Objectives Explain the mathematical relationship among the speed, wavelength, and frequency of electromagnetic radiation. Discuss the dual wave-particle nature of light. Discuss the significance of the photoelectric effect and the line-emission spectrum of hydrogen to the development of the atomic model. Describe the Bohr model of the hydrogen atom. Section 1 The Development of a New Atomic Model Chapter 4

Properties of Light The Wave Description of Light Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space. Together, all the forms of electromagnetic radiation form the electromagnetic spectrum. Section 1 The Development of a New Atomic Model Chapter 4

Section 1 The Development of a New Atomic Model Chapter 4 Electromagnetic Spectrum

Properties of Light, continued Wavelength () is the distance between corresponding points on adjacent waves. Frequency (v) is defined as the number of waves that pass a given point in a specific time, usually one second. Section 1 The Development of a New Atomic Model Chapter 4

Section 1 The Development of a New Atomic Model Chapter 4 Wavelength and Frequency

Properties of Light, continued Frequency and wavelength are mathematically related to each other: c = v In the equation, c= speed of light (in m/s) 3.00 X 108  = wavelength = (in m) v = frequency = (in s1 or Hz). Section 1 The Development of a New Atomic Model Chapter 4

Properties of light, continued • What is the relationship between wavelength and frequency? • Sample problems: • 1. What is the wavelength of the yellow sodium emission, which has a frequency of 5.09 X 10 14 Hz?

Properties of light continued • Sample #2 • What is the frequency of violet light with a wavelength of 408 nm?

The Photoelectric Effect The photoelectric effect refers to the emission of electrons from a metal when light shines on the metal. Couldn’t be explained with the wave theory of light. Example- 3 baseballs vs. 12 ping pong balls Section 1 The Development of a New Atomic Model Chapter 4

Section 1 The Development of a New Atomic Model Chapter 4 Photoelectric Effect

Properties of light • The Particle Description of Light • Each particle of light contains a specific amount of energy (quanta). • Einstein called these light packets photons

The Photoelectric Effect, continued The Particle Description of Light, continued German physicist Max Planck proposed the following relationship between a quantum of energy and the frequency of radiation: E = hv E = energy, in joules v = frequency, in s−1 his constant known as Planck’s constant; h = 6.626  1034 J• s. Section 1 The Development of a New Atomic Model Chapter 4

The Photoelectric Effect, continued The Particle Description of Light, continued A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy. The energy of a particular photon is directly proportional to the frequency. Section 1 The Development of a New Atomic Model Chapter 4

Particle description of light • Sample problems • #1 What is the energy per photon of radiation with a frequency of 6.75 X 10 15 Hz? • #2 The spectral line of lithium occurs at 671 nm. Calculate the energy of this light.

Bohr Model of the atom -Bohr studied hydrogen gas -noted that hydrogen’s emission spectrum had certain lines -he said these must represent specific energy levels in the hydrogen atom -Problem-doesn’t work for atoms with more than one electron Section 1 The Development of a New Atomic Model Chapter 4

Section 1 The Development of a New Atomic Model Chapter 4 Hydrogen’s Line-Emission Spectrum

When an electron falls to a lower energy level, a photon is emitted, and the process is called emission. Energy must be added to an atom in order to move an electron from a lower energy level to a higher energy level. This process is called absorption. Section 1 The Development of a New Atomic Model Chapter 4 Bohr Model of the Hydrogen Atom, continued

Section 1 The Development of a New Atomic Model Chapter 4 Photon Emission and Absorption

Objectives Discuss Louis de Broglie’s role in the development of the quantum model of the atom. Compare and contrast the Bohr model and the quantum model of the atom. Explain how the Heisenberg uncertainty principle and the Schrödinger wave equation led to the idea of atomic orbitals. Section 2 The Quantum Model of the Atom Chapter 4

Objectives, continued List the four quantum numbers and describe their significance. Relate the number of sublevels corresponding to each of an atom’s main energy levels, the number of orbitals per sublevel, and the number of orbitals per main energy level. Section 2 The Quantum Model of the Atom Chapter 4

Electrons as Waves If light can act as waves or particles, electrons can act as a particle or wave French scientist Louis de Broglie suggested that electrons be considered waves confined to the space around an atomic nucleus. Section 2 The Quantum Model of the Atom Chapter 4

The Heisenberg Uncertainty Principle German physicist Werner Heisenberg proposed that it is impossible to study both the position and velocity of an electron at the same time---- this is known as Heisenberg uncertainty principle Section 2 The Quantum Model of the Atom Chapter 4

The Schrödinger Wave Equation In 1926, Austrian physicist Erwin Schrödinger developed an equation that treated electrons in atoms as waves. Together with the Heisenberg uncertainty principle, the Schrödinger wave equation laid the foundation for modern quantum theory. Quantum theory describes mathematically the wave properties of electrons and other very small particles. Section 2 The Quantum Model of the Atom Chapter 4

The Schrödinger Wave Equation, continued Electrons do not travel around the nucleus in neat orbits, as Bohr had postulated. Instead, they exist in certain regions called orbitals. An orbital is a three-dimensional region around the nucleus that indicates the probable location of an electron. Section 2 The Quantum Model of the Atom Chapter 4

Atomic Orbitals and Quantum Numbers Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals. This is an electron’s address- no two electrons in an atom have the same 4 quantum numbers. Section 2 The Quantum Model of the Atom Chapter 4

Quantum numbers • The principal quantum number, symbolized by n, indicates the main energy level occupied by the electron. • The angular momentum quantum number, symbolized by l, indicates the shape of the orbital. • The magnetic quantum number, symbolized by m, indicates the orientation of an orbital around the nucleus. • The spin quantum number has only two possible values—(+1/2 , 1/2)—which indicate the two fundamental spin states of an electron in an orbital.

Objectives List the total number of electrons needed to fully occupy each main energy level. State the Aufbau principle, the Pauli exclusion principle, and Hund’s rule. Describe the electron configurations for the atoms of any element using orbital notation,electron-configuration notation, and, when appropriate, noble-gas notation. Section 3 Electron Configurations Chapter 4

Electron Configurations The arrangement of electrons in an atom is known as the atom’s electron configuration. The lowest-energy arrangement of the electrons for each element is called the element’s ground-state electron configuration. Section 3 Electron Configurations Chapter 4

Rules Governing Electron Configurations According to the Aufbau principle, an electron occupies the lowest-energy orbital that can receive it. According to the Pauli exclusion principle, no two electrons in the same atom can have the same set of four quantum numbers. According to Hund’s rule, orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron Section 3 Electron Configurations Chapter 4

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