1 Chapter 5 Electrons in Atoms Section 5.1Light and Quantized EnergyLight and Quantized Energy Section 5.2Quantum Theory and the AtomQuantum Theory and the Atom Section 5.3Electron ConfigurationElectron Configuration Where is the electron? Electrons are most important for reactivity of atoms because… When two atoms come near each other, their outermost electrons will interact.

Background In the early 1900’s it was clear that Thomson’s and Rutherford’s atomic models could not explain reactivity of elements. Several studies focused on the behavior of light with matter. Results led to a more and more detailed atomic model, especially about the electrons in an atom. 2 H Modern atomic models grew out of the study of light. H Light consists of electromagnetic waves, (with electric and magnetic properties). Helectromagnetic waves travel through empty space. (see picture) H Waves transfer energy HTravel at the speed of light

3 HWavelength ( [lambda] ) is the distance between the crests. (or the shortest distance between equivalent points on a continuous wave.) (SI unit meter or nanometer) HFrequency ( [nu] ) is the number of wave cycles per unit of time (usually per second, s -1 = Hertz (Hz)) HAmplitude is the wave’s height from the origin to a crest. Waves

4 3L’s: Long wavelength, Low frequency, Low energy shh: Short wavelength, high frequency, high energy

5 Electromagnetic Spectrum Electromagnetic radiation includes gamma rays, x-rays, ultraviolet light (UV), visible light, infrared (IR), microwaves, and radio waves. We only see visible light.

6 All electromagnetic waves travel at the speed of light: c = 3.0 x 10 8 m/s. Formula c =  * or = c/  note: and  are “inversely proportional” (one increases, the other decreases proportionally)

7 The wave model of light cannot explain all of light’s characteristics. In 1900, German physicist Max Planck studied the light emitted by heated objects leading him to a surprising conclusion: 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’s constant has a value of x 10 –34 J ● s. Quantum

The photoelectric effect describes that electrons are emitted from a metal’s surface when light of a certain frequency shines on it.

Albert Einstein proposed in 1905 that light has a dual nature. (wave + particle) A beam of light has wave-like and particle-like properties. A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy. The Particle Nature of Light

10 What is the smallest amount of energy that can be gained or lost by an atom? A.electromagnetic photon B.beta particle C.quantum D.wave-particle

11 What is a particle of electromagnetic radiation with no mass called? A.beta particle B.alpha particle C.quantum D.photon

12 Emission spectrum of an element animation 16 An emission spectrum shows only the frequencies of electromagnetic waves that are emitted by the atoms (here in those colors, the rest is dark).

13 The emission spectrum is unique for each element. We know the atmosphere of the sun from measuring the emission spectrum Noble gases when energized give of colored light: helium pink, argon lavender, krypton whitish, xenon blue and neon orange

14 He explained the hydrogen emission spectrum: After first absorbing energy, the electrons “jump” to a higher energy level (orbit further outside). The electron jumps back soon after, releasing the same amount of energy in form of light. Neils Bohr (1885 – 1962) suggested that electrons orbit around the nucleus at specific distances, which relates to the electron’s energy (energy level). The farther out, the higher the energy. Without this motion and energy, electrons would be drawn into the positive nucleus

15 compare to climbing up and down a ladder: you must step on a rung. You can’t step between the rungs. The lowest allowable energy state of an atom is called its ground state. When an atom gains energy, it is in an excited state.

Each orbit was given a number, called the quantum number, n. Hydrogen’s single electron is in the n = 1 orbit in the ground state. When energy is added, the electron moves to the n = 2 orbit.

17 Bohr’s model explained the hydrogen’s spectral lines, but failed to explain any other element’s lines.

18 The Quantum Mechanical Model of the Atom Louis de Broglie (1892–1987) hypothesized that particles, including electrons, also have wavelike properties. Electrons orbit the nucleus only in whole-number wavelengths.

19 The de Broglie equation predicts that all moving particles have wave characteristics.

20 Next, Werner Heisenberg showed it is impossible to take any measurement of an object without disturbing it. The Heisenberg uncertainty principle states that it is fundamentally impossible to know precisely both the velocity and position of a particle at the same time. It’s impossible to assign a fixed path of the electron around the nucleus, the only quantity that can be known is the probability for an electron to occupy a certain region around the nucleus.

21 Schrödinger treated electrons as waves in a model called the quantum mechanical model of the atom. Schrödinger’s equation applied equally well to elements other than hydrogen. The wave function predicts a three-dimensional region around the nucleus called the atomic orbital.

22 The Quantum Mechanical Model designates energy levels as “principal quantum numbers” (n). The average distance from the nucleus increases with increasing n = 1, 2, 3, 4… Within each principal energy level, the electrons occupy energy sublevels (as many as the value of n)

23 Each energy sublevel relates to orbitals of different shape.

24 Electron probability clouds are called Atomic Orbitals one s (spherical) and three p orbitals

25 Four of the five d orbitals have the same shape but different orientations in space. Each orbital can be occupied by 2 electrons 2n 2 The maximum number of electrons that can occupy a principal energy level is given by the formula 2n 2

Which atomic orbitals have a “dumbbell” shape? A.s B.f C.p D.d

Who proposed that particles could also exhibit wavelike behaviors? A.Bohr B.Einstein C.Rutherford D.de Broglie