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Arrangement of Electrons in the Atom Summarizing Key Concepts: Radiant Energy: Light is a form of electromagnetic radiation. Its energy is transmitted in a form of waves. All waves can be described by their wavelength (), frequency (), amplitude, and speed. The wavelength and the frequency are indirectly related to each other – when the wavelength is short, the frequency is high and vise versa. The electromagnetic spectrum spans a wide range of wavelengths from radio (longest wavelength – lowest frequency and lowest energy) to X-rays (shortest wavelength – highest frequency and highest energy). In a vacuum, all electromagnetic waves travel at a speed of 3.00 x 10 8 m/sec. Quantum Theory: All electromagnetic waves have dual nature and may be described as both waves and particle. Particles of light are called photons. Energy is emitted or absorbed by matter in quanta – specific amounts. Another Look at the Atom: When sunlight (visible, white light) is passed through a prism, the resulting visible spectrum is the continuous spectrum – shows all the colors of the ROYGBIV. In contrast to the continuous spectrum produced by white (visible) light, when a sample of an element is heated and the emitted light is passed through a prism, a bright-line spectrum is observed. An element’s atomic emission spectrum consists of a series of fine lines of individual colors – known as the bright-line spectrum. The Bohr model proposes that the energy of electrons is quantized (allowed only in specific amounts) and electrons spin in specific orbits, each with a different amount of energy, around the nucleus. Electrons enter the lowest energy level that is available to them - the ground state. Upon absorbing energy, electrons move to higher energy levels - the excited state. The excited state is short living. According to the Bohr model of the atom, hydrogen’s atomic emission spectrum = bright line spectrum, results from electrons dropping from higher-energy atomic orbits (excited state) to lower-energy atomic orbits (ground state). The Heisenberg uncertainty principle states that it is impossible to know precisely the velocity (momentum) and the location (position) of a particle at the same time. A New Approach to the Atom: The quantum mechanical model (cloud or Schrödinger model) of the atom explains the properties of atoms by treating the electron as a wave and by including the idea of quantized energies. Electrons occupy atomic orbitals. An orbital is a region in the space around the atom’s nucleus where an electron with a particular amount of energy can be found 90% of the time. An orbital may occupy up to two electrons spinning in opposite spins. Principle energy levels consist of sublevels such as s,p,d, and f. Each sublevel contains a different number of orbitals. 1orbital in the s sublevel, 3 orbitals in the p sublevel, 5 orbitals in the d sublevel, and 7 orbitals in the f sublevel. The shape of the orbital depends on the sublevel – an orbital in the s sublevel has a spherical shape while – an orbital in the p sublevel has a dumbbell shape. Electrons Configuration and Notation: The arrangement of electrons in the atom is called the atom’s electron configuration. Electron configurations are prescribed by three rules: the aufbau principle – states that in the ground state electrons occupy the lowest energy orbitals available, the Pauli exclusion principle – states that only up to 2 electrons can occupy an orbital, and the Hund’s rule – describes how electrons fill orbitals of equal energy so that a maximum number of unpaired electrons results. Electrons related to the atom’s highest principle energy level are referred to as valance electrons. Valence electrons determine the chemical properties of an element. Electron configuration may be represented using orbital diagrams (arrows), electron configuration notation, noble-gas electron configuration, and Lewis-dot diagrams for valence electrons. Key Equations and Relationships: Electromagnetic wave relationship: c = x ν (c = speed of light, = wavelength, and ν = frequency). = c and = c Energy of a quantum or a photon: Equantum(photon) = h x ν (E = energy, h = Plank’s constant, and ν = frequency). Energy change of an electron: ∆E = E higher energy level -E lower energy level Vocabulary: amplitude atomic emission spectrum (bright-line spectrum) atomic orbital aufbau principle electromagnetic radiation electromagnetic spectrum electron configuration electron-dot diagram energy sublevel excited state frequency ground state Heisenberg’s uncertainty principle Haund’s rule Pauli exclusion principle Photon Plank’s constant (6.626 x 10-34 J x Sec) Principle energy level Principle quantum number Quantum Quantum mechanical model of the atom Speed of light in vacuum (3.00 x 108 m/sec) Valence electrons Wavelength