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Chapter 14 “The Periodic Table” Pre-AP Chemistry Charles Page High School Stephen L. Cotton.

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1 Chapter 14 “The Periodic Table” Pre-AP Chemistry Charles Page High School Stephen L. Cotton

2 Section 14.1 Organizing the Elements u OBJECTIVES: Explain how elements are organized in a periodic table.

3 Section 14.1 Organizing the Elements u OBJECTIVES: Compare early and modern periodic tables.

4 Section 14.1 Organizing the Elements u OBJECTIVES: Identify three broad classes of elements.

5 Section 14.1 Organizing the Elements u By the year 1700, only about 13 elements had been identified u As more were discovered, we needed a way to organize the elements.

6 Section 14.1 Organizing the Elements u Chemists used the properties of elements to sort them into groups. u By the mid-1800s, about 70 elements were known to exist

7 Mendeleev’s Periodic Table u Dmitri Mendeleev – Russian chemist u Arranged elements in order of increasing atomic mass u Thus, the first “Periodic Table”

8 Mendeleev u Left blanks for undiscovered elements u Based on the blanks, new elements were discovered u 1894 found Argon, within 5 years found He, Ne, Kr, Xe, Rn

9 A better arrangement u In 1913, Henry Moseley – British physicist, arranged elements according to increasing atomic number Co & Ni; Ar & K; Te & I u The arrangement used today

10

11 Spiral Periodic Table Another possibility: Spiral Periodic Table

12 The Periodic Law says: u When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

13 The Periodic Law says: u Horizontal rows = periods There are 7 periods u Vertical column = group (or family) Similar physical & chemical properties Identified by number & letter

14 Areas of the periodic table u Three classes of elements are: 1) metals 2) nonmetals 3) metalloids (semi-metals)

15 Areas of the periodic table 1) Metals: electrical conductors, have luster, ductile, malleable 2) Nonmetals: generally brittle and nonlustrous, poor conductors of heat and electricity

16 Areas of the periodic table 3) Metalloids: border the line Properties are intermediate between metals and nonmetals

17 Section 14.1 Classifying the Elements u OBJECTIVES: Describe the information in a periodic table.

18 Section 14.1 Classifying the Elements u OBJECTIVES: Classify elements based on electron configuration.

19 Section 14.1 Classifying the Elements u OBJECTIVES: Distinguish representative elements and transition metals.

20 Electron Configurations in Groups u Elements can be sorted into different groupings based on their electron configurations

21 Groups of elements u Group 1A – alkali metals u Hydrogen is not part of this group

22 1s11s1 1s 2 2s 1 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4 f 14 5d 10 6p 6 7s 1 H 1 Li 3 Na 11 K 19 Rb 37 Cs 55 Fr 87 Do you notice any similarity in these configurations of the alkali metals?

23 Groups of elements u Group 2A – alkaline earth metals Do not dissolve well in water, hence “earth metals”

24 Group 1A are the alkali metals (not Hydrogen) Group 2A are the alkaline earth metals H

25 Groups of elements u Group 7A – halogens Means “salt-forming”

26 Electron Configurations in Groups 1) Noble gases are the elements in Group 8A u Electron configuration has the outer s and p sublevels completely full

27 He 2 Ne 10 Ar 18 Kr 36 Xe 54 Rn 86 1s21s2 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 3p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 Do you notice any similarity in the configurations of the noble gases?

28 u Group 8A are the noble gases u Group 7A is called the halogens

29 Electron Configurations in Groups 2) Representative Elements are in Groups 1A – 7A u Display wide range of properties, thus a good “representative” u Outer s and p electron configurations are NOT filled

30 1A 2A3A4A5A6A 7A 8A u Elements in the 1A-7A groups are called the representative elements outer s or p filling

31 Electron Configurations in Groups 3) Transition metals are in the B columns of the periodic table u s sublevel full, and is now filling the d sublevel

32 Electron Configurations in Groups 4) Inner Transition Metals are located below the main body of the table, in two horizontal rows u s sublevel full, and is now filling the f sublevel

33 Section 14.2 Periodic Trends u OBJECTIVES: Describe trends among the elements for atomic size.

34 Section 14.2 Periodic Trends u OBJECTIVES: Explain how ions form.

35 Section 14.2 Periodic Trends u OBJECTIVES: Describe periodic trends for first ionization energy, ionic size, and electronegativity.

36 Trends in Atomic Size u How do you measure the size of 1 atom? u The electron cloud doesn’t have a definite edge. u Measure the Atomic Radius - this is half the distance between the two nuclei of a diatomic molecule.

37 Atomic Size u Measure the Atomic Radius - this is half the distance between the two nuclei of a diatomic molecule. } Radius

38 Periodic Table Trends u Influenced by three factors: 1. Energy Level Higher energy level is further away. 2. Charge on nucleus (# protons) More charge pulls electrons in closer. u 3. Shielding effect (a blocking effect?)

39 What do they influence? u Energy levels and Shielding have an effect on the GROUP (  ) u Nuclear charge has an effect on a PERIOD (  )

40 #1. Atomic Size - Group trends u As we increase the atomic number (or go down a group)... u each atom has another energy level, u so the atoms get bigger. H Li Na K Rb

41 #1. Atomic Size - Period Trends u Going from left to right across a period, the size gets smaller. u Electrons are in the same energy level. u But, there is more nuclear charge. u Outermost electrons are pulled closer. NaMgAlSiPSClAr

42 Atomic Number Atomic Radius (pm) H Li Ne Ar 10 Na K Kr Rb 3 Period 2

43 Ions u Some compounds are composed of particles called “ions” u An ion is an atom (or group of atoms) that has a positive or negative charge

44 Ions u Atoms are neutral because the number of protons equals electrons u Ions are formed when atoms gain or lose electrons

45 Ions u Metals tend to LOSE electrons, from their outer energy level Sodium loses one: there are now more protons (11) than electrons (10), and thus a positively charged particle is formed = “cation” The charge is written as a number followed by a plus sign: Na 1+ Now named a “sodium ion”

46 Ions u Nonmetals tend to GAIN one or more electrons Chlorine will gain one electron Protons (17) no longer equals the electrons (18), so a charge of -1 Cl 1- is re-named a “chloride ion” Negative ions are called “anions”

47 #2. Trends in Ionization Energy u Ionization energy is the amount of energy required to completely remove an electron (from a gaseous atom). u Removing one electron makes a 1+ ion. u The energy required to remove only the first electron is called the first ionization energy.

48 Ionization Energy u The second ionization energy is the energy required to remove the second electron. Always greater than first IE. u The third IE is the energy required to remove a third electron. Greater than 1st or 2nd IE.

49 SymbolFirstSecond Third H He Li Be B C N O F Ne Table 6.1, p. 173

50 SymbolFirstSecond Third H He Li Be B C N O F Ne Why did these values increase so much ?

51 What factors determine IE u The greater the nuclear charge, the greater IE. u Greater distance from nucleus decreases IE u Filled and half-filled orbitals have lower energy, so achieving them is easier, lower IE. u Shielding effect

52 Shielding u The electron on the outermost energy level has to look through all the other energy levels to see the nucleus. u Second electron has same shielding, if it is in the same period

53 Ionization Energy - Group trends u As you go down a group, the first IE decreases because... The electron is further away from the attraction of the nucleus There is more shielding.

54 Ionization Energy - Period trends u All the atoms in the same period have the same energy level. u Same shielding. u But, increasing nuclear charge u So IE generally increases from left to right. u Exceptions at full and 1/2 full orbitals.

55 First Ionization energy Atomic number He u He has a greater IE than H. u Both elements have the same shielding since electrons are only in the first level u But He has a greater nuclear charge H

56 First Ionization energy Atomic number H He Li has lower IE than H more shielding further away l These outweigh the greater nuclear charge Li

57 First Ionization energy Atomic number H He Be has higher IE than Li same shielding l greater nuclear charge Li Be

58 First Ionization energy Atomic number H He B has lower IE than Be same shielding greater nuclear charge l By removing an electron we make s orbital half-filled Li Be B

59 First Ionization energy Atomic number H He Li Be B C

60 First Ionization energy Atomic number H He Li Be B C N

61 First Ionization energy Atomic number H He Li Be B C N O u Oxygen breaks the pattern, because removing an electron leaves it with a 1/2 filled p orbital

62 First Ionization energy Atomic number H He Li Be B C N O F

63 First Ionization energy Atomic number H He Li Be B C N O F Ne u Ne has a lower IE than He u Both are full, u Ne has more shielding u Greater distance

64 First Ionization energy Atomic number H He Li Be B C N O F Ne Na has a lower IE than Li Both are s 1 Na has more shielding l Greater distance Na

65 First Ionization energy Atomic number

66 Driving Forces u Full Energy Levels require lots of energy to remove their electrons. u Noble Gases have full orbitals. u Atoms behave in ways to try and achieve a noble gas configuration.

67 2nd Ionization Energy u For elements that reach a filled or half-filled orbital by removing 2 electrons, 2nd IE is lower than expected. u True for s 2 u Alkaline earth metals form 2+ ions.

68 3rd IE u Using the same logic s 2 p 1 atoms have an low 3rd IE. u Atoms in the aluminum family form 3+ ions. u 2nd IE and 3rd IE are always higher than 1st IE!!!

69 Trends in Ionic Size: Cations u Cations form by losing electrons. u Cations are smaller than the atom they came from – not only do they lose electrons, they lose an entire energy level. u Metals form cations. u Cations of representative elements have the noble gas configuration before them.

70 Ionic size: Anions u Anions form by gaining electrons. u Anions are bigger than the atom they came from – have the same energy level, but greater nuclear charge u Nonmetals form anions. u Anions of representative elements have the noble gas configuration after them.

71 Configuration of Ions u Ions always have noble gas configurations (a full outer level) u Na atom is: 1s 2 2s 2 2p 6 3s 1 u Forms a 1+ ion: 1s 2 2s 2 2p 6 u Same configuration as neon. u Metals form ions with the configuration of the noble gas before them - they lose electrons.

72 Configuration of Ions u Non-metals form ions by gaining electrons to achieve noble gas configuration. u They end up with the configuration of the noble gas after them.

73 Ion Group trends u Each step down a group is adding an energy level u Ions therefore get bigger as you go down, because of the additional energy level. Li 1+ Na 1+ K 1+ Rb 1+ Cs 1+

74 Ion Period Trends u Across the period from left to right, the nuclear charge increases - so they get smaller. u Notice the energy level changes between anions and cations. Li 1+ Be 2+ B 3+ C 4+ N 3- O 2- F 1-

75 Size of Isoelectronic ions u Iso- means the same u Iso electronic ions have the same # of electrons u Al 3+ Mg 2+ Na 1+ Ne F 1- O 2- and N 3- all have 10 electrons u all have the same configuration: 1s 2 2s 2 2p 6 (which is the noble gas neon)

76 Size of Isoelectronic ions? u Positive ions that have more protons would be smaller. Al 3+ Mg 2+ Na 1+ Ne F 1- O 2- N 3-

77 #3. Trends in Electronegativity u Electronegativity is the tendency for an atom to attract electrons to itself when it is chemically combined with another element. u They share the electron, but how equally do they share it? u An element with a big electronegativity means it pulls the electron towards itself strongly!

78 Electronegativity Group Trend u The further down a group, the farther the electron is away from the nucleus, plus the more electrons an atom has. u Thus, more willing to share. u Low electronegativity.

79 Electronegativity Period Trend u Metals are at the left of the table. u They let their electrons go easily u Thus, low electronegativity u At the right end are the nonmetals. u They want more electrons. u Try to take them away from others u High electronegativity.

80 The arrows indicate the trend: Ionization energy and Electronegativity INCREASE in these directions

81 Atomic size and Ionic size increase in these directions:

82 Summary Chart of the trends: Figure 6.22, p.178


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