1. Cross-Disciplinary: Seeing Atoms - The STM
Image of reconstruction on a clean gold surface.
STM image of graphite
Silicon diode

2. Chapter 4
Section 1 Atomic Structure
Objectives
Explain Dalton’s atomic theory, and describe why it was more successful than Democritus’s theory.
State the charge, mass, and location, of each part of an atom according to the modern model of the atom.
Compare and contrast Bohr’s model with the modern model of the atom.

3. Chapter 4
Section 1 Atomic Structure
What Are Atoms?
Our understanding of atoms required many centuries.
The idea of an atom—which means “unable to be divided”—dates back to the Greek philosopher Democritus, who lived in the fourth century BCE.
John Dalton developed an atomic theory in 1808.
Like Democritus, Dalton proposed that atoms could not be divided. Dalton’s was the first atomic theory with a scientific basis.

4. What Are Atoms? continued
Chapter 4
Section 1 Atomic Structure
What Are Atoms? continued
An atom is the smallest part of an element that still has the element’s properties.
Atoms are the building blocks of molecules.

5. Chapter 4 What’s in an Atom?
Section 1 Atomic Structure
What’s in an Atom?
Atoms are made of protons, neutrons, and electrons.
At the center of each atom is a small, dense nucleus with a positive electric charge.
The nucleus is made of protons (a subatomic particle that has a positive charge) and neutrons (a subatomic particle that has no charge).
Moving around outside the nucleus is a cloud of electrons: subatomic particles with negative charges.

6. What’s in an Atom? continued
Chapter 4
Section 1 Atomic Structure
What’s in an Atom? continued
Unreacted atoms have no overall charge.
Although atoms are made of charged particles, they do not have an overall charge because they have an equal number of protons and electrons whose charges exactly cancel.
To the right is shown a helium atom, which is made of two protons, two neutrons, and two electrons.

7. Chapter 4 Models of the Atom
Section 1 Atomic Structure
Models of the Atom
Bohr’s model compares electrons to planets.
In 1913, the Danish scientist Niels Bohr suggested that electrons in an atom move in set paths around the nucleus much like the planets orbit the sun in our solar system.
In Bohr’s model, electrons can only be in certain energy levels. Bohr’s model of electrons is illustrated on the following slide.

8. Chapter 4
Section 1 Atomic Structure
Building Model

9. Models of the Atom, continued
Chapter 4
Section 1 Atomic Structure
Models of the Atom, continued
Electrons act more like waves.
By 1925, Bohr’s model of the atom no longer explained electron behavior.
A new model was proposed, in which electrons behave more like waves on a vibrating string than like particles.

10. Models of the Atom, continued
Chapter 4
Section 1 Atomic Structure
Models of the Atom, continued
An electron’s exact location cannot be determined.
It is impossible to determine both the exact location of an electron in an atom and the electron’s speed and direction.
The best scientists can do is calculate the chance of finding an electron in a certain place within an atom.

11. Models of the Atom, continued
Chapter 4
Section 1 Atomic Structure
Models of the Atom, continued
Electrons exist in energy levels.
The number of filled energy levels an atom has depends on the number of electrons.
The figure to the right shows how the first four energy levels are filled.

12. Models of the Atom, continued
Chapter 4
Section 1 Atomic Structure
Models of the Atom, continued
Electrons are found in orbitals within energy levels.
An orbital is a region in an atom where there is a high probability of finding electrons.
An s orbital is shaped like a sphere:
A p orbital is dumbbell shaped and can be oriented three different ways in space:

13. Models of the Atom, continued
Chapter 4
Section 1 Atomic Structure
Models of the Atom, continued
Every atom has between one and eight valence electrons.
Valence electrons are found in the outermost shell of an atom and determine the atom’s chemical properties.
Valence electrons are the electrons in an atom that participate in chemical bonding.

14. Chapter 4
Section 1 Atomic Structure
Valence Electrons

15. Section 2 A Guided Tour of the Periodic Table
Chapter 4
Objectives
Relate the organization of the periodic table to the arrangement of electrons within an atom.
Explain why some atoms gain or lose electrons to form ions.
Determine how many protons, neutrons, and electrons an atom has, given its symbol, atomic number, and mass number.
Describe how the abundance of isotopes affects an element’s average atomic mass.

16. Organization of the Periodic Table
Section 2 A Guided Tour of the Periodic Table
Chapter 4
Organization of the Periodic Table
The periodic table groups similar elements together.
This organization makes it easier to predict the properties of an element based on where it is in the periodic table.
Elements are listed in order of number of protons, because the periodic law states that when elements are arranged this way, similarities in their properties will occur in a regular pattern.

17. Organization of the Periodic Table, continued
Section 2 A Guided Tour of the Periodic Table
Chapter 4
Organization of the Periodic Table, continued
The periodic table helps determine electron arrangement.
Horizontal rows in the periodic table are called periods.
Just as the number of protons an atom has increases as you move from left to right across a period, so does its number of electrons.

18. Organization of the Periodic Table, continued
Section 2 A Guided Tour of the Periodic Table
Chapter 4
Organization of the Periodic Table, continued
Elements in the same group have similar properties.
A group is a vertical column of elements in the periodic table.
Atoms of elements in the same group have the same number of valence electrons, so these elements have similar properties.

19. Chapter 4 Some Atoms Form Ions
Section 2 A Guided Tour of the Periodic Table
Chapter 4
Some Atoms Form Ions
An ion is an atom or group of atoms that has lost or gained one electrons and has a negative or positive charge.
A lithium atom loses one electron to form a 1+ charged ion:
A fluorine atom gains one electron to form a 1 charged ion:

20. Section 2 A Guided Tour of the Periodic Table
Chapter 4
Ion

21. How Do the Structures of Atoms Differ?
Section 2 A Guided Tour of the Periodic Table
Chapter 4
How Do the Structures of Atoms Differ?
The atomic number, Z, of an atom equals the number of protons in the nucleus.
The mass number, A, of an atom equals the number of protons plus the number of neutrons in the nucleus.

22. Section 2 A Guided Tour of the Periodic Table
Chapter 4
Nucleus

23. Section 2 A Guided Tour of the Periodic Table
Chapter 4
Atomic Number

24. Section 2 A Guided Tour of the Periodic Table
Chapter 4
Mass Number

25. How Do the Structures of Atoms Differ? continued
Section 2 A Guided Tour of the Periodic Table
Chapter 4
How Do the Structures of Atoms Differ? continued
An isotope is an atom that has the same number of protons as other atoms of the same element do but that has a different number of neutrons.
Example: Hydrogen has three isotopes, shown below.
Some isotopes are more common than others.

26. How Do the Structures of Atoms Differ? continued
Section 2 A Guided Tour of the Periodic Table
Chapter 4
How Do the Structures of Atoms Differ? continued
If you know the atomic number and mass number of an atom, you can calculate the number of neutrons it has.
Example: uranium-235 has a mass number of 235. Like all uranium atoms, it has an atomic number of 92. The number of neutrons it has is therefore:
Mass number (A): 235
Atomic number (Z): –92
Number of neutrons: 143

27. Section 2 A Guided Tour of the Periodic Table
Chapter 4
Isotopes

28. How Do the Structures of Atoms Differ? continued
Section 2 A Guided Tour of the Periodic Table
Chapter 4
How Do the Structures of Atoms Differ? continued
Because the mass of a single atom is so tiny, atomic masses are usually expressed in atomic mass units.
An atomic mass unit (amu) is equal to one twelfth of the mass of a carbon-12 atom.
The average atomic mass for an element is a weighted average of the masses of all naturally-occurring isotopes of an element.

29. Chapter 4 Average Atomic Mass
Section 2 A Guided Tour of the Periodic Table
Chapter 4
Average Atomic Mass

30. Chapter 4
Section 3 Families of Elements
Objectives
Locate alkali metals, alkaline-earth metals, and transition metals in the periodic table.
Locate semiconductors, halogens, and noble gases in the periodic table.
Relate an element’s chemical properties to the electron arrangement of its atoms.

31. How Are Elements Classified?
Chapter 4
Section 3 Families of Elements
How Are Elements Classified?
The elements are classified into three groups.
Most elements are metals, elements that are shiny and conduct heat and electricity well.
Nonmetals, all except hydrogen of which are found on the right side of the periodic table, may be solids, liquids, or gases at room temperature.
Between these groupings are semiconductors, elements that can conduct electricity under certain conditions.

32. How Are Elements Classified? continued
Chapter 4
Section 3 Families of Elements
How Are Elements Classified? continued
The periodic table below shows the distribution of metal, nonmetals, and semiconductors in the periodic table.

33. Chapter 4
Section 3 Families of Elements
Metals
The alkali metals, found in Group 1 of the periodic table, are very reactive.
The alkaline-earth metals, which include calcium, are found in Group 2 of the periodic table, and are somewhat less reactive than the alkali metals.
The transition metals, such as gold, iron, and mercury, occupy Groups 3–12 of the periodic table.

34. Chapter 4 Nonmetals Section 3 Families of Elements
Carbon is found in three different forms and can form many compounds.
Nonmetals and their compounds are plentiful on Earth.
Halogens, such as chlorine, are located in Group 17 of the periodic table.
Noble gases, such as neon, make up Group 18 of the periodic table. They are unreactive.

35. Chapter 4 Nonmetals, continued
Section 3 Families of Elements
Nonmetals, continued
Semiconductors are intermediate conductors of heat and electricity.
Silicon is the most familiar semiconductor.
Silicon is an important part of computer chips, as well as other semiconductor devices such as transistors, LED display screens, and solar cells.

36. Section 4 Using Moles to Count Atoms
Chapter 4
Objectives
Explain the relationship between a mole of a substance and Avogadro’s constant.
Find the molar mass of an element by using the periodic table.
Solve problems converting the amount of an element in moles to its mass in grams, and vice versa.

37. Chapter 4 Bellringer Section 4 Using Moles to Count Atoms
Sometimes when you are dealing with numbers of things, it is convenient to have a special unit that designates a specific number of the objects. Below are examples of special units that are used to count objects.
1. How many objects are in each sample?

38. Chapter 4 Bellringer, continued
Section 4 Using Moles to Count Atoms
Chapter 4
Bellringer, continued
2. What if you want to use six sticks of butter, but you only have a large block of butter and a scale? How could you get the equivalent of six sticks of butter without the mess of dividing the large block into sticks?

39. Chapter 4 Counting Things
Section 4 Using Moles to Count Atoms
Chapter 4
Counting Things
There are many different counting units: for example, eggs are packaged by the dozen.
The mole is useful for counting small particles.
A mole (abbreviation: mol) is the number of particles that is the same as the number of atoms of carbon in 12 g of carbon-12.
Avogadro’s constant is the number of particles per mole of a substance: × 1023

40. Section 4 Using Moles to Count Atoms
Chapter 4
The Mole

41. Section 4 Using Moles to Count Atoms
Chapter 4
Avogadro’s Number

42. Counting Things, continued
Section 4 Using Moles to Count Atoms
Chapter 4
Counting Things, continued
Moles and grams are related.
The mass in grams of 1 mol of a substance is called its molar mass.
For example, 1 mol of carbon-12 atoms has a molar mass of g.
The molar mass of an element is its average atomic mass, which is listed in the periodic table.

43. Section 4 Using Moles to Count Atoms
Chapter 4
Molar Mass

44. Calculating with Moles
Section 4 Using Moles to Count Atoms
Chapter 4
Calculating with Moles
To convert between moles and grams and vice versa, you can use a conversion factor: a ratio that is derived from the equality of two different units.
Let’s say that a shopkeeper knows that exactly 10 gumballs have a total mass of 21.4 g. This relationship can be written as either one of two equivalent conversion factors:

45. Section 4 Using Moles to Count Atoms
Chapter 4
Conversion Factor

46. Section 4 Using Moles to Count Atoms
Chapter 4
Math Skills
Conversion Factors What is the mass of exactly 50 gumballs?
1. List the given and unknown values. Given: mass of 10 gumballs = 21.4 g Unknown: mass of 50 gumballs = ? g

47. Chapter 4 Math Skills, continued
Section 4 Using Moles to Count Atoms
Chapter 4
Math Skills, continued
2. Write down the conversion factor that converts number of gumballs to mass.
The conversion factor you choose should have the unit you are solving for (g) in the numerator and the unit you want to cancel (number of gumballs) in the denominator.

48. Chapter 4 Math Skills, continued
Section 4 Using Moles to Count Atoms
Chapter 4
Math Skills, continued
3. Multiply the number of gumballs by this conversion factor, and solve.
107 g

49. Calculating with Moles, continued
Section 4 Using Moles to Count Atoms
Chapter 4
Calculating with Moles, continued
An element’s molar mass can be used as a conversion factor.
The diagram below shows how to set up the conversion factor, depending on whether you want to convert from amount to mass or the other way around.

50. Section 4 Using Moles to Count Atoms
Chapter 4
Math Skills
Converting Amount to Mass Determine the mass in grams of 5.50 mol of iron.
1. List the given and unknown values. Given: amount of iron = 5.50 mol Fe molar mass of iron = g/mol Fe Unknown: mass of iron = ? g Fe

51. Chapter 4 Math Skills, continued
Section 4 Using Moles to Count Atoms
Chapter 4
Math Skills, continued
2. Write down the conversion factor that converts moles to grams.
The conversion factor you choose should have what you are trying to find (grams of Fe) in the numerator and what you want to cancel (moles of Fe) in the denominator.

52. Chapter 4 Math Skills, continued
Section 4 Using Moles to Count Atoms
Chapter 4
Math Skills, continued
3. Multiply the amount of iron by this conversion factor, and solve.
307 g Fe

53. Section 4 Using Moles to Count Atoms
Chapter 4
Math Skills
Converting Mass to Amount Determine the amount of iron present in 352 g of iron.
1. List the given and unknown values. Given: mass of iron = 352 g Fe molar mass of iron = g/mol Fe Unknown: amount of iron = ? mol Fe

54. Chapter 4 Math Skills, continued
Section 4 Using Moles to Count Atoms
Chapter 4
Math Skills, continued
2. Write down the conversion factor that converts grams to moles.
The conversion factor you choose should have what you are trying to find (moles of Fe) in the numerator and what you want to cancel (grams of Fe) in the denominator.

55. Chapter 4 Math Skills, continued
Section 4 Using Moles to Count Atoms
Chapter 4
Math Skills, continued
3. Multiply the mass of iron by this conversion factor, and solve.
6.30 mol Fe

56. Section 4 Using Moles to Count Atoms
Chapter 4
Concept Mapping

57. Understanding Concepts
Chapter 4
Standardized Test Prep
Understanding Concepts
1. Why do atoms gain or lose electrons?
A. to balance the charges between the nucleus and the electron cloud
B. to obtain a more stable electron configuration through a full outermost orbital
C. to place electrons in higher energy levels than are occupied in the atom
D. to reduce the amount of energy required to bring atoms closer together

58. Understanding Concepts
Chapter 4
Standardized Test Prep
Understanding Concepts
1. Why do atoms gain or lose electrons?
A. to balance the charges between the nucleus and the electron cloud
B. to obtain a more stable electron configuration through a full outermost orbital
C. to place electrons in higher energy levels than are occupied in the atom
D. to reduce the amount of energy required to bring atoms closer together

59. Understanding Concepts
Chapter 4
Standardized Test Prep
Understanding Concepts
2. Why are the Group 18 elements nonreactive?
F. They have no valence electrons.
G. They combine to form stable molecules.
H. Their outermost energy levels are completely filled.
I. They are too rare to react with significant amounts of other elements.

60. Understanding Concepts
Chapter 4
Standardized Test Prep
Understanding Concepts
2. Why are the Group 18 elements nonreactive?
F. They have no valence electrons.
G. They combine to form stable molecules.
H. Their outermost energy levels are completely filled.
I. They are too rare to react with significant amounts of other elements.

61. Understanding Concepts
Chapter 4
Standardized Test Prep
Understanding Concepts
3. Antimony is a shiny, brittle solid that conducts electricity under some conditions but does not conduct in other conditions. How is antimony classified on the modern periodic table?
A. metals
B. nonmetal
C. semiconductor
D. transition element

62. Understanding Concepts
Chapter 4
Standardized Test Prep
Understanding Concepts
3. Antimony is a shiny, brittle solid that conducts electricity under some conditions but does not conduct in other conditions. How is antimony classified on the modern periodic table?
A. metals
B. nonmetal
C. semiconductor
D. transition element

63. Understanding Concepts
Chapter 4
Standardized Test Prep
Understanding Concepts
4. Beryllium is located on the same row of the periodic table as fluorine, while iodine is located in the same column. Identify which element, beryllium or iodine, will form an ion by gaining one electron, as fluorine does, and explain your answer.

64. Understanding Concepts
Chapter 4
Standardized Test Prep
Understanding Concepts
4. Beryllium is located on the same row of the periodic table as fluorine, while iodine is located in the same column. Identify which element, beryllium or iodine, will form an ion by gaining one electron, as fluorine does, and explain your answer.
Answer: Iodine will form an ion by gaining one electron, because all of the elements within a column have the same valence electron structure.

65. Chapter 4 Reading Skills
Standardized Test Prep
Reading Skills
Read the passage below. Then answer the question.
Particle accelerators are devices that speed up charged particles to speeds close to the speed of light in order to smash them together and observe the results. In many cases, these collisions form a new atomic nucleus. This nucleus attracts electrons and becomes a neutral atom. Atoms formed this way can either be an isotope of a known element or a previously unknown element.

66. Chapter 4 Reading Skills
Standardized Test Prep
Reading Skills
5. Determine how scientists can judge whether the newly formed material is a new element or a new isotope of an existing element.

67. Chapter 4 Reading Skills
Standardized Test Prep
Reading Skills
5. Determine how scientists can judge whether the newly formed material is a new element or a new isotope of an existing element.
Answer: They can investigate its chemical and physical properties and compare them to known elements.

68. Interpreting Graphics
Chapter 4
Standardized Test Prep
Interpreting Graphics
Base your answer to question 6 on the illustration below, which shows the ionization of a fluorine atom.

69. Interpreting Graphics
Chapter 4
Standardized Test Prep
Interpreting Graphics
6. Why is the fluoride ion larger than the fluorine atom?
F. The electrons experience a greater electrical repulsion.
G. The interaction between the electrons and the protons is stronger.
H. The ion has more protons than electrons so it is not as stable as the atom.
I. The addition of another electron makes the ion substantially more massive than the atom.

70. Interpreting Graphics
Chapter 4
Standardized Test Prep
Interpreting Graphics
6. Why is the fluoride ion larger than the fluorine atom?
F. The electrons experience a greater electrical repulsion.
G. The interaction between the electrons and the protons is stronger.
H. The ion has more protons than electrons so it is not as stable as the atom.
I. The addition of another electron makes the ion substantially more massive than the atom.