1. The document discusses the progression of atomic theory from ancient Greek philosophers to modern quantum mechanical models. Key contributors and their discoveries are outlined, including Dalton's atomic theory, Thomson's discovery of the electron, and Rutherford's gold foil experiment. 2. Features of the periodic table are explained, including its organization by atomic number and properties that can be predicted from an element's location. Isotopes and how to calculate average atomic mass are also covered. 3. The formation of ions through gaining or losing electrons and predicting ionic charges from the periodic table are summarized. Ionic compounds are defined as electrically neutral combinations of cations and anions.

1. Chapter 2:
Atoms, Molecules,
and Ions
Chemistry 105

2. Atomic Theories of Matter
 Theories about the makeup of our
world have been around for
centuries:
5th Century BCE:
4th Century BCE:
Chemistry 105 2

3. Atomic Theories
 17th Century AD:
 19th Century AD:
Chemistry 105 3

4. Basis for Dalton’s theory
 Law of constant composition

 Law of conservation of mass

 Law of multiple proportions

Chemistry 105 4

5. Dalton’s Atomic Theory
 Dalton’s theory consists of 4 postulates:
1. Each element is composed of
2. All atoms of a given element are identical – but
3. Atoms of one element cannot
4. Compounds are formed when
Chemistry 105 5

6. Late 19th century atomic theory
 In the 1850s, the discovery of cathode
rays advanced the field of physics
Chemistry 105 6

7. Discovery of the electron
 J.J. Thomson (1897)
 Thomson observed that regardless of the material of
the cathodes in the tube,
Chemistry 105 7

8. Thomson’s Conclusions
 Based on the ways that the cathode rays
interacted with electric and magnetic
fields, he concluded that
 He concluded
 These particles would later be known as
 Using experimental data, Thomson was able
to successfully derive

Chemistry 105 8

9. Discovery of the electron
 Robert Millikan (1909)
 Using X-rays as a
_________________,
Millikan shot ______
__________________
_________________ ,
suspending the
droplets between
charged plates to
determine the charge
of an electron
Chemistry 105 9

10. Millikan’s conclusions

 Therefore, the charge of an electron is
 Using Thomson’s charge to mass ratio,
Millikan concluded the mass of electron to be
 Actual mass of electron:
Chemistry 105 10

11. Radioactivity
 1896 – Henri Bacquerel and his
students, Pierre and Marie Curie, noted
 By 1910, the work of scientists like the
Curies and Ernst Rutherford had
Chemistry 105 11

12. Radioactivity
 Three types of radiation were discovered by Ernest
Rutherford:



Chemistry 105 12

13. The gold foil experiment
 Rutherford shot a beam
of ______________ at a
small piece of foil,
expecting __________
____________________
______, according to
existing models of the
atom
 Instead,
Chemistry 105 13

14. Rutherford’s conclusions
 Since most of the alpha particles were
 He also concluded that since some of the
particles were slightly deflected,

Chemistry 105 14

15. Progression of the atomic model
Chemistry 105 15

16. Other prominent discoveries
 1919 –
 1932 –
Chemistry 105 16

17. Modern atomic theory
 Based on the experiments of the past,



Chemistry 105 17

18. Comparing the subatomic particles
 Protons and neutrons have
 Electrons, by contrast,

Chemistry 105 18

19. Current atomic theory
 Based on the discoveries of the early 20th century and
the development of quantum mechanics in the mid-20th
century, the most current form of atomic theory is the
quantum-mechanical model of the atom
Chemistry 105 19

20. The quantum mechanical model
 Like the Rutherford model,
 Due to the nature of electrons,
 Instead, we think of electrons
 We can predict the most likely locations for
these electrons

Chemistry 105 20

21. The Periodic Table 21
 Scientists have been attempting to group
and classify elements since the days of
Aristotle
 However, the idea of an arrangement of the
elements is a relatively new phenomenon
Chemistry 105 21

22. Early periodic tables
 1828 – Johann Wolfgang Döbereiner
noticed trends where elements could be
grouped together
 1869 – Dmitri Mendeleev arranged the
known elements by

 Therefore,

were predicted in such a way
 1914 – Henry Moseley
Chemistry 105 22

23. Modern Periodic Table
23
Chemistry 105 23

24. Features of the periodic table
 Elements are arranged in a repeating, periodic pattern in
order of atomic number
 The horizontal rows (7) of the periodic table are known as
periods
 The vertical columns (18) of the periodic table are known as
groups or families
 Groups are numbered 1-18 (IUPAC) or IA-VIIIA and IB to VIIIB
(Chemical Abstracts Service, CAS)
 Common groups:





Chemistry 105 24

25. Regions of the Periodic Table
 The “staggered staircase”
 The line that
 Elements that appear on this line
 Referred to as

 Nonmetals

 Metals

 Special subgroups of metals


Chemistry 105 25

26. What does the table tell us?
 In addition to helping distinguish metal from
nonmetal, the table actually gives us other
important pieces of information
Elemental
symbol
Atomic
number (# of Name of
protons in element
nucleus)
Atomic
mass
Chemistry 105 26

27. Other information 27
 Protons and electrons


 Neutrons

Chemistry 105 27

28. Isotopes 28
 Atoms with
 Isotopes have
Chemistry 105 28

29. Card Question #1
 How many protons, neutrons, and
electrons are in arsenic-75?
A. 33 protons, 75 neutrons, 33 electrons
B. 18 protons, 57 neutrons, 18 electrons
C. 33 protons, 33 neutrons, 42 electrons
D. 33 protons, 42 neutrons, 33 electrons
Chemistry 105 29

30. Atomic mass
 The standard for atomic mass is the
carbon-12 isotope
 Defined as
 1 mole of carbon-12 atoms
 All other atomic and molar masses are
measured relative to the mass of the
carbon-12 isotope
Chemistry 105 30

31. Atomic weight
 Since multiple isotopes can exist for a
given element, we take an average when
discussing the atomic weight
 Example: carbon
Atomic weight =
Atomic weight =
Chemistry 105 31

32. Card Question #2
 Magnesium has three isotopes, Mg-24, Mg-25, and Mg-26.
Using the data below, determine the average atomic mass for
magnesium.
Atomic mass
Isotope Abundance
(amu)
Mg-24 78.99% 23.98504
Mg-25 10.00% 24.98584
Mg-26 11.01% 25.98259
A. 24.98 amu
B. 24.31 amu
C. 25.38 amu
D. 28.71 amu
Chemistry 105 32

33. Molecules
 With the exception of the noble gases,
 Several elements exist in nature in molecular form –
 Examples:
 Molecules made up of two atoms

 Compounds composed of molecules that contain
Chemistry 105 33

34. Molecular compounds
 Most molecular compounds consist of
 Chemical formulas:

 Molecular formula

 Empirical formula

Chemistry 105 34

35. Determining Empirical Formulas
 The empirical formula of a substance is
often determined using a technique known
as elemental analysis
 Elemental analysis is often performed
using
Chemistry 105

36. Elemental analysis by GC-MS
 As discussed before, GC is
used to
 The mass spectrometer is able
to determine
Chemistry 105

37. Ions
 Recall that ions come in two forms: cations and
anions
 Cations are positively charged, anions are negatively
charged
 How do ions become charged?



 Charges typically ranges from for anions
and . for cations
Chemistry 105 37

38. Predicting ionic charges
 Atoms will gain or lose electrons to obtain the
same number of electrons as
 Noble gas configurations are favored because
 We can then use the periodic table to
 For each element moved toward the left,
 For each element moved toward the right,
Chemistry 105 38

39. Common charges
 Alkali metals have
 Alkaline earth metals have
 Chalogens have
 Halogens have
Chemistry 105 39

40. Ionic compounds
 Ionic compounds are
 Ionic compounds are
 Ionic compounds must be

Chemistry 105 40

41. Writing Formulas
 Because compounds are electrically
neutral, one can determine the formula of a
compound this way:



Chemistry 105 41