Structure/Bonding

Organic Molecule

- a carbon-containing molecule, centered by carbon

- accompanied by oxygen, hydrogen, nitrogen, and/or phosphorous

- carbohydrates, proteins, lipids, and nucleic acids

Carbon

- group 4A element
- can form 4 covalent bonds
- able to bond one another to form long chains and rings

Nucleus

the positively charged dense center of an atom that is surrounded by a cloud of negatively charged electrons

Protons

positively charged particles

neutrons

electrically neutral particles

Atomic Number (Z)

number of protons in an atom's nucleus

Mass Number (A)

number of protons plus neutrons

Isotopes

atoms with the same atomic number but different mass numbers

Atomic Mass

weighted average mass in amu of an element's naturally occurring isotopes

Wave Equation

- mathematical equation which describes the behavior of a specific electron in an atom
- the wave function, or orbital, is the solution of the wave equation

s orbitals

spherical, nucleus at the center

p orbitals

dumbbell-shaped, nucleus at middle

d orbitals

elongated dumbbell shaped, nucleus at the center

Node

region of zero electron density, separates 2 lobes of each p orbital

Ground-State Electron Configuration

listing of orbitals occupied by an atom's electrons

Aufbau Principle

lowest energy orbitals fill first in the order of 1s -> 2s -> 2p -> 3s -> 3p -> 4s -> 3d

Pauli Exclusion Principle

only 2 electrons can occupy an orbital, and they must be of opposite spin

Hund's Rule

if 2 or more empty orbitals of equal energy are available, electrons occupy each with parallel spins until all orbitals have 1 electron

Chemical Bonding Theory

- atoms surround carbon at corners of a regular tetrahedron
- atoms form bonds because the resulting compound is more stable than the separate atoms

Valence Shell

atom's outermost shell

Ionic Bond

- ions held together by an electrostatic attraction
- formed as a result of electron transfers

covalent bond

- formed by sharing of electrons
- organic compounds have covalent bonds

Molecule

a neutral collection of atoms held together by covalent bonds

Electron-Dot Structures

represents valence shell electrons of an atom as dots

Line-Bond Structures

indicates 2-electron covalent bond as a line drawn between atoms

Lone Pair

valence electrons not used in bonding

Valence Bond Theory

the idea that covalent bonds are formed when orbitals of different atoms overlap

Bond Strength

measured by the amount of energy released when a bond forms and absorbed when a bond breaks

Bond Length

ideal distance between nuclei that leads to maximum stability

Bond Angle

angle formed between 2 adjacent bonds

sp3 Hybrid Orbitals

combination of an s orbital and 3 p orbitals

bond angle: 109.5°

geometry: tetrahedral

sp2 Hybrid Orbitals

combination of an s orbital and 2 p orbitals

bond angle: 120°

geometry: trigonal planar

sp Hybrid Orbitals

combination of 2 s orbitals with a single p orbital, gives 2 sp hybrids

bond angle: 180°

geometry: linear

Molecular Orbital Theory

a description of bonding in terms of molecular orbitals, which are orbitals associated with an entire molecule rather than an individual atom

Bonding MO

molecular orbital that is lower in energy than the atomic orbitals from which it is formed

Antibonding MO

molecular orbital that is higher in energy than the atomic orbitals from which it is for

Condensed Structures

C-H or C-C single bonds are not shown, they are understood

Rules for Drawing Skeletal Structures

- carbon atoms aren't usually shown
- carbon atom is assumed to be at each intersection of 2 lines and at the end of each line
- hydrogen atoms bonded to carbon aren't shown
- atoms other than carbon and hydrogen are shown

Sigma Bonds

circular cross-section and are formed by head-on interaction

Pi Bonds

formed by sideways interaction of p orbitals