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## Structure of the Atom

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**Structure of the atom**• Atoms • Protons • Neutron • Electron • Nucleus**Historical Background**• Continuous theory of Matter: a solid body can be divided and subdivided into smaller pieces without limits. • Discontinuous theory of Matter: particles so small and indestructible ie Democritus and Leucippus**Continued**• Dalton’s Atomic Theory • 1. All elements are composed of atoms, which are indivisible and indestructible particles • 2. All atoms of the same element are exactly alike**Dalton’s theory cont**• 3. Atoms of different elements are different • 4. Compounds are formed by the joining of atoms of two or more elements. In any compound the atoms of the different elements in the compound are joined in a definite whole number ratio**Law of Conservation of Mass**• Originated with Antoine Lavoisier • States that matter can be neither created nor destroyed**Law of Definite Proportions**• Determined by Joseph Proust • That the proportion by mass of the elements in a given compound is always the same • For example in water the mass of oxygen is always 8 times the mass of the hydrogen**Law of Multiple Proportions**• Certain pairs of elements can combine to form one and only one compound (NaCl) • Masses of one element that combine with a fixed mass of the other element form simple whole-number ratios**Discovery of the Electron**• William Crookes- high voltage to a crookes tube and that these cathode rays are deflected by magnetic field • JJ Thompson- deflected by a fundamental particles in a tube called electrons**Discovery of Proton**• Rutherford-Gold foil experiments found that something in the nucleus caused deflections and he named it protons • Discovered alpha particle, beta rays and atomic structure for nuclear physics**Energy levels**• Bohr-definite orbits in which the electrons encircle the nucleus • Define ground states of electrons are most stable • Define excited states of the electrons is energetically unstable**Energy levels cont**• 7 energy levels within an atom • K is the lowest then L M N O P Q all called shells • This is equal to energy levels 1-7**Neutrons**• James Chadwick discovered the neutron • Same mass as a proton but has no electrical charge**Models of the atoms**• They range from Dalton’s up to the quantum mechanical model. Which basically states that light has a dual nature it can behave both as waves and as particles.**Basic vocabulary to know**• Atomic number * Orbitals • Isotopes *Alpha particles • Planck’s constant * Quanta • Wavelength *Atomic mass • Frequency *Mass number • Wave velocity * Atomic mass unit**When light is a wave has properties of**• Wavelength=Lamda • Frequency = hz or f • Wave velocity = v = f lambda**Electromagnetic spectrum**• Speed of light = 3.00 X 108 m/s • C = speed of light • Includes visable light, IR UV radio x-rays gamma radar microwaves • Frequency increases the wavelength decreases on the scale**Light as energy**• Planks constant = h • H = 6.6 X 10 -34 joule/hz • E= hf is the formula • C= f/lambda**Quantum Numbers:four numbers used to describe the electrons**in an atom.**Schrodingerdescribed an atomic model with electrons in three**dimensions. This model required three coordinates, or three quantum numbers, to describe where electrons could be found.**The three coordinates from Schr–dinger's wave equations**are the principal (n), angular (l), and magnetic (m) quantum numbers. These quantum numbers describe the size, shape, and orientation in space of the orbitals on an atom.**1. Principal (shell) quantum number - n**• Describes the energy level within the atom. • Energy levels are 1 to 7 • Maximum number of electrons in n is 2n2**2. Momentum (subshell) quantum number - l**• Describes the sublevel in n • Sublevels in the atoms of the known elements are s - p - d - f • Each energy level has n sublevels. • Sublevels of different energy levels may have overlapping energies.**The momentum quantum number also describes the shape of the**orbital. • Orbitals have shapes that are best described as spherical (l = 0), polar (l = 1), or cloverleaf (l = 2). • Orbitals even take on more complex shapes as the value of the angular quantum number becomes larger.**3. Magnetic quantum number - m**• Describes the orbital within a sublevel**s has 1 orbital**• p has 3 orbitals • d has 5 orbitals • f has 7 orbitals • Orbitals contain 1 or 2 electrons, never more.**malso describes the direction, or orientation in space for**the orbital. • This diagram shows the three possible orientations of a p orbital - px, py, pz. Atomic orbitals are studied in great detail in a college "theoretical inorganic chemistry" class. If you are curious, study these websites**4. Spin quantum number -s**• This fourth quantum number describes the spin of the electron. • Electrons in the same orbital must have opposite spins. • Possible spins are clockwise or counterclockwise.**Rules governing the combinations of quantum numbers:**• Three quantum numbersn, l, and mare integers. • The principal quantum number (n) cannot be zero. • n must be 1, 2, 3, etc.**The angular quantum number (l) can be any integer between 0**and n - 1. • For n = 3, l can be either 0, 1, or 2.**The magnetic quantum number (m) can be any integer between**-l and +l. • For l = 2, m can be either -2, -1, 0, +1, or +2. • The spin quantum number (s) is arbitrarily assigned the numbers +1/2 and -1/2.**Pauli Exclusion Principle:**• No two electrons in an atom have the same set of four quantum numbers.**Hund's Rule:**• Electrons will enter empty orbitals of equal energy, when they are available.**Quantum Chemistry: Describes the way atoms combine to form**molecules and the way molecules interact with one another, using the rules of quantum physics.