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Unit 2: Atomic Structure and Nuclear Chemistry

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1 Unit 2: Atomic Structure and Nuclear Chemistry

2 Chapter 4 Atomic structure

3 4.1 Defining the atom

4 Atom Smallest particle of an element that retains the properties of the element

5 What discoveries lead to the Atomic Theory?
Democritus – Father of the Atom 400 B.C. Atomos: Greek for “indivisible” Philosophy – not Science No measured or experimental support

6 John Dalton – Father of the Modern Atom
1808 All elements are composed of tiny indivisible particles called atoms. Atoms of the same element are identical. Atoms of different elements are different. Atoms combine in simple whole number ratios. Atoms of one element are never changed to atoms of another element during chemical reactions.

7

8 Sizing up the Atom What instruments are used to observe individual atoms? Despite their small size, atoms are observable with scanning electron microscopes. Radii fall between 5 x m – 2 x m 50 – 200 pm (picometer) Example 1 Example 2

9 4.2 structure of the nuclear atom

10 Subatomic Particles Electrons Protons Neutrons Nucleus

11 Electrons J.J. Thomson – 1897 Discovered the electron using a cathode ray tube (CRT) Negatively charged particles

12 Protons E. Goldstein – 1886 Discovered the proton by careful observations of another ray in the Cathode Ray tube Positively charged particles

13 Neutrons James Chadwick – 1932 Discovers the neutron
Neutrons are the “glue” that holds the nucleus of the atom together.

14 Subatomic Particles Electrons Protons Neutrons Nucleus Atomic Charges:
Neutral atom: Equal # of Protons & Electrons Element dependant on # of Protons Number of Electrons can change – creates charged atoms (called IONs)

15 “Plum Pudding Model” Electrons evenly distributed in an atom filled with uniform positive chare First Atomic Model Example

16 The Atomic Nucleus Ernest Rutherford – 1911
Using the “Gold Foil” experiment, Rutherford determines: An atom is mostly space. There is a nucleus in the middle of the atom containing the protons The electrons orbit a large distance away from the nucleus. Proposes a “Solar System” or “Orbital” model of the atom Cute Summary of History

17 Atomic Particle Summary
Name Symbol Charge Mass (amu) Electron e- -1 Practically 0 proton p+ +1 1 neutron n

18 4.3 distinguishing among atoms

19 Atomic Number Number of protons in the nucleus of an atom
Each element has a unique atomic number. The number of electrons usually equals the atomic number in a neutral atom, but doesn’t need to.

20 Mass Number The total number of protons and neutrons in an atom
Atoms of the same element can have different mass numbers Mass number is NOT normally found on the periodic table Shorthand notation Example: Gold

21 Number of Neutrons Number of Neutrons = Mass # - Atomic #

22 Sample Problem 4.2 How many protons, electrons, and neutrons are in each atom?

23 Isotopes Atoms with the same number of protons, but different numbers of neutrons Isotopes of an element have the same atomic number, but different mass numbers Nuclear Symbol or Isotopic symbol: shows number of protons & mass number of an atom

24 Nuclear or Isotopic Symbols
Examples Carbon -12 Carbon -14 Nuclear Symbol: Name - Mass # Isotopic Symbols Mass Number Atomic Number

25 Atomic Mass: A Weighted Average
Atomic Mass Unit: (amu) Unit of mass for atomic nuclei 1 amu = 1/12 the mass of Carbon-12 Atomic Mass: Weighted average mass of all the naturally occurring isotopes in a sample of an element

26 Sample Problem 4.5 Element X has two naturally occurring isotopes. The isotope with a mass of amu has a relative abundance of 19.91%. The isotope with a mass of amu has a relative abundance of %. Calculate the atomic mass of element X.

27 Chapter 25: Nuclear Chemistry
Regular Chemistry Nuclear Chemistry Deals with the arrangement of atoms to form compounds Never about the changing of the nucleus Elements NEVER change to other Elements Deals with the decay of unstable isotopes to form a stable nucleus About the changing of the nucleus Elements CAN change to other Elements

28 25.1 Nuclear Radiation Radiation Radioactive decay: Radioisotope:
The penetrating light rays and/or particles emitted by a radioactive source Radioactive decay: The spontaneous emission of radiation by an unstable nucleus Radioisotope: An isotope that has an unstable nucleus and undergoes radioactive decay

29 High-Energy Radiation
Types of Radiation Property Alpha Beta Gamma Composition Alpha Particle (helium nucleus) Beta Particle (electron) High-Energy Radiation Symbol α β γ Charge 2+ 1- Mass (amu) 4 1/1840 Penetrating Power Low Tissue Paper (0.05 mm) Moderate Skin or Foil (4 mm) Very high Lead/Concrete Entire body

30 Radiation Examples Alpha Radiation Beta Radiation Gamma Radiation
Uranium-238 to Thorium-234 Beta Radiation Carbon-14 to Nitrogen-14 Summary: What has really happened? Gamma Radiation Thorium-230 to Radium-226 Thorium-234 to Protactinium-234

31 25.2 Nuclear Transformations
Why does the nucleus stay together? Strong Nuclear Force Short range, attractive force that acts among nuclear particles Neutrons and Protons attract one another! Much stronger than electrical or gravitational force Electromagnetic Force Repulsive force between protons. Tries to pull the nucleus apart. Stable Nucleus Correct balance of Strong Nuclear & Electromagnetic Forces Correct p+ to n ratio MOST ATOMS ARE STABLE!!

32 Band of Stability 1:1 Ratio Line Band of Stability

33 Most common transformation particles
Radiation Name Symbol & Iso. Notation Charge Mass Alpha particle α, +2 ~4 amu Beta particle β -1 1/1840amu (nothing) Gamma radiation γ “none” Positron β+ +1 Neutron n ~1 amu Proton p+

34 Nuclear Stabilization Equations
Alpha emission: Uranium-238 Beta emission: Carbon-14 Positron emission: Oxygen-15 Neutron emission: Silver-107

35 Additional Example Beta Absorption of Krypton - 81

36 Transformation Examples
Silicon-27  ______ + β Bismuth-214  _____ + α Aluminum-27 + α  Silicon-30 + ____

37 25.3 Fission and Fusion Fission: Fusion:
Large nucleus breaking down into smaller nuclei Fusion: Smaller nuclei combining to larger nucleus

38 Youtube: Nuclear Reaction Overview

39 10/18 Warm-up Watch the following youtube video on carbon dating. Carbon dating video Watch the following youtube videos on the strong and weak nuclear force. Video 1 Video 2

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