Title: Atomic Structure
1Atomic Structure
2Father of Atomic TheoryJohn Dalton
1766-1844
3Daltons Model of the Atom
An atom is a hard sphere that is uniform
throughout.
4Daltons Theory
- Atoms are indestructible particles ( False)
- Atoms are the smallest particle of an element and
still have all the properties of that element - All atoms of the same element are alike (False)
- Elements differ because atoms differ. They
always differ in the number of protons. - Atoms will combine to form compounds.
- Only whole atoms combine
- Atoms combine in a ratio of small whole numbers.
5J.J. Thomson (1856-1940)
- Discovered the electron by passing electric
current through gases at low pressure using a
cathode -ray tube
6J.J. Thompson
- He proposed that an atom consisted of a solid,
positively charged sphere and the negatively
charged electrons were imbedded in the surface of
the atom - cookie dough or plum pudding model
7Robert Millikan (1868-1953)
- He measured the charge of an electron and
calculated the mass by spraying oil droplets,
which fell on electrically charged plates - He calculated the charge of an electron to be 1.6
x 10-19 coulomb and the mass of an electron to be
9.11 x 10-28 gram, which is about 2000 times
lighter than an atom of hydrogen
8Ernest Rutherford (1831-1937)
- In 1911, he performed the gold foil experiment by
directing a narrow beam of alpha particles at a
very thin sheet of gold foil - To his surprise, the majority of the alpha
particles passed straight through the gold atoms,
without deflection and a small fraction bounced
off the gold foil at large angles
9Gold Foil Experiment
10Gold Foil Experiment
11Rutherford
- He proposed that the atom is mostly empty space
and that all the positive charge and almost all
the mass are concentrated in a small region which
he called the nucleus. - The nucleus is composed of protons and neutrons
- If an atom were the size of a football stadium,
then its nucleus would be the size of a marble
12Rutherfords model of the Atom
protons
neutrons
13Neils Bohr (1885-1962)
- Proposed that electrons orbit the nucleus in
fixed orbits
The protons and neutrons are in the nucleus. The
electrons are in specific orbits around the
nucleus. (Sorry, the colors are not
cooperating!!!)
14Rutherford video
- http//cwx.prenhall.com/petrucci/medialib/media_po
rtfolio/text_images/006_RUTHERFORD.MOV
15Excited state Vs. ground state
- When an electron absorbs energy, it jumps to a
higher energy, called the excited state. When an
electron emits energy, it falls from the excited
state, back to the ground state. - The emission of energy creates spectral lines
that are specific to each element - An atom in the ground state has the same number
of electrons that it has in the excited state.
The number of electrons does not change, only the
energy that the electrons have changes.
16Modern Atomic theory
- All elements are composed of atoms. An atom is
the smallest particle of an element that can
enter into combination with other elements. - All atoms of the same element are chemically
alike. They may differ in mass. - Atoms of different elements are chemically
different. - Atoms are not divided, created, or destroyed by
ordinary chemical or physical means.
17Subatomic particles
symbol
charge
relative mass
location
Particle
nucleus
1
Proton
H1
nucleus
1
Neutron
0
n1
-
shells energy levels
e-
0
Electron
18A
? Atomic mass
X
Symbol ?
Z
? Atomic number
Atomic number protons
Mass number protons neutrons
In an atom the number of electrons the number
of protons or total total -
1923
Na
11
Atomic number
11
Mass number
23
protons
11
neutrons
23 11 12
electrons
11
(only for atoms in the ground state)
20Isotopes
- Atoms of the same element that have different
numbers of neutrons - Example 12C and 14C are isotopes
- Carbon-12 has 6 protons and 6 neutrons
- Carbon-14 has 6 protons and 8 neutrons
21Isotopes
- Isotopes are uniformly mixed in nature
- The atomic mass on the periodic table is the
weighted average mass of the naturally occurring
isotopes of that element - The closer the number of neutrons is to the
number of protons, the more stable the isotope is
22Isotope sample problem
- Imaginary element X has two isotopes, 17X and
21X. 65 of all isotopes of X are 17X. What is
the atomic mass of X? - Change your percent to a decimal and multiply by
the mass. Then, add answers together. - 17X .65 x 17 11.05
- 21X .35 x 21 7.35
- 18.40 amu
- Your answer should be somewhere between the
values of your isotopes. Always remember to
multiply by the percentages.
23One for you to try
- Imaginary element Z has three isotopes, 30Z,
34Z and 35Z. 20 are 30Z, 50 are 34Z, and 30
are 35Z. What is the atomic mass of Z? - 30Z .20 x 30 6
- 34Z .50 x 34 17
- 35Z .30 x 35 10.5
- 33.5 amu
24Bohr diagrams
- When drawing a Bohr diagram, you need to know the
number of protons, neutrons, and the electron
configuration of the species youre drawing. - Remember, the protons and neutrons are located in
the nucleus. - The electrons are drawn on the correct orbitals
around the nucleus according to their electron
configurations.
25Atoms vs. ions
- All atoms are neutral.
- All atoms have the same number of protons as
electrons. - Ions are charged particles.
- Atoms form ions when they gain or lose electrons.
26Metal ions vs. Nonmetal ions
- Metals form positive ions because they lose
electrons. - Nonmetals form negative ions because they gain
electrons.
27Ions
- Atoms want to form ions in order to have a
completed outer shell consisting of 8 electrons. - (Elements 1-5 only need 2 electrons to have a
completed outer shell since the first energy
level can only hold 2)
28How many electrons to gain or lose?
- The last number in the electron configuration is
the number of valence electrons. - Use this to figure out how many electrons to gain
or lose. - Atoms with 1-3 valence electrons will lose all
their valence electrons. - Atoms with 5-7 will gain as many electrons as
needed to make 8. - Atoms with 4 can either gain or lose 4.
29Lewis electron dot diagrams
- Use the number of valence electrons of the atom
to place the corresponding number of dots around
the symbol for the atom. -
- Al
- F
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