Atomic Number

• number of protons in the nucleus of each atom

• number of protons determines which element it is

Each element has a different number of protons

What number on the Periodic Table is the atomic number?

• If we measure in grams, it is just too small of a number. We need to use a different measuring unit.

Atomic Mass

• nucleus contains most of the mass (about 99%) because protons and neutrons are far more massive than electrons

• mass of a proton is about the same as a neutron. The mass of each is approximately 1,800 times greater than the mass of the electron.

• the mass of an atom

• unit of measurement for atomic particles on the Periodic Table is the atomic mass unit (amu)

• mass of a proton or a neutron is equal to 1 amu

• atomic mass is determined from the Carbon-12 atom

Atomic Mass

• number of protons and neutrons

• this will always be a whole number (can’t have part of a proton or neutron)

if pulling from the Periodic Table, round to a whole number

if given in a problem, use that to determine other items

Mass Number

Isotopes

• not all the atoms of an element have the same number of neutrons

• atoms of the same elementthat have different numbersof neutrons

[they must have the same number of protons]

• different elements have different isotopes: some a lot, some very few

If the Mass Number is just the number of protons and neutrons, why are atomic masses on the periodic table not whole number? Why are some whole numbers?

Isotopes

• The average atomic mass of an element is the weighted-average mass of the mixture of its isotopes

• For example, 80% of boron found in nature isboron-11, and 20% is boron-10

[ you will NOT have to calculate this ]

Electrons• In a neutral atom, the number of electrons is equal to

the number of protons

Element SymbolMass

NumberAtomic

NumberProtons Neutrons Electrons

Boron B 11 5 5 6

Carbon C 12 6 6 6

Oxygen O 16 8 8 8

Sodium Na 23 11 11 12

Copper Cu 64 29 29 35

5

6

8

11

29

Oxygen O 18 8 10 88

• Periodic means "repeated in a pattern"

• Dmitri Mendeleev, Russian (1860’s), searched for a way to organize the elements

• arranged the elements in order of increasing atomic masses

• elements with similar properties were grouped together

Organizing the Elements

Organizing the Elements

• left blank spaces to keep the elements lined up according to their chemical properties

• predicted properties of undiscovered elements

• had some discrepancies (problems) in his table

• since Mendeleev’s pattern repeated, it was considered to be periodic. Today, this arrangement is called the Periodic Table of Elements

• “Father of the Periodic Table”

Organizing the Elements

• Henry G.J. Moseley, English (1913), arranged elements based on their increasing atomic numbers instead of an arrangement based on atomic masses

• resolved discrepancies in Mendeleev’s arrangement

• the current periodic table uses Moseley's arrangement of the elements

Changes in the Periodic Table

Periodic Table

• arrangement of the elements in order of their atomic number so that elements with similar properties fall in the same column or group

• when elements are arranged in order of increasing atomic number, elements with similar properties appear at regular intervals

Periodic Law

Periodic Table of the Elements Current ViewMCHS Periodic Table of the Elements

1 18

1

Hhydrogen

1.0

2 13 14 15 16 17

2

Hehelium

4.0

3

Lilithium

7.0

4

Beberyllium

9.0

5

Bboron

10.8

6

Ccarbon

12.0

7

Nnitrogen

14.0

8

Ooxygen

16.0

9

Ffluorine

19.0

10

Neneon

20.2

11

Nasodium

23.0

12

Mgmagnesium

24.3

3 4 5 6 7 8 9 10 11 12

13

Alaluminium

27.0

14

Sisilicon

28.1

15

Pphosphorus

31.0

16

Ssulphur

32.1

17

Clchlorine

35.5

18

Arargon

40.0

19

Kpotassium

39.1

20

Cacalcium

40.1

21

Scscandium

45.0

22

Tititanium

47.9

23

Vvanadium

50.9

24

Crchromium

52.0

25

Mnmanganese

54.9

26

Feiron

55.8

27

Cocobalt

58.9

28

Ninickel

58.7

29

Cucopper

63.5

30

Znzinc

65.4

31

Gagallium

69.7

32

Gegermanium

72.6

33

Asarsenic

74.9

34

Seselenium

79.0

35

Brbromine

79.9

36

Krkrypton

83.8

37

Rbrubidium

85.5

38

Srstrontium

87.6

39

Yyttrium

88.9

40

Zrzirconium

91.2

41

Nbniobium

92.9

42

Momolybdenum

95.9

43

Tctechnetium

[98]

44

Ruruthenium

101.0

45

Rhrhodium

102.9

46

Pdpalladium

106.4

47

Agsilver

107.9

48

Cdcadmium

112.4

49

Inindium

114.8

50

Sntin

118.7

51

Sbantimony

121.8

52

Tetellurium

127.6

53

Iiodine

126.9

54

Xexenon

131.3

55

Cscaesium

132.9

56

Babarium

137.3

57

Lalanthanum

138.9

72

Hfhafnium

178.5

73

Tatantalum

180.9

74

Wtungsten

183.8

75

Rerhenium

186.2

76

Ososmium

190.2

77

Iriridium

192.2

78

Ptplatinum

195.1

79

Augold

197.0

80

Hgmercury

200.6

81

Tlthallium

204.4

82

Pblead

207.2

83

Bibismuth

209.0

84

Popolonium

[209]

85

Atastatine

[210]

86

Rnradon

[222]

87

Frfrancium

[223]

88

Raradium

[226]

89

Acactinium

[227]

104

Rfrutherfordium

[261]

105

Dbdubnium

[262]

106

Sgseaborgium

[266]

107

Bhbohrium

[264]

108

Hshassium

[269]

109

Mtmeitnerium

[268]

110

Dsdarmstadtium

[271]

111

Rgroentgenium

[272]

112

Cncopernicium

[285]

113

Uutununtrium

[286]

114

Flflerovium

[289]

115

Uupunupentium

[288]

116

Lvlivermorium

[293]

117

Uusunuseptium

[294]

118

Uuoununoctium

[294]

58

Cecerium

140.1

59

Prpraseodymium

140.9

60

Ndneodymium

144.2

61

Pmpromethium

[145]

62

Smsamarium

150.4

63

Eueuropium

152.0

64

Gdgadolinium

157.3

65

Tbterbium

158.9

66

Dydysprosium

162.5

67

Hoholmium

164.9

68

Ererbium

167.3

69

Tmthulium

168.9

70

Ybytterbium

173.0

71

Lulutetium

175.0

90

Ththorium

232.0

91

Paprotactinium

231.0

92

Uuranium

238.0

93

Npneptunium

[237]

94

Puplutonium

[244]

95

Amamericium

[243]

96

Cmcurium

[247]

97

Bkberkelium

[247]

98

Cfcalifornium

[251]

99

Eseinsteinium

[252]

100

Fmfermium

[257]

101

Mdmendelevium

[258]

102

Nonobelium

[259]

103

Lrlawrencium

[262]