10/26/15 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. 1 10/26/15 Empedocles (450BC) •  4 elements: – _____________ – _____________ – _____________ – _____________ • Everything was different combinaDons of these • MaGer could be endlessly divided •  This idea didn’t really change unDl _______! Democritus (_______) • MaGer is ___________________ divisible. • MaGer is made up of “eternal, indivisible, indestrucDble and infinitely small substances which cling together in different combinaDons to form the objects percepDble to us” • “_________” From :
hGp://www.historyworld.net/wrldhis/
PlainTextHistories.asp?historyid=ac20#ixzz1UvX6le4i 100 Greek Drachma,
1967
2 10/26/15 §  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 aGract, like charges repel (Coulomb’s Law, which the Greeks knew a liGle about) §  Kite experiment (among others): §  Electric charges run from + to – §  ________________________ 3 10/26/15 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 4 10/26/15 Dalton’s Atomic Theory Problems with Dalton’s Atomic Theory? 1. maGer is composed of indivisible parDcles ____________________________________________ 2. all atoms of a parDcular element are idenDcal _______________________________________________
_______________________________________________
______________________________________ 3. different elements have different atoms YES! 4. atoms combine in certain whole-­‐number raDos YES! Called __________________________________ 5. In a chemical reacDon, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements. Yes, except __________________________________ ____________________________________________ ____________________________________________ 5 10/26/15 Up unIl 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 ______________ •  ________________
________________
________________
________________
______ 6 10/26/15 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 7 10/26/15 Rutherford’s Gold Foil Experiment Gold Foil AnimaDon –  alpha (α) parDcles: _______ ___________directed at thin metal foil –  most parDcles made it through → _____________ –  others were deflected back → since alpha parDcles are posiDve, they had to bounce off of something _________ So…there is a dense __________________________
__________________________
__________________________
__________________ Rutherford’s experiment led to the nuclear view of the atom (_______/ published _____) (side note-­‐ it was actually Geiger-­‐ Marsden Experiment. ScienDsts 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 Dssue paper and it came back and hit you. On consideraDon, I realized that this scaGering backward must be the result of a single collision, and when I made calculaDons 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 8 10/26/15 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. 9 10/26/15 JJ Thomson •  Determined _____________ __________ (_______) –  Used anode rays –  Found Ne deflected in two different paths using what we now call mass spectroscopy Millikan’s Experiment 10 10/26/15 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 ___________ of an _________________. R. A. Millikan - Measured the charge of the electron
(1909).
In his famous “oil-drop” experiment, Millikan was able to
determine the charge on the electron independently of its
mass. Then using Thompson’s charge-to-mass ratio, he
was able to calculate the mass of the electron.
e = 1.602 10 x 10-19 coulomb
m = 9.1091 x 10-28 gram
Goldstein - Conducted “positive” ray experiments that
lead to the identification of the proton. The charge
was found to be identical to that of the electron and
the mass was found to be 1.6726 x 10-24 g.
11 10/26/15 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, creaDng an excited state. –  The concept of energy levels accounts for the emission of disDnct wavelengths of electromagneDc radiaDon during flame tests. Bohr’s Orbit Model (1913) Electrons occupy
orbitals around the
nucleus according to
their _______.
12 10/26/15 Glenn Seaborg
(1912-1999 ) •  Discovered ___ new elements. •  Only living person for whom ______ _________________
____________. Which brings us to the modern day view of the atom…. 13 10/26/15 ATOMIC STRUCTURE The atom is mostly ___________________ • protons and neutrons in the _______________. • the number of electrons is ______________the number of protons. • electrons in space ______________________. • extremely small. • One teaspoon of water has _______________ _____________________________________________________
_________________________. ATOMIC COMPOSITION •  Protons (___) –  posiDve (+) electrical charge –  mass = 1.672623 x 10-­‐24 g –  relaDve mass = 1.007 atomic mass units (____) •  but we can round to 1 •  Electrons (___) –  negaDve (-­‐) electrical charge –  relaDve mass = 0.0005 amu •  but we can round to 0 •  Neutrons (___) –  no electrical charge –  mass = 1.009 amu •  but we can round to 1 14 10/26/15 The following four slides are for addiDonal informaDon only; you will not be tested on the fundamental parDcles. However, they could appear as extra credit on a test or quiz. Subatomic ParIcles can also be further broken down into Fundamental ParIcles •  Quarks –  component of protons & neutrons –  6 types •  Up, down •  Strange, charm •  Top, boGom He
•  3 quarks = 1 proton or 1 neutron 15 10/26/15 Subatomic ParDcles 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 16 10/26/15 Subatomic ParDcles 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, ___ 13 Al 26.981 Atomic number
Atom symbol
AVERAGE Atomic Mass
17 10/26/15 Atoms are neutral because the
numbers of _____________________
- the opposite charges cancel.
–
•  11 electrons
•  11 negative charges
+
•  11 protons
•  11 positive charges
Ions § A charged atom because of a gain or loss of electrons. § If an atom is neutral, the __________________ § If it has ___________, the atom has a 1+ charge § If it has ___________, the atom has a 1-­‐ charge 18 10/26/15 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 -­‐-­‐-­‐> ____________ 19 10/26/15 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 –  = ____________________________ A
•  Mass Number (A) –  =____________________________ Z
10
5
B
•  NOT on the periodic table…(that is the AVERAGE atomic mass on the table) •  Ex: A boron atom can have ______________________ A = 20 10/26/15 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 sDpulated that all atoms of a parDcular element were idenDcal –
______________________________________
______________________________ •  In 1912, J.J. Thomson discovered that this was not accurate –  In an experiment measuring the mass-­‐to-­‐
charge raDos of posiDve ions in neon gas, he made a remarkable discovery: •  _________________________________ •  _________________________________ •  All of the atoms had 10 protons, however some had ________________ 21 10/26/15 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
22 10/26/15 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.
23 10/26/15 Learning Check Which of the following represent isotopes of the same element? Which element? 234 92
X 234 X 235 X 238 X 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 ___________________ 24 10/26/15 CounIng 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 negaDve charge, add an extra electron. For each posiDve charge, subtract an electron (Don’t add a proton!!! That changes the element!) Learning Check – CounDng State the number of protons, neutrons, and electrons in each of these ions. 39 K+ 19 16O -­‐2
8 20 41Ca +2 #p+ ______ ______ _______ #no ______ ______ _______ #e-­‐ ______ ______ _______ 25 10/26/15 Learning Check – CounDng 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 is 1) 14 2) 16 3) 34 C. The element is 1) Si 2) Ca 3) Se D. Another isotope of this element is 1) 34X 2) 34X 3) 36X 16 14 14 26 10/26/15 Atomic Symbols: Nuclide NotaDon l Nuclide_________________________________ l Show the name of the element, a hyphen, and the mass number in hyphen notaDon _______________ l Show the mass number and atomic number in nuclear symbol from mass number atomic number Nuclide notaIon: p+, charge, and average atomic mass Mass number
(________________)
37
Atomic number
17
(number of _______)
number of ________
A-Z =20
As atoms have no charge, the number
of electrons is the same as the number
of protons. This atom has ___________.
Cl
27 10/26/15 Nuclide notaIon – ions Mass number
Atomic number
23
+
11Na
number of neutrons=
1+ charge ______________ _____
than the number of protons. This
atom has __________.
Nuclide notation –ions
Mass number
Atomic number
16
2–
O
8
number of neutrons=
___charge means ________________
than the number of protons. This
atom has _____________.
28 10/26/15 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 29 10/26/15 Isotopes and Average Atomic Mass •  We are used to calculaDng #’s of p+, no and e-­‐ using whole numbers; however on the Periodic Table we o•en see a decimal number à 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 quanDty 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 ______ _____________________________________
_______________________________ 30 10/26/15 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 g relaDve mass = 1.007 atomic mass units (amu) but we can round to 1* Electrons (e-­‐) relaDve mass = 0.0005 amu but we can round to 0* Neutrons (no) mass = 1.009 amu but we can round to 1* *most Dmes, like now; when we get to nuclear chemistry, we will not be able to! ComparaDve 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 10
Science
70%
Final
70%
30
31 10/26/15 To Calculate Average Atomic Mass •  You add up _____________________________for each isotope to get the weighted average –  FracDonal 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 32 10/26/15 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 33 10/26/15 If a mass is not specifically given for an isotope •  Then make the assumpDon that the mass is the same as the atomic mass number –  It isn’t exactly correct, but it will be close AVERAGE ATOMIC MASS
11B 10B •  Boron is 20% 10B and 80% 11B. That is, 11B is 80 percent abundant on earth. •  For boron, atomic weight= 34 10/26/15 CalculaIng & 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 35