Atomic History and Structure: What comes to mind when you think of the term “atom”? How do we know what we know about atoms? List any people you can.

Atomic History and Structure:

What comes to mind when you think of the term “atom”?

How do we know what we know about atoms? List any people you can think of.

Thales of Miletus (________)

• Noticed what we call ________________ with amber– Things would be attracted to it when rubbed– It was a “magical property”

• The term electron _________________ _____________________________________________________

Kanada (~_________BC)• Indian attributed with first proposing the

idea of atoms (called “________” or “____”)• 5 elements

– _______________– _______________– _______________– _______________– _______________

• Atoms were indestructable and eternal

Empedocles (450BC)

• 4 elements:– _____________– _____________– _____________– _____________

• Everything was different combinations of these

• This idea didn’t really change until _______!

Leucippus (~_______ BC)

•Proposed the idea of atoms•That two things exist •__________•__________

Democritus (_______)

•Student of Leucippus•Matter is made up of “eternal, indivisible, indestructible and infinitely small substances which cling together in different combinations to form the objects perceptible to us”•“_________”

From :http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=ac20#ixzz1UvX6le4i

100 Greek Drachma, 1967

Aristotle 384 BC – 322 BC•Originally opposed the idea of atoms, then•Added ____________or ______________ to the four elements:

• earth (cold and dry) • air (hot and moist)• fire (hot and dry)• water (cold and moist)

•The differences in matter where a result of ____________________ ________________________

• Changing the balance could change matter

• ex: what we know as copper changed to gold

Benjamin Franklin (_____________) Franklin believed object had 1 of 2 charges (+/-) Opposites attract, like charges repel (Coulomb’s Law,

which the Greeks knew a little about) Kite experiment (among others):

Electric charges run from + to – ________________________

Words he gave us: ____________________________________________

_________________________________________________________________________

J.L. Proust (_____*)

• Law of constant composition:– ____________________________________

____________________________– In other words…a given compound always

has the same composition, regardless of where it comes from.• Ex: H2O is ______________________

______________________________

*not published or recognized until 1811

Dalton’s Atomic Theory ~____• John Dalton (1766-1844)

proposed an atomic theory

• While this theory was not ______________ ____________________________________and brought about chemistry as we know it today instead of alchemy

Dalton’s Atomic Symbols

Dalton’s Atomic Theory

Problems with Dalton’s Atomic Theory?1. matter is composed of indivisible particles

____________________________________________2. all atoms of a particular element are identical

____________________________________________________________________________________________________________________________________

3. different elements have different atomsYES!

4. atoms combine in certain whole-number ratiosYES! Called __________________________________

5. In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.Yes, except __________________________________ ____________________________________________ ____________________________________________

Michael Faraday (______) atoms contain particles with ___________

______________ structure of atoms related to electricity

The electron was the fundamental ________________________________

JJ Berzelius (__________)• Came up with how we write chemical

formulas– _____________ for elements– _______________to indicate numbers of

each element (he used superscripts, though!)

– Considered one of the fathers of modern chemistry• Along with

–John Dalton–Antoine Lavoisier–Robert Boyle

Up until the 1900’s….

• Atomic structure was thought about, but not well known. It took a few more people to really put things together, and build off of each other’s knowledge to come up with what we know today.

• Lord William Thomson Kelvin (________)– Proposed the Plum

Pudding Model, but ______________• ________________

______________________________________________________

JJ Thomson • Discovered __________ (_____) – cathode ray tube– Called electrons corpuscles

• Name electron came from George Johnstone Stoney, who proposed the concept in 1874 and 1881, and the word came in 1891

• Named the “Plum Pudding” model of the atom (________)

Cathode Ray Tube

Hantaro Nagaoka (______)• Proposed the planetary(Saturnian) model

of the atom– _______________________– Electrons bound to the nucleus via

________________________• Both were _____________ by Rutherford• He abandoned the model in ______ due to

errors that were not confirmed by new studies (charged rings)

Rutherford’s Gold Foil Experiment– alpha (α) particles: _______

___________directed at thin metal foil

– most particles made it through → _____________

– others were deflected back → since alpha particles are positive, they had to bounce off of something _________

So…there is a dense ________________________________________________________________________________________________

Gold Foil Animation

Rutherford’s experiment led to the nuclear view of the atom (_______/ published _____)

(side note- it was actually Geiger- Marsden Experiment. Scientists Hans G. and undergraduate Ernest M. worked for Rutherford.)

“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive center, carrying a charge.[2]”

—Ernest Rutherford

Gold Foil and the Models of the Atom

James Chadwick ( )

• Worked with ___________ ______________________.• Proved the existence of the

________________.• same mass as a proton, but

with _______________• its mass was about ______

______ than the proton's.

JJ Thomson

• Determined _____________ __________ (_______)– Used anode rays– Found Ne deflected in two

different paths using what we now call mass spectroscopy

R. A. Millikan - Measured the charge of the electron (1909).

In his famous “oil-drop” experiment, Millikan was able todetermine the charge on the electron independently of itsmass. Then using Thompson’s charge-to-mass ratio, hewas able to calculate the mass of the electron.

e = 1.602 10 x 10-19 coulombe/m = 1.7588 x 108 coulomb/gramm = 9.1091 x 10-28 gram

Goldstein - Conducted “positive” ray experiments thatlead to the identification of the proton. The chargewas found to be identical to that of the electron andthe mass was found to be 1.6726 x 10-24 g.

Millikan’s Experiment

X-rays

.

Millikan’s Experiment

- X-rays give some electrons a charge- Some drops would hover (not fall)

- From the mass of the drop and the charge on the plates, he calculated the mass of an electron

Millikan oil drop experiment

• Millikan did another experiment to determine the mass of the –ve particles (electrons). The experiment used mainly to determine the magnitude of the electron charge and using e/m to get m- value.

30

Niels Bohr (1885-1962)• Bohr Model or the Solar System Model

– Niels Bohr in ________ introduced his _______ ______________________________________

– Electrons _______________________, which are also called _________________.

– An electron can “jump” from a lower energy level to a higher one upon absorbing energy, creating an excited state.

– The concept of energy levels accounts for the emission of distinct wavelengths of electromagnetic radiation during flame tests.

Bohr’s Orbit Model (1913)

Electrons occupy orbitals around the nucleus according to their _______.

Glenn Seaborg(1912-1999 )

• Discovered ___ new elements.

• Only living person for whom ______ _____________________________.

Which brings us to the modern day view of the

atom….

ATOMIC STRUCTURE

•protons and neutrons in the _______________.

•the number of electrons is ______________the number of protons.

•electrons in space ______________________.

•extremely small.

• One teaspoon of water has _______________

______________________________________________________________________________.

The atom is mostly___________________

ATOMIC COMPOSITION• Protons (___)

– positive (+) electrical charge– mass = 1.672623 x 10-24 g– relative mass = 1.007 atomic mass units (____)

• but we can round to 1• Electrons (___)

– negative (-) electrical charge– relative mass = 0.0005 amu

• but we can round to 0• Neutrons (___)

– no electrical charge– mass = 1.009 amu

• but we can round to 1

The following four slides are for additional information only; you will

not be tested on the fundamental particles. However, they could

appear as extra credit on a test or quiz.

Subatomic Particles can also be further broken down into Fundamental Particles

• Quarks– component of protons & neutrons– 6 types

• Up, down• Strange, charm• Top, bottom

• 3 quarks = 1 proton or 1 neutron

He

Subatomic Particles and Quarks

What about electrons?

• Electrons are electrons• They are not made

from quarks• Which is why

they weigh so much less than p+ or no

• Classified as a lepton

Subatomic Particles

More information at http://www.lns.cornell.edu/~nbm/NBM_INTRO_TO_HEP1.htm

Atomic Number, Z

All atoms of the same element have the same ____________ __________in the nucleus, ___

13Al

26.981

Atomic number

Atom symbol

AVERAGE Atomic Mass

+

–

• 11 electrons• 11 negative charges

• 11 positive charges• 11 protons

Atoms are neutral because the numbers of _____________________ - the opposite charges cancel.

IonsA charged atom because of a gain or loss of electrons.If an atom is neutral, the __________________If it has ___________, the atom has a 1+ chargeIf it has ___________, the atom has a 1- charge

IONS • Taking away electrons from an atom gives a

_____________________________

• Adding electrons to an atom gives an _______ ______________________________

• Atoms may _____________________

• To tell the difference between an atom and an ion, look to see if there is a charge in the superscript!

• Examples: Na+ Ca+2 I- O-2 compared to

Na Ca I O

PREDICTING ION CHARGES

In general

• metals lose electrons ---> _______________

• nonmetals gain electrons ---> ____________

Charges on Common Ions

By losing or gaining e-, atom has same number of ___________________________.

Mass Number, A• C atom with 6 protons and 6 neutrons is the mass

standard – = ____________________________

• Mass Number (A)– =____________________________

• NOT on the periodic table…(that is the AVERAGE atomic mass on the table)

• Ex: A boron atom can have A = ______________________

A

Z

10

5B

A

Z

10

5B

Atomic Math

On periodic table- but not all PTs look exactly like this set up, but they have the same information

Think Back…• John Dalton stipulated that all atoms of a

particular element were identical– ______________________________________

______________________________• In 1912, J.J. Thomson discovered that this

was not accurate– In an experiment measuring the mass-to-

charge ratios of positive ions in neon gas, he made a remarkable discovery:

• _________________________________• _________________________________• All of the atoms had 10 protons, however some

had ________________

Isotopes• atoms with the same number of protons (___) but a

different ___________________________– same element, different ____________________

1H (___________): A=1 Z=1

2H (___________): A=2 Z=1

3H (___________): A=3 Z=1

Isotopes & Their Uses

Isotopes & Their Uses

The _____________ content of ground water is used to discover the source of the water, for example, in municipal water or the source of the steam from a volcano.

Learning Check

Which of the following represent isotopes of the same element? Which element?

234 X 234

X235

X238

X

92 93 92 92

Atomic Math: Summary• Atomic number (Z)

– ________________________________– ________________________________

• (Atomic) Mass Number (A)– ______________________________________

______________________________________• Atomic Mass (also called Atomic Weight)

– _______________________________(accounts for all the isotopes) is ___________________

Counting Protons, Neutrons, and Electrons

• Protons: Atomic Number (from periodic table)• Neutrons: Mass Number minus the number of protons

(mass number is protons and neutrons because the mass of electrons is negligible)

• Electrons: – If it’s an atom, the protons and electrons must be

the SAME so that it is has a net charge of zero (equal numbers of + and -)

– If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!)

Learning Check – Counting

State the number of protons, neutrons, and electrons in each of these ions.

39 K+ 16O -2 41Ca +2

19 8 20

#p+ ______ ______ _______

#no ______ ______ _______

#e- ______ ______ _______

Learning Check – Counting

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#p+ _______ _______ _______

#no _______ _______ _______

#e- _______ _______ _______

Learning Check

An atom has 14 protons and 20 neutrons.A. Its atomic number is

1) 14 2) 16 3) 34

B. Its mass number is1) 14 2) 16 3) 34

C. The element is1) Si 2) Ca 3) Se

D. Another isotope of this element is1) 34X 2) 34X 3) 36X

16 14 14

Atomic Symbols: Nuclide NotationNuclide_________________________________Show the name of the element, a hyphen, and the

mass number in hyphen notation

_______________

Show the mass number and atomic number in

nuclear symbol frommass number

atomic number

Nuclide notation: p+, charge, and average atomic mass

37

Mass number (________________)

Cl17Atomic number (number of _______)

A-Z =20number of ________

As atoms have no charge, the number of electrons is the same as the number of protons. This atom has ___________.

Nuclide notation – ions

23Mass number Na+

11Atomic number number of neutrons=

1+ charge ______________ _____ than the number of protons. This atom has __________.

Nuclide notation –ions

16Mass number

O2–8Atomic number

number of neutrons= ___charge means

________________ than the number of protons. This atom has _____________.

Learning Check

Write the nuclear symbol form for the following atoms or ions:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 46 e- ___________

Learning Check

1. Which of the following pairs are isotopes of the same element?2. In which of the following pairs do both atoms have 8 neutrons?

A. 15X 15X 8 7

B. 12X 14X 6 6

C. 15X 16X 7 8

Isotopes and Average Atomic Mass• We are used to calculating #’s of p+, no and e-

using whole numbers; however on the Periodic Table we often see a decimal number Why?

• Atomic Mass (on the Periodic Table) – The average of the isotopic masses _________

____________________________________________________________________________

– In a weighted average we must assign greater importance – give greater weight – to the quantity that occurs ______________________

Isotopes and Atomic Mass

• The atomic mass for each element on the periodic table reflects the ____________ _________________________________ in nature.

• The mass on the periodic table is ______ ____________________________________________________________________

AMUs and Atomic Weight•________________(____) is the unit for relative atomic masses of the elements

• 1 amu =__________________________ • 1 amu = 1.6605x10-24 grams

Protons (p+)mass = 1.672623 x 10-24 grelative mass = 1.007 atomic mass units (amu) but we can round to 1*

Electrons (e-)relative mass = 0.0005 amu but we can round to 0*

Neutrons (no)mass = 1.009 amu but we can round to 1*

*most times, like now; when we get to nuclear chemistry, we will not be able to!

Comparative Example – Your Grades

• To calculate your overall average, we use a weighted average instead of a simple average since different tasks are worth more

• For example:

/100 Your mark

Exams 30 80%

Course work

30 75%

Applied Science

10 70%

Final 30 70%

To Calculate Average Atomic Mass

• You add up _____________________________for each isotope to get the weighted average– Fractional abundance _____________________

• Ex: If something has 3 isotopes:

Example

• Naturally occurring copper exists with the following abundances:

• 69.17% is Cu-63 w/ atomic mass 62.93 amu• 30.83% is Cu-65 w/ atomic mass 64.93 amu

Learning Check:

3 Isotopes of Ar occur in nature

• 0.337% as Ar-36, 35.97 amu• 0.063% Ar-38, 37.96 amu• 99.6% Ar-40, 39.96 amu

• Calculate the Average Atomic Mass

• In J.J. Thomson’s experiment, he found that the percent abundances of neon are as follows:– Neon – 20 = 90.51%– Neon – 21 = 0.27%– Neon – 22 = 9.22%

• Calculate the average atomic mass of neon showing all of your work

If a mass is not specifically given for an isotope

• Then make the assumption that the mass is the same as the atomic mass number– It isn’t exactly correct, but it will be close

AVERAGE ATOMIC MASS

• Boron is 20% 10B and 80% 11B. That is, 11B is 80 percent abundant on earth.

• For boron, atomic weight=

10B

11B

Calculating & Abundance• Chlorine has two isotopes: chlorine-35 (mass

34.97 amu) and chlorine-37 (mass 36.97 amu). • What is the percent abundance of these two

isotopes if chlorine's atomic mass is 35.453?

Problem 1• The two naturally occurring isotopes of nitrogen are

nitrogen-14, with an atomic mass of 14.003074 amu, and nitrogen-15, with an atomic mass of 15.000108 amu. What are the percent natural abundances of these isotopes?

• The atomic mass of nitrogen is 14.00674amu

End of Chapter