Title: Structure of the Atom Atomic Theory
1Structure of the Atom Atomic Theory
2AlchemyB.C.
- Before there were chemists, alchemists studied
matter in an effort to make gold from other
metals.
3Leucippus Democritus460 - 370 BC
- Atomists Theory of Matter
- Matter is made of invisible, pebble like
particles called atoms. - Like pieces of a mosaic
- BUT this was not backed by experimental evidence
- Godless
4Aristotle384 - 322 B.C.
- Believed that matter was composed of 4 elements
- Earth
- Air
- Fire
- Water
- Spiritual elements
5Epicurius341 - 270 BC
- Opposed Aristotle Plato teachings
- Tried again to bring the Atomists theory to the
forefront - Denied
-
- . . . and the Dark Ages ensued
6Daltons Atomic Theory (early 1800s)
- 1. All elements are composed of atoms
- atoms are indestructible cant be changed
- 2. All atoms of an element are exactly alike
- 3. Atoms of different elements have
different masses - 4. Compounds are formed by joining two or more
elements in whole number ratios
7Thomson and the Cathode Ray Tube(late 1800s)
- Thomson concluded that the atom was made of
smaller particles. - Discovered particles with negative charge
- Electron
- No matter what metals were used they all produced
electrons - Therefore all elements (atoms) contain electrons
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9 - Soon after Thomsons discovery of the electron,
the proton was discovered, SO - Thomson theorized a new model of the atom.
10Rutherfords Gold Foil Experiment
11 charge
charge
12Rutherfords Gold Foil Experiment
13Rutherfords Model (early 1900s)
Experiments with alpha particles
- OBSERVATIONS
- most ? particles went straight through
- few ? particles were deflected or bounced back
- CONCLUSIONS
- atoms are mostly empty space
- few ? particles came close to or hit a positive
particle in the atom
14Rutherfords Planetary Model
- Electrons orbit a large, positive nucleus
- Electrons emit energy as they fall toward the
nucleus
15Bohr Model of the Atom(early 1900s)
- Electrons have definite, fixed orbits
- Electrons have a definite energy
- orbits farther from the nucleus have greater
energy
16Orbital 2
Orbital 1
energy level shell orbital
17Electron-cloud model Wave-mechanical
modelQuantum . . . Model Modern Model
18Basic Atomic Structure
19Atoms are not solid spheres, they are composed of
. . . Subatomic particles
- Electron e-
- found outside the nucleus in orbitals
- Proton p
- found inside nucleus
- Neutron n0
- found inside nucleus
20Atomic Number
The number of protons defines the element
- Each element has a different atomic number 1, 2,
3, 4, 5, 6, 7, 8, 9, 10 . . . - The atomic number is equal to the number of
protons
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22Mass Numbera.k.a. Atomic Mass
- the mass of the atom is contained in the nucleus
- Masses of electrons are negligible
- it takes 1836 e- to equal the mass of 1p
or 1no
23- atomic mass p no
- 1 p 1 amu or 1/12 the mass of C atom
- 1 no 1 amu or 1/12 the mass of C atom
Carbon - 12 is the standard that all masses are
compared to. All other elements have relative
masses
24- How do you determine the number of neutrons in an
atom? - How do your determine the number of electrons in
an atom?
Atoms are neutral
25Atoms of the same element are not necessarily
alike . . .
Same atomic number different mass number
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27Isotopic Notation
- How many protons?
- How many neutrons?
a.k.a. H-1
28Isotopic Notation
- How many protons?
- How many neutrons?
a.k.a. H-2
29Isotopic Notation
- How many protons?
- How many neutrons?
a.k.a. H-3
30How is atomic mass calculated?
- Mass p no
- BUT since the number of neutrons in an atom can
vary . . . - Mass H 1 Mass H 2 Mass H 3
- The atomic mass is an AVERAGE mass of the
isotopes - BUT!!!!!! Is the mass of Hydrogen is 1.00794 and
not 2???????
31Weighted average
- Test grades 50
- HW 10
- Labs 40
- Test avg 85
- HW avg 90
- Lab avg 75
What is your MP average?
32Average atomic mass of H
- 1amu x .9999 .9999
- 2amu x .0001 .0002
1.0001
Do NOT use division in a weighted average!!!!
33Electron Configurations
34Different E levels hold different s of e-
- E level 1 2 e-
- E level 2 8 e-
- E level 3 18 e-
- E level 4 32 e-
But NEVER more than 8 outermost
35You can tell an atoms electron configuration
based on its location in the periodic table
36Electron Configuration
12.0111 C 6 2 - 4
37Practice Problems
- What is the electron configuration of potassium?
- 2-8-8-1
- How many electrons does Phosphorus have in its
2nd E level? - 8
- How many e- does sodium have in its first
orbital? - 2
- How many e- does iron have in its 3rd E shell?
- 14
38e- in higher E levels have more E
39Valence electrons
- Outermost number of electrons
- Never more than eight
- Highest energy
40How many valence electrons?
- hydrogen
- potassium
- Sodium
- Lithium
- Magnesium
- Calcuim
- Barium
- Fluorine
- chlorine
- Neon
- Argon
- Krypton
41Notice anything?
- Elements (atoms) in the same group have the
same number of valence e- - The of valence e- corresponds to the last digit
of the group number
42Lewis Dot Structure
- Method of showing valence electrons
- Never more than 8 total
Symbol represents the kernel Dots show valence
electrons
43Draw Lewis Dot diagrams
- lithium
- beryllium
- fluorine
- argon
44Ions
45Ions are particles that carry a charge
- The charge an ion carries is the DIFFERENCE
between the p and e-
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47- Ions form because atoms want to have a full outer
energy level. - Want an electron configuration like the nearest
noble gas. - They will do this the easiest way possible.
- Na loses 1 electron Na1
- Cl gains 1 electron Cl-1
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49Practice Problems
- What is the charge on an ion with 7p and 5e- ?
- What is the charge on an ion with an atomic
number of 8 and 5e-? - What is the charge on an ion with an atomic mass
of 35 if this atom has 18 neutrons and 18
electrons?
50Draw Lewis Dot diagrams
- Cl -
- Ca 2
- Lithium ion
- Beryllium ion
- Fluoride ion
51Electron Orbital Notation
- e- dont actually zoom around the nucleus on
little electron highways as seen in the Bohr
Model of the Atom. - THEREFORE
- true electron configuration isnt that easy!
52- Each principle orbital 1, 2, 3, 4 . . . is
divided into suborbitals s,p,d f - These are some shapes of the orbitals
53- s can hold 2 electrons
- p can hold 6 electrons
- d can hold 10 electrons
- The size of the suborbital is the same for any
one energy level - 3s, 3p, 3d are the same size
- 4s, 4p 4d are the same size but larger than the
3s
54- When writing orbital notation
- Orbital Suborbital of electrons
- or
- level sublevel number (oh my!)
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56Ground State vs. Excited state
- So far weve discussed e- in their ground state
57Ground State e-
- Definition e- occupy lowest possible energy
levels - Most stable electron configuration
- The electron configurations on your periodic
table show e- in their ground state - ex. 2 - 8 - 6
58Excited State e-
- Definition e- of an atom occupy higher E levels
when lower E levels are still vacant - ex. 2 - 7 - 7
- ex. 2 - 3 - 1
Can hold up to 8 here.
Can hold up to 8 here.
59Ground state 2 - 6Excited state 2 - 5 - 1
60Ground State to Excited State
61Excited State to Ground State
62Spectroscopy
- Emission lines of elements
- Bright line spectra
63- If you hold a prism to light you will see a
continuous spectrum of color. - ROYGBIV
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65Emission lines
- Visible light produced by electrons are confined
to narrow lines of color called bright line
spectra. - These emission lines are used to identify
elements - fingerprints
66Spectra of some elements
67THE END