OC Chapter 2 HW

Sigma bond

1.its highest electron density between the nuclei of the bonding atoms 2. formed by the overlap of orbitals along the internuclear axis

Straight-chain alkanes are named according to the number of C atoms in the chain.

1C-Methane 3C-Propane 4C-Butane 6C-Hexane

sp^2 hybrid orbitals

1. A group of sp^2 hybrid orbitals assumes a trigonal planar geometry 2. The formation of sp^2 hybrid orbitals leaves one unhybridized p orbital

Pi bond

1. A multiple bond always contains at least one pi bond. 2. A pi bond is formed by the sideways overlap of two p orbitals

Van der Waals forces

1. All covalent compounds exhibit van der Waals forces 2. Van der Waals forces are a very weak attraction between temporary dipoles.

IUPAC rules of naming an alkane

1. Each substituent must be numbered, even if there are two or more of the same group in the compound. 2. Number the longest continuous chain in the direction that gives the lowest number to the substituent at the first branch point 3. The parent name is obtained by finding the longest continuous carbon chain.

CH2CH3-Ethyl CH2CH2CH2CH3-Butyl

CH3-Methyl CH2CH2CH2CH2CH3-pentyl

Alkyl group

A substituent such as methyl in an organic compound

Cracking- increases proportion of more volatile, lower-molecular weight hydrocarbons

Reforming-Hydrocarbons in light gasoline and naphtha are converted to aromatic hydrocarbons and highly branched alkanes.

Orbitals overlap to form the C-C sigma bond in ethane

Sp^3-Sp^3

Nonpolar molecules such as alkanes are not soluble in water, because the hydrogen bonding in water is too strong to be disrupted by the weak attraction between the alkane and water molecules.

The exclusion of nonpolar molecules from water is called the hydrophobic effect

To name a simple cycloalkane, the number of carbon atoms in the ring gives the parent name

and the prefix cyclo is added before this part of the name

The alkanes form a homologous series. This means that

each successive alkane differs from the previous one by a -CH2-group

Natural gas is mostly methane mixed with some ethane and propane and smaller amounts of other low-

molecular-weight alkanes, which release energy when they are burned.

Paraffin hydrocarbons is an older name for alkanes

testifies to the low level of reactivity of these hydrocarbons

In an organic reaction, the process of oxidation results in an increase in the number of C-Z bonds or a decrease in the number of C-H bonds,

where Z is an element with a greater electronegativity than H.

An alkyl group is named according to the number of C atoms it contains. An alkyl group with three carbon atoms joined in a straight chain is called a propyl group

whereas a methyl group has one carbon atoms.

Double bond

1 sigma+ 1 pi bond

Alkanes physical properties

1. Alkanes have lower boiling points than polar compounds of comparable size 2. Alkanes are nonpolar compounds 3. The melting point of alkanes generally increases as the number of carbon atoms in the chain increases.

Parent chain of an alkane

1. If the first substituent is the same distance from both ends, the chain is numbered to give the second substituent the lowest number 2. The chain is numbered to give the first substituent the lowest number

Cycloalkane

1. If there is an alkyl chain containing more C atoms than there are in the ring, the ring is named as a cycloalkyl substituent 2. If there is a single substituent on the ring there is no need to specify its position. 3. The parent name is given by the number of carbon atoms in the ring.

Covalent bond

1. In a stable covalent bond, nucleus-electron attractions dominate the system 2. If the two atoms in a covalent bond approach too closely, the system will become less stable. 3. As two atoms from a covalent bond, the energy of the system decreases.

Sp^3 hybrid orbitals

1. One s and three p orbitals mix to produce four sp^3 hybrid orbitals 2. The four sp^3 orbitals of a particular set are equal to each other in energy. 3. THe axes of sp^3 hybrid orbitals are directed towards the corners of a tetrahedron 4. The sp^3 hybrid orbitals are lower in energy than the p orbitals and higher in energy than the s orbitals.

Single covalent bond according to the valence bond model

1. Single bonding orbital is shared between the two atoms 2. The bonding electrons are most likely to be found between the two nuclei 3. two atoms bond by the overlap of a half-filled orbital from each atom

Structural isomers

1. Structural isomers are also called constitutional isomers 2. Structural isomers differ in the way their atoms are connected to each other 3. Structural isomers are different compounds

Alkane

1. The bond angles are close to 109.5 2. The general formula for alkanes is CnH2n+2 3. All C-C bonds in an alkane are single bonds

Combustion of alkanes

1. The combustion of alkanes is an exothermic reaction 2. CO2 is one of the products formed by complete combustion of an alkane

The changes that occur when a covalent compound boils

1. The compound becomes less ordered and intermolecular forces are broken 2. The stronger the intermolecular forces, the greater the amount of energy required for the change from liquid to gas

H2C=C=CH2

1. The end carbon atoms are sp2 hybridized 2. The pi bonds are perpendicular to each other 3. The central carbon is sp-hybridized Recall the relative orientation of the two pi bonds in HC=-C where each carbon is sp-hybridized, The central carbon forms two sigma and two pi bonds

Alkane structure and boiling point

1. The larger the surface area of an alkane molecule the higher the boiling point of the compound 2. A branched alkane has a lower boiling point than an unbranched alkane with the same molecular weight.

The C-C and C-H bonds of alkanes are nonpolar.

Alkanes exhibit only induced dipole-induced dipole intermlecular forces, causing their boiling points to be lower than alcohols of similar size

Orbital hybridization model

Chemical bonding approach describes pi-bond formation as the side to side overlap of atomic p orbitals

An alkane is a hydrocarbon that contains only C-C sigma bonds.

Each C atom in the structure is singly bonded to four other atoms and possesses tetrahedral geometry.

The heat released when a substance is burned is called the heat of combustion for that substance.

For alkanes, the amount of heat released increases as the number of C atoms in the compound increases but decreases as the amount of branching increases for the same number of C atoms.

An alkane parent chain is always numbered to give the first substituent the lowest possible number

If the first substituent is the same distance from both ends, the chain is numbered to give the second substituent the lowest possible number

crude oil fractions

Light gasoline and naphtha, kerosene, refinery gas, gas oil

Valence bond model- Describes bonding as the overlap of half-filled orbitals from two atoms

Molecular orbital model- Describies bonding as the combination of all atomic orbitals of all the atoms in a molecule

Compounds with the same molecular formula are called isomers. Systematic nomenclature helps us to distinguish between the two isomers of C4H10.

One of these has four carbon atoms in a continuous chain; the other is a three-carbon chain with a branch on the central carbon atom.

Prefix- identity, location, and number of substituents Suffix- Functional group of class of compound

Parent name- Number of C atoms in the longest continuous C chain

The more stable an alkane is to start with, the lower the amount of energy released when that compound undergoes combustion.

The heat of combustion can therefore be used to determine the relative stability of two isomers, since isomers always contain the same number of carbon atoms and any differences in energy released will be due to branching.

A momentary change in the electron density surrounding an atom or a molecule causes it to have a temporary dipole even if its not normally polar.

The induces a similar effect in a nearby molecule or atom and there will be a weak attraction between the two particles as a result. These weak interactions are called van der Waals forces.

According to the molecular orbital model of covalent bonding, orbitals are viewed as wave functions. Two orbitals may combine constructively to produce a bonding molecular orbital, which is lower in energy than the original atomic orbitals.

The same two orbitals may combine destructively to produce an antibonding molecular orbital, which is higher in energy than the original atomic orbitals.

When a substance is boiled, energy is required to overcome the attractive forces between molecules

The stronger these forces, the greater the amount of energy required to overcome them. Thus, the boiling point will be higher.

A number of different structural features affect the boiling point of a given alkane. THe higher the molecular weight of the alkane, the higher the boiling point whereas a branched alkane will have a lower boiling point than an unbranched isomer

These factors are all dependent on the strength of the intermolecular forces eperienced between individual alkane molecules.

In order to form four hybrid bonding orbitals of equal energy, one s and three p orbitals from the valence shell of a C atom "mix" to form four sp^2 hybrid orbitals.

These orbitals are equal in shape and energy and are arranged in a tetrahedral geometry.

Each C atom in an alkane is sp^3 hybridized and each C-C single bond is formed by the overlap of the hybridized orbital with an atomic orbital of another atom.

This overlap is along the internuclear axis in each case and so every C-C single bond is a sigma bond.

According to the valence bond model, a single covalent bond is formed by the overlap of two half-filled orbitals, one from each atoms.

This produces a new shared orbital where the highest electron density is between the two nuclei.

The hybridization of one s and two p orbitals will result in the formation of 3 sp^2 hybrid orbitals.

This will leave one unhybridized p orbitals, which is/are at right angles to the hybrid orbitals.

The hybridization of 1 s and 1 p orbital will result in the formation of two sp hybrid orbitals.

This will leave two unhybridized p orbitals, which are at right angles to the hybrid orbitals.