Section 5.1 Models of the Atoms Key Concepts: What was inadequate about Rutherford’s model? What was the new proposal in the Bohr model of the atom? What does the quantum mechanical model determine about the electrons in an atom? How do sublevels or principal energy levels differ?

Quantum Mechanical Model Vocabulary Energy Levels Quantum Quantum Mechanical Model Atomic Orbital

The Development of Atomic Models Key Concept: Rutherford’s atomic model could not explain the chemical properties of the elements. RUTHERFORD ATOMIC MODEL: Rutherford’s model could not explain why metals or compounds of metals produce characteristic colors when heated by flame.

The Development of Atomic Models Key Concept: Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus. BOHR ATOMIC MODEL: Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus. energy levels: each electron in the atom has a fixed energy level quantum: the amount of energy necessary to move an electron from one energy level to another energy level.

Rutherford Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge.

Bohr Model In 1913, the Danish scientist Niels Bohr proposed an improvement. In his model, he placed each electron in a specific energy level.

Bohr Model According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus.

The Wave Model

The Wave Model Today’s atomic model is based on the principles of wave mechanics. According to the theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun.

The Wave Model In fact, it is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has. According to the modern atomic model, at atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make an atom neutral.

Electron Cloud: A space in which electrons are likely to be found. Electrons whirl about the nucleus billions of times in one second. They are not moving around in random patterns. Location of electrons depends upon how much energy the electron has.

Electron Cloud: Depending on their energy they are locked into a certain area in the cloud. Electrons with the lowest energy are found in the energy level closest to the nucleus Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.

Greek X Dalton Thomson Rutherford Bohr Wave Indivisible Electron Nucleus Orbit Electron Cloud Greek X Dalton Thomson Rutherford Bohr Wave

Section 5.2 Electron Arrangement in Atoms Key Concepts: What are the three rules for writing the electron configurations of elements? Why do actual electron configurations for some elements differ from those assigned using the aufbau principle?

Vocabulary Electron Configurations Aufbau Principle Pauli Exclusion Principle Hund’s Rule

Electron Configurations What do s, p, d, f mean?   Electron Configurations   Related Resources • General Chemistry • Spectroscopy • CHEM 101 • Chemistry Glossary   Key Concept: Three rules – The aufbau principle, the Pauli exclusion principle, and Hund’s rule – tell you how to find the electron configurations of atoms. Aufbau Principle: Electrons occupy the orbitals of lowest energy first. Pauli Exclusion Principle: An atomic orbital may have at most two electrons. Either one or two electrons may can occupy an s or p orbital. To occupy the same orbital, two electrons must have opposite spins, designated by arrows. Hund’s Rule: Electrons are filled into orbitals singly, first, and then paired once orbitals have at least one electron.  From Other Guides • Physics • Homework/Study Tips • Geology • Geography • Mathematics • Biology   The orbital names s, p, d, and f stand for names given to groups of lines in the spectra of the alkali metals. These line groups are called sharp, principal, diffuse, and fundamental. The orbital letters are associated with the angular momentum quantum number, which is assigned an integer value from 0 to 3. s correlates to 0, p = 1, d = 2, and f = 3.The angular momentum quantum number can be used to give the shapes of the electronic orbitals. s orbitals are spherical; p orbitals are polar. It may be simpler to think of these two letters in terms of orbital shapes (d and f aren't described as readily). The electron configuration of an atom denotes the distribution of electrons among available shells. The standard notation lists the subshell symbols, one after another. The number of electrons contained in each subshell is stated explicitly. For example, the electron configuration of beryllium, with an atomic (and electron) number of 4, is 1s22s2 or [He]2s2.

Electron Configurations Key Concept: Three rules – The aufbau principle, the Pauli exclusion principle, and Hund’s rule – tell you how to find the electron configurations of atoms. What do s, p, d, f mean?   The orbital names s, p, d, and f stand for names given to groups of lines in the spectra of the alkali metals. These line groups are called sharp, principal, diffuse, and fundamental. The orbital letters are associated with the angular momentum quantum number, which is assigned an integer value from 0 to 3. s correlates to 0 (Spherical) p = 1 d = 2 f = 3. The electron configuration of an atom denotes the distribution of electrons among available shells. The standard notation lists the subshell symbols, one after another. The number of electrons contained in each subshell is stated explicitly. For example, the electron configuration of beryllium, with an atomic (and electron) number of 4, is 1s22s2 or [He]2s2.

Aufbau Diagram Key Concept: Three rules – The aufbau principle, the Pauli exclusion principle, and Hund’s rule – tell you how to find the electron configurations of atoms.

Electron Configurations  Key Concept: Three rules – The aufbau principle, the Pauli exclusion principle, and Hund’s rule – tell you how to find the electron configurations of atoms. Filling Order for Electrons:

Section 5.3 Physics and the Quantum Mechanical Model

Light Source of the quantum mechanical model! The light emitted from atoms gives us clues about the energies of the electrons. Electrons behave as particles and waves

Waves Amplitude: the wave’s height from origin to crest Wavelength (λ): distance between crests; measured in nm. Frequency (v): number of wave cycles to occur during a certain amount of time; measured in hertz or 1/s

Electromagnetic waves c = λ ν where c= 3.0 x 108 m/s Spectrum: a series of colors that occurs when light passes through a prism, like a rainbow Atomic spectrum: formed when atoms absorb energy, forcing electrons into higher energy levels Electrons then lose energy by emitting light as they fall to lower energy levels The light is made up of only a few specific frequencies, depending on the element Each frequency is a different color

Atomic Emission Spectra Atomic emission spectrum: the discrete lines formed when an element emits certain frequencies of light Each line represents one exact frequency of light emitted by the atom The light is emitted as electrons fall from one energy level to another, like from n=4 to n=1 They are like atomic fingerprints; every element is unique Spectrum for Barium and Hydrogen Spectrum for all Elements Atomic Absorption and Emission Spectra Ground state electrons: those in their lowest possible energy levels Excited state electrons: electrons that have been raised to higher energy levels than the ground state

Atomic Emission Spectra Light emitted by an electron moving from a higher to lower energy level has a frequency directly proportional to the energy change of the electron Equation describing energy change of the electron E = h x ν (h = 6.626 x 10-34J/s) Different energy level drops result in different frequencies (and colors) of light

More on Quantum Mechanics Remember that both light and electrons behave as both particles and waves! Heisenberg Uncertainty Principle: it is impossible to know exactly both the velocity and the position of a particle at the same time.

Heisenberg Uncertainty Principle How do you find keys in a dark room? Does hitting the keys with light impact the location of the keys? Why or why not? If you want to locate an electron, you must also use light. Photons hitting electrons (which have very little mass) result in unpredictable motion of the electron Measuring the position of the electron changes its velocity!

Quantum Mechanics- kinda weird http://www.teachersdomain.org/resources/phy03/sci/phys/fund/quantum/index.html http://www.teachersdomain.org/resources/phy03/sci/phys/matter/quantumcafe/index.html - Quantum Cafe

Group Work Complete 5.3 Worksheet