Understanding Atomic Structure Presentation

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2. Resources Bellringers Chapter Presentation Transparencies Standardized Test Prep Visual Concepts Math Skills

3. Atoms and the Periodic Table Chapter 4 Table of Contents Section 1 Atomic Structure Section 2 A Guided Tour of the Periodic Table Section 3 Families of Elements Section 4 Using Moles to Count Atoms

4. Section 1 Atomic Structure Chapter 4 Objectives • ExplainDalton’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.

5. Section 1 Atomic Structure Chapter 4 Bellringer When scientists wanted to find out what an atom was, they were not able to look directly at what the atom was made of. They had to make inferences from the results of many different experiments. It was like trying to describe a picture, such as the one on the next slide, with only small portions visible.

6. Section 1 Atomic Structure Chapter 4 Bellringer 1. Write four sentences describing what you can see of the above picture. 2. What information or parts of the picture would make your descriptions more accurate without revealing the entire picture?

7. Section 1 Atomic Structure Chapter 4 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.

8. Section 1 Atomic Structure Chapter 4 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.

9. Section 1 Atomic Structure Chapter 4 Atom

10. Section 1 Atomic Structure Chapter 4 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.

11. Section 1 Atomic Structure Chapter 4 Parts of the Atom

12. Section 1 Atomic Structure Chapter 4 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 heliumatom, which is made of twoprotons, two neutrons, andtwo electrons.

13. Section 1 Atomic Structure Chapter 4 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.

14. Section 1 Atomic Structure Chapter 4 Building Model

15. Section 1 Atomic Structure Chapter 4 Bohr Model of the Atom

16. Section 1 Atomic Structure Chapter 4 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.

17. Section 1 Atomic Structure Chapter 4 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.

18. Section 1 Atomic Structure Chapter 4 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.

19. Section 1 Atomic Structure Chapter 4 Electron Energy Levels

20. Section 1 Atomic Structure Chapter 4 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:

21. Section 1 Atomic Structure Chapter 4 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.

22. Section 1 Atomic Structure Chapter 4 Valence Electrons

24. Section 2 A Guided Tour of the Periodic Table Chapter 4 Objectives • Relatethe 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.

25. Section 2 A Guided Tour of the Periodic Table Chapter 4 Bellringer One way to organize a large group of objects is to arrange them into groups of similar objects. This is how scientists organize all of the many elements. Practice the skill of categorizing by arranging the magazines listed below into similar groups. Calling All Girls Homeopathic Medicine Modern Housekeeping Computer World Sports and Scores Easy Car Repairs Beautiful Homes Calling All Boys The Health Newsletter Auto Racing All About Computing Football Stories The Healthy Man Home Decorating Read Aloud Stories Sporting Times Classic Cars Building a Web Site Child’s Play The Healthy Woman Home Makers Magazine Family Computing Golf for Everyone The Sports Car Story Beautiful Homes Nursery Rhymes Good Nutrition Car Trends How to Use the Internet Tennis Tips

26. Section 2 A Guided Tour of the Periodic Table Chapter 4 Bellringer 1. What criteria did you use for grouping the magazines? 2. Once you arrange the magazines into groups, could you sort the material further to make it even more organized?

27. 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.

28. 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.

29. 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.

30. 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.

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

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

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

34. 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:

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

36. 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.

37. 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

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

39. 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.

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

41. Section 3 Families of Elements Chapter 4 Objectives • Locatealkali 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.

42. Section 3 Families of Elements Chapter 4 Bellringer Are you familiar with some of the elements on the periodic table? There are probably many more elements that you have never heard of before. You may be surprised to learn that even though you have never heard of a certain element before, by looking at the periodic table, you can guess some of the characteristics of that element. The periodic table organizes elements into groups that have similar characteristics. 1. The elements below are classified as metals. You may be familiar with some of these elements. If you know of a specific use for an element listed below, write it down. Silver, Ag Gold, Au Tin, Sn Copper, Cu Lead, Pb Mercury, Hg Aluminum, Al Platinum, Pt 2. Can you think of any characteristics that the metals have in common? Do any of the metals have similar uses?

43. Section 3 Families of Elements Chapter 4 Bellringer 3. The elements below are classified as nonmetals. You may be familiar with some of these elements. If you know of a specific use for an element listed below, write it down. Helium, He Chlorine, Cl Oxygen, O Iodine, I Neon, Ne Carbon, C 4. Look at the periodic table and notice where each of the elements listed in questions 1 and 3 is located. Where are the metals located? Where are the nonmetals located?

44. Section 3 Families of Elements Chapter 4 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.

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

46. Section 3 Families of Elements Chapter 4 Metals • The alkali metals, found in Group 1 of the periodic table, are very reactive. • The alkaline-earth metals, whichinclude calcium, are found in Group 2 of the periodic table, andare somewhat less reactive than the alkali metals. • The transition metals, such as gold, iron, and mercury, occupy Groups3–12 of the periodic table.

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

48. Section 3 Families of Elements Chapter 4 Nonmetals, continued • Semiconductors are intermediateconductors 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.

49. Section 3 Families of Elements Chapter 4 Comparing Metals, Nonmetals, and Metalloids

50. Section 4 Using Moles to Count Atoms Chapter 4 Objectives • Explainthe 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.