atomic structure understand the experimental design and conclusions used in the development of...
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ATOMIC STRUCTURE
Understand the experimental design and conclusions used in the
development of modern atomic theory, including Dalton's
Postulates, Thomson's discovery of electron properties,
Rutherford's nuclear atom, and Bohr's nuclear atom. (TEKS 6A)
(CCRS VII 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)
Demonstrate safe practices during laboratory and field
investigations. (TEKS 1A) (CCRS I C-3)
[Concept Recommendations]
Atomic Theories. [Rutherford, Thomson]
Structure of the atom. (not electron configuration)
Isotopes and Average Atomic Mass
Charges
Introduce Ions
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,
Rutherford's nuclear atom, and Bohr's nuclear atom. (TEKS 6A)
(CCRS VII 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)
Demonstrate safe practices during laboratory and field
investigations. (TEKS 1A) (CCRS I C-3)
[Concept Recommendations]
Atomic Theories. [Rutherford, Thomson]
Structure of the atom. (not electron configuration)
Isotopes and Average Atomic Mass
Charges
Introduce Ions
A World of Particles
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).
A “theory” indicates that an explanation is supported by
overwhelming evidence.
An Atom- the 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 AtomAnd scientists that led us there!
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.
~460 BCE:Democritu
s
His hypothesis: atoms are eternally unchanging and indivisible (he was not able to prove his thoughts due to lack of technology)
Solid Sphere Model
Models of the AtomAnd scientists that led us there!
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 properties3) Compounds are formed by a combination of two or more different elements4) A chemical reaction is a rearrangement of atoms
Father of Atomic Theory; First to show proof of atomsExperiment: He observed elements combine in whole number ratios to form compounds; Matter is NOT created or destroyed in chemical reactions.
1803 John
Dalton:
Models of the ATOMAnd scientists that led us there!
Experiment: Zapped atoms with electricityConclusion: atoms consist of negatively charged electrons found inside positively-charged spheres; this is called the “plum pudding” model
1897 J.J.
Thomson Plum Pudding Model
Models of the ATOMAnd scientists that led us there!
His experiment: gold-foil experiment using alpha particlesConclusion: atoms contain a small, massive, and positively-charged particle called a nucleus.
1911Rutherford discovered
the nucleus
Which led to…
Models of the ATOMAnd scientists that led us there!
Experiment: Observed light is given off when elements are exposed to flame or electric fields
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.
1913Bohr
Solar System Model
Models of the ATOMAnd scientists that led us there!
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
1927Heisenber
g
Models of the ATOMAnd scientists that led us there!
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
1932Chadwic
k
Quick Review
• Atomic number: number of protons
• protons: positively charged; located in nucleus
• identifier for element; (change the number of protons, change the element)
Atomic Number
SSulfur
16
32.066
Atomic Mass: average mass of element; weighted average
Mass Number: sum of protons & neutrons; atom specific
Neutrons: neutral charge; in nucleus
•
SSulfur
16
32.066
Atomic Mass
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
•6) sulfur-32•7) phosphorous-31•8) silver-109•9) calcium-41•10) lithium-7
•Atomic Homework
Use the previous notes to fill in the blanks and answer the
questions.
# of protons = _____# of electrons = _____# of neutrons = _____Identity of atom = ______Are the # of protons & electrons equal? ______
# of protons = _____# of electrons = _____# of neutrons = _____Identity of atom = ______Are the # of protons & electrons equal? ______
A B
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:
(Mass # I1)(%abundanceI
1) + (Mass # I
2)(%abundance I
2)
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)
I1 = isotope #1
I2 = isotope #2
OR… Calculating Average Atomic Mass by converting % to
decimal first.
PracticeIsotope mass (u) relative abundanceMg-24 23.985 0.7870Mg-25 24.986 0.1013 Mg-26 25.983 0.1117