Lesson 6: The Development of a New Atomic Model

The Development of a New Atomic Model

I promise you won't be "Bohr"-ed...

​Light's Contribution to Atomic Structure

​Scientists who studied the structure of the atom struggled to understand why the negatively charged electrons were not just pulled into the nucleus with the positively charged protons. It turned out, studying the way matter emits light provided some answers to the structure of the atom.

​Electromagnetic Radiation

Before 1900, scientists thought light purely behaved as a wave​. However, they soon discovered that light also behaved as a particle in some respects. It has since been accepted that light behaves as both and its wavelike characteristics helped scientists determine the structure of the atom.

​Electromagnetic Radiation

Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space. Examples of electromagnetic radiation are visible light, x-rays, gamma rays, microwaves, and UV rays. All of these types of radiation form the electromagnetic spectrum.

​Electromagnetic Radiation

All electromagnetic waves move at the speed of 3.00 x 10⁸ m/s through empty space and slightly slower through matter. Wave patterns are repetitive and can be measured by wavelength and frequency.

Multiple Choice

True or False: The speed of light is constant.

• True

• False

​Wavelength and Frequency

Wavelength is the distance between corresponding points on adjacent waves. Usually, we use peaks (the highest point on the wave) or troughs (the lowest point on the wave) to measure wavelengths. Frequency is the number of waves that pass a specific point in space during a given time interval (usually one second). Frequency is measured in hertz.

​Frequency, Wavelength, and Speed

​When solving for the wavelength or frequency, we can use the speed of light and the other factor to find the missing value. Because the speed of light is constant, the product of wavelength and frequency is constant. This means if one goes up, then the other goes down proportionately. This is called an inverse proportion and frequency and wavelength are inversely proportional to each other.

Multiple Choice

_______________ is the distance between two corresponding points on a wave of electromagnetic radiation.

• wavelength

• frequency

• light

• radiation

Multiple Choice

As frequency goes up, wavelength goes _____________.

• up

• down

• nowhere

​Key Term

• Photoelectric Effect - ​refers to the emission of electrons from a metal when a light shines on it.

​Max Planck

​Max Planck was the first to attempt an explanation of the photoelectric effect by studying the emission of light by hot objects. He proposed that they released energy in packets or particles, not continuously as would be expected if the light were behaving as a wave. He called these packets quanta which are the smallest unit of energy that can be gained or lost by an atom.

​Max Planck

Planck proposed the formula, E = hv. E is energy, v is the frequency of the radiation, and h is a physical constant now called Planck's Constant. Planck's constant is 6.626 x 10^-34 Joules x seconds.

Multiple Choice

The smallest unit of energy lost or gained by an atom is called a __________________.

• quantum

• photon

• electron

• proton

​Albert Einstein

​In 1905, Einstein expanded on Planck's theory by proposing the dual-wave particle nature of these energy packets in light. Einstein called these energy packets photons which are particles of electromagnetic radiation containing a quantum of energy. These particles have no mass.

​Albert Einstein and Photons

Multiple Choice

Does light behave as a particle or a wave?

• wave

• particle

• yes (both)

​Hydrogen-Atom Line-Emission Spectrum

​When current is passed through a gas, the atoms increase in potential energy. The lowest energy state of an atom is called the ground state and any state higher in energy than the ground state is the excited state of the atom. When a current was run through a tube containing hydrogen gas, the tube emitted a pinkish glow. When that light was emitted through a prism, there were 4 specific bands of light that were shown, each one being distinct from the others.

​Hydrogen-Atom Line-Emission Spectrum

​The visible spectrum of light is continuous, but the emission of light from the hydrogen gas tube contained discrete bands. What does this tell us? The energy levels within the hydrogen atom were fixed and discrete, not continuous. This meant that there were distinct energy levels within the hydrogen atom that the electrons would orbit in. This discovery helped Neils Bohr develop a model of the atom that helped explain the absorption and emission of energy.

​Key Terms

• ​emission - the emission of a photon when an electron falls from a higher energy level to a lower one.

• ​absorption - the process of adding energy to an atom and causing an electron to move from a lower energy state to a higher one.

Multiple Choice

An atom in its lowest energy state is in the ____________________.

• ground state

• excited state

Multiple Choice

_______________ is when the energy level of an atom decreases and a photon is emitted.

• emission

• absorption