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# Chapter 7 Atomic Structure and Periodicity - PowerPoint PPT Presentation

Chapter 7 Atomic Structure and Periodicity. 7.1-7.2 7.3-7.4 7.5-7.8 7.9-7.11 7.13. Properties of Light. Electromagnetic radiation- the way energy travels through space. This energy travels at the speed of light. Waves. Three characteristics: 1.Wavelength 2.Frequency 3. Speed

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### Chapter 7Atomic Structure and Periodicity

7.1-7.2

7.3-7.4

7.5-7.8

7.9-7.11

7.13

• Electromagnetic radiation- the way energy travels through space.

• This energy travels at the speed of light.

• Three characteristics:

• 1.Wavelength

• 2.Frequency

• 3. Speed

• Wavelength =distance between two peaks (in meters)

• Frequency = number of waves per second (cycles per second)

• Speed= travels at speed of light (meters per second)

• Inverse relationship b/t. frequency and wavelength.

• Examples:

• Planck discovered:

• Energy is gained or lost in whole number quantities of hv

• Planck’s constant h = 6.626 x 10-34 J.s

• So Planck determined that energy is quantized (measured) in small packets called hv.

• Change in energy can be calculated by:

• Delta E = nhv

• n = intergers (1,2,3…)

• h = 6.626x10-34 J.s (Planck’s constant)

• v = frequency of EM radiation absorbed or emitted.

• Einstein viewed electromagnetic radiation as travelling in a stream of particles called “photons”

• E photon = hv= hc/lamda

• Energy is quantized. It occurs in units called quanta.

• Electromagnetic radiation exhibits wavelike properties and particulate properties also.

• EM radiation shows wavelike and particulate properties.

• Electrons exhibit particulate and wavelike properties.

• m = h/lamdav or lamda = h/mv

• Examples:

• Excited hydrogen atoms emit light!

• Hydrogen bonds are broken and H atoms release energy….

• Excess energy is released by emitting light of different wavelengths.

Figure 7.7 A ChangeBetween Two Discrete Energy Levels Emits a Photon of Light

Line Spectrum vs. Continuous Hydrogen Atom

• Bohr proposed that an electron orbits the nucleus in a rigidly defined energy level.

Energy Atom = E photon = E e-final- E e-initial

Continuous Spectrum Hydrogen Atom

• White light is a contiuous spectrum.

• The Hydrogen Emission Spectrum is a LINE spectrum

• Atoms in excited states exhibit line spectrum not continous spectrum.

E = -2.178 x 10 Hydrogen Atom-18(Z2/n2)

Z= nuclear charge

n = the size of the radius (the larger the value of n, the larger the orbit radius)

(-) sign means: energy of the electron bound to the nucleus is lower than if electron were at infinity.

At infinite distance, no interaction occurs and the energy is zero.

Bohr model cont’d

Examples… Hydrogen Atom