Unit 1: Atomic Structure

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Unit 1 Atomic Structure Electron Configuration
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I. Theories and Models

• Scientific Model A pattern, plan,
  representation or description designed to show
  the structure or workings of an object, system or
  concept.

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A. Greeks

• 400 B.C.
• Democritus
• particle theory- matter could not be divided into
  smaller and smaller pieces forever, eventually
  the smallest possible piece would be obtained and
  would be indivisible.
• called natures basic particle atomos-indivisible
• no experimental evidence to support theory

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B. John Dalton

• 1808
• English school teacher
• Established first atomic theory
• Matter is composed of atoms.
• Atoms of a given element are identical to each
  other, but different from other elements.
• Atoms cannot be divided nor destroyed.
• Atoms of different elements combine in simple
  whole-number ratios to form compounds.
• In chemical reactions, atoms are combined,
  separated or rearranged.
• Model tiny, hard, solid sphere

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C. JJ Thomson

• 1897
• cathode ray tube experiment
• given credit for discovering electrons, resulting
  in the electrical nature of an atom
• Plum pudding model sea of positive charges with
  negative charges embedded evenly throughout.

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Ernest Rutherford

• 1911
• Gold Foil (Alpha Scattering) Experiment

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• Conclusions
• atom is mostly empty space
• most of mass of atom is in the nucleus
• nucleus is positively charged
• Model

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E. Niels Bohr

• 1913
• Rutherfords student
• electrons arranged in energy levels (orbits)
  around the nucleus due to variation in energies
  of electrons
• higher energy electrons are farther from nucleus
• Planetary Model

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F. Quantum Model

• 1924-current
• Collaboration of many scientists
• Better than Bohrs model because it describes the
  arrangement of e- in atoms other than H
• Based on the probability (95 of time) of finding
  and e- or an e- pair in a 3D region around the
  nucleus known as an orbital
• Model (on board)

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II. General Structure of Atom

• nucleus

• e- cloud

• center of atom
• p n0 located here
• positive charge
• most of mass of atom, tiny volume
• very dense

• surrounds nucleus
• e- located here
• negative charge
• most of volume of atom, negligible mass
• low density

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III. Quantification of the Atom

• A. Atomic Number - the number of p in nucleus
• All atoms of the same element have the same
  atomic number.
• Periodic table is arranged by increasing atomic
  number.
• if atom is electrically neutral, then the
• p e-

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• B. Mass Number - the total number of p n0 in
  nucleus of an atom.
• Round the atomic weight to a whole number
• n0 mass number - atomic number

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• C. Ions atoms of an element with the same
  number of p that have gained or lost e-,
  therefore having a or charge
• atoms form ions in order to be more stable like
  the noble gases
• anion ion with negative charge (gained e-)
• non-metal elements tend to form anions (ex. S2-)
• change the end of the element name to ide
  (sulfide ion)
• cation ion with a positive charge (lost e-)
• metal elements H tend to form cations (ex.
  Sr2)
• Roman numerals may be used in the name of some
  metal ions that can lose various numbers of e-
  (ex. Tin (IV) ion)

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• D. Isotopes atoms of an element having the
  same number of p, but a different number
  of n0, resulting in a different mass number.
• Two ways to represent isotope symbols
• or C-14
• Write mass after the element name
• carbon-14

mass
mass
atomic
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Isotopes of Hydrogen
Name Symbol e- n0 p Mass Atomic
Hydrogen-1 (protium) 1 0 1 1 1
Hydrogen-2 (deuterium) 1 1 1 2 1
Hydrogen-3 (tritium) 1 2 1 3 1
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• E. Average Atomic Mass weighted average of all
  natural isotopes of an element expressed in amu
  (atomic mass units).
• based on abundance of isotopes
• steps for calculating
• change to decimal
• multiply decimal and mass number
• add all results
• place amu unit with answer
• amu1/12 mass of C-12 isotope

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IV. Electromagnetic Radiation

• A. Properties
• 1. Form of energy which requires no substrate
  to travel through.

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• 2. Exhibits properties of a sine wave

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• a. wavelength distance between
  consecutive crests (Greek letter lambda
  ?)
• b. frequency wave cycles passing a
  given point over time
  (seconds) (Greek letter nu ? )
• measured in Hertz (Hz) 1/s, s-1, or
  per second
• c. all types of ER travel in a vacuum at
  the speed of light (c) 3.00 x
  108 m/s

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• 3. light equation
• c??
• ? ? are inversely (indirectly)
  proportional (as one increases, the
  other decreases)

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energy ? are directly related (as one
increases/decreases, so does the other energy
equation Eh? h Planks constant 6.63 x
10-34 Js
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V. Emission/Absorption Spectra

• The e- is the only SAP that absorbs/emits
  energy.
• A. Absorption Spectrum when an e- absorbs
  energy, it moves from the ground state (most
  stable arrangement of e-) to an excited state
  (which is not stable)
• B. Emission Spectrum - when an e- emits energy,
  it falls from the excited state back to ground
  state, releasing energy in the form of
  electromagnetic radiation, which may be visible
• unique to each atom
• http//chemistry.bd.psu.edu/jircitano/periodic4.ht
  ml

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VI. Electron Configuration

• A. Describes the arrangement of e- in an atom
• 1. each main energy level is divided
  into sublevels
• 2. each sublevel is made up of orbitals,
  each of which can hold up to 2 e-
• chart

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Sublevel of orbitals shape
s 1
p 3
d 5
f 7
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• 3. due to main energy levels getting closer
  together, sublevels overlap

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• 4. Aufbau principle states that e- fill
  orbitals of lower energy sublevels first
• 5. Abbreviated Configurations use the
  preceding noble gas symbol (in brackets)
  to represent the filled inner core of e-.
  Then write the remaining configuration for
  the atom.

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• 6. Orbital Configurations- arrangement of e-
  within
• sublevels
• 2 rules determine arrangement
• a. Hunds Rule each orbital within
  a sublevel receives 1 e- before it gets 2
• orbitals in the same energy sublevel are
  degenerate (of equal energy)
• b. Pauli Exclusion Principle no 2 e- in
  an orbital can have the same
  spin.
• clockwise spin counterclockwise
  spin
• exceptions