Download Essential Question: What type of model did Thompson ,Rutherford

Essential Question: What type of model did
Thompson, Rutherford, and Bohr propose about
the atom.
ATOMIC STRUCTURE
Atom- smallest particle of an element that
retains its identity in a chemical reaction
History of the atom:
Greeks thought matter is composed of fire,
water, and wind.
Democritus (460 BCE- 370 BCE)
•Suggested existence of atoms
•Said atoms were indivisible earth
and indestructible
Essential Question: What is John Dalton’s atomic
theory?
Dalton (1808)
 Used
experimental
methods to
transfer
Democritus’s
ideas into
scientific theory
Atomic Theory
 Elements are composed
of indivisible atoms
 All atoms of a given
element are identical
 Atoms of different
elements are different
therefore have different
masses
 Compounds are formed
by a combination of
different elements,
J.J Thomson (1897)
•
•
•
Discovered electrons
by passing an
electric current
through gas at a low
temperature
Named the
negatively charged
particles electrons
An atom was a
positively charged,
jelly-like, with
negatively charged
electrons scattered
throughout. Ex:
Raisins in plum
pudding model
Rutherford’s Experiment
Ernest Rutherford (1911)
•
•
•
•
•
•
Tested “plum pudding theory” by using alpha
particles (positive charged particles smaller than an
atom)
Directed alpha particles at a thin sheet of gold foil
Alpha particles should have passed through the
sheet, but instead most passed through, but some
were greatly deflected and some bounced back.
Concluded that atoms have a dense central core,
nucleus, while the remainder is mainly empty
space
Developed the concept of a nucleus (protons and
neutrons) found in the nucleus and electrons are
around the nucleus
Could not explain chemical properties of elements
Bohr’s Model
Neil Bohr (1913)
•
•
•
•
•
Proposed the planetary model
Said that electrons are found in specific
circular pathways (energy levels or orbits)
around the nucleus
Every possible orbit has a fixed amount of
electrons
Lowest energy is found in the energy level
closest to the nucleus
Electrons can jump from electrons level to
electron level therefore electrons must
gain/loose energy as travel from energy
level to energy level
Comparison of Models:
Quantum of Energy:
• Amount of energy (photon)
required to move an electron
from 1 energy level to another
energy level.
• Energy levels are closer together
in higher energy levels, therefore
requires energy to go from
different energy levels (Less
energy higher up)
Essential Questions: What is the quantum wave
mechanical model of an atom? What are orbitals?
Quantum Mechanical Model (WaveMechanical Model)
•
•
Proposed by Erwin Schrödinger
(1926)
Said levels (shells) have distinct
amounts of electrons moving in
areas called orbital
Orbital:
• Region in which there
is a high probability of
finding an electron
(based on the
electron posses by
the electrons.)
• Looks like a cloud
around the nucleus
Essential Questions: What is the structure of an atom?
What is the atomic number and mass number?
Structure of the atoms:
 Atoms are composed of protons, neutrons
and electrons
Neutron:
 Found
in nucleus
 No charge
 Mass= 1 amu
 Symbol 10n
Atomic mass unit (amu) – 1/12 the mass of
Carbon-12 atom
Proton:
•
Found in nucleus
+ charge
Symbol 11P or 111H
Mass = 1 amu

Number of protons = the number of electrons
•
•
•
Atomic Number
 Number of protons in
an atom
 Periodic Table is
arranged according
to increasing atomic
number
Electrons
►





Found in orbital outside nucleus
Negative charge
Mass of 1/1836 amu
Symbol 0-1e
Number of electrons = number of protons
Ex.: Na- atomic # is 11, therefore 11 protons
and 11 electrons
► **All atoms are neutral, because the number of
protons equals the number of electrons***
►
Mass number- sum of the protons and neutrons in an
atom
Ex: 35 17 Cl 17 protons +
18 neutrons = 35 is the mass number
24
12
Mg
12 protons +
12 neutrons = 24 mass number
Essential Question: What is an isotope?
Isotopes
• Atoms of the same
element with different
number of neutrons
• Therefore have a
different mass
• Chemically alike because
they have same number
of electrons and protons
which are responsible for
chemical behavior
• Ex.: C-14
 8 neutrons
14 C
•
6
•
•
C-12
 6 neutrons
12
Essential Questions: What is atomic mass? What is mass
number?
Atomic Mass:
► Average
mass of atoms in a naturally
occurring sample of an element.
► Reflects both mass and relative abundance
of isotopes as they occur in nature.
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
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

Atomic Problems:
What is the most abundant isotopes of
element oxygen( atoms mass = 15.9994
amu)
O-16 because 15.9994 is closet to 16
What is the most abundant isotope of the
element gold? (atomic mass =196.9665
amu)
Au-197
An element consists of two isotopes. Isotope A
has an abundance of 75.00% and its mass is
14.000 amu. Isotope B has an abundance of
25.00% and its mass is 15.000 amu. What is
the atomic mass of the element?
Isotope A Isotope B
25%
75%
14.000 amu
15.000 amu
Convert % into decimals
Atomic mass = (14.000 amu x.7500) + (15.000
amu x .2500) = 14.25 amu
Carbon has two naturally occurring stable
isotopes. Most carbon atoms -98.89% is
C-12, while the remaining 1.108% is C13. What is the atomic mass of carbon?
Known
Unknown
98.89% C-12 atomic mass = amu
1.108% C-13
12amu x 0.9889 = 11.87 amu
13 amu x 0.01108 = 0.1440 amu
11.87amu + 0.1440 amu =12.01 amu
Essential Question: What is an ion?
Ion:
• An atom that has lost or gained
electrons.
Positive ion – lost electrons.
Ex: B +3 lost 3 electrons
Negative ion –gained electrons
Ex: Cl-1
Refer to periodic table
Oxidation states- number of electrons lost
or gained by an atom to become an ion.
 Some elements have multiple oxidation
states, depending on what substance they
bond to.
Ex: S-2,+4,+6
 Loose or gain electrons to become stable.
How many electrons, protons, and neutrons are in
the following ions?
F-1
N-3
Na+1
Cl+5
Mg
+2
• There are 7 energy levels (shells) .
• They are numbered 1-7.
• Energy level 1 is closest to the nucleus with the
least amount of energy.
• Each successive energy level is further away
from the nucleus, but has progressively more
energy.
The energy level (shell)
corresponds to the row
(period)
number in the periodic
table.
Essential Questions: What are energy levels?
How many electrons does each level contain?
What are valence electrons?
• Each energy level (shell) can contain a
maximum number of electrons.
1st level- 2 electrons
2nd level-8 electrons
3rd level-18 electrons
4th level -32 electrons
Essential Question: What is electron configuration?
Electron configuration-arrangement of electrons by energy level (shel
Exs.” Mg 2-8-2
1st level-2 electrons
2nd level-8 electrons
3rd level-2 electrons
What is the configuration of krypton?
Kr 2-8-18-8
1st level –2 electrons
2nd level-8 electrons
3rd level-18 electrons
4th level-8 electrons
Valence Electrons- electrons in the outermost
energy level .
Ex: Be 2-2
Cl-2-8-7
Corresponds to group number in the periodic
table.
Group 2 elements have 2 valence electrons:
Be 2-2
Mg 2-8-2
Ca 2-8-8-2
Ba 2-8-18-18-8-2
Valence electrons are those that are involved in
a bond.
 Valence electrons are those that an atom gains
or loses to become an ion.
Ex: Na 2-8-1
Na+1

F 2-7
F-1 2-8
Essential Questions? What is the ground state?
What is the excited state ? What is quanta?
Ground state:
 Electrons occupy the lowest energy levels.
 Given on the periodic table.
Ex: C 2-6
N 2-5
Excited State:
 When an electron temporarily moves to a higher
energy level.
 Electrons absorb energy when they move to a higher
energy level.
Exs.: C 2-4 ground state
2-3-1 excited state
Cl 2-8-7 ground state
2-7-8 excited state
B 2-3 ground state
1-4 excited state
• Electrons are arranged different from what is on the
periodic tables
Quanta
• Amount of energy absorbed by an electron
moving to a higher energy level
• Often see its a color
• Atom is unstable
• Electrons will go back to its original level,
therefore releasing the energy (quanta)
Spectrum:
• Pattern of light
produced by an atom
• Distinctive for each
element ( like a finger
print)