1. Chapter 2
Atoms and Elements
Dr. S. M. Condren

2. Dalton’s Atomic Theory
Postulates
proposed in 1803
know for first exam
Dr. S. M. Condren

3. Dalton’s Atomic Theory
Postulate 1
An element is composed of tiny particles called atoms.
All atoms of a given element show the same chemical properties.
Dr. S. M. Condren

4. Dalton’s Atomic Theory
Postulate 2
Atoms of different elements have different properties.
Dr. S. M. Condren

5. Dalton’s Atomic Theory
Postulate 3
Compounds are formed when atoms of two or more elements combine.
In a given compound, the relative number of atoms of each kind are definite and constant.
Dr. S. M. Condren

6. Dalton’s Atomic Theory
Postulate 4
In an ordinary chemical reaction, no atom of any element disappears or is changed into an atom of another element.
Chemical reactions involve changing the way in which the atoms are joined together.
Dr. S. M. Condren

7. Structure of the Atom protons Composed of: protons neutrons electrons
found in nucleus
relative charge of +1
relative mass of amu
Dr. S. M. Condren

8. Structure of the Atom neutrons Composed of: protons neutrons electrons
found in nucleus
neutral charge
relative mass of amu
Dr. S. M. Condren

9. Structure of the Atom electrons Composed of: protons neutrons
found in electron cloud
relative charge of -1
relative mass of amu
Dr. S. M. Condren

10. ATOM COMPOSITION The atom is mostly empty space
protons and neutrons in the nucleus.
the number of electrons is equal to the number of protons in a neutral atom.
electrons in space around the nucleus.
extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.
Dr. S. M. Condren

11. Radioactivity Alpha – helium-4 nucleus Ra226  Rn222 + He4(a)
Beta – high energy electron
U239  Np b-1
Gamma – energy resulting from transitions from one nuclear energy level to another
Ni60*  Ni g
Dr. S. M. Condren

12. Penetrations of Radioactive Emissions
Dr. S. M. Condren

13. Isotopes & Their Uses 9943Tc Emits gamma rays
Heart scans with radioactive technetium-99.
9943Tc
Emits gamma rays
Dr. S. M. Condren

14. The modern view of the atom was developed by Ernest Rutherford (1871-1937).
Dr. S. M. Condren

15. Rutherford’s Model of the Atom
atom is composed mainly of vacant space
all the positive charge and most of the mass is in a small area called the nucleus
electrons are in the electron cloud surrounding the nucleus
Dr. S. M. Condren

16. Nucleus If nucleus is 1” The atom would be 1.5 miles in diameter
Dr. S. M. Condren

17. Ions Ion cations anions ionic compounds
electrostatically charged atom or group of atoms
cations
positive ions
anions
negative ions
ionic compounds
combination of cations and anions
zero net charge
Dr. S. M. Condren

18. Atomic number, Z the number of protons in the nucleus
the number of electrons in a neutral atom
the integer on the periodic table for each element 13
Atomic number Al
Atom symbol
26.981
Atomic weight
Dr. S. M. Condren

19. Dr. S. M. Condren

20. Imaging
Dr. S. M. Condren

21. Which best represents the poles?
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22. Quantum Corral http://www.almaden.ibm.com/vis/stm/corral.html
Dr. S. M. Condren

23. Mass Number, A
C atom with 6 protons and 6 neutrons is the mass standard
= 12 atomic mass units (u)
Mass Number (A) = # protons + # neutrons
A boron atom can have A = 5 p n = 10 u
Dr. S. M. Condren

24. Isotopes
atoms of the same element which differ in the number of neutrons in the nucleus
designated by mass number
Dr. S. M. Condren

25. Isotopes of Hydrogen H-1, 1H, protium
1 proton and no neutrons in nucleus
only isotope of any element containing no neutrons in the nucleus
most common isotope of hydrogen
Dr. S. M. Condren

26. Isotopes of Hydrogen H-2 or D, 2H, deuterium
1 proton and 1 neutron in nucleus
Dr. S. M. Condren

27. Isotopes of Hydrogen H-3 or T, 3H, tritium
1 proton and 2 neutrons in nucleus
radioactive
electron antineutrino
Dr. S. M. Condren

28. The radioactive isotope 14C has how many neutrons? 6, 8, other
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29. protons, neutrons, electrons
The identity of an element is determined by the number of which particle?
protons, neutrons, electrons
Dr. S. M. Condren

30. Mass Spectrometer a simulation is available at
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31. Mass spectrum of C6H5Br
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32. Atomic Masses and Isotopic Abundances
natural atomic masses =
SUM[(atomic mass of isotope)
*(fractional isotopic abundance)]
Dr. S. M. Condren

33. Example: Chlorine has two isotopes, Cl-35 and Cl-37, which have masses of and amu, respectively. The natural atomic mass of chlorine is amu. What are the percent abundances of the two isotopes?
let x = fraction Cl-35
y = fraction Cl-37
x + y = 1
y = 1 - x
(AW Cl-35)(fraction Cl-35) + (AW Cl-37)(fraction Cl-37) =
Thus: *x *y =
*x *(1-x) =
x = <=> % Cl-35
Thus % Cl-37
Dr. S. M. Condren

34. Molar Mass-Molecular Weight
Sum
atomic masses
represented by formula
atomic masses => gaw
molar mass => MM
Dr. S. M. Condren

35. Example What is the molar mass of ethanol, C2H5O1H1?
MM = 2(gaw)C + (5 + 1)(gaw)H + 1(gaw)O
= 2(12.011)C + 6( )H + 1( )O =
= g/mol
Significant figures rule for multiplication
Significant figures rule for addition
Sequence – multiplication then addition,
apply significant figure rules in proper sequence
Dr. S. M. Condren

36. The Mole a unit of measurement, quantity of matter present
Avogadro’s Number
6.022 x 1023 particles
Latin for “pile”
Dr. S. M. Condren

37. One Mole of each Substance
Clockwise from top left:
1-Octanol, C8H17OH;
Mercury(II) iodide, HgI2;
Methanol, CH3OH; and
Sulfur, S8.
Dr. S. M. Condren

38. Example
How many moles of carbon dioxide molecules are there in 10.00g of carbon dioxide?
MM = 1(gaw)C + 2(gaw)O = g/mol
#mol CO2
= (10.00g)
/ /
(1 mol/44.01g)
= mol
Dr. S. M. Condren

39. Mendeleev’s Periodic Table
Missing elements: 44, 68, 72, & 100 amu
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40. Properties of Ekasilicon
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41. Modern Periodic Table
the elements are arranged according to increasing atomic numbers
Dr. S. M. Condren

42. Periodic Table of the Elements
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43. Organization of Periodic Table
period - horizontal row
group - vertical column
Family Names
Group IA alkali metals
Group IIA alkaline earth metals
Group VIIA halogens
Group VIIIA noble gases
transition metals
inner transition metals
lanthanum series rare earths
actinium series trans-uranium series
Dr. S. M. Condren

44. Dr. S. M. Condren

45. ELEMENTS THAT EXIST AS MOLECULES
Allotropes of C
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46. Dr. S. M. Condren

47. ELEMENTS THAT EXIST
AS DIATOMIC MOLECULES
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48. AS POLYATOMIC MOLECULES
ELEMENTS THAT EXIST
AS POLYATOMIC MOLECULES
S8 sulfur molecules
White P4 and polymeric red phosphorus
Dr. S. M. Condren