Chapter 1-A Review of General Chemistry

Created by kmcdaniel223 

Upgrade to
remove ads

What are constitutional isomers?

-compounds that have the same molecular formula but differ in the way that atoms are connected

What does the term valence describe?

-the number of bonds usually formed by each element

How many bonds does hydrogen prefer to form?

-1

How many lone pairs does hydrogen prefer to form?

-0

How many bonds does carbon prefer to form?

-4

How many lone pairs does carbon prefer to form?

-0

How many bonds does nitrogen prefer to form?

-3

How many lone pairs does nitrogen prefer to form?

-1

How many bonds does oxygen prefer to form?

-2

How many lone pairs does oxygen prefer to form?

-2

How many bonds does F prefer to form?

-1

How many lone paris does F prefer to form?

3

How many bonds does neon prefer to form?

-0

How many lone pairs does neon prefer to form?

-4

How many bonds do halogens (F, Cl, BR, or I) prefer to form?

-1

How many lone pairs do halogens prefer to form?

-3

How many electrons does the first shell of an atom hold?

-2

How many electrons does the second shell of an atom hold?

-8 electrons

What are organic compounds?

-are derived from living organisms
-contain carbon atoms

What are inorganic compounds?

-derived from non-living things
-lack carbon atoms

What is a covalent bond?

-a bond formed through the sharing of electrons between atoms

How is the number of valence electrons determined?

-by consulting the periodic table of elements
-the number of valence electrons in an atom is identified by its group number in the periodic table

What happens (in terms of energy) when electrons are shared to form a bond?

-there is a decrease in energy, indicated by a negative value in delta H

What happens as atoms move closer to ideal separation distance?

-energy continues to be lowered

At some point, what happens?

-the force of repulsion between the nuclei beings to overwhelm the forces of attraction, causing the energy of the system to increase

What does the lowest point on an energy diagram represent?

-the lowest energy (most stable) state

What does this state determine?

-both the bond length and the bond strength

What is the octet rule?

-atoms bond in such a way so as to achieve the electron configuration of a noble gas
-outer shell will have 8 electrons (with the exception of H)

What is a lone pair?

-a pair of unshared or nonbonding electrons

What is a formal charge?

-a charge associated with any atom that does not exhibit the appropriate number of valence electrons

How do you calculate formal charge on an atom?

1. determine the appropriate number of valence electrons for an atom (by consulting the periodic table)
2. determine whether the atom exhibits the appropriate number of electrons

What are the three categories that chemists classify bonds into?

-covalent
-polar covalent
-ionic

What do these categories emerge from?

-the electronegativity values of the atoms sharing a bond

What is electronegativity?

-a measure of the ability of an atom to attract electrons

What is the electronegativity of carbon?

-2.5

Of nitrogen?

-3.0

Of oxygen?

-3.5

Of flourine?

-4.0

Of chlorine?

-3.0

Of sulfur?

-2.5

What electronegativity trends does the periodic table exhibit?

-increases from the right to the left
-increases from bottom to the top

What if the difference in electronegativity between atoms is less than 0.5?

-the electrons are considered to be equally shared between the two atoms, resulting in a covalent bond

What if the difference in electronegativity between atoms is between 0.5 and 1.7?

-the electrons are not shared equally between the atoms, resulting in a polar covalent bond

What occurs when polar covalent bonds are formed?

-electrons tend to shift away from lower electronegativity atoms to higher electronegativity atoms

What is this withdrawl of electrons called?

-induction

What does induction cause?

-the formation of partial positive and partial negative charges

What happens if the difference in electronegativity is greater than 1.7?

-electrons are not shared at all, resulting an ionic bond

What is an ionic bond the result of?

-the force of attraction between the two oppositely charged ions

What is an atomic orbital?

-a region of space where there is a high probability (90-95%) of finding an electron; a region of space that can be occupied by electron density

Describe the shape/properties of electrons?

-electrons are not purely particles, they have wavelike properties as well

What is a wave equation?

-an equation that is constructed to describe the total energy of a hydrogen atom

What does it take into account?

-the wavelike behavior of an electron that is in the electric field of a proton

What is the wave equation solved to give?

-a series of solutions called wavefunctions

What does each wavefunction correspond to?

-an allowed energy level for the electron

What are the three possible phases of an electron's wavefunction?

-(+), typically represented by the color red
-(-), typically represented by the color blue
-(0), known as a node

What are the three atomic orbitals that most organic compound utilize?

-1s
-2s
-2p

How many electrons can occupy the 1s orbital? How many nodes does it have?

-can be occupied by 2 electrons
-has no nodes

How many electrons can occupy the 2s orbital? How many nodes does it have?

-can be occupied by 2 electrons
-has 1 node

How many two p orbitals are there?

-3

How many electrons can occupy each 2p orbital? How many nodes does it have?

-can be occupied by 2 electrons
-has 1 node

What are degenerate orbitals?

-orbitals with the same energy level

What do the Aufbau principle, the Pauli exclusion principle, and Hund's rule help to determine?

-the order in which atomic orbitals are filled

What is the Aufbau principle?

-the lowest-energy orbital is filled first

What is the Pauli exclusion principle?

-each orbital can accommodate a maximum of two electrons that have the opposite spin

What is Hund's rule?

-when dealing with degenerate orbitals (such as p orbitals), one electron is placed in each degenerate orbital first, before electrons are paired up

Two waves/atomic orbitals that approach each other can interfere in which two possible ways?

-constructively; or
-destructively

What does constructive interference produce?

-a wave with a larger amplitude

What does destructive interference result in?

-waves canceling each other, which produces a node

According to valence bond theory, what is a bond?

-the sharing of electron density between two atoms as a result of the constructive interference of their atomic orbitals

When two hydrogen atoms bond, where is the electron density of this bond located?

-primarily on the bond axis

What type of bond is this?

-a sigma bond

What is the definition of a sigma bond?

-a bond that is characterized by circular symmetry with respect to the bond axis

What is molecular orbital theory?

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

What are some of the key distinctions between atomic orbitals and molecular orbitals?

-atomic orbitals are regions of space associated with an individual atom while a molecular orbital is associated with an entire molecule

According to MO theory, what happens when two atomic orbitals overlap constructively?

-they cease to exist, and are replaced by two molecular orbitals that are each associated with the entire molecule

In simple hydrogen bond, what two molecular orbitals can be formed?

-bonding MO
-antibonding MO

What is the bonding MO a result of?

-constructive interference of the original two atomic orbitals

Is the bonding MO high in energy or low in energy? Does it have any nodes?

-low in energy
-has no nodes

What is the antibonding MO a result of?

-destructive interference of the two original atomic orbitals

Is the antibonding MO high in energy or low in energy? Does it have any nodes?

-high in energy
-has one node

Why are MOs a more complete analysis of bonds?

-because they include both constructive and destructive interference

What must the number of MOs created be equal to?

-the number of atomic orbitals that were used

What type of bonds does MO theory better describe?

-double bonds

What are hybridized atomic orbitals?

-atomic orbitals that are combinations of different orbital types (such as s and p)

Is the hybridization process a real physical process that the orbitals undergo?

-no
-it is a mathematical procedure that is used to arrive at a satisfactory description of the observed bonding

What type of hybridization does the C in CH4 undergo?

-sp3

What orbitals are combined to form the sp3 orbitals?

-2s orbital and the 2px, 2py, and 2pz orbital

How do the 4 sp3 orbitals compare in energy?

-they are degenerate (equal)

Why must the orbitals be equal in energy?

-to form four equal-energy symmetrical C-H bonds

What type of hybridization do the carbons in CH2CH2 undergo?

-sp2

What orbitals are combined to form the sp2 orbitals?

-2s orbital and 2 2p orbitals

What then remains?

-one 2p orbital

What can the 2 2p orbitals of CH2CH2 do?

-form a pi bond

Where does the pi overlap occur?

-above the plane of the molecule and below the plane of the molecule

What does this mean?

-that the pi bonds are not closely tied to the plane of the molecule

Describe the MO theory of pi bonds

-p orbitals can overlap constructively to form a pi bonding MO
-p orbitals can overlap deconstructively to form a pi anti-bonding MO

Describe the anti-bonding MO

-an extra node is formed, the molecule is at high energy

What is the molecular formula of ethane?

-CH3CH3

What is the number of sigma bonds and pi bonds that are used by the carbons in ethane?

-4 sigma bonds

What is the molecular formula of ethylene?

-CH2CH2

What is the number of sigma bonds and pi bonds that are used by the carbons in ethylene?

-3 sigma bonds, 1 pi bond

What is the molecular formula of acetylene?

-CHCH

What is the number of sigma bonds and pi bonds that are used by the carbons in acetylene?

-2 sigma bonds, 2 pi bonds

Rank the C-C bond length of ethane, ethylene, and acetylene increasing order

1. acetylene
2. ethylene
3. ethane

Rank bond energy of ethane, ethylene, and acetylene increasing order

1. ethane
2. ethylene
3. acetylene

What is an atom's steric number used for?

-to determine an atom's hybridization/geometry

What is an atom's steric number equal to?

-number of sigma bonds plus number of lone pairs

What does the steric number indicate?

-the number of electron pairs (bonding and nonbonding) that are repelling each other

What does this repulsion cause?

-the electron pairs to arrange themselves in three-dimensional space so as to achieve maximal distance from each other

What is this principle called?

-valence shell electron pair repulsion (VSEPR) theory

What will the hybridization of a central atom be with a steric number of 4?

-sp3

What will the hybridization of a central atom be with a steric number of 3?

-sp2

What will the hybridization of a central atom be with a steric number of 2?

-sp

What will the hybridization of a central atom be with a steric number of 1?

-not applicable

What electron group geometry will all sp3 hybridized atoms form?

-tetrahedral

What molecular geometry will be formed by an sp3 hybridized atom with no lone pairs?

-tetrahedral

With one lone pair?

-trigonal pyramidal

With two lone pairs?

-bent

What electron group geometry will all sp2 hybridized atoms form?

-trigonal planar

What molecular geometry will be formed by an sp2 hybridized atom with no lone pairs?

-trigonal planar

With one lone pair?

-bent

What electron group geometry will all sp hybridized atoms form?

-linear

What molecular geometry will all sp hybridized atoms form?

-linear

What is dipole moment?

-a measurement that is used to calculate the degree of induction

What is induction?

-shifting of electrons within their orbitals towards atoms with greater electronegativities

How is dipole moment calculated?

-by multiplying the amount of partial charge by the distance of separation (between the partial positive and partial negative charges)

What does measuring the dipole moment of a particular bond allow for?

-the calculation of the percent ionic character of that bond

When dealing with a compound that has more than one polar bond, what must be done?

-you must take the vector sum of individual dipole moments

What is this vector sum called?

-the molecular dipole moment

To be polar, what must a molecule have?

-polar bonds; and
-asymmetric geometry

What happens if a molecule does not have asymmetric geometry?

-polar bonds will cancel each other out

What are intermolecular forces?

-electrostatic, attractive forces between individual molecules

What are electrostatic forces?

-forces that occur as a result of attraction between opposite charges

What are the three classifications of electrostatic attractions for neutral molecules?

-dipole-dipole interaction
-hydrogen bonding
-london dispersion forces/fleeting dipole-dipole interaction

Rank these three classifications in order from strongest to weakest

-hydrogen bonding
-dipole-dipole interactions
-london dispersion forces

What are dipole-dipole interactions?

-attractions that occur between a partial positive charge on one molecule and a partial negative charge on another molecule

What does the resulting net attraction result in?

-elevated melting point
-elevated boiling point

Is a hydrogen bond an actual bond? If not, what is it?

-no, it is not a bond
-it is a specific type of dipole-dipole interaction

What type of molecules hydrogen bond?

-very polar molecules that contain hydrogen and
either O, N, F, or Cl

Describe hydrogen bonding

-when a hydrogen atom is connected to an electronegative atom, the hydrogen will bear a partial positive charge
-this positive charge can interact with a lone pair from an electronegative atom of another molecule

What are compounds with H atoms that are capable of forming H-bonds called?

-protic

How do the strength of hydrogen bonds compare to covalent bonds?

-H bonds are 20 times weaker

What do H bonds result in?

-higher melting temperatures
-higher boiling points

What are london dispersion forces?

-fleeting dipole-dipole interactions

What will the constant random motion of electrons in a molecule sometimes produce?

-an electron distribution that is not evenly balanced with the positive charge of the nuclei

What does this result in?

-a temporary dipole, which can induce a temporary dipole in a neighboring molecule

What does this result in?

-a fleeting attraction between the two molecules

Why are london dispersion forces stronger for higher molecular weight hydrocarbons?

-because these compounds have larger surface areas that can accommodate more interactions

What does this result in?

-compounds of higher molecular weight will generally boil at higher temperatures

See More

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set