Chapter 3 Atoms and Elements

Transcription

1 Chapter 3 Atoms and Elements 1

2 Elements Elements are pure substances that cannot be separated into simpler substances by ordinary laboratory processes the building blocks of matter listed on the inside front cover of this text 2

3 Some Elements and Their Names Names come from: planets mythological figures minerals colors geographic locations famous people 3

4 Chemical Symbols Chemical Symbols represent name of element consist of one to two letters and start with capital 1-Letter Symbols 2-Letter Symbols C carbon Co cobalt N nitrogen Ca calcium F fluorine Al aluminum O oxygen Mg magnesium 4

5 Chemical Symbols from Latin Names Ag silver, from argentum Au gold, from aurum 5

6 Learning Check Write the correct chemical symbols for each of the following elements: A. iodine B. iron C. magnesium D. zinc E. nitrogen 6

7 Solution Write the symbols for each of the following elements: A. iodine = I (I 2 ) B. iron = Fe C. magnesium = Mg D. zinc = Zn E. nitrogen = N (N 2 ) 7

8 On the periodic table, Groups and Periods elements are arranged according to similar properties groups contain elements with similar properties in vertical columns periods are horizontal rows of elements arranged according to atomic size 8

9 Periodic Table of Elements Group numbers use the letter A for representative elements (Groups 1A 8A) use the letter B for transition elements (Groups 3B 12B) 9

10 Group 1A, the alkali metals, includes lithium, sodium, potassium, rubidium, and cesium. Group 7A, the halogens, includes chlorine, bromine, and iodine. 10

11 Learning Check Identify the element described by the following: 1. Group 7A, Period 4 A. Br B. Cl C. Mn 2. Group 2A, Period 3 A. beryllium B. boron C. magnesium 3. Group 5A, Period 2 A. phosphorus B. arsenic C. nitrogen 11

12 Solution Identify the element described by the following: 1. Group 7A, Period 4 A. Br 2. Group 2A, Period 3 C. magnesium 3. Group 5A, Period 2 C. nitrogen 12

13 Metals, Nonmetals, and Metalloids The heavy zigzag line separates metals and nonmetals. Metals are located to the left. Nonmetals are located to the right. Metalloids are located along the heavy zigzag line between the metals and nonmetals. 13

14 Properties of Metals, Nonmetals, and Metalloids Metals are shiny and ductile are good conductors of heat and electricity Nonmetals are dull, brittle, and poor conductors are good insulators Metalloids are better conductors than nonmetals, but not as good as metals are used as semiconductors and insulators as a general rule they have the appearance of metals and the properties and characteristics of nonmetals 14

15 Comparing a Metal, Nonmetal, and Metalloid 15

16 Dalton's Atomic Theory In Dalton's atomic theory, atoms: are tiny particles of matter of an element are similar to each other and different from other elements of two or more different elements combine to form compounds are rearranged to form new combinations in a chemical reaction 16

17 Rutherford's Gold Foil Experiment In Rutherford s gold foil experiment, positively charged alpha (α ) particles were aimed at atoms of gold. Most went straight through. Occasionally one was deflected. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close. 17

18 Structure of the Atom An atom consists of a nucleus that contains protons and neutrons electrons in a large, empty space around the nucleus 18

19 Subatomic Particles in the Atom 1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the carbon-12 atom. Protons have a positive (+) charge. Electrons have a negative ( ) charge. Neutrons are neutral. Like charges repel and unlike charges attract. 19

20 Atomic Number The atomic number is specific for each element is the same for all atoms of an element is equal to the number of protons in an atom usually appears above the symbol of an element in the Periodic Table Atomic Number Symbol 11 Na 20

21 Atomic Number = Protons in Atom For example, atomic number = number of protons: Atomic number H is 1; every H atom has one proton Atomic number of C is 6; every C atom has six protons Atomic number of Cu is 29; every Cu atom has 29 protons 21

22 Learning Check Use the periodic table to fill in the atomic number, number of protons, and number of electrons for each of the following elements: (NB: atoms have zero net charge) Element Atomic Number N Zn S Protons Electrons 22

23 Solution Use the periodic table to fill in the atomic number, number of protons, and number of electrons for each of the following elements: (NB: atoms have zero net charge) Element Atomic Number Protons Electrons N Zn S So the number of electrons will equal the number of protons for any neutral charge atom. 23

24 Atomic Symbols and Subatomic Particles Examples of number of subatomic particles for atoms: Atomic symbol O P Zn p + 15 p + 30 p + 8 n 16 n 35 n 8 e - 15 e - 30 e - 24

25 Isotopes Isotopes are atoms of the same element have different mass numbers have same number of protons but different numbers of neutrons Mass Numbers 24 Mg 25 Mg 26 Mg

26 Learning Check Naturally occurring carbon consists of three isotopes: 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of the following: Isotope 12 C 13 C 14 C protons neutrons electrons 26

27 Solution Naturally occurring carbon consists of three isotopes: 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of the following: Isotope 12 C 13 C 14 C protons neutrons electrons

28 Learning Check 1. Which of the pairs are isotopes of the same element? 2. In which of the pairs do both atoms have 8 neutrons? A. B. 15 X 8 12 X 6 15 X 7 14 X 6 C. 15 X 16 X

29 Learning Check 1. Which of the pairs are isotopes of the same element? B. 12 X 6 14 X 6 2. In which of the pairs do both atoms have 8 neutrons? C. 15 X 7 16 X 8 29

30 Atomic Mass Atomic mass is the weighted average of all naturally occurring isotopes of that element number on the periodic table below the chemical symbol with two decimal places 30

31 Calculating Atomic Mass To calculate atomic mass, use an experimental percent abundance of each isotope of the element multiply the percent abundance by the atomic mass of that isotope sum the total mass of each isotope 31

32 Calculating Atomic Mass To calculate atomic mass of Cl, use experimental data for both isotopes of Cl: Isotope atomic mass x % abundance 35 Cl amu x = amu Cl amu x = amu 100 Atomic mass of Cl = amu 32

33 Electromagnetic Spectrum As frequency increases, energy increases: E = hν The electromagnetic spectrum shows the arrangement of wavelengths of electromagnetic radiation, with the visible range from 700 to 400 nm. 33

34 Elements Have a Unique Atomic Spectrum When light from an element that is heated passes through a prism, it separates into a unique set of distinct lines of color called an atomic spectrum. Strontium Barium 34

35 Electron Energy Levels Energy levels are assigned numbers n = 1, 2, 3, 4, and so on increase in energy as the value of n increases are like the rungs of a ladder, with the lower energy levels nearer the nucleus Energy levels have a maximum number of electrons equal to 2n 2. Energy level Maximum number of electrons n = 1 2(1) 2 = 2(1) = 2 n = 2 2(2) 2 = 2(4) = 8 n = 3 2(3) 2 = 2(9) = 18 35

36 Changes in Electron Energy Level Electrons move to a higher energy level when they absorb energy. When electrons fall back to a lower energy level, light is emitted. The energy emitted or absorbed is equal to the differences between the two energy levels. 36

37 Electron Configurations in Periods Period 1 H 1 electron in 1 st energy level. 1s 1 He 2 electrons in 1 st energy level. 1s 2 Period 2 Energy Level 1 st 2 nd e- Config. Li 2 1 1s 2 2s 1 Be 2 2 1s 2 2s 2 B 2 3 1s 2 2s 2 2p 1 C 2 4 1s 2 2s 2 2p 2 N 2 5 1s 2 2s 2 2p 3 O 2 6 1s 2 2s 2 2p 4 F 2 7 1s 2 2s 2 2p 5 Ne 2 8 1s 2 2s 2 2p 6 37

38 Electron Configurations in Periods Period 3 Energy Level 1 st 2 nd 3 rd e- Config. Na s 2 2s 2 2p 6 3s 1 Mg s 2 2s 2 2p 6 3s 2 Al s 2 2s 2 2p 6 3s 2 3p 1 Si s 2 2s 2 2p 6 3s 2 3p 2 P s 2 2s 2 2p 6 3s 2 3p 3 S s 2 2s 2 2p 6 3s 2 3p 4 Cl s 2 2s 2 2p 6 3s 2 3p 5 Ar s 2 2s 2 2p 6 3s 2 3p 6 Period 4 Energy Level 1 st 2 nd 3 rd 4 th K [Ar]4s 1 Ca [Ar]4s 2 38

39 Electron Configurations Beyond 20 Energy Level 1 st 2 nd 3 rd 4 th 5 th 6 th 7 th Number of Electrons

40 Electron Orbital Filling & the Periodic Table 1s 2 2s 2 2p 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2 1s 2 2s 2 2p 6 3s 2 3p 6

41 Learning Check Write the electron configuration for the following elements: C Si O N 41

42 Solution Write the electron arrangement for the following elements: C = 1s 2 2s 2 2p 2 Si = 1s 2 2s 2 2p 6 3s 2 3p 2 O = 1s 2 2s 2 2p 4 As = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 3 U = [Rn] 7s 2 6d 1 5f 3 NB: The sum of the superscripts will equal the atomic number of the element for neutral atoms. 42

43 Group Number and Valence Electrons For representative elements in Groups 1A 8A, chemical properties are due to the number of valence electrons. Valence electrons are the number of electrons in the outermost energy level (the s & p electrons for that period). The group number gives the number of valence electrons for the representative elements. Group Number # Valence Electrons 1A 1 2A 2 3A 3 4A 4 5A 5 6A 6 7A 7 8A 8 43

44 Electron-Dot Symbols Electron-dot symbols are also known as Lewis structures represent the valence electrons as dots placed on sides of symbol Possible electron-dot symbols for magnesium, with the electron arrangement of 2,8,2, include 2 valence electrons, represented as dots can be drawn in more than one way Mg Mg Mg Mg Mg Mg 44

45 Electron-Dot Symbols for Selected Elements 45

46 Learning Check Question: Write the electron-dot symbol for each of the following elements: Cl, C, N. Solution: Cl C N 46

47 Atomic Size Atomic size is determined by the atom s atomic radius, the distance between nucleus and outermost electrons increases for representative elements from top to bottom of the periodic table decreases within a period due to increased number of protons in nucleus 47

48 Atomic Size 48

49 Ionization Energy Ionization energy is the energy required to remove one of the outermost electrons from an atom Na(g) + energy (ionization) Na + (g) + e decreases down a group, increases across a period from left to right 49

50 Metallic Character An element with metallic character is one that loses electrons easily. Metallic character is more prevalent in metals on left side of periodic table is less for nonmetals on right side of periodic table that do not lose electrons easily 50

51 Summary of Trends in Periodic Table 51

52 Learning Check Given the following elements: C P Cl Which is the largest atom? Which has the highest ionization energy? Which has the electron configuration 1s 2 2s 2 2p 6 3s 2 3p 3 52

53 Solution Given the following elements: C P Cl Which is the largest atom? Which has the highest ionization energy? Which belongs to Group 5A? C Cl P 53