Chem exam 4

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

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

Standing waves: A wave that remains fixed in position and is formed by the interference of two waves traveling in opposite directions

Energy oscillates in place instead of propagating, like in electron wave patterns in atoms

Equation relating the speed of light, wavelength, and frequency

c = λ x v

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 things like incandescent solids

Photoelectric effect. It was observed that electrons could be ejected from a metal's surface if the FREQUENCY was greater than some threshold frequency

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

Classical wave theory: A wave's energy depends on its intensity (which depends on its amplitude), not frequency. Now, a new light model was needed

Explain how the photoelectric effect supports the particle nature of light. A wave increases in energy when iits ntensity increases, BUT a particle increases in energy when its frequency increases.

Ejecting electrons takes a certain amount of energy that was not satisfied with light with increased intensity, but it was with increased frequency that demands light behave like a particle

New model of light: Light behaves like a wave and a particle

Blackbody radiation: The light emitted by an object that absorbs all radiation and re-emits energy based only on its temperature

An example is a metal oven that can be heated to high temperatures and is a convenient and ideal emitter for study

Describe how blackbody radiation, the photoelectric effect, and line spectra led to the quantum model of the atom.

Classical physics thought energy output would increase without limit at short wavelengths, but experiments showed that it peaked and decreased (known as the UV catastrophe).

Max Planck proposed that energy is quantized, it can only be emitted/absorbed in quanta with energy proportional to its frequency E = hv

This idea introduced the concept of energy quantization and quantum theory

Compare emission and absorption in the Bohr model—what determines if a photon is emitted or absorbed? When energy is released, light is emitted

When energy is absorbed, a photon is absorbed

Wave-particle duality: The idea that light and matter exhibit wave and particle-like behavior

Significant because it shows that

Ionic compound properties. Ionic solids are rigid and brittle crystalline structures

Poor conductors of electricity

Likely water-soluble

Excellent conductors of heat and electricity in solution or melted

Covalent compound properties: Electrically neutral with a weaker attraction between them

They have lower melting and boiling points

Many are gases or liquids at room temperature

Form softer solids than ionic compounds

Likely water INSOLUBLE

Poor conductors of heat and electricity in any state

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

Pauli Exclusion Principle: No two electrons in the same atom can have the same set of all 4 quantum numbers

What is the relationship between valence-electron configuration and periodic trends?

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

Johann Balmer

derived an equation based on the four visible line spectra for hydrogen

Quantum mechanics

describes matter using quantization of energy, wave-particle duality, and the Heisenberg uncertainty principle

Louis de Broglie

extended the wave-particle duality of light that Einstein used to resolve the photoelectric-effect paradox to material particles

He modeled electrons as circular standing waves required to have only integer wavelengths

The Heisenberg uncertainty principle. It is fundamentally impossible to determine simultaneously and exactly both the position and the momentum of a particle

Principal quantum number (n)

describes the location (shell) of the orbital

-Allowed values of n = 1, 2, 3, …..

-Orbitals with the same n value are in the same shell

-Defines the general size/energy of the orbital

-Higher n values are larger, higher in energy, and farther from the nucleus

The angular momentum quantum number (l)

defines the shape of the orbital

-Allowed values depend on the shell: l = 0, 1, 2, …, n-1

-Orbitals with the same l value in the same subshell

-The higher the l value, the higher the angular momentum of an electron in the orbital

Magnetic quantum number (ml)

defines the z-component of the angular momentum

-Allowed values of ml = -l, …, 0, …., l for a total of 2l + 1 values for a given value of l

Spin quantum number (ms)

defines the electron spin

-It has nothing ot do with position or the Schrodinger equation

-It describes the behavior of an electron's magnetism

-Allowed values of ms = ± 1/2 with spin up +1/2 and spin down -1/2

Valence electrons: The electrons in the outermost shell of a ground-state atom determine how an element reacts

Core electrons: The electrons occupying the inner shell orbitals

Valence shell: Outermost shell of electrons in a ground-state atom

Periodic properties that govern the chemical behavior of elements

1. Size (radius) of atoms and ions

2. Ionization energies

3. Electron affinities

Covalent radius

is defined as 1/2 the distance between the nuclei of two identical atoms when they are joined by a covalent bond

The size of the atom (and its covalent radius) ____ down a group

Increases

The size of the atom (and its covalent radius) ___ across a period

Decreases

Effective nuclear charge

Zeff is the pull exerted on a specific electron by the nucleus, taking into account any electron-electron repulsions. Zeff = Z - shielding

Isoelectronic species: Atoms and ions that have the same electron configuration

First Ionization energy: The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state

Electron affinity: The energy change for the process of adding an electron to a gaseous atom to form an anion

Bond length: The internuclear distance at the lowest potential energy

Polar covalent bond. It forms when the electrons are pulled toward one atom, causing a partial negative charge and a corresponding partial positive charge on the other atom. This separation of charge (dipole) acts as a tiny electric field

Electronegativity: The measure of the tendency of an atom to attract shared electrons to itself

Lewis symbol: A depiction of an atom or ion that represents the valence electrons with dots around the elemental symbol

Free radicals: Molecules that contain an odd number of electrons

Electron-deficient molecules areeldom seen but in Group 2 Be compounds and Group 13 B compounds. Hypervalent molecules - often seen, especially in the third period or below, with the central atom having up to 12 electrons

Lewis structure: A diagram of a molecule or an ion that shows lone pairs and bonding pairs of electrons

A pure covalent bond

occurs whenever the same type of atom is involved

Isaac Newton

White light is composed of a mixture of colored streams of high-speed "corpuscular" particles.

Christiaan Huygens's

Light as waves that can be reflected and refracted

Thomas Young's

Interference of light through slits suggests waves, not corpuscles

James Clerk Maxwell's

Theory of electromagnetic radiation; classical thermodynamics vs classical mechanics (Newtonian motion)

Modern understanding of light: It is an electromagnetic radiation wave and a particle

Rayleigh-Jeans Law: The maxima in the blackbody curves λ max shift to shorter wavelengths as the temperature increases

Max Planck

-Planck derived a theoretical expression for blackbody radiation that fit the experimental observations exactly within experimental error over all wavelengths.

-The atoms vibrated at an increasing frequency or decreased wavelength as the temperature increased

-Planck assumed that the vibrating atoms required quantized energies, which he could not explain.

E = hv where n = 1, 2, 3, 4 …

Niels Bohr Model

-Bohr used Planck's quantization of energy and Einstein's photon explanation with his own assumptions that emission/absorption of photons resulted from electrons moving between orbits in an atom

-As a result, he could reproduce Rydberg's empirical equation from fundamental constants

Electron configuration subshell labels include:

-Principal quantum shell number (n)

-Letter of subshell (l)

-Number of electrons in subshell

What is the periodic trend for electronegativity? EA increases from left to right across a period, bottom to top within a group

If n = 1, what can l be?

l = 0

If n = 4, what can l be?

l = 0, 1, 2, 3

If l = 2, what is the lowest value n can have? What values can ml be?

n = 3

ml = -2, -1, 0, 1, 2

Davisson and Germer

demonstrated that electrons could be diffracted, with interference patterns only possible with waves

Erwin Schrodinger

-Built upon de Broglie's relation to develop a fundamental equation for quantum mechanics that determines the energies of electrons: Ĥψ = Eψ

Ĥ = Hamiltonian operator (set of mathematical functions)

ψ = wavefunction of the particle (a mathematical equation)

E = total energy of the particle