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Chapter 3 Chemistry 3 1 Energy and Energy Changes energy is the capacity to do work or transfer heat all forms of energy are either kinetic or potential kinetic energy is the energy that results from motion Ek 1 2 mu 2 m mass u velocity thermal energy form of kinetic energy and it is the energy associated with the random mo tion of atoms and molecules potential energy is the energy possessed by an object virtue of its position Has two forms chemical energy and electrostatic energy chemical energy is the energy stored within the structural units of chemical substances electrostatic energy is potential energy that results from the interaction of charged parti cles law of conservation of energy amount of energy in the universe is constant energy can be neither created nor destroyed when one form of energy disappears the same amount of energy must appear in another form or forms the SI unit of energy joule J 3 2 The Nature of Light the term light refers to visible light Electromagnetic spectrum consists of radio waves microwave radiation infrared radia tion visible light ultraviolet radiation x rays and gamma rays ultraviolet radiation causes sunburn waves are categorized by wavelength frequency and amplitude wavelength is the distance between identical points on successive waves frequency is the number of waves that pass through a particular point in 1 second amplitude is the vertical distance from the midline of a wave to the top of the peak or the bottom of the trough c speed of light 2 99 x 10 8 m s speed wavelength and frequency of a wave are all related c visible wavelengths are usually expressed in nanometers microwave and xray wavelengths are expressed in centimeters and angstroms Maxwell proposed that visible light consisted of electromagnetic wave electromagnetic wave has an electric field component and a magnetic field component Double Slit Experiment when one light passes through a slit a bright light is generated BUT when the light passes through two spaced slights a series of light and dark lines interference pattern occurs 3 3 Quantum Theory blackbody radiation emits electromagnetic radiation over a wide range of wavelengths Ex the red glow of the element of an electric stove and the bright white of a tungsten lightbulb Planck proposed that radiant energy could be emitted or absorbed only in discrete quantities like small packages or bundles quantum is the smallest quantity of energy that can be emitted or absorbed in the form of electromagnetic radiation E h e is the energy of a single quantum of energy h Planck s constant is 6 63 x 10 34 J x s photoelectric effect where electrons are ejected from the surface of a metal exposed to light threshold frequency minimum frequency Einstein suggested that a beam of lights is really a stream of particles called photons Ephoton h 3 4 Bohr s Theory of The Hydrogen Atom line spectra are emission of light only at specific wavelengths ground state the lowest energy state of an atom excited state energy state is higher n 1 3 5 Wave Properties of Matter Brogile suggested that if energy light can behave like a stream of particles photons then perhaps particles like electrons can exhibit wavelike properties de Brogile wavelength h mu 3 6 Quantum Mechanics Heinsenberg uncertainty principle it is impossible to know simultaneously both the momentum p and the position of a particle with certainty quantum mechanics does not allow to specify the exact location of an electron in an tome but it does define the region where the electron is most likely to be at a given time 3 7 Quantum Numbers three quantum numbers are required to describe the distribution of electron density in an atom principle quantum number angular momentum quantum number and the magnetic quantum number Principle Quantum Number n principle quantum number designates the size of the orbital The larger n the greater the average distance of an electron in the orbital from the nucleus therefore the larger orbital can have integral numbers 1 2 3 etc corresponds to the quantum number in Bohr s model of the hydrogen atom Angular Momentum Quantum Number l angular momentum quantum number describes the shape of the atomic orbital the values of l are integers that depend on the value of the principal quantum number n for n values of l range from 0 to n 1 L 0 orbital designation s L 1 orbital designation p L 2 orbital designation d L 3 orbital designation f a collection of orbitals with the same value of n is called a shell one or more orbitals with the same n and l values are referred to as a subshell Magnetic Quantum Number ml magnetic quantum number ml describes the orientation of the orbital in space the value of ml depends on the value of l L 0 L Electron Spin Quantum Number ms Electromagnetic theory states that a spinning charge generates a magnetic field and this mo tion causes the electron to behave like a magnet there are two possible spins of an electron electron spin quantum number ms two possible directions of spin opposite each other ms has two possible values 1 2 and 1 2 3 8 Atomic Orbitals s orbitals tum number increases p orbitals when l 0 each s subshell contains one orbital and s orbital all s orbitals are spherical in shape but differ in size which increases as the principle quan when the principal quantum number n is 2 or greater there is a p subshell for which n 2 three p orbitals the 3 p orbitals are diedntilca in size shape and energy but differ from one another only in orientation d orbitals and other higher energy orbitals occurs when the principal quantum number n is 3 or greater f orbitals occur when accounting for element of atomic numbers greater than 57 3 9 Electron Configuration electron configuration which is how the electrons are distributed in the various atomic or bitals Pauli Exclusion Principle no two electrons in an atom can have the same four quantum numbers If so they must have a differnt ms value one must be positive and one negative Aufbau principle determines the electron confiuguraiton Hund s Rule the most stable arrangement of electrons in orbitals of equal energy is the one in which the number of electrons with the same spin is maximized An electron will occupy an empty orbital rather than one that already contains an electron diagmagnetic those with all paired electrons paramagnetic those with one or more unpaired electrons are attracted to magnetic fields Rules for Writing Electron Configurations 1 2 3 4 Electrons will reside in the

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Rutgers CHEMISTRY 161 - Chapter 3 Chemistry

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