CHEMISTRY ELECTRONS IN ATOMS 1913 Niels Bohr proposed

CHEMISTRY “ELECTRONS IN ATOMS”

1913 – Niels Bohr proposed that the energy of the electron in the H atom was quantized allowed energy levels for the electron = ORBITS (electron can only have certain amounts of energy, not any possible amount)

Niels Bohr - Bohr Model RULE 1: Electrons can orbit only at certain allowed distances from the nucleus. RULE 2: Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. Also, an atom absorbs energy when an electron gets boosted from a low-energy orbit to a highenergy orbit.

Bohr’s Model of the atom

Electron Orbitals Ground state-the original energy level of an electron before becoming excited Excited state-describe an electron that has become excited

Photons are a particle of radiation or an individual quantum of light Quantum is a finite quantity of energy that can be gained or lost by an atom

Practice Question Using the Bohr’s Model of the atom, if an electron in an atom of hydrogen goes from energy level 6 to energy level 2, what is the wavelength and frequency of the EM radiation emitted?

Practice Bohr’s Model Which transition occurs when a hydrogen atom emits light with a wavelength of 434 nm? A) The electron jumps from n=2 to n=4 B) The electron jumps from n=2 to n=5 C) The electron falls from n=4 to n=2 D) The electron falls from n=5 to n=2

1926 – Erwin Schrödinger applied known wave equations to electrons

Quantum Mechanical Model In 1926 the Quantum Model was formed It states that electrons do not have precise orbits or paths Electrons move about in a cloud around the nucleus in what appears to be a random pattern The Quantum Model only predicts where an electron is likely to be found

Heisenberg Uncertainty Principle Heisenberg stated that you may know the location of an electron or the velocity of electron but you may not know both simultaneously

Quantum Model of the Atom In the quantum model, the nucleus is not surrounded by orbits, but by atomic orbitals Atomic Orbitals: a 3 -D (three dimensional) region around the nucleus where a certain electron can be located

Explanation of the Quantum Theory

Quantum Mechanical Model Electrons emits energy in the form of radiation Low energy electrons are found near the nucleus; high energy electrons are found further away from the nucleus

The Quantum Model is based on understanding the behavior of light Light is composed of Electromagnetic (EM) waves EM spectrum shows all forms of radiation

Electromagnetic Spectrum

Electromagnetic Spectrum Encompasses all forms of electromagnetic radiation, with the only differences in the types of radiations is their frequencies and wavelengths. The Speed of Light remains the same always.

Waves Wavelength: ( ) the distance between wave crests measured in m or nanometers (nm) Amplitude: height of wave from origin to crest Trough-the lowest point on a wave Crest-the highest point on a wave

Frequency Frequency: ( ) the number of wave cycles that pass a given point in a given time Frequency is measured in Hertz (Hz) 1 Hertz = 1/s