Download Atomic Theory and Structure Notes

ATOMIC STRUCTURE TEKS
Understand the experimental design and conclusions used in the
development of modern atomic theory, including Dalton's
Postulates, Thomson's discovery of electron properties,
ATOMIC STRUCTURE
Understand the experimental design and conclusions used
in the
development of modern atomic theory, including Dalton's
Rutherford's nuclear atom, and Bohr's nuclear atom. (TEKS 6A)
(CCRS VII B-1)
Postulates, Thomson's discovery of electron properties,
Rutherford's nuclear atom, and Bohr's nuclear atom. (TEKS
Use isotopic composition to calculate
6A) average atomic mass of an
(CCRS VII B-1)
element. (TEKS 6D) (CCRS II B-1)
Use isotopic composition to calculate average atomic mass
of an
element. (TEKS 6D) (CCRS II B-1)
Research and describe the history of chemistry and contributions of
scientists. (TEKS 3F)
Research and describe the history of chemistry and
contributions of
scientists. (TEKS 3F)
Demonstrate safe practices during laboratory and field
investigations. (TEKS 1A) (CCRS I C-3)
Demonstrate safe practices during laboratory and field
[Concept Recommendations] investigations. (TEKS 1A) (CCRS I C-3)
[Concept Recommendations]
Atomic Theories. [Rutherford, Thomson]
Atomic Theories. [Rutherford, Thomson]
Structure of the atom. (not electronStructure
configuration)
of the atom. (not electron configuration)
Isotopes and Average Atomic MassIsotopes and Average Atomic Mass
Charges
Introduce Ions
Charges
Introduce Ions
A World of
Particles
A “theory”
indicates that an
explanation is
supported by
overwhelming
evidence.
A model
is a simplified representation of
something you want to explain
(so a model that represents
the structure of an atom is
called an atomic model).
An Atomthe smallest unit of an element
that retains the chemical
properties of that element and
can exist as a separate particle.
Atomic theory:
All matter is made up of
atoms, and helps us
make accurate
predictions about the
behavior of matter.
Models of the Atom
And scientists that led us there!
~460 BCE:
Democritus
Solid Sphere
Model
His question: Democritus wondered how many
times it would be possible to break a piece of
matter in half, if the pieces would just keep
getting smaller forever. He thought that if he
could just keep breaking matter in half he would
eventually end up with the smallest bit of matter
possible. This led to what we know as the atom.
His hypothesis: atoms are eternally unchanging
and indivisible (he was not able to prove his
thoughts due to lack of technology)
Models of the Atom
And scientists that led us there!
1803
John
Dalton:
Father of Atomic Theory; First to show proof of
atoms
Experiment: He observed elements combine in
whole number ratios to form compounds; Matter is
NOT created or destroyed in chemical reactions.
4 Postulates of Theory:
1) all matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different
elements
4) A chemical reaction is a rearrangement of atoms
Models of the ATOM
And scientists that led us there!
1897
J.J. Thomson
Plum Pudding
Model
Experiment: Zapped atoms with
electricity
Conclusion: atoms consist of
negatively charged electrons
found inside positively-charged
spheres; this is called the “plum
pudding” model
Models of the ATOM
And scientists that led us there!
1911
Rutherford
discovered
the nucleus
Which led to…
His experiment: gold-foil experiment
using alpha particles
Conclusion: atoms contain a small,
massive, and positively-charged particle
called a nucleus.
Models of the ATOM
And scientists that led us there!
Experiment: Observed light is given off when
elements are exposed to flame or electric fields
1913
Bohr
Solar System
Model
Conclusion: an atom consists of a dense,
positively-charged nucleus, containing nearly all
the atom’s mass, surrounded by electrons traveling
in specific allowed orbits, like the planets around a
star—sometimes called the “planetary” model.
Models of the ATOM
And scientists that led us there!
1927
Heisenberg
Proposed a cloud model of the atom—
Experiment: “Thought experiment” He imagined a
microscope that could an electron and to measure its
position. He found that the electron's position and
momentum did indeed obey the uncertainty relation he
had derived mathematically
Conclusions:
 Electrons are located in clouds, not neat orbits
 Tells you where the electron is most likely to be found
(a matter of probability).
 Named the Uncertainty Principle
Models of the ATOM
And scientists that led us there!
1932
Chadwick
Discovered the neutron.
Experiment: He followed up on the work performed by
Ernest Rutherford. Chadwick bombarded alpha rays
at beryllium. When struck, the beryllium emitted
mysterious neutral rays.
Conclusion: He reasoned that neutrons were
important in holding the positively charged protons
together
Quick Review
Atomic Number
•
16
S
Sulfur
32.066
Atomic number: number of
protons
• protons: positively
charged; located in
nucleus
• identifier for element;
(change the number of
protons, change the
element)
Atomic Mass
Atomic Mass: average mass
of element; weighted
average

16
S
Sulfur
32.066
Mass Number: sum of
protons & neutrons; atom
specific

Neutrons: neutral charge; in
nucleus

•
How can we determine the number
of Electrons?
# of protons = # of electrons (in a neutral atom)
Valence electrons: electrons in the outer most
energy level; determines reactivity of element
Valence
electrons
•Atomic Homework
• 6)
sulfur-32
• 7)
phosphorous-31
• 8)
silver-109
• 9)
calcium-41
• 10)
lithium-7
Use the previous notes to fill in the
blanks and answer the questions.
A
# of protons = _____
# of electrons = _____
# of neutrons = _____
Identity of atom = ______
Are the # of protons &
electrons equal? ______
B
# of protons = _____
# of electrons = _____
# of neutrons = _____
Identity of atom = ______
Are the # of protons &
electrons equal? ______
ISOTOPES


Isotope: atoms of the same elements with
different number of neutrons
** Isotopes have different masses
Mass Number: # of p+ + # of n O
– specific to the isotope; may be different from
mass on periodic table
Isotope Notation
•
Write the isotope notation for the
three isotopes of Helium shown
below.
Average Atomic Mass
The average atomic mass is a
weighted average mass of all
the naturally occurring isotopes
of an element based on the
abundance of the element in
nature.
Calculating Average Atomic Mass
Formula:
I1 = isotope #1
I2 = isotope #2
(Mass # I1)(%abundanceI1) + (Mass # I2)(%abundance I2)
100
Example: Hydrogen is 99% 1H, 0.8% 2H, and 0.2% 3H.
(1)(99)+ (2)(.8)+(3)(.2)
100
= 1.01 amu (rounded answer)
OR… Calculating Average Atomic
Mass by converting % to decimal first.
Practice
Isotope
Mg-24
Mg-25
Mg-26
mass (u)
23.985
24.986
25.983
relative abundance
0.7870
0.1013
0.1117