Unit 1: Structure and Bonding

Question 1

Define organic chemistry

Answer 1

The study of carbon containing compounds

Question 2

Why did the results of the experiments carried out by Wohler contribute to the demise of the “vital force” theory?

Answer 2

Vitalism = widespread belief that organic compounds were formed by a vital force present only in living organisms
- refuted by Wohler
- Wohler reported the synthesis of urea, a component of many body fluids, from nonliving materials
- Since then it’s recognized that organic molecules obey the same natural laws as inorganic substances, and the category of organic compounds has evolved to include both natural and synthetic compounds that contain carbon

Question 3

Organic molecules

Answer 3

*definition not identified but most agree:

Defining trait of organic molecules is the presence of carbon as the principal element, bounded to hydrogen and other carbon atoms. Most are formed by living things, although they’re also formed by geological and artificial processes

Question 4

Are all carbon-containing compounds classified as organic?

Answer 4

NO.
- ex. carbonates and cyanides, simple oxides (CO, CO2)

Question 5

What are organic compounds key components of?

Answer 5

Plastics, soaps, perfumes, sweeteners, fabrics, pharmaceuticals

Question 6

Describe the basic structure of the atom

Question 7

Atomic number

Answer 7

• The number of protons in the nucleus; each proton carriers a charge of +1
• Denoted by Z
• Almost all the MASS of an atom is contained within a nucleus which carries a positive electric charge whose value identifies each element and is known as the atomic number of the element
• In the neutral atom, the Z protons within the nucleus are balanced by Z electrons outside it

Question 8

Atomic weight

Answer 8

Weight measurements can only be made on the massive (but unknown) numbers of atoms that are observed in chemical rxns

Question 9

Electron

Answer 9

The fundamental carriers of negative electric charge
- almost all the volume of an atom consists of empty space in which electrons reside
- quantum particle = location at any moment cannot be specified
- electron cloud = the volume of space in which the electrons of an atom have a significant probability of being found
- radius of an atom defined arbitrarily, such as the boundary in which the electron can be found with 95% probability

Question 10

Neutron

Answer 10

• no electrical charge
• mass is almost the same as the proton
• most nuclei contain roughly equal numbers of neutrons and protons = these two particles together account for almost all the mass of the atom

Question 11

Mass number

Answer 11

The sum of the numbers of protons and neutrons in the nucleus
- represented by the symbol A
- Z is the atomic number, N is the neutron number
- Z + N = A

Question 12

Proton

Answer 12

Carriers of positive electric charge in the nucleus
- nuclear charge same as the electron charge

Question 13

What single parameter uniquely characterizes the atom of a given element?

Answer 13

Atomic number (Z) = the number of protons in the nucleus

Question 14

Nuclide

Answer 14

Any particular kind of nucleus
- ex. a nucleus of atomic number 7 is a nuclide of nitrogen
- characterized by the pair of numbers (Z, A)

Question 15

Isotopes

Answer 15

Two nuclides have the same atomic number but different mass numbers

Question 16

Nodal plane

Question 17

Node

Answer 17

Regions of zero electron probability

Question 18

Orbital

Answer 18

The volume of space in which the electron can be found within 95% probability
- probability density is greatest at r = 0 (at the nucleus) and decreases steadily with increasing distance; falls off smoothly with increasing r
- at very large values of r, the electron probability density is very small but not zero
- four types of orbitals (s, p, d, and f) have different shapes, and one orbital can hold max 2 electrons. p, d, f orbitals have different sublevels, thus can hold more electrons
- e configuration is unique to each element; energy level is determined by the period and the number of electrons is given by the atomic number
- orbitals on different energy levels are similar to each other, but occupy different areas in space. Ex. 1s and 2s both have s orbital characteristics but are found in different energy levels and they occupy different spaces around the nucleus

Question 19

Quantum mechanics

Answer 19

The study of matter and its interactions with energy on the scale of atomic and subatomic particles

Question 20

Wave function

Question 21

What 3 things happen to s orbitals as n increases?

Answer 21

1. They become larger, extending farther from the nucleus
2. They contain more nodes. This is similar to a standing wave that has regions of significant amplitude separated by nodes, points with zero amplitude
3. For a given atom, the s orbitals also become higher in energy as n increases because of their increased distance from the nucleus

Question 22

Ground-state electronic configuration

Question 23

Hund’s rule

Answer 23

The lowest-energy electron configuration for an atom is the one that has the maximum number of electrons with parallel spins in degenerate orbitals

Question 24

Pauli exclusion principle

Answer 24

Pauli’s Exclusion Principle states that no two electrons in the same atom can have identical values for all four of their quantum numbers. In other words, (1) no more than two electrons can occupy the same orbital and (2) two electrons in the same orbital must have opposite spins

Question 25

Aufbau principle

Answer 25

We construct the periodic table by following the aufbau principle
- First determine the number of electrons in the atom, then add electrons one at a time to the lowest-energy orbital available without violating the Pauli principle

Question 26

Valence electrons

Answer 26

Electrons in the outermost shell
- Electrons in filled inner orbitals are closer to the nucleus and more tightly bound to it, so they are rarely involved in chemical reactions

Question 27

3 main types of chemical bonds

Answer 27

1. Ionic bonds: result from electrostatic forces that exist between ions of opposite charge. These bonds typically involves a metal with a nonmetal.
2. Covalent bonds: result from the sharing of electrons between two atoms. The bonds typically involves one nonmetallic element with another.
3. Metallic bonds: found in solid metals (copper, iron, aluminum) with each metal bonded to several neighboring groups and bonding electrons free to move throughout the 3-dimensional structure

Question 28

Lewis Dot symbols

Answer 28

• representation of valence electrons
• allows you to keep track of valence electrons during bond formation

Question 29

Octet Rule

Answer 29

Atoms tend to lose, gain, or share electrons to reach a total of eight valence electrons, called an octet
- we know from quantum mechanics that the number 8 corresponds to one ns and three np valence orbitals, which together can accommodate a total of eight electrons
- two exceptions to the rule: He, which has a full n=1 shell, and H, which tends to gain or share its one electron to achieve the electron configuration of helium
- atoms often gain, lose, or share electrons to achieve the same number of electrons as the noble gas closest to them in the periodic table

Question 30

VSEPR (valence-shell electron-pair repulsion theory)

Answer 30

Simple model based on the fact that electrons repel each other, and that it is reasonable to expect that the bonds and non-bonding valence electron pairs associated with a given atom will prefer to be as far apart as possible

Question 31

Bond strength

Answer 31

aka bond dissociation energy
- the difference in potential energy between the lowest energy state (at the optimal internuclear distance) and the state where the two atoms are completely separated

Question 32

Covalent bond

Answer 32

The mutual attraction between negatively charged electron pair and two atoms’ positively charged nuclei
- strength of a covalent bond depends on the extent of overlap of the orbitals involved ; extensive overlap forms stronger bonds
- every covalent bond in a given molecule has a characteristic length and strength

Question 33

Ionic bond

Question 34

Lewis structure

Question 35

Lone-pair electron

Question 36

Nonbonding electron

Question 37

Sigma bond

Answer 37

Two electrons of opposite spin that form a bond with cylindrical symmetry

Question 38

Valence bond theory

Answer 38

In this model, covalent bonds are considered to for from the overlap of two atomic orbitals on different atoms, each orbital containing a single electron. The electrons become paired in the orbital overlap bonding the atoms together
- describes a chemical bond as the overlap of atomic orbitals

Question 39

Bond length

Answer 39

The optimum distance between two bonded nucleis wherein the energy reaches its lowest (most stable) value; aka the optimal internuclear distance
- the bond is stable because at this point, the attractive and repulsive forces combine to create the lowest possible energy configuration

Question 40

Bond angle

Question 41

Hybridization

Answer 41

1. Hybrid orbitals do not exist in isolated atoms. They are formed only in covalently bonded atoms
2. Hybrid orbitals have shapes and orientations that are very different from those of the atomic orbitals in isolated atoms.
3. A set of hybrid orbitals is generated by combining atomic orbitals. The number of hybrid orbitals in a set is equal to the number of atomic orbitals that were combined to produce the set
4. All orbitals in a set of hybrid orbitals are equivalent in shape and energy
5. The type of hybrid orbitals formed in a bonded atom create the molecular geometry as predicted by the VSEPR theory
6. Hybrid orbitals overlap to form sigma bonds
7. Lone pair electrons are often contained in hybrid orbitals

Question 42

sp3 hybrid

Answer 42

sp3 orbitals formed from mixing one s and three p orbitals
- hybridizing allows for the carbon to form stronger bonds than it would with unhybridized s or p orbitals

Question 43

pi bond

Question 44

sp2 hybrid

Question 45

sp hybrid

Question 46

What are the bond angles associated with sp3, sp2, and sp hybridized carbon atoms respectively?

Answer 46

109.5, 120, 180

Question 47

A single bond is a…

Answer 47

sigma bond
- sigma bonds are made by the overlap of 2 hybrid orbitals or the overlap of a hybrid orbital and a s orbital from H

Question 48

A double bond is made of…

Answer 48

A sigma bond and a pi bond
- pi bonds are made by the overlap of 2 unhybridized p orbitals

Question 49

A triple bond is made of…

Answer 49

A sigma bond and 2 pi bonds

Question 50

In what orbitals are lone pair electrons usually contained in?

Answer 50

Hybrid orbitals

Question 51

Lone pair electrons

Answer 51

An unshared pair of electrons

Question 52

Antibonding MO

Question 53

Bonding MO

Question 54

Molecular orbital (MO) theory

Question 55

Isomers

Answer 55

Different compounds that have the same molecular formula
- prevalence of organic isomers reflects the versatility of carbon in forming strong bonds to itself adn to other elements

Question 56

Constitutional isomers

Answer 56

When the group of atoms that make up the molecules of different isomers are bonded together in fundamentally different ways