Modern Atomic Theory

Ms. Hoang ACP Chemistry

Summary

Visible light is a small section of the EM spectrum

Light exhibits wave-like and particle-like properties

To characterize wave, scientists use wavelength, frequency, speed (and amplitude)

Short wavelength = (high/low) frequency = (high/low) energy

Long wavelength = (high/low) frequency = (high/low) energy

Wavelength determines color of light

White light is light of all wavelengths

Objects around us absorb visible light of different wavelengths and emit light of different wavelengths. That is why objects appear to have colors.

Concept Check-in

What color is a banana under white light?

Yellow

What color is a banana under green light?

Black

Objectives

Use light and wave formulae to calculate wavelength and frequency of light

Contrast continuous spectra with line spectra

Explain why the emission spectra of elements are line spectra rather than continuous spectra

Light and Wave formulae

chhE

cሺm sΤሻ= λሺmሻ× ν(s−1) h = 6.626 x 10-34 J.s | 1nm = 1.00 x 10-

9m

Example

A photon has an energy of 4.00 x 10-19J.

Find the frequency of the radiation

Find the wavelength of the radiation

Find the color of the photon if possible

E = 4.00 x 10-19J = (6.626 x 10-34J.s)(ν)

ν = E/h =

cሺm sΤሻ= λሺmሻ× ν(s−1)

4.96×10− 7𝑚=496×10−9𝑚=496𝑛𝑚→𝐵𝐿𝑈𝐸

𝐸=h ν

Your turn

A photon has an energy of 3.00 x 10-19J.

Find the frequency of the radiation

Find the wavelength of the radiation

Find the color of the photon if possible

Your turn

A bright line spectrum contains a line with a wavelength of 518 nm.

The color of the line is:

A. Violet

B. Green

C. Yellow

E. Red

The energy is:

A. 5.12 x 10-23 J

B. 3.84 x 1019 J

C. 5.12 x 1023 J

D. 3.84 x 10-19 J

Flame Test revisit

chhE

Flame Test revisit

Energy is quantized

Flame Test revisit

Types of spectra

Continuous vs. Line

How do we know? Spectroscope

Types of spectra

_______ light = contains light of all wavelengths __________

Light from an excited element (electrical current) = contains light of _______ wavelengths _____________

Question: Why do atoms emit line spectra?

Hydrogen atom

Emission Spectrum for Hydrogen

Bohr Model of the Atom

Electrons go in orbits around the nucleus like the solar system

Each orbit is a discrete

Only works for Hydrogen atom

n = 3

n = 2

n = 1

Emission and Absorption Spectra

Cosmos – Hiding in the Light

Wave Mechanical Model of the Atom

Orbitals = electron cloud = probability map of finding electrons = easier to find electrons in the shaded regions

The size of an atom is described as 90% probability of finding an electron at a given point in space