Overall Chemistry Exam 4 Concepts

How does light behave?

Modern understanding: light behaves as electromagnetic radiation (wave) AND particle

What color on the visible light spectrum has the highest WAVELENGTH?

Red

What color on the visible light spectrum has the highest frequency and energy?

Purple

What did Isaac Newton think about light?

He thought that white light was composed of a mixture of color, streams of high speed" “corpuscular” particles

Christian Huygens

Light as waves that can be reflected and refracted

Thomas Young

Interference of light through slits suggest waves, not corpuscles

James Clerk Maxwell

theory of electromagnetic radiation; “classical electrodynamics” vs. classical mechanics (Newtonian motion)

What are standing waves?

They are quantized waves that are constrained by boundaries to discrete wavelengths with nodes

What is a blackbody?

Such as a metal oven that can be heated to a very high temperature and is a convenient and ideal emitter for study that approximates the behavior of many materials when heated

What are ionic bonds?

Electrostatic attractions between oppositely charged cations and anions

What are characteristics of ionic solids?

Rigid and brittle crystalline structures

High melting and boiling points

Poor conductors of electricity

Likely water soluble

Excellent conductors of heat/electricity in solution or melted

What is a covalent bond?

Atoms that are held to each other by sharing valence electrons

What are characteristics of covalent compounds?

Electrically neutral with weaker attractions between them

Lower melting/boiling point

Many are gases are room temperature

Form softer solids than ionic compounds

Likely water insoluble

Poor conductors of heat and electricity in any state

What did the Rayleigh-Jeans law do?

-It was a model developed to predict wavelength distribution as a function of temperature based on physics

-It stated: the maxima in the blackbody curves, λmax, shift to shorter wavelengths as the temperature increases

-At longer wavelengths, theoretical models fit the observed experimental blackbody curves well but at shorter wavelengths, it was a UV catastrophe

What did Max Planck do?

-He derived a theoretical expression for blackbody radiation that fit the experimental observations exactly (within experimental error) over all wavelengths

-He developed his theoretical treatment on the premise that the atoms composing the atom vibrated

-The atoms vibrated at increasing frequencies (or decreasing wavelengths) as the temperature increased

-Planck assumed that the vibrating atoms required quantized energies which he was unable to explain

-E = hv where n = 1, 2, 3, 4

What was the Photoelectric effect?

-It had been observed that electrons could be ejected from the surface of a metal by light if the frequency was greater than some threshold frequency

-However, the KE of the ejected electrons DID NOT depend on the light brightness but increased with increasing frequency of the light

-Acc. to classical wave theory: a wave’s energy depends on its intensity, which depends on its amplitude, not frequency

What did Einstein do?

-He solved Planck’s problem and the photoelectric effect

-He incorporated Planck’s quantization findings into the particle view of light

-He found that light striking the metal should not be viewed as a wave but as photons with energy dependent on their frequency E= hv

-Therefore, light behaves as a light and a particle

Why is the electron in a Bohr hydrogen atom bound less tightly when it has a quantum number of 3 than when it has a quantum number of 1? (HW 16)

n = 3 is farther from the nucleus than n = 1 and the electrons are held less because they are further away

What are the periodic properties of elements?

1. Size (radius) of atoms and ions

2. Ionization energies

3. Electron affinities

What is the Paul Exclusion Principle?

No 2 electrons in the same atom can have exactly the same set of all the 4 quantum numbers

What is a travelling wave?

A wave that moves through space, transferring energy from one location to another (ex: light or sound waves)

What is Hund’s rule?

The orbitals within a subshell must first be filled spin up to maximize the number of unpaired electrons before pairing electrons

Line Spectra

A series of distinct wavelengths (lines) of light emitted or absorbed by atoms, corresponding to specific electronic transitions between energy levels

Continuous spectra

A seamless range of all wavelengths or colors of light, with no gaps between them, produced by sources like incandescent solids

What is wave-particle duality and its significance?

Wave-particle duality is the idea that light and matter exhibit both wave-like and particle-like behavior. It is significant because it shows that energy and particles at the atomic scale cannot be described by classical physics, forming the foundation of quantum theory

How does the photoelectric effect support the particle nature of light?

A wave increases in energy when intensity increases, and a particle increases in energy when frequency increases.

Because ejecting electrons takes a certain amount of energy, and light did not accomplish this when intensity was increased, but did accomplish this with increased frequency that demands that light behaves like a particle

Explain the relationship between valence-electron configuration and periodic trends.

The number of valence electrons increases as you go from left to right

Compare emission and absorption in the Bohr model—-what determiines if a photon is emitted or absorbed?

When energy is released, light is emitted

When energy is absorbed, a photon is absorbed

Describe the Bohr model of the hydrogen atom and how it accounts for discrete emission
lines.

It describes the hydrogen atom as an electron orbiting the nucleus in specific,
fixed energy levels rather than in a continuous range. The electron can move between these
levels only by absorbing or emitting a discrete amount of energy equal to the difference between
them. When the electron falls from a higher to a lower energy level, it emits light of a specific
wavelength, producing the discrete emission lines seen in hydrogen’s line spectrum

Heisenberg uncertainty principle

It is fundamentally impossible to determine simultaneously and exactly both the position and the momentum of a particle

Principle quantum number (n)