ideal bond length

orbital with one electron from each atom overlaps

sigma bonding

Same shaded region overlaps horizontally

results in single bonds

Sigma Antibonding

Opposite shaded regions overlap horizontally

pi bonding

side to side overlap of same shaded p orbitals

anti pi bonding

side to side opposite shaded overlap of p orbitals

Hybridized orbitals

an atom ( besides hydrogen) bonds with atomic orbitals to create new ones that are more effective for bonding

sp³ Hybridization

one s orbital with 3 p to form 4 degenerate sp³ orbital

Tetrahedral

109.5 degree bond angle

sp² Hybridization

one s orbital with 2 p to form 3 sp² and one unhybridized p orbital

trigonal planar

120 degree bond angle

sp hybridization

one s with one p to form 2 hybridized sp leaving behind 2 u hybridized p orbitals

linear

180 degree bond angle

Hybridization and Electron Density

2 regions of electron density = sp

3 regions of electron density = sp²

4 regions of electron density = sp³

Electron density exception

radicals are not counted

sigma bonding in Kekule structures

Number of Bonding Regions + number of hydrogens

Ex: This has 28

pi bonding in kekule structures

Extra lines in the bonding regions

Ex: this has 4

Linear (sp) = 2 pi bonds

4 example if there are 4 pi bonds then there are 2 sp

Trigonal Planar (sp²) = 1 pi bond

4 example if there are 4 pi bonds then there are 4 sp²

Tetralhedral = 0 pi bonds

find this by finding number of bonding regions then subtraction number is sp² and sp

VESPR Theory

Builds upon hybridization

influence of lone pairs on molecular geometry

Molecular Geometry takes into consideration lone pairs while Electronic does not

Trigonal Planar Electronic Geometry that includes one lone pair

Bent Molecular Geometry

Less than 120 degrees bond angle

Tetrahedral electron geometry that includes one lone pair

Trigonal Pyramidal Molecular Geometry

107 degree bond angle

Tetrahedral Molecular Geometry that includes 2 lone pairs

Bent Molecular Geometry

105 degree Bond angle

shorter bonds are stronger

Higher Bond Order

More shorter

Increase S character

Increased bond strength and decreased length

% s character = (number of s orbitals/ number s orbitals + number of p orbitals) * 100

Hydrogen Halides

The Bigger the Halogen, The longer the bond

indicator of polarity

=

Molecular with polar bonds can still be non polar if the polar bonds cancel each other out

Molecular Dipole Moment

Represents Sum of all dipole moment in a molecule

Dispersion Forces (LDF)

weakest type of IMF

When comparing Constitutional Isomers

More branched structures have weaker LDF

Larger atoms have stronger dispersion forces

Dipole-Dipole Interaction

Next strongest IMF

More polar bonds makes it stronger

H Bond (Strongest IMF)

When Bonded to O,N, or F

Similiar IMF =

Better solubility

To be an Hydrogen donor

hydrogen needs to be connected to O,N, or F

Hydrogen Acceptor

O,N,or F needs a lone pair

methine group

CH

methylene group

CH₂

Methyl group

CH₃