Final Exam CH 101

Covalent Bond

Atoms of similar electronegativity (generally 2 nonmetals) share electrons

Ionic Bonds

transfer of electrons occurs due to atoms with a very large difference in electronegativity (metal and nonmetal)

Metal

Low ionization, low electronegativity (cations)

Non-metal

High ionization, high electronegativity (anions)

Ionization Energy

minimum energy needed to completely remove an electron from atom

Electronegativity

tendency to attract electrons

Naming Binary Ionic Compounds

name of cation followed by nonmetal anion with -ide ending

Transition Metals

+1 +2 or +3 charge (indicated by roman numeral)

Polar Covalent Bond

Difference in electronegativity is small (2 nonmetals)

Nonpolar Covalent Bond

Difference in electronegativity is ~ 0 (2 nonmetals or between C and H)

Bond dipole

unequal sharing of electrons that can exist in a covalent bond

Octet Rule

Nonmetals achieve closed valence shells of 8 electrons by sharing electrons

Steps for Drawing Lewis Structures

1) count # of valence electrons

2) if 2 atoms are present, draw a single bond (2 e-) between each atom (if 3 or more atoms are present, place the least electronegative, nonH atom in the center, then draw a single bond to connect the central atom to the surrounding atoms)

3) place all remaining valence e- on atoms as lone pairs

4) give octet to every atom that requires it

Bond Energy

Energy input required to break a bond

Bond length

distance between the nuclei of 2 atoms engaged in a bond

Formal Charge Formula

FC (atom) = # VE - Non Bounded - ½ B e-

Formal Charge definition

electron counting method for covalent bonds (assuming e- are shared equally) & hypothetical charge assigned to an atom as a tool to help evaluate molecular stability and predict reactivity

Resonance structure

alternate lewis structure depiction of the same molecule where atom connectivity remains the same, and the number of electrons remains the same… but the electrons are simply distributed around differently

Resonance Structure Hierarchy Rule 1

each atom that requires an octet has an octet

Resonance Structure Hierarchy Rule 2

Total number of atoms with nonzero formal charges is minimized

Resonance Structure Hierarchy Rule 3

If a formal charge has to exist (and it can be placed on different atoms), place the formal charge on the most appropriate atom (taking into consideration EN)

Convert the name “calcium chloride” into a chemical formula.

CaCl₂

Convert the formula Na₂SO₄ into a name.

Sodium sulfate

What is a polyatomic ion?

A covalently bonded group of atoms that carries a charge (e.g., NO₃⁻, SO₄²⁻).

What is a bond dipole?

An unequal sharing of electrons in a covalent bond, shown with a dipole arrow toward the more electronegative atom.

What are the octet rule exceptions?

Exceptions: H (2 e⁻), Group 3A (6 e⁻), expanded octets (row 3+).

Define bond order

Bond order = # of shared bonds

What is the relationship between bond order, length, and strength?

Higher bond order → shorter and stronger bonds. Lower bond order → longer and weaker bonds.

What is hybridization?

The mixing of atomic orbitals to form hybrid orbitals for bonding.

What is the ideal gas law?

PV = nRT.

Sigma bond

covalent bond formed by direct orbital overlap along the axis connecting the two nuclei

Pi bond

covalent bond formed by side to side overlap of p orbitals above and below the internuclear axis

Electron Domain

Area where electrons are likely to be found (lone pairs or bonds) around central atom

Electron domain geometry

3D arrangement of electrons around a central atom

Molecular geometry

3D arrangement of atoms in a molecule

Hybridized orbital

orbital formed by combination of atomic orbitals

bond angle and electron domain geometry with two electron domains?

180 degrees and lienear

bond angle and electron domain geometry with three electron domains?

120 degrees and trigonal planar

molecular geometry for four electron domains with two being lone pairs?

bent (109.5)

molecular geometry for four electron domains with one being a lone pair?

trigonal pyramidal (109.5)

molecular geometry for three electron domains with one being a lone pair?

bent (bond 120)

What is bond angle determined by?

The bond angle of a molecule is determined by the electron domain geometry, which is based on the total number of electron domains around the central atom, but is then influenced and distorted by the presence of lone pairs, leading to the specific molecular geometry.

Count σ bonds + lone pairs on the atom = number of hybrid orbitals.

• 4 → sp³

• 3 → sp²

• 2 → sp

hybridized orbitals make what type of bonds

make sigma bonds or hold lone pairs

un-hybridized p orbitals make what type of bonds

make pi bonds or remain empty

Molecular orbital

def: model used to describe the electronic structure of molecules using quantum theory. importance: detailed information regarding the electromagnetic properties of molecules

HOMO

highest occupied molecular orbital

LUMO

lowest unoccupied molecular orbital

antibonding molecular orbital

higher energy molecular orbital * (ant on E)

bonding molecular orbital

lower energy molecular orbital

paramagnetic

molecules with unpaired electrons, attracted to an external magnetic field

diamagnetic

molecules with all electrons paired, not attracted to an external magnetic field

difference of importance of hybridization and MO

hybridization gives the geometry of a molecule and its bonds, MO gives electromagnetic properties of molecules

difference in definition of hybridization and MO

hybrid- model used to describe the orbital structure of atoms engaged in bonding, MO model used to describe electronic structure of molecules using quantum theory

Ideal Gas Law

Pv = nRT

Partial Pressure

pressure a single gas in a mixture exerts if it alone occupied the volume

Intermolecular Forces

Attractive interactions that keep molecules together

Intramolecular Forces

Bonds within a molecule holding atoms together

London Dispersion forces

Temporary induced dipole that results from molecular motion (greater atom/molecule, greater force)- weakest Intermolecular (REQURIEMENTS- all molecules and atoms)

Dipole-dipole interactions

When molecular dipoles from two molecules are attracted to each other , second weakest intermolecular force (REQUIREMENTS: two polar molecules)

Hydrogen Bonding

When a partial positive hydrogen atom on one molecule bonds with a partial negative N O or F atom on a second molecule, strongest intermolecular force (REQUIREMENTS: partial (+) H and partial (-) N, O, or F) (NO CH)

Greater Strength of Intermolecular forces does what to boiling and melting points?

Greater Boiling and Melting Points

Molecular Dipole

the uneven distribution of charge within a molecule, resulting in a partially positive end and a partially negative end, which gives the molecule a net polarity and a dipole moment

Solution

homogenous (uniform throughout) mixture containing solvent and solute

Molar Concentration

moles solute/ liters solution

Density

mass per unit volume of a substance (often g / mL)

Solution

Homogeneous mix of 2+ substances where one substance (solute) is dissolved in another (solvent)

Solute

Typically present in smaller amount- the substance that is dissolved into the solvent

Solvent

Typically present in larger amount- the substance that dissolves the solute

Solubility

The maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature to form a saturated solution.

Insoluble

Describes a substance (solute) that will not dissolve in a particular solvent.

Miscible

MIXABLE Describes two liquids that are completely soluble in each other in all proportions, forming a homogeneous solution (e.g., ethanol and water). (example of NON miscible is oil and water)

Detergent

a amphipathic (hydrophilic and hyrophobic parts) molecule made of a nonpolar hydrophobic tail and a polar hydrophilic head

Micelle

hydrophobic tails point inward and the hydrophilic heads point outward. (A spherical structure formed by the aggregation of detergent molecules in an aqueous solution)

Function of a Micelle

It dissolves nonpolar (hydrophobic) substances like grease and oil by trapping them in its hydrophobic core, allowing the entire structure to be washed away by water.

Vapor Pressure

The pressure exerted by the vapor of a liquid in a closed container at a given temperature, representing the liquid's tendency to evaporate.

Boiling Point

The temperature at which the vapor pressure of a liquid equals the surrounding atmospheric pressure, causing the liquid to turn into a vapor.

Melting Point

Temperature at which a solid becomes a liquid at atmospheric pressure

Atmospheric Pressure vs. Vapor Pressure

When a liquid's vapor pressure is less than the atmospheric pressure, it remains a liquid. Evaporation occurs at the surface.

Atmospheric Pressure vs. Boiling Point

A liquid boils when its vapor pressure equals the atmospheric pressure. Lowering the atmospheric pressure (e.g., at high altitude) lowers the boiling point.

Thermodynamics

Are reactants or products energetically favored?

study of energy and its transformations- interested in starting and ending points in E

Kinetics

How fast will the reaction happen and by what mechanism?

study of the process by which reactants form products • Interested in rates and mechanism (how fast and by which route)

1st Law of Thermodynamics

Energy is neither created nor destroyed…but energy can be converted from one form to another

∆E universe = 0

∆E universe = ∆E surroundings + ∆E system

Endothermic

delta H > 0, heat energy absorbed by system causing surroundings to cool, enthalpically UNfavorable (ex: ice pack)

(within thermo and enthalpy H)

Exothermic

delta H < 0, heat energy exits system causing surroundings to warm, enthalpically FAVorable(ex: hot hands)

(within thermo and enthalpy H)

Enthalpy

heat content of reaction, (endo or exothermic)

Entropy

amount of disorder, related to the # of ways energy can be distributed in a system

Bond Dissociation Energy

the energy input required to break 1 mole of a bond in the gas phase

Weak bonds

more reactive; require less energy to break

Strong bonds

more stable; require more energy to break

∆ H formula relating to bonds

∆H = sum of Bond Dissociation Energy of bonds broken - sum of Bond Dissociation Energy bonds formed

Gibbs Free Energy Equation

∆G = ∆H -T∆S

T= Temperature (K)

Spontaneous

∆G<0, products lower in energy than reactants, reaction proceeds

Non-spontaneous

∆G>0, products higher in energy than reactants, reaction does NOT (non) proceed

Entropically Favorable

∆S>0 (POSITIVE) increase in disorder, nature likes disorder

Entropically Unfavorable

∆S<0 (NEGATIVE) decrease in disorder, nature likes disorder

Larger Ea means what for the speed of the reaction

Slower

Smaller Ea means what for the speed of the reaction

Faster

3 ways to speed up a reaction

1. Increase temperature

2. Increase concentration of reactants

3. Use a catalyst

Equilibrium

Point at which the forward rate = reverse rate and concentrations of reactants and products remains constant