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Chapter 2 Atoms, molecules, and ions

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1 Chapter 2 Atoms, molecules, and ions
The Atomic Theory History The Structure of the Atom Proton, Neutron, Electron Atomic Number, Mass Number Isotopes The Periodic Table DAB/CAS/CSU/2010

2 Matter

3 Brownian Motion

4 Atomic theory Atoms are incredibly small.
What we know about them is based on indirect evidence.

5 History of atomic theory
500 BC Democritus proposed the idea of atom but had no experimental data to support Believed that all matter consists of very small, indivisible particles, which he named atomos (meaning uncuttable or indivisible). 1800 Dalton proposed an atomic theory supported by an experimental data

6 Dalton’s atomic theory: Support
Support for his theory came when he began looking at the masses of elements that combined with each other He found that elements combine by simple ratio by mass

7 Dalton’s atomic theory:
All matter is composed of tiny indivisible particles called atoms. All atoms of the same element are identical (having same size, mass, and chemical properties). The atoms of one element are different from the atoms of all other elements. Atoms of two or more elements can combine in small whole number ratios to form compounds. A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction.

8 Dalton’s atomic theory: Support
Law of Definite Proportion Different samples of the same compound always contain its constituent elements in the same proportion Law of Multiple Proportions If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers. Example: CO & CO2

9 Dalton’s atomic theory: Support
Law of Conservation of Mass Matter can neither be created nor destroyed The mass of atoms before and after reaction is conserved

10 Dalton’s atomic theory: Support
Law of Conservation of Mass

11 Dalton’s atomic theory:
Problems with Daltons Theory Atoms of the same element have different masses Atoms have subatomic particles (protons, electrons, neutrons.) So, Dalton’s theory is not completely correct!

12 The structure of the atom

13 Subatomic Particles Particle Symbol Charge Relative Mass (amu) Electron e Proton p+ + 1 Neutron n 0 1

14 Subatomic Particles: Discovery
Electron was discovered by JJ Thomson in ~1900 using his cathode ray tube. Electron charge was found by American Robert Millikan ~ 1910 by an oil-drop experiment. Proton was found by the adaptation of cathode ray tube ~ 1900. Neutron was discovered by Chadwick in 1932.

15 The Electron Discovery
1890’s discovery of radiation lead to discovery of electron Radiation – the emission and transmission of energy through space in the form of waves Used cathode ray tube Cathode – negatively charged plated, emits an invisible ray Anode – positively charged tube

16 Thomson’s plum pudding model of the atom

17 Subatomic Particles: Discovery
Rutherford’s Gold Foil Experiment: Plum pudding model: atom has a weak positive charge. Rutherford tested the idea by positively charged particles at gold foil. He expected particles to pass through. His results surprised him.

18 Movie on Gold Foil Experiment

19 Subatomic Particles: Discovery
Rutherford’s Gold Foil Experiment: Results Atoms is mostly empty space. Protons are found in the dense nucleus in the center of the atom.

20 Location of Subatomic Particles
10-13 cm electrons protons neutrons 10-8 cm nucleus

21 Rutherford’s Model: Problem:
Could not explain why electrons would not spiral into the nucleus.

22 Implications of Rutherford’s Exp’t.
Nucleus – at the center of the atom Dense central core within the atom Contains positively charged particle (protons) Protons carry the same charge as that of electron Mass of protons is 1840 times that of electron Neutrons – neutral particles within the nucleus having a mass slightly greater than that of protons

23 Particle Mass (g) Coulumb Charge unit Electron x x 10-19 -1 Proton x x 10-19 +1 Neutron x

24

25 ATOMS TO ELEMENTS What makes elements different from one another?
The number of protons, electrons, and neutrons in them. Example: Gold and Mercury

26 Counts the number of protons in an atom
Atomic Number, Z Counts the number of protons in an atom

27 Atomic Number on the Periodic Table
11 Na Atomic Number Symbol

28 All atoms of an element have the same number of protons
11 Na 11 protons Sodium

29 Learning Check State the number of protons for atoms of each of the following: A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons C. Barium 1) 137 protons 2) 81 protons 3) 56 protons

30 Counts the number of protons and neutrons in an atom
Mass Number, A Counts the number of protons and neutrons in an atom Mass Number, A = p + n n = A - p

31 Atomic Symbols Show the mass number and atomic number
Give the symbol of the element mass number 23 Na sodium-23 atomic number 11

32 Number of Electrons Number of protons = Number of electrons
An atom is neutral The net charge is zero Number of protons = Number of electrons + 2 + (-2) = 0 Atomic Number =Number of protons Atomic number = Number of electrons

33 Subatomic Particles in Some Atoms
O P Zn 8 p+ 8 n 8 e- 15 p+ 16 n 15 e- 30 p+ 35 n 30 e-

34 Subatomic Particles in Some Atoms
O P Zn 8 p+ 8 n 8 e- 15 p+ 16 n 15 e- 30 p+ 35 n 30 e-

35 What happens when atoms losses electrons?
When Na losses 1 electron? 11 p+ 11 e- 2311Na+ 2311Na +11 -10 1 11 p+ 11 e- 12 n 11 p+ 10 e- 12 n

36 What happens when atoms gains electrons?
When Cl gains 1 electron? 17 p+ 17 e- 3517Cl- 3517Cl +17 - 18 - 1 17 p+ 17 e- 18 n 17 p+ 18 e- 18 n

37 What happens when atoms gains electrons?
When O gains 2 electron? 8 p+ 8 e- 168O 168O + 8 - 10 - 2 8 p+ 8 e- 8 n 8 p+ 10 e- 8 n

38 Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35Cl 37Cl chlorine chlorine - 37 17 p+ 18 n 17 e- 17 p+ 20 n 17 e-

39 Learning Check 6 6 6 #p _______ _______ _______
Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C C 14C #p _______ _______ _______ #n _______ _______ _______ #e _______ _______ _______ 6 6 7 6 8

40 Learning Check An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom 1) 30 2) 35 3) 65 B. Number of neutrons in the zinc atom C. What is the mass number of a zinc isotope with 37 neutrons? 1) 37 2) 65 3) 67

41 Learning Check Write the atomic symbols for atoms with the following: A. 8 p+, 8 n, 8 e- ___________ B. 17p+, 20n, 17e- ___________ C. 47p+, 60 n, 47 e- ___________ 16O 8 37Cl 17 107Ag 47

42 Atomic Mass on the Periodic Table
11 Na 22.99 Atomic Number Symbol Atomic Mass

43 Atomic Mass Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.

44 Example of an Average Atomic Mass
Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine. 35 x 75.5 = x 24.5 = 9.07


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