1. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 1 Chapter 2Atoms and Elements

2. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 2 Chapter 2 Goals Write the name of the element from its symbol or its period and group number Nonmetal or metal? Describe the parts of an atom Determine number of protons, neutrons, and electrons using the atomic and mass numbers Isotopes Electron configurations

3. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 3  Elements are pure substances that cannot be separated into simpler substances by ordinary laboratory processes.  Elements are the building blocks of matter.  There are 114 elements known today. gold carbon aluminum Elements

4. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 4 Sources of Some Element Names

5. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 5  Every element has a symbol that represents its name.  Symbols consist of 1 or 2 letters.  Only the first letter in a symbol is capitalized. Examples: 1-Letter Symbols 2-Letter Symbols C carbon Co cobalt N nitrogenCa calcium F fluorine Al aluminum O oxygen Mg magnesium Symbols of Elements

6. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 6 Several symbols are derived from Latin names. Some examples are shown below: copper, Cu (cuprum) gold, Au (aurum) iron, Fe (ferrum) silver, Ag (argentum) Symbols from Latin Names

7. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 7 Carbon, oxygen, and hydrogen are the most abundant elements in the human body. Elements in the Body

8. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 8  The physical properties of an element can be observed right down to the atomic level Physical Properties

9. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 9 Periodic Table

10. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 10 The periodic table arranges elements according to similar properties. Periodic Table

11. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 11 On the periodic table, each vertical column is called a group of elements. A group contains elements with similar chemical and physical properties. Each group is identified by a group number at the top of the column. The representative elements have group numbers of 1A – 8A. The transition elements use the letter “B.” Groups on the Periodic Table

12. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 12 Groups and Group Numbers

13. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 13 Numbering Groups One numbering system for groups assigns the letter A to the representative elements and the letter B to the transition elements. Another system assigns the numbers 1-18 to the columns across the periodic table.

14. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 14 Group Numbers Group numbers

15. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 15 Several groups of representative elements are classified by name. Group 1AAlkali Metals Group 2AAlkaline Earth Metals Group 7A Halogens Group 8ANoble Gases Representative Elements

16. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 16 Names of Some Representative Groups

17. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 17 On the periodic table, each horizontal row is called a period. A period is identified by a number such as 1, 2, 3, or 4. Periods on the Periodic Table

18. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 18 Location of Periods Period 4

19. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 19 NONMETALS METALOIDS Metals, Nonmetals, and Metalloids METALS

20. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 20  Metals  Are located to the left of the heavy line.  Are shiny, ductile, and good conductors.  Metalloids  Are elements along the heavy line.  Have properties of both metals and nonmetals.  Nonmetals  Are located to the right of the heavy line.  Are dull, brittle, poor conductors, and good insulators. Metals and Nonmetals

21. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 21 Comparing A Metal, Metalloid, and Nonmetal

22. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 22 2.3 The Atom 2.4 Atomic Number and Mass Number Chapter 2 Atoms and Elements

23. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 23  Matter is composed of tiny particles called atoms.  Atoms in each element are similar and different from atoms of other elements.  Atoms of two or more different elements combine in simple ratios to form compounds.  A chemical reaction involves changes in the arrangements of atoms. Atomic Theory

24. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 24 Subatomic Particles  Chemists are interested in three particles in atoms: protons, electrons, and neutrons.  Protons have a positive (+) charge; electrons have a negative (-) charge.  Like charges repel and unlike charges attract.

25. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 25 Subatomic Particles

26. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 26 Rutherford’s Gold-Foil Experiment  Most positive particles aimed at atoms of gold went straight through the atoms. Only a few were deflected.  Rutherford concluded that atoms have a small, dense nucleus with a positive charge.

27. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 27  An atom consists of a nucleus and a cloud of electrons.  The nucleus contains all of the protons and neutrons.  The rest of the atom, which is mostly empty space, is occupied by the electrons. Structure of the Atom

28. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 28  The atomic number is equal to the number of protons in an atom.  On the periodic chart, the atomic number appears above the symbol of an element. Atomic Number 11 Na Atomic Number Symbol

29. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 29 Atomic Numbers and Protons for Lithium and Carbon Atoms

30. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 30  An atom is electrically neutral; the net charge is zero.  In an atom, the number of protons is equal to the number of electrons. # protons = # electrons  Therefore, the atomic number is also equal to the number of electrons in a neutral atom. Electrons in An Atom

31. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 31  The mass number gives the total number of protons and neutrons in the nucleus. Mass number = # protons + # neutrons Mass Number

32. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 32  The atomic symbol represents a particular atom of an element.  The atomic symbol shows the mass number in the upper left corner and the atomic number in the lower left corner.  For example, an atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: mass number 23 Na atomic number 11 Atomic Symbol

33. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 33  When we know the atomic symbol of an atom, we can determine the number of protons (p + ), neutrons, (n), and electrons (e - ). 163165 O P Zn 81530 8 p + 15 p + 30 p + 8 n16 n35 n 8 e - 15 e - 30 e - Information from Atomic Symbols

34. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 34 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. 12 C 13 C 14 C 6 6 6 protons ______ ______ ______ neutrons ______ ______ ______ electrons______ ______ ______ Learning Check

35. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 35 12 C 13 C 14 C 6 6 6 Protons 6 6 6 Neutrons6 7 8 Electrons 6 6 6 Solution

36. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 36 Chapter 2Atoms and Elements 2.5 Isotopes and Atomic Mass 24 Mg 25 Mg 26 Mg 12 12 12

37. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 37  Isotopes are atoms of the same element that have different mass numbers.  Isotopes have the same number of protons, but different numbers of neutrons.  Most elements have two or more isotopes. Isotopes

38. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 38 Isotopes of Magnesium In naturally occurring atoms of magnesium, there are three isotopes. 24 Mg makes up 78.9% of magnesium atoms. 25 Mg makes up 10.0% and 26 Mg makes up 11.1%. 24 Mg 25 Mg 26 Mg 12 12 12

39. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 39  Atomic mass is the weighted average mass of all the isotopes of that element.  The atomic mass of each element is compared to 12 C, which a mass of 12 amu.  The atomic mass of each element is listed below the symbol of the element on the periodic table. Atomic Mass

40. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 40 Atomic Mass of Magnesium  The individual atomic masses of all the isotopes contribute to the atomic mass of Mg.  As a weighted average, the atomic mass is not a whole number.

41. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 41 Using the periodic table, specify the atomic mass of each element (round to the tenths place): A.calcium__________ B. aluminum__________ C. lead__________ D. barium__________ E. iron__________ Learning Check

42. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 42 Using the periodic table, specify the atomic mass of each element (round to the tenths place): A.calcium40.1 B. aluminum27.0 C. lead207.2 D. barium137.3 E. iron55.9 Solution

43. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 43 To calculate atomic mass, use the percent(%) abundance of the isotopes and the mass of each isotope of that element. mass isotope(1) x (%) + mass isotope (2) x (%) + … 100 100 Calculating Atomic Mass

44. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 44 Atomic Mass for Cl  The atomic mass of chlorine is the weighted average of two isotopes 35 Cl and 37 Cl.

45. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 45 Cl-35 is 75.8 % and Cl-37 is 24.2% of natural chlorine. Using the given atomic mass of each isotope, calculate the contribution of each isotope to the atomic mass of Cl. 35.0 x 75.8 = 26.5 100 37.0 x 24.2 = 8.95 100 Add together = 35.45 = atomic mass Cl Calculating Atomic Mass for Chlorine

46. Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 46 Isotopes of Some Elements and Their Atomic Mass