Electrons in Atoms Chapter 4

RUTHERFORD MODEL

A NEW ATOMIC MODEL The ____________ model of the atom was a great improvement, but it was incomplete. In the early 20 th century, a new model was evolving based on the ________________ and ________________ of light by matter. The studies revealed a very intimate relationship between ______________ and ______________. Rutherford emission absorption electrons light

Chemists found Rutherford’s nuclear model an improvement but more experiments were being conducted. In the early 1900s, scientists began to unravel the puzzle of chemical behavior. The had observed that certain elements emitted ____________________ when heated in a flame. Visible Light

PROPERTIES OF LIGHT Before 1900, light was thought be behave solely as a __________. ___________________________ is a form of energy that exhibits wave-like behavior as it travels through space – ALL FORMS travel at the speed of light: ____________ m/s Including Gamma Rays, X-Rays, Ultraviolet, Visible Light, Infrared, Microwaves, and Radio Waves (AM and FM) (listed in order of strength) wave Electromagnetic Radiation 3.00 x 10 8

ELECTROMAGNETIC SPECTRUM

VISIBLE LIGHT The visible spectrum includes the colors: ______, ______, __________, ________, _________, ____________, and ____________. (ROY G BIV) RedOrange Yellow Green Blue Indigo Violet

The significant feature about waves is their ______________ nature. repetitive

CHARACTERISTICS OF WAVES ____________________ is the distance between corresponding points on adjacent waves. It is measure in ______________________. Wavelength Nanometers (nm)

________________ is the number of waves that pass a given point in a specific time, usually “per second.” It is measured in _____________ (Hz). Frequency Hertz

INVERSE RELATIONSHIP

PARTICLE THEORY OF LIGHT In the 1900s, scientists conducted _____ experiments that could not be explained by the wave theory of light. 2

1. Photoelectric Effect The Photoelectric Effect refers to the emission of ______________ from a metal when light shines on that metal. The mystery is that this would only happen if the light’s frequency was above a certain ____________, regardless of how long the light shone on it. According to the ___________ Theory, light should have been able to know electrons loose no matter what frequency. electrons minimum Wave

In 1900, the German Physicist, _______________ (1858 – 1947) began searching for an explanation as he studied the light emitted from heated objects. Max Planck

Max Planck suggested that Electromagnetic Energy was NOT ___________ like a wave, but was in small, specific bursts. A _________ is the minimum amount of energy that can be lost or gained by an electron. He demonstrated mathematically that the energy of a QUANTUM is related to the frequency of the emitted radiation by the equation where E is energy and h is Planck’s constant, and v is frequency. continuous Quantum

DUAL WAVE-PARTICLE THEORY OF LIGHT Albert Einstein furthered the new theory suggesting that light had a ____ _____________ quality. He used the term __________ as a particle of electromagnetic radiation having zero mass and carrying a quantum of energy. Dual Wave-Particle photon

DUAL WAVE-PARTICLE THEORY OF LIGHT

2. BOHR AND THE HYDROGEN LINE EMISSION SPECTRUM Terminology: Ground State: the lowest energy state of an atom. Excited State: the state at which an atom has a higher energy level than it’s ground state Emission: when an excited atom returns to ground state, it gives off energy in the form of electromagnetic radiation. Ex. Neon signs, fireworks!

Neils Bohr (1913) experimented with ______________. “Excited” hydrogen gives off a _______ glow. He narrowed the beam and put it through a prism and expected a _____________________, like a rainbow. This did not happen. hydrogen pinkish continuous spectrum

Was not a continuous spectrum Gave off only specific frequencies of light Lead to the :

EnergyMovement of Electrons ExampleLight?Required? AbsorptionAbsorbedLower to higher energy level N = 1 to n = 3NoYes EmissionReleasedHigher to lower energy level N = 4 to n = 2Yes

What color is the light when a hydrogen atom falls from n = 4 to n = 2? (look on reference table, last page Blue!

BOHR MODEL Still using today: ___________________ Shortcomings: – 1.Only used hydrogen – 2.Said electrons “orbited” the nucleus Energy levels