1. Chapter 3 Atoms and Elements
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2. Understanding the Chemical World
The connection between the microscopic atom and the macroscopic element is the key to understanding the chemical world
Figure 3.1; page 52

3. Atoms Atoms are the smallest identifiable units of an element
Similarities and differences on the atomic scale correlate with similarities and differences on the macroscopic scale
Figure 3.2; page 53

4. Atoms (continued)
A single grain of sand contains approximately 1 ×1020 atoms; page 52

5. Protons Determine the Element
Atomic number, Z, represents the number of protons in the nucleus of an atom
Charge of a proton is assigned numerical value of +1
Amu is a unit of mass defined as 1/12 the mass of a carbon-12 nucleus and is equivalent to 1.67 × 10−24 g
Protons constitute a significant part of the mass of an atom
Mass of a proton is 1.0 atomic mass units (amu)

6. Concept Check 3.1
The graphite in a pencil and the gemstone diamond are composed entirely of pure carbon atoms. Even though these substances appear and behave very differently, what about the nucleus do these carbon atoms have in common that identify them as carbon?

7. Concept Check 3.1 Solution
Diamonds and graphite are composed of carbon atoms with six protons in the nucleus.
It is the number of protons in the nucleus that determines an element’s identity.

8. Chemical Symbols
Symbols are abbreviations of the chemical name, which can be based on:
The English name of the element: hydrogen  H
The Greek or Latin name: ferrum (iron)  Fe

9. Chemical Symbols (continued)
Their place of discovery: europium  Eu
The scientist honored by the naming: curium  Cm
Curium was named after Marie Curie, a co-discoverer of radioactivity; page 55

10. Periodic Table of Elements
Figure 3.4; page 55

11. Electrons
A neutral atom has as many electrons outside its nucleus as protons within its nucleus
Opposing charges of protons and electrons hold electrons within a spherical region surrounding the nucleus
Atoms can lose and gain one or more of its electrons
Figure 3.3; page 54

12. Determining the Charge of an Atom
The charge of an atom is the sum of the charges contributed by its protons (a 1+ charge for each proton) and electrons (a 1− charge for each electron)
Neutrons have no charge and therefore do not contribute to the charge of an atom
Charged atom is called an ion

13. Determining the Charge of an Atom (continued)
Figures 3.5 and 3.6; page 56

14. Concept Check 3.2
How many protons and electrons are in the Li+ ion?

15. Concept Check 3.2 Solution
Lithium (Li) has an atomic number of 3; therefore, it has 3 protons in its nucleus.
A nucleus with 3 protons (1+ charge each) has a charge of 3+. Neutral Li needs 3 electrons outside of the nucleus (1− charge each) for a total charge of 3− resulting in a neutral atom.
Li+ ion has 3 protons in the nucleus and 2 electrons outside of the nucleus for a total charge of 1+.

16. Neutrons
Neutrons have almost the same mass as protons but carry no electrical charge
The number of neutrons in the atoms of an element can vary
Known as isotopes
Can be naturally occurring or man-made
Figure 3.7; page 57

17. Neutrons (continued)
The sum of neutrons and protons in an atom is called the mass number (A) of the atom
Naturally occurring sodium atoms have 11 protons and 12 neutrons in their nuclei, and they have a mass number of 23

18. Protons, Neutrons, and Electrons
Decoding an element’s symbol, where:
Z is the atomic number
A is the mass number
C is the charge
X is the symbol of the element

19. Protons, Neutrons, and Electrons (continued)
Atomic number = Number of protons
Number of neutrons = A − Z
Number of electrons = Z − C
Neutral atoms = X − A

20. Concept Check 3.3 The three isotopes of the element hydrogen are:
Protium
Deuterium
Tritium
How many protons, electrons, and neutrons are in each isotope of hydrogen?

21. Concept Check 3.3 Solution
Each isotope of hydrogen has an atomic number of 1 and therefore has 1 proton in the nucleus and the neutral atoms have 1 electron outside the nucleus.
Subtracting the atomic number from the mass number gives the number of neutrons in each isotope.
Protium 1 − 1 = 0 neutrons
Deuterium − 1 = 1 neutron
Tritium 3 − 1 = 2 neutrons

22. Concept Check 3.4
How many protons, neutrons, and electrons are in the following radioactive ion of potassium?

23. Concept Check 3.4 Solution
Protons = Z = 19
Neutrons = A − Z = 40 − 19 = 21
Electrons = Z − C = 19 − 1 = 18

24. Atomic Mass
Atomic masses listed on the periodic table are weighted averages of the masses of each naturally occurring isotope for that element
Silver has two naturally occurring isotopes
One has a mass of about 107 amu, and the other has a mass of about 109 amu
Ag-107 has an abundance of 51.84%
Ag-109 has an abundance of 48.16%

25. Atomic Mass (continued)
Calculate the average atomic mass of silver
Silver has two naturally occurring isotopes
One has a mass of amu (abundance of 51.84%)
The other has a mass of amu (abundance of 48.16%)
amu (0.5184) = amu
amu (0.4816) = amu amu

26. Concept Check 3.5
Chlorine has two principle isotopes, 35Cl with a mass of amu and 37Cl with a mass of amu. The atomic weight of chlorine is amu. Which of the two isotopes is most abundant in a sample of chlorine?

27. Concept Check 3.5 Solution
The atomic weight of chlorine ( amu) is closer to the mass of 35Cl ( amu) than that of 37Cl ( amu); therefore, the sample contains more 35Cl than 37Cl. On the planet Earth, chlorine contains 75.77% 35Cl and 24.23% 37Cl.

28. Periodic Law
Mendeleev listed the known elements in order of increasing atomic mass
He noticed that certain similar properties would recur in a periodic fashion and grouped them together
His tabulation is the precursor to today’s periodic table
Russian Professor Dmitri Mendeleev, who arranged the first periodic table; page 61

29. Mendeleev
Proposed that elements would be discovered to fill in gaps in the table
Proposed that some measured atomic masses were wrong
Summarized a large number of observations
The underlying reasons for periodic behavior were still unknown
The Bohr model and the quantum mechanical model were needed to explain the observations

30. Bohr Diagrams/Electron Configurations
Based on the behavior of electrons as particles
Electron orbits
Each orbit is specified with an integer, n, called the orbit’s quantum number
Niels Bohr (1885–1962); Page 62

31. Bohr Model
In the Bohr model, electrons occupy orbits that are at fixed energies and fixed radii
Figure 3.10; page 62

32. Bohr Diagrams/Electron Configurations (continued)
Atoms with full outer orbits are extremely stable
Atoms with outer orbits that are not full are less stable and undergo chemical reactions attempting to fill the outer orbits

33. Concept Check 3.6
Based on electron configurations, would you expect Li, O, or Ne to be the least reactive?

34. Concept Check 3.6 Solution
Of the three elements, only Ne has a filled outer orbit (also called an octet). Elements that have atoms with filled octets are inert.

35. Concept Check 3.7
Which pair of elements would be expected to show similar chemical properties?
C and Al
K and Na
F and Ar
Li and Mg

36. Concept Check 3.7 Solution
Answer (2)
C and Al
K and Na
F and Ar
Li and Mg
Both K and Na have the same number of valence electrons (outer orbiting electrons) and therefore belong to the same group in the periodic table of elements. They are expected to show similar chemical properties.

37. Quantum Mechanical Model
Quantum mechanical orbitals resulted from discoveries showing that the electron, which was thought of as a particle, also displayed properties that are associated with waves
Replaced Bohr’s orbits with orbitals, which is a representation of electron location as the probability of finding it in a certain region of space
Orbitals are grouped into shells and fill similarly to Bohr’s orbit

38. Figure 3.13: Quantum Mechanical Model
Figure 3.13; page 67

39. Determinism and Quantum Mechanics
Discovery of quantum mechanics challenged the idea that our universe behaves deterministically
Electrons, protons, and neutrons do not appear to behave deterministically
Subatomic world is indeterminate
Bohr and quantum mechanical models are useful even though Bohr’s, by experiment, has been shown to be invalid

40. Concept Check 3.8
Which statement is true of the Bohr model but not of the quantum mechanical model?
Electrons move in circular orbits around a nucleus.
Electrons can exhibit wave behavior.
The exact path of an electron within an atom cannot be specified.

41. Concept Check 3.8 Solution
Electrons move in circular orbits around a nucleus.
The Bohr model describes electrons moving in circular orbits of specific fixed positions around a nucleus. Although rather simple, the Bohr model does help explain periodic properties. The quantum mechanical model better describes the behavior of electrons in the atom.

42. Families of Elements Known as group of elements
Based on outer electron configurations
Important vertical columns
Alkali metals (group 1A)
Alkaline earth metals (group 2A)
Chalcogens (group 6A)
Halogens (group 7A)
Noble gases (group 8A)

43. Element Families
Figure 3.16; page 69

44. Metals, Nonmetals, and Metalloids
Figure 3.17; page 70

45. Molecular Elements Some elements occur as diatomic molecules
Figure 3.18; page 71

46. Mole Concept
Relates the mass of a sample of an element to the number of atoms within it so that the number of atoms can be determined by weighing
The unit of comparison is called a mole and corresponds to 6.022×1023
Number is known as Avogadro’s number
Figure 3.19; page 72

47. Avogadro’s Number
Determined that the numerical value of the atomic mass of an element in amu is equal to the molar mass of that element in grams per mole
The relationships of grams, moles, and atoms can be used as conversion factors
Amadeo Avogadro (1776–1856); Page 71

48. Concept Check 3.9
The average pre-1982 United States penny contained 3.11 g of copper. How many moles of copper did the pre-1982 penny contain?

49. Concept Check 3.9 Solution
The number of moles of Cu in a pre-1982 U.S. penny is:

50. Concept Check 3.10
An 85.0 kg-human contains about 4.25 g of the element magnesium. How many atoms are present in 4.25 g of Mg?

51. Concept Check 3.10 Solution
How many atoms are present in 4.25 g of Mg?

52. Chapter Summary Molecular concept Societal impact
Atomic number, mass number, and its charge
Chemical processes that occur in the surrounding are caused by changes in atoms or molecules that compose matter
Atomic mass is equal to molar mass
Molar masses help calculate the number of atoms in a given object simply by weighing it
Molar mass
Atoms that are not where they are supposed to be located cause pollution
Bohr Model and quantum mechanical model
Microscopic models are directly applicable in explaining why elements form the compounds that they do