Principles of Chemistry Exam for April

Top left

Ionization energy increases where...

bottom right

Atom radius increases where....

bonded atoms

To infer electron charge distribution in a molecule based on both differences of electronegativity between ________ ______ and molecular structure and geometry.

valence electrons

The properties of chemical compounds are influenced by how _________ ________ distribute among different atoms. This charge distribution can be inferred from molecular structure.

molecule

lone pairs are electron rich regions of _________

bonding electrons

some atoms exert stronger attractive forces on _______ _______ than other atoms.

Ionization energy trends

moving to the right side of the periodic table in a row, electrons in orbitals are at lower energy (harder to ionize).

electronegativity

is a measure of the decrease in the energy of a system if bonding electrons are localized in the vicinity of a given type of atom.

Electronegativities

the electron withdrawing ability of an atom can be used to estimate partial charges on bonded atoms.

dipole moment

the existence of dipole+ and dipole- partial charges creates a "_____ _____" in the bond.

+ and _

the dipole moment of the bond is represented by an arrow from the _ to the _ partial charge

polar

bigger the electronegativity difference more ______ the bond

molecular polarity

a molecules interaction with light (photons) and other molecules depends on bond polarity AND overall ______ ______.

lone pairs

Remember: electron density is also impacted by ______ _____.

may

even if there are no bond electronegativity differences, a molecular structure ______ have electron density differences and be a polar molecule.

vectors

bond dipole moments are added like "_______"

tetrahedral

Methane, CH4, ________, all angles 109.5 degrees

symmetry

molecular polarity can be inferred by analyzing the "_________" of its atomic charge distribution.

fully symmetrical

non-polar molecules have ______ ________ charge distributions.

polar

hydrocarbons that are modified with polar groups can become _______ molecules.

84

earth's atmosphere normally traps ___% of the solar energy re-emitted by the planet's surface.

greenhouse effect

This phenomenon is called "______ _______" and helps to keep an average Earth temperature of 15 degrees C or 59 degrees F.

visible

Greenhouse Effect step 1:

Earth receives energy from the sun (radiation), most of it is ______ light.

infrared

Greenhouse Effect step 2:

Earth surface absorbs the solar energy and releases it as ________ radiation.

re-emitted

greenhouse effect step 3:

some of the IR energy is absorbed by gas molecules in the atmosphere and __-________ (in the form of IR raditation) back to the Earth's atmosphere.

CO2 molecules

IR does interact with _____ _______

change

substances considered greenhouse gases absorb and reemit IR radiation. For a molecule to absorb IR radiation, there should be a ______ in its net molecular dipole moment when it vibrates.

dipole

stretching the bond doesn't change the ______

net charge

non-polar molecules, like CO2, absorb only for those vibrations that generate a ____ _______ in dipole moment to non-zero dipole.

NP

Is CF4 polar or non polar?

P

Is CHF3 polar of nonpolar?

P

is NH3 polar or nonpolar?

P

Is O3 polar or nonpolar?

bonding

in general, _______ electrons are not evenly distributed between the two atoms in a bond.

electronegativity

_________ is a measure of the ability of an atom in a bond to attract electrons to itself.

bond polarity

differences in electronegativities between atoms in a bond lead to an unequal distribution of charge (______ ______).

polar the bond

the larger the difference of electronegativities, the more _____ ____ ______.

molecular polarity

______ ______ refers to the charge distribution in the entire molecule.

symmetry

molecular polarity can be inferred by analyzing the "_______" of the charge distribution (consider bond polarity, lone pair distribution, and overall shape).

IR radiation

Non-polar molecules and molecules with more than one non-polar bond can absorb ___ _______. (IR active)

CO2

Non-polar molecules/ions that absorb IR radiation: CF4, C2H6, N3-, _____

NCl3

Polar molecules with non-polar bonds that absorb IR: O3, ____

forensic science

the determination of a substance's identity based on the analysis of its molecular structure is a fundamental analytical tool in ______ ______.

objects

based on symmetry, we may think the molecule could be non-polar.

however, molecules are dynamic ______ and polar ends are separated by non-polar middle hydrocarbon.

hydrophilic

Water attractive surface

hydrophobic

water repellant surfaces

with other particles

molecular geometry, bond polarity, and molecular polarity affect how a molecule interacts ____ ______ ______ (atoms, ions, molecules)

collective

Physical properties

(e.g., state of matter, density, boiling and melting points, vapor pressure, heat capacity, solubility)

arising from ________ IMFs.

stronger

__________ IMFs mean stronger intermolecular attractions (harder to break - higher energy/heat needed) leading to:

higher boiling points

stronger IMFs mean stronger intermolecular attractions (harder to break - higher energy/heat needed) leading to:

1) ____ _____ _____ (bp) liq->gas (also leads to higher melting points)

lower vapor pressures

stronger IMFs mean stronger intermolecular attractions (harder to break - higher energy/heat needed) leading to:

2) _____ _____ _____ (gas leaving a liquid surface - breaking liq-liq IMFs) - this is the same as lower volatility!

higher viscosity

stronger IMFs mean stronger intermolecular attractions (harder to break - higher energy/heat needed) leading to:

3) ______ _______ (how easily a liquid flows - highly viscous liquids flow slowly - like honey or oil vs. water or alcohols.

intermolecular

Stronger IMFs mean stronger ___________ attractive cause more energy needed.

polar covalent bonds

nonmetallic elements can combine to form molecules with ______ ______ _____.

interactions

many physical properties of molecular compounds are determined by the strength of the _______ between their molecules.

attract or repel

interactions between molecules arise from their charged regions (from electrons and protons) that ______ __ _______ each other with forces that vary depending on the intermolecular distance.

polarizability

the relative strength of IMFs between different types of molecules depends on molecular properties such as:

-bond polarity

-molecular polarity

-_________

polarizability

measure of how electrons in an atom, molecule or ion are affected by (attracted/repelled) the presence of other atoms, molecules or ions in their vicinity.

polarizes

the presence of other partial charges _______ the molecule and creates an "induced dipole moment," which may be new or strengthen an existing one.

II because it is bigger

1 has 14P+ and 14e- but is smaller

2 has 10 P+ and 10 e- but is bigger

Which is more polarizable?

2 because of its more electrons

1 has 10 P+ and 10 e-

2 has 14 p+ and 14 e-

they are both the same size

which is more polarizable?

larger

polarizability is generally larger with more electrons over a _______ volumes and a more exposed area (shape effects).

permanent

when two atoms or molecules get close together, the IMF interactions between electrons and protons induce ___________ dipole moments ( temporary polarization) that cause the particles to attract each other.

major contribution

dispersion forces (induced dipoles) are the _____ _______ to IMFs between atoms and molecules of most substances.

all

____ molecules interact via dispersion forces created by interactions between induced dipoles.

induced dipoles

the easier it is to create these _____ _______, the stronger are the dispersion forces.

regions

more polarizable molecule are larger ones with more polarizable ______

more

molecules with a large surface area, such as those with flat or elongated geometries, are likely to be _____ polarizable than those with more compact spherical shapes.

additional

molecular polarity is an ______ contribution to IMFs.

dipole-dipole

in the case of polar molecules additional contributions to the IMFs arise from the presence of permanent molecular dipoles moments in the system. These types of IMFs are called _____-_____ forces.

additional

dipole-dipole forces are an ______ attractive contribution, besides dispersion forces, to the total IMFs between polar molecules.

dipole-dipole

total IMFs = dispersion + ______-_______

F,O,N

bond polarity is particularly relevant in molecules in which H is bonded to ___,____,___

hydrogen bond

the particular bond dipole-dipole interaction that occurs between a hydrogen atom bonded to a N, O, or F atom and another N, O, or F atom is called a "______ ___"

(an IMF bonding interaction, not a covalent bond)

smaller

the energy needed to overcome IMFs interactions is _______ than what is normally required to break a covalent bond

high

in general, lubricants (oils) are expected to have high viscosities and low volatilities (= _____ IMFs)

reduces

the presence of "branches" ________ the effective contact area over which molecules can interact, decreasing IMFs.

volatilities

Lower IMFs lead to lower:

melting points

boiling points

viscosities

and higher

_________

different

when _______ types of substances are in contact with each other in a mixture, additional types of interactions may occur.

stronger

Mixing and potential energy

particles are more likely to adopt those states where the IMFs between them are ______ (lower potential energy, Ep)

configurations

Mixing and configuration effects

particles are more likely to adopt states with more ______ (more ______ -> more time spent on those states)

intermolecular interactions

the physical properties of a molecular compounds, "emerge" from the ________ _______ among the millions of molecules present in macroscopic sample of the material. (such as boiling point, vapor pressure, viscosity, miscibility)

intermolecular forces

_______ ______ arise because atoms, molecules, and ions have charged regions in a particle that may be unevenly distributed and dynamic. (changing)

energy

the stronger the intermolecular forces, the more ______ is required to separate the molecules from each other.

hydrogen bonding

the physical properties of many molecular compounds are determined by the polarity and polarizability of their molecules and the possibility of _______ _______.