1. Atomic Structure

2. What is Scientific Theory? An explanation of the way the world works, based on observations.

3. Explain why the ideas on atoms proposed by Dalton constitute a theory, while the ideas proposed by Democritus do not?

4. Democritus’s ideas were not based on experimental results and did not explain chemical reactions. It was just his believe. Dalton’s ideas did both of these.

5. Answer 1. Atomic number is the number of proton in an atom. Mass number is number of proton and neutron of an atom. 2. Atoms with the same number of Proton but different number of neutrons.

6. Answer 3. Three Protium, Deuterium, and Tritium They all belong to element Hydrogen.

7. The Development of Atomic Models The atomic model has changed as scientists learned more about the atom’s structure. Look at fig. 5.2 on pg.128 Read the captions of all atomic models Draw the models with captions and time line.

8. Review Democritus (Greek philosopher,460 B.C. – 370 B. C.) believed that matter consisted of tiny, indivisible, unchangeable particles called atoms. By using experimental methods, Dalton, (English Physicist, 1766 – 1844), transformed Democritus ideas on atoms into a scientific theory.

9. Dalton’s Theory 1. All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical. 3. Atoms of different elements chemically combine to form compounds. 4. Chemical reactions occur when atoms are separated, joined, or rearranged.

10. Rutherford’s Atomic Model Rutherford (1911) discovered that an atom has a small, dense, positively charged nucleus. Electrons move around the nucleus.

11. Concept Check Who first discovered that atom has a positively charged nucleus?

12. Inadequacies of the Model His model only explained a few simple properties of atom. Rutherford model failed to explain why object change colors when heated - first glow dull red, then yellow and then white.

13. Concept Check What was inadequate in Rutherford’s model of the atom? He could not explain why metals give off light when they are heated.

14. The Bohr Atomic Model Neils Bohr (1913) proposed that an electron is found only in specific (fixed) circular path or orbit around the nucleus, called energy levels.

15. Quantum Jump An electron can jump from one energy level to another called quantum (sudden, discrete) jump. To move from one energy level to another, an electron must gain or lose just the right amount of energy.

16. Ground and Excited States The lowest energy level is called the ground state. If an electron gains energy it can move to a higher energy level. It is now in an excited state. The electrons in an atom cannot be between energy levels.

17. Energy Levels The energy levels are not equally spaced. The higher energy level are closer together and takes less energy to move from one level to other.

18. Energy Levels of H

19. Electron Cloud Model (1926) The electron cloud model is a visual model of the probable locations of electrons in an atom. The probability of finding an electron is higher in the denser regions of the cloud.

20. Electron Distribution The maximum number of electrons that can occupy a principal energy level is given by the formula 2n 2, where n is the principal quantum number.

21. Structure of the Nuclear Atom (sec. 4.2) In an atom there are three kinds of subatomic particles: electrons, protons, and neutrons.

22. Structure of the Nuclear Atom 2 In the nuclear atom, the protons and neutrons are located in the nucleus. Electrons are distributed around the nucleus and occupy almost all the volume of the atom.

23. Why Elements are Different? ( sec 4.3 ) Elements (or atoms) are different because they contain different numbers of protons.

24. Distinguishing Between Atoms-cont. In a normal condition the number of electron is equal to the number of proton. That’s why atom is electrically neutral in a normal condition.

25. How are atoms of hydrogen different from atoms of oxygen? Hydrogen atom has one proton and oxygen atom has eight protons.

27. Atomic Number (Z) The atomic number of an element is the number of protons in the nucleus of an atom of that element.

28. Atomic Number – cont. Because all hydrogen atoms have one proton, the atomic number of hydrogen is 1. Oxygen atom has eight protons. What is the atomic number of oxygen?

29. Remember In a neutral atom number of protons equal to number of electrons.

30. Practice Problem How many protons and electrons are in each atom? A. fluorine (atomic number=9) B. calcium (atomic number=20) C. aluminum (atomic number=13) D. nitrogen (atomic number=7)

31. Inside an Atom

32. Mass Number (A) Most of the mass of an atom is concentrated in its nucleus. The total number of protons (Atomic no. Z) and neutrons in an atom is called the mass number (A).

34. Applying Concept 1. A helium atom has two protons and two neutrons. What is it’s mass number? 2. A carbon atom has six protons and six neutrons. What is it’s mass number?

35. xxxMass Number – cont. Why the mass of an electron is not considered in mass number? Because electron is about 2000 times lighter than proton and neutron.

36. Applying Concept How do you calculate mass number? Mass number (A)=Atomic number (Z) + number of neutrons (N). A = Z + N

37. Use of Mass Number Is used to calculate the number of neutrons. Number of neutrons = mass number – atomic number N = A - Z

38. Checking Concept How do you find the number of neutrons in an atom?

39. Checking Concept –cont. Oxygen atom has an atomic number of 8 and a mass number of 16. What is the number of neutrons in oxygen?

40. Determining the Composition of an Atom How many protons, electrons, and neutrons are in each atom? Atomic No. Mass No. Neon1020 Iron2655 Gold79197

41. Answer Neon: p = 10 e =10 n = 10 Iron: p=26 e = 26 n = 29 Gold: p=79 e = 79 n = 118

42. Short Hand Notation The composition of any atom can be represented in short hand notation using atomic number and mass number. Ex. Gold Atom 197 Au 79

43. Applying Concept How many electrons does the gold atom have? In gold atom the atomic number is 79, which is it’s number of proton which is also equal to number of electron.

44. Applying Concept - more Please open your text book to pg. 112. Do practice problem 17 and 18.

45. You can also refer to atoms by using the mass number and the name of the element. For example: gold -197.

46. Isotopes Isotopes are atoms that have the same number of protons but different numbers of neutrons.

47. Isotopes – cont. Because isotopes of an element have different numbers of neutrons, they also have different mass numbers. They are chemically alike because # of protons and electrons are same.

48. Isotopes

49. Hydrogen Isotopes Hydrogen has three known isotopes. Protium – no neutron, 1 proton Deutorium (heavy water) – 1 neutron, 1 proton Tritium – 2 neutron, 1 proton

50. Isotopes of Neon Neon 20, neon 21, neon 22 Text book pg 113.

51. Atomic Mass The average mass of an element’s atom – mainly depends on the mass of proton and neutron.

52. Atomic Mass The unit of measurement is atomic mass unit (amu). one amu is equal to 1.66 x 10 −24 g.

53. One amu is equal to 1/12 the mass of a carbon atom, or approximately the mass of one hydrogen atom. The carbon -12 atom has a mass of 12 amu (six protons and six neutrons in its nucleus)

54. Isotopes of Hydrogen Isotopes# of Protons # of Neutron # of Electrons Protium101 Deuterium111 Tritium121

55. Isotopes

56. Periodic Table - 1 A periodic table is an arrangement of elements in which the elements are separated into groups according to their properties.

57. Periodic Table - 2 Each element is identified by its symbol placed in a square. The elements are listed in order of increasing atomic number, from left to right and top to bottom.

58. Periodic Table - 3 The atomic number of the element is shown centered above the symbol. Hydrogen (H), the lightest element, is in the top left corner. Helium (He), atomic number 2, is the top right.

59. Periodic Table - 4 Each horizontal row of the periodic table is called a period. There are seven periods. Within the period the properties of the elements vary as you move across it from element to element.

60. Periodic Table - 5 Each vertical column of the periodic table is called a group, or family. Elements within a group have similar chemical and physical properties. Each group is identified by a number and letter A or B.