ATOMIC STRUCTURE Understand the experimental design and conclusions used in the development of modern atomic theory, including Dalton's Postulates, Thomson's.

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