Download Mass Number, A

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 (________) •  No2ced what we call ________________ with amber – Things would be a;racted to it when rubbed – It was a “magical property” • The term electron _________________ ___________________________________
__________________ Kanada (~_________BC) •  Indian a;ributed with first proposing the idea of atoms (called “________” or “____”) •  5 elements –  _______________ –  _______________ –  _______________ –  _______________ –  _______________ •  Atoms were indestructable and eternal Empedocles (450BC) •  4 elements: – _____________ – _____________ – _____________ – _____________ • Everything was different combina2ons of these •  This idea didn’t really change un2l _______! Leucippus (~_______ BC) • Proposed the
idea of atoms
• That two things
exist
• __________
• __________
Democritus (_______) • Student of Leucippus • Ma;er is made up of “eternal, indivisible, indestruc2ble and infinitely small substances which cling together in different combina2ons to form the objects percep2ble to us” • “_________” From :
h;p://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 a;ract, like charges repel (Coulomb’s Law, which the Greeks knew a li;le about) §  Kite experiment (among others): §  Electric charges run from + to – §  ________________________ §  Words he gave us: §  ____________________________________________
____________________________________________
_____________________________ J.L. Proust (_____*) •  Law of constant composi2on: – 
____________________________________
____________________________ – In other words…a given compound always has the same composi2on, regardless of where it comes from. • Ex: H2O is ______________________ ______________________________ *not published or recognized un2l 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. ma;er is composed of indivisible par2cles ____________________________________________ 2. all atoms of a par2cular element are iden2cal _______________________________________________
_______________________________________________
______________________________________ 3. different elements have different atoms YES! 4. atoms combine in certain whole-­‐number ra2os YES! Called __________________________________ 5. In a chemical reac2on, 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 par2cles 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 unJl 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 Gold Foil Anima2on –  alpha (α) par2cles: _______ ___________directed at thin metal foil –  most par2cles made it through → _____________ –  others were deflected back → since alpha par2cles are posi2ve, 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. Scien2sts 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 2ssue paper and it came back and hit you. On considera2on, I realized that this sca;ering backward must be the result of a single collision, and when I made calcula2ons 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 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
e/m = 1.7588 x 108 coulomb/gram
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.
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 par2cles (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, crea2ng an excited state. –  The concept of energy levels accounts for the emission of dis2nct wavelengths of electromagne2c radia2on 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 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 (___) –  posi2ve (+) electrical charge –  mass = 1.672623 x 10-­‐24 g –  rela2ve mass = 1.007 atomic mass units (____) •  but we can round to 1 •  Electrons (___) –  nega2ve (-­‐) electrical charge –  rela2ve 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 addi2onal informa2on only; you will not be tested on the fundamental par2cles. However, they could appear as extra credit on a test or quiz. Subatomic ParJcles can also be further broken down into Fundamental ParJcles •  Quarks –  component of protons & neutrons –  6 types •  Up, down •  Strange, charm •  Top, bo;om •  3 quarks = 1 proton or 1 neutron He
Subatomic Par2cles 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 Par2cles 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
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 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 –  = ____________________________ 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 = 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 s2pulated that all atoms of a par2cular element were iden2cal – 
______________________________________
______________________________ •  In 1912, J.J. Thomson discovered that this was not accurate –  In an experiment measuring the mass-­‐to-­‐
charge ra2os of posi2ve 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? 234 235 238 X
X
X
X
92 93 92 92 234 Atomic Math: Summary •  Atomic number (Z) –  ________________________________ –  ________________________________ •  (Atomic) Mass Number (A) –  ______________________________________ ______________________________________ •  Atomic Mass (also called Atomic Weight) –  _______________________________(accounts for all the isotopes) is ___________________ CounJng 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 nega2ve charge, add an extra electron. For each posi2ve charge, subtract an electron (Don’t add a proton!!! That changes the element!) Learning Check – Coun2ng 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-­‐ ______ ______ _______ Learning Check – Coun2ng 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 Atomic Symbols: Nuclide Nota2on l Nuclide_________________________________ l Show the name of the element, a hyphen, and the mass number in hyphen nota2on _______________ l Show the mass number and atomic number in nuclear symbol from mass number atomic number Nuclide notaJon: 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
Nuclide notaJon – 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 _____________.
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 calcula2ng #’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 quan2ty 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 g rela2ve mass = 1.007 atomic mass units (amu) but we can round to 1* Electrons (e-­‐) rela2ve mass = 0.0005 amu but we can round to 0* Neutrons (no) mass = 1.009 amu but we can round to 1* *most 2mes, like now; when we get to nuclear chemistry, we will not be able to! Compara2ve 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
To Calculate Average Atomic Mass •  You add up _____________________________for each isotope to get the weighted average –  Frac2onal 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 assump2on 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= CalculaJng & 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