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Chapter 5 Nuclear atomic model did not explain how the atom’s electrons are arranged in the space around the nucleus. Did not explain the differences in chemical behavior among the elements. Scientists discovered that an element’s chemical behavior is related to the arrangement of the electrons in its atom. Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space. (Ex: visible light, radio waves, X rays) Wavelength is the shortest distance between equivalent points on a continuous wave (units: meters, centimeters, nanometers) Frequency is the number of waves that pass a given point per second. (units: hertz; one hertz (Hz) = one wave per second = s^ -1) Amplitude of a wave is the wave’s height from the middle to the top or from the middle to the bottom The speed of light (c) is the product of its wavelength (λ) and its frequency (ν). C = λν As wavelength increases, frequency decreases and as frequency increases, wavelength decreases. All electromagnetic waves have the same speed, but have different wavelengths and frequencies. Higher Frequency Lower Frequency Sunlight is an example of white light. When sunlight passes through a prism, you see a continuous spectrum of colors. (visible spectrum) Rainbows form when drops of water in the air scatters white light from the sun into the spectrum of colors that you see. The electromagnetic spectrum includes all forms of electromagnetic radiation. The sequence of the visible spectrum is red, orange, yellow, green, blue, indigo, violet (Roy G. Biv) As frequency increases, energy increases. Energy increases What is the wavelength of a microwave having a frequency of 3.44 X 109 Hz (or 1/s)? C = λν 3. 00 X 108 m/s = λ (3.44 X 109 Hz) λ = 8.72 X 10-2 m What is the frequency of green light, which has a wavelength of 4.90 X 10-7 m? An X-ray has a wavelength of 1.15 X 10-10 m. What is its frequency? What is the wavelength of an electromagnetic wave that has a frequency of 7.8 X 106 Hz? The temperature of an object is a measure of the average kinetic energy of its particles. When objects are heated up, they gain more energy. Max Planck studied why objects gave off light when heated. He found that matter can gain or lose energy only in small, specific amounts called quanta. A quantum is the minimum amount of energy that can be gained or lost by an atom. Planck proved that the energy of a quantum is related to the frequency of the emitted radiation. E = hν E = energy; h = Planck’s constant; ν = frequency Planck’s constant = 6.626 X 10-34 J·s Unit for energy = joules (J) Matter can only have certain amounts of energy No amounts of energy between these values exist (Child building wall of blocks) In the photoelectric effect, electrons called photoelectrons are given off from a metal’s surface when light of a certain frequency shines on the surface. Einstein said electromagnetic radiation has both wavelike and particle-like natures. So a beam of light has many wavelike characteristics, but also is a stream of tiny particles, or bundles of energy, called photons. A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy. What is the energy of a photon from the violet portion of the rainbow if it has a frequency of 7.23 X 1014 s-1 ? E = hν E = (6.626 X 10-34 J·s) x (7.23 X 1014 s-1) E = 4.79 X 10-19 J What is the energy of each of the following types of radiation? 6.32 X 1020 s-1 9.50 X 1013 Hz 1.05 X 10 s-1 The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by atoms of the element. Only certain colors appear in a certain element’s atomic emission spectrum so only certain frequencies of light are emitted. Bohr studied the hydrogen atom to learn about energy states. The lowest energy state possible of an atom is called its ground state. When an atom gains energy, it is said to be in an excited state. Bohr also suggested that electrons move around the nucleus only in certain circular orbits. The smaller the electron’s orbit, the lower energy level the atom is in. The larger the electron’s orbit, the higher energy level the atom is in. Bohr assigned a quantum number to each orbit. The quantum numbers are n=1, n=2, n=3, and so on. Bohr’s model was the foundation for atomic models that came later, but his model was actually wrong because electrons do not move around the nucleus in orbits. De Broglie studied to see if electrons (particles) could behave like waves. His equation is λ = h/mv Wavelength = Planck’s constant/ mass x volume His equation predicts that all moving particles have wave characteristics The Heisenberg uncertainty principle says that it is impossible to know both the velocity and position of a particle at the same time. Schrodinger’s quantum mechanical model of the atom describes atomic orbitals, which are regions around the nucleus where electrons can be. Atomic orbitals do not have an exact size. Principal quantum numbers indicate the size and energies of atomic orbitals. The letter ‘n’ represents an atom’s major energy levels called principal energy levels. Principal energy levels contain energy sublevels. Principal energy level 1 has 1 sublevel. Principal energy level 2 has 2 sublevels. Principal energy level 3 has 3 sublevels and so on.