Chapter 18: Atomic Models

18.1 – Models Help Us Visualize the Invisible World of Atoms

18.1 Models Help Us Visualize the Invisible World of Atoms

We cannot see atoms directly, but we can generate images of them indirectly.

Scanning Tunneling Microscope (STM) – Produces images by dragging a needle back and forth over the surface of a sample.

18.1 Models Help Us Visualize the Invisible World of Atoms

An STM is also used to push atoms into desired positions.

The STM opened up the field of nanotechnology.

Nanotechnology – Building incredibly small circuits and motors atom by atom.

18.1 Models Help Us Visualize the Invisible World of Atoms

Physical model – A representation of a very large or small object shown at a convenient scale.

Conceptual Model – An explanation that treats what is being explained as a system.

18.1 Models Help Us Visualize the Invisible World of Atoms

System – The interactions among component parts matter most.

An STM can only show the positions of atoms and not actual images!

18.2 – Atoms Can Be Identified by the Light They Emit

18.2 – Atoms Can Be Identified by the Light They Emit

An atom emits light when it loses energy.

Each element produces its own distinctive glow.

White light is separated into its color components by a prism.

Spectroscope – Instrument used to observe the color components of any light source.

18.2 – Atoms Can Be Identified by the Light They Emit

Atomic Spectrum – The pattern of frequencies formed by a given element.

18.3 Niels Bohr Used the Quantum Hypothesis to Explain Atomic Spectra

Light travels as a wave, but strikes as a particle.

Quantum Hypothesis – States that a beam of light is a stream of zillions of discrete particles.

Photon – A particle of light. Quantum – The smallest unit of something.

18.3 – Niels Bohr Used the Quantum Hypothesis to Explain Atomic Spectra

Bohr said that potential energy of an electron in an atom depends on the electron’s distance from the nucleus.

The more energy added, the more the electron moves away from the nucleus.

Bohr concluded there must be a number of distinct energy levels.

18.3 – Niels Bohr Used the Quantum Hypothesis to Explain Atomic Spectra Bohr gave each

energy level a principal quantum number n, where n is always some integer.

Bohr’s model of the atom is known as the Planetary model.