Chem 20A Midterm

Intensive vs. Extensive Properties

Intensive properties: independent of size

Law of Definite Proportion

Atoms combine in specific ratios to form different compounds

Atomic Theory of Matter

Significance: summarized conservation of mass and definite proportion; coined "atom". The two main things that Dalton got wrong: Atoms are not indivisible and indestructible

Law of Multiple Proportions

The amounts of one element that combine with 1g of another element is in ratios of small integers

Avogadro’s Hypothesis

Know how to predict the final volume of the reactants or products: At the same T and P

Cathode Ray Tube Experiment

Bending electrons with electric and magnetic field

Significance: charge-to-mass ratio

Oil Drop Experiment

Significance: charge of e⁻

How was be able to calc the charge of an e without knowing the number of e in each drop ?

Know that # of electrons in each drop must be integer x electron, so difference must also be integer x charge of an electron, smallest integer is 1, so if we can find the smallest difference, the smallest difference must be 1 x electron charge

Gold Foil Experiment

Significance: discovery of the nucleus

why gold foil exp. disproved the plum pudding model and proved the existence of nucleus

shooting alpha particles, if no nucleus they would have all went through but some deflected off of the nucleus

Mass Spectrometry

Significance: discovery of isotopes

1. how to calculate avg. atomic mass from abundance and mass of isotopes

avg atomic mass = sum(abundance)(mass)

2. count # protons, # neutrons, # electrons from chemical symbol

mass # charge

atomic symbol

protons: charge of +1; nucleus (# protons = atomic #)

neutrons: neutral; in nucleus, “glue” that holds nucleus together (mass # = # protons + # neutrons)

electrons: -1 charge (charge = # protons - # electrons)

Blackbody Radiation

Significance: energy is quantized

classical physics: no energy level; all “light bulbs” are turned on

most intense color does not depend on temperature

quantam mechanics: energy level => gap between the energy levels is proportional to the frequency of light bulb

=> higher frequency light bulbs are harder to turn on

at lower temperature, not a lot of energy, can only turn on low frequency light bulbs “color = low-freq light”

at higher temperature, lot more energy, can turn on higher frequency light bulbs, color shifts to higher frequency

Photoelectric Effect

Significance: discovery of photons

one photon can only eject one electron

explain experimental observations

i. increasing intensity → more electrons ejected but energy of photon is the same so KE stays the same

ii. below threshold frequency, electrons cannot be ejected. below threshold frequency photons do not have enough energy to eject electrons

iii. increase frequency of light, increase KE. increase frequency of photon → increase E of photon → move energy leftover after ejecting electron → electron has higher KE

de Broglie Wavelength

λ = h / mv (for electrons)

Two-slit experiment with e⁻

Significance: e⁻ has wave-like behavior. Interference pattern was observed.

• electrons + two-slit → interference pattern

• only waves can have constructive and destructive interference

  • electrons have wave-like behavior

Mole

Know how to convert between grams ↔ moles ↔ atoms/molecules

Empirical Formula vs. Molecular Formula

Know how to calculate percent mass composition

Composition of Atoms

Protons: Charge: +1

Electromagnetic Radiation

Equation for wavelength of photon: c = λν

Absorption and Emission of Photons

Equation for absorption and emission: Eₚₕₒₜₒₙ = |ΔE|

Bohr Atom Energy

Eₙ = −2.18 × 10⁻¹⁸ J (z² / n²)

de Broglie Wavelength

λ = h / mv (for particles)

Wavefunction

describes the amplitude of the wave at different locations.

Quantum Numbers

n (shell): 1

Nodes

For an orbital

Effective Nuclear Charge

Closer electrons are less shielded and have a stronger nuclear attraction

Three Rules for Electron Configuration

1. Add electrons to the orbital with the lowest energy