Unit 3: Properties of Substances and Mixtures

The bigger the wavelength the lower the

frequency

All electromagnetic radiation travels at the same

velocity (3.0 × 10⁸Hz)

400 nm

Violet

750 nm

Red

Visible light is only a

small part of the electromagnetic spectrum

Wavelengths in order of increasing size

gamma rays → x rays → UV → visible light → infrared → microwaves → radiowaves

Planck’s Postulate

electromagnetic energy (such as light) can be emitted only in quantized form; in other words, energy and light exist in ‘packets’ we today call photons

Effect of UV or visible light

Causes electrons to transition to different energy levels

Infrared Radiation

Causes molecules to vibrate

Microwave radiation

Causes molecules to rotate

n_f=2

The visible emission lines observed by Balmer

Why does infrared light have a lower frequency than visible light?

Because it has a longer wavelength

The Paschen Series

Involves an electron moving from an excited state to a n=3 ground state

Lyman Series

Always involves an electron moving from an excited state to a n=1 ground state

What is the spin of an electron denoted by?

A half arrow

If half arrows in an electron configuration point in the same direction then the electrons

have a parallel spin

If the energy of a given wavelength is smaller than the energy required to cause a photoelectric effect then

it is impossible to eject electrons from that material using that form of radiation

Aufbau Principle

Ensures that electrons are placed in the lowest energy orbitals that can hold them, delivering a ground state electron configuration for that element or ion.

Hund’s Rule

If there are multiple electrons (more than one) occupying a sub level, the electrons will be placed singly into equal energy orbitals with the same spin before the electrons are paired with an orbital (opposite signs)

The Pauli Exclusion Principle

Electrons traveling in pairs will have opposite signs

What is a pattern in valence shells of metals?

Metals generally have their valence shells less than half full.

The highest energy electrons for a transition metal are in the

d sub level

Infrared radiation is associated with

transitions in molecular vibrations

What can infrared radiation be used to detect?

Functional groups and types and strengths of bonds

UV/Visible light can be used to detect

movement/transition of electrons

Emission of UV/Visible light radiation

brings electrons back to the ground state

Absorption of UV/Visible light radiation

excites electrons

Photoelectron Spectroscopy

uses high energy x rays to remove electrons from an atom and provide info about atomic structure specifically sub shell numbers and electron numbers

Photoelectric effect

When energy strikes a metal surface, photons are ejected from the metal if the initial energy is a high enough value

What is the visible light region?

400nm-750nm

The energy required to ionize the atom ____ as the principle quantum number of electron increases

decreases

Uncertainty Principle

There is a limit to how precisely the position and momentum of a particle can simultaneously be measured

What does the uncertainty principle help explain?

How particles can have wavelike properties

What group of elements have the largest number of unpaired electrons?

Rare earth metals b/c there are seven 4f orbitals so the number of unpaired electrons can be as high as seven.

Hund’s rule states that

the lowest energy is attained by maximizing the number of electrons with the same electron spin

s orbital

-Spherical

-1 orbital per energy level

-Symmetrical around the nucleus with no angular dependence

p orbital

-Dumbbell-Shaped (two lobes on opposite sides of the nucleus)

-3 orbitals per energy level

-Each p orbital has a region of zero probability at the nucleus.

Ground State

The most stable electron configuration. It is the electron configuration in which the electrons are in the lowest possible energy state

n decreases as

an electron gets closer to the nucleus

Electromagnetic radiation is also known as

radiant energy because it carries energy through space

At what speed do ALL electromagnetic radiation move through a vacuum?

3.0 × 10⁸m/s (the speed of light)

Why do different types of electromagnetic radiation have different properties?

Their differences are due to their different wavelengths

What is frequency expressed in?

Cycles per second

What does the wave model of light not explain?

(1) the emission of light from hot objects (blackbody radiation)

(2) the emission of electrons from metal surfaces on which light shines (the photoelectric effect)

(3) the emission of light from electronically excited gas atoms

Quantum

Smallest quantity of energy that can be emitted or absorbed as electromagnetic radiation

A minimum frequency of light

different for different metals, is required for the emission of electrons. If light has frequency less than that, no electrons are emitted

Under the right conditions, photons striking a metal surface

can transfer their energy to electrons in the metal

Work function

The certain amount of energy required for the electrons to overcome the attractive forces holding them in the metal

If the photons striking the metal have less energy than the work function,

the electrons do not acquire sufficient energy to escape from the metal

What will cause electrons to be emitted from a metal?

Only if and when the frequency is such that photons have energy greater than the work function of the particular metal, electrons are emitted

Increasing the intensity of the light source

DOES NOT lead to the emission of electrons from a metal

What leads to or changes the emission of electrons from a metal?

Changing the FREQUENCY of the incoming light

What happens as n becomes infinitely large?

The radius increases and the energy of attraction between the electron is completely separated from the nucleus and the energy of the electron is zero

Bohr’s model can only explain the

line spectra for a hydrogen atom

What two important ideas did Bohr’s model introduce?

-Electrons exist only in certain discrete energy levels, which are described by quantum numbers

-Energy is involved in the transition of an electron from one level to another

In the Dr.Broglie hypothesis and uncertainty principle an electron’s behavior is described in terms of

its waves

The result of the Broglie hypothesis and uncertainty principle is a model that precisely describes the energy of the electron while describing its location not precisely but rather in

terms of probabilities

The 1s orbital is centered on

the nucleus

What does it mean when the 1s orbital is said to be symmetrical and centered on the nucleus?

The electron density at a given distance from the nucleus is the same regardless of the direction in which we proceed from the nucleus

Anomalus Electron Configuration ending of Chromium

3d⁵4s¹

Anomalus Electron Configuration ending of Copper

3d¹⁰4s¹

Picometer conversion

1.0×10^-12m

Angstrom Conversion

1.0×10^-10

Micrometer Conversion

1.0×10^-6m

Bohr’s model of the atom does not adequately predict

the ionization energy of the valence electrons for elements other than hydrogen

Hund’s Rule

The lowest energy configuration for an atom is the one having the maximum number of unpaired electrons allowed by the Pauli principle in a particular set of degenerate orbitals