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ELECTRONS IN THE ATOM

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ELECTRONS IN THE ATOM UNIT 4 OBJECTIVES Explain how atomic emission spectra can be used to identify elements Describe Bohr s model of the atom. – PowerPoint PPT presentation

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Title: ELECTRONS IN THE ATOM


1
ELECTRONS IN THE ATOM
  • UNIT 4

2
OBJECTIVES
  • Explain how atomic emission spectra can be used
    to identify elements
  • Describe Bohrs model of the atom.
  • Describe the Quantum Mechanical model of the atom
  • Write elements electron configurations.

3
HOW DO WE KNOW WHAT THE STARS ARE MADE OF?
4
ATOMIC EMISSION SPECTRA
  • When an element is heated, its atoms absorb
    energy and become excited
  • To become stable again, these excited and
    unstable atoms then release the energy as light
  • If this light is passed through a prism the
    elements atomic emission spectrum is produced

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7
ATOMIC EMISSION SPECTRA
  • An elements atomic emission spectrum is the set
    of wavelengths (colors) of light given off when
    atoms of that element are excited (e.g. heated)
  • Each elements emission spectrum is unique and
    can be used to identify the element
  • It is the elements fingerprint

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10
HOW DO WE KNOW WHAT THE STARS ARE MADE OF?
  • Scientist analyze the light from a star using
    spectroscopes (similar to powerful prisms)
  • Match the frequencies of light to the known
    spectra of the elements
  • Stars are made of the same stuff as the rest of
    the Universe 73 hydrogen, 25 helium, and the
    last 2 is all the other elements

11
LIGHT
  • Visible light is a type of electromagnetic
    radiation
  • All other electromagnetic radiation is invisible
  • Electromagnetic (EM) radiation is energy that
    travels through space in the form of
    electromagnetic waves
  • The electromagnetic spectrum encompasses all
    forms of electromagnetic radiations

12
increasing energy
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14
BOHRS MODEL OF THE ATOM
  • Bohr studied the emission spectrum of hydrogen
    and developed his model of the atom
  • The Bohr model describes the atom as a small,
    positively charged nucleus surrounded by
    electrons that travel in circular orbits around it

15
THE BOHR MODEL OF THE ATOM
  • Each orbit or ring has a distinct energy
    levels or quantum number (n)
  • the bigger the number the higher the energy
  • Electrons in smaller orbits closer to the nucleus
    have less energy than electrons found in larger
    orbits farther from the nucleus

16
BOHRS ATOM CONTINUED
  • The lowest energy state of an atom is its ground
    state
  • When an atom gains energy (through heating for
    example) it is in an excited state
  • in an excited state the electron absorbs the
    energy jumps to higher energy level
  • when it falls back down to its ground state it
    releases excess energy in the form of light

17
BOHR MODEL CONTINUED
  • Because electrons jump between orbitals that have
    specific energy levels only certain colors can be
    given off
  • This is how Bohr explained hydrogens emission
    spectrum

Transition color of light emitted
n 3 to n 2 red
n 4 to n 2 blue-green
n 5 to n 2 blue
n 6 to n 2 violet
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19
Wait!
  • Bohrs model explained the emission spectrum of
    Hydrogen, but it did not explain the emissions of
    any other element!

20
THE QUANTUM MECHANICAL MODEL OF THE ATOM
  • Electrons behave like waves
  • It is impossible to know the exact location or
    the velocity of an electron in an atom
  • (they dont travel in circular orbits around the
    nucleus)
  • Although its impossible to describe the exact
    location or describe how they are moving, the
    model describe the probability that electrons
    will be found in certain locations around the
    nucleus

21
ATOMIC ORBITALS
  • An atomic orbital is a three-dimensional pocket
    of space around the nucleus that the electron is
    most likely to be found
  • An electron has a 90 chance of being found
    within that space
  • That is the best we can do!

22
ATOMIC ORBITALS
23
ORGANIZATION OF ATOMIC ORBITALS ORGANIZATION OF ATOMIC ORBITALS ORGANIZATION OF ATOMIC ORBITALS ORGANIZATION OF ATOMIC ORBITALS
1. Principal energy level (n) 2. Energy Sublevel 3. Orbitals
value n 1-7 s, p. d, f 1, 3, 5, 7
description -(n) indicates relative size and energy of orbital -As (n) increases so do energy and size -sublevels are labeled according to shape s spherical p dumbbell d/f varied -each sublevel has a certain number of orbitals s 1 p 3 d 5 f 7 -each orbital can hold two electrons
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26
ELECTRON CONFIGURATION
  • An atoms electron configuration is the way an
    atoms electrons are distributed among the
    orbitals of an atom
  • The most state stable electron configuration is
    an atoms ground state
  • Ground state all electrons are in the lowest
    possible energy state
  • Electron configuration represented by writing
    symbol for the orbital and a superscript to
    indicate the number of electrons in the orbital
    Li 1s2 2s1

27
increasing energy
28
Each orbital can hold two electrons
4d
5s
4p
Energy
3d
4s
3p
3s
2p
?
?
?
?
?
?
2s
?
?
1s
?
?
29
The Pauli Exclusion Principle
  • The two electrons in an orbital must spin in
    opposite directions ??

??
?
?
?
??
??
??
??
??
3p
3s
30
HUNDS RULE
  • Negatively charged electrons repel each other,
    so
  • Electrons wont pair up unless they have to
  • Once there is one electron in every orbitalthe
    pairing will begin!

Add an electron
Add an electron
Add an electron
31
DRAW THE ORBITAL DIAGRAM AND WRITE THE ELECTRON
CONFIGURATION FOR
  • Carbon
  • Helium
  • Potassium

32
ELECTRON CONFIGURATION
  • The periodic table can be divided into four
    distinct blocks based on valence electron
    configuration
  • electron configuration explain the recurrence of
    physical and chemical properties

33
SHORTHAND (NOBLE GAS) NOTATION
  • Shows electron filling starting from previous
    noble gas
  • Na 1s22s22p63s1
  • Noble gas configuration Ne3s1

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35
WRITE THE FOLLOWING ELECTRON CONFIGURATIONS IN
NOBLE GAS NOTATION
  • Fluorine
  • Titanium
  • Beryllium
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