General Chemistry Midterm

What is Ionization Energy

Energy required to remove an electron from an atom

Is Ionization Energy Positive or Negative

Positive because it requires a lot of energy to remove an electron from an atom’s outer shell

What is Electron Affinity

Energy absorbed by an atom after gaining an electron

Is Electron Affinity Positive or Negative

Negative because the electrons that these atoms are absorbing have a negative charge to them

What is Lattice Energy

Energy released when going from a gas to an ionic solid

Is Lattice Energy Positive or Negative

Can be negative when discussing lattice formation when you go from a gas to a solid but can be positive with lattice disassociation where you go from a solid to a gas

What is the Energy Required to Affect the Transformation (Enthalpy)

Energy product - Energy Reactant

What Does a Positive Enthalpy Mean

how much energy is required to affect the transformation, this is unfavorable

What does a Negative Enthalpy Mean

how much energy is released during the transformation, this is favorable

Are all Electron Affinities Positive

Most are but the ones in group II and VIII of the periodic table

How Does Covalent Bonding Work

a pair of electrons concentrate in the internuclear region and hold the two positive nuclei together

What Determines the Energy In a Covalent Molecule

distance between the atoms

What is the Distance For Which Covalent Molecules Have A Minimum Energy

the bond distance/length

What is the Energy Required to Break the Bond and Separate the Atoms

the bond energy

What Happens in Covalent Bonding When Two Atoms are Getting Closer to Ideal Bond Length

the molecule becomes more stable because their outer electron shells overlap and the positive nucleus of one attracts the electron of the other

What Happens In Covalent Bonding When Atoms Are Far Apart From Ideal Bond Length

the molecule has a potential energy of zero, atoms act independently

What Happens In Covalent Bonding When Atoms Are Too Close Together

the molecule becomes very unstable due to internuclear repulsion

How To Read A Lennard Jones Model

• x-axis: distance between atoms, rr

• y-axis: potential energy, VV

• Bottom of well: equilibrium distance → most stable, lowest potential energy

• Left of minimum: atoms too close → Pauli repulsion

• Right of minimum: atoms attract → dipole-dipole attraction

• Slope down: attraction

• Slope up: repulsion

What is a Polar Covalent Bond

when atoms have different electronegativities so one atom pulls more than the other

What is Electronegativity

atom’s ability to attract electron within its own molecule

What is Pauling’s Equation Relating Bond Energy and Electronegativity

E(AB)= 0.5[E(AA)+E(BB)] + 23(Xa-Xb)²

What Does Pauling’s Equation Tell Us

a more polar bond will have a greater difference in electronegativity

What Atoms Form Ionic Bonds

atoms w/ large electronegativity differences

What Atoms Form Covalent Bonds

atoms w/ small electronegativity differences

How Is Bond Polarity Quantified

for two charges of equal magnitude and separated by a distance r, the dipole moment is (DM = Qr)

How are Electronegativity and Ionic Character Related

• Δχ = difference in electronegativities

• Δχ↑ → polarity ↑ → ionic character ↑

• Δχ<1→ generally covalent/molecular

• Δχ>2.0 → generally ionic

• % ionic character=100δ

How To Calculate Ionic Character

measured dipole moment /calculated dipole moment

How Does Ionic Bonding Work

atoms are driven to fill their valence shells (octet or duet)

How Does Element Charge Affect the Size of the Ions

cations are smaller (add more protons so you swallow the electrons) and anions are larger (gaining extra electrons increases electron to electron repulsion)

How Do You Calculate Lattice Energy

K [Q1Q2/r]

What Are Some Characteristics of Lattice Energy

-it increases as cations increase (more charge = more LE)

-it is the driving force of forming ionic compounds

What Does A Born Haber Model Do

-calculates lattice energy

-applies primarily to ionic compounds

-overall energy change can be measured

How To Use A Born Haber Cycle

1. Find the overall energy change

2. List all the other energies individually

3. Write one equation which includes your unknown

4. Solve for your unknown

What Significance Does the Bond Energy of a Covalent Bond Have

-determines the ability to isolate a molecule

-tells you how much energy is required to break the bond

-generally decreases as you go down the periodic groups on the table

Why Are Average Bond Energies Significant

if the sum of the bond energies for the bonds broken is greater than that of the bonds broken then the reaction will be favored

∆E = sum(bonds broken) - sums(bonds formed)

What Electrons Participate in Reactions

only the valence electrons can participate

What Are Atoms In the Same Periodic Table With Same Valence Electrons Called

isoelectronic

What did Lewis Contribute to Chemistry

introduced the group of 8

What Did Langmuir Contribute to Chemistry

atoms form a chemical bond by sharing pairs of electrons to attain a stable shell configuration

How Do You Calculate Limiting Reactant

1. calculate molar mass

2. find mols

3. smaller number in ratio is your answer

How To Calculate Percent Yield

(actual yield/ theoretical yield) x 100

How To Solve Combustion Analysis

• Find C from CO₂ → convert to mol C

• Find H from H₂O → convert to mol H

• Find O by mass difference

• Convert O mass → mol O

• Divide all moles by the smallest

• Multiply to get whole numbers → empirical formula

How To Find the Empirical Formula From %

1. assume 100g of a substance

2. divide this mass by molar mass

3. divide by smallest number

4. look and adjust ratios

How To Determine Molecular Formula

molar mass/empirical formula mass

What Did JJ Thompson Contribute to Chemistry

using the cathode ray experiment determined the charge to mass ratio of an atom

What Did Millikan Contribute to Chemistry

using oil drop experiment determined the charge of an electron to be 1.6×10^-19

What Did Rutherford Contribute to Chemistry

using gold foil experiment found that the nucleus is dense and concentrated

How Does a Mass Spectrometer Work

it ionizes → accelerates → deflects → detects
Separates ions by mass to charge ratio
x-axis = mass to charge ratio; y-axis = relative abundance.
Higher peak = more abundant isotope.

What Is a Dative Bond

where one atom provides both electrons

What Is an Orbital

a place to put electrons

What Are Some Terms To Use When Under An Octet

hypovalent, electronically unsaturated, electron deficient

What Is a Lewis Base

the electron that donates an electron

What is a Lewis Acid

the electron pair acceptor

How Do You Calculate Formal Charges

Formal Charge = group valence electrons - number of lone pair electrons - number of bonds

What is a Resonance Structure

the average of two composite structures