Chapter 2 Lecture General Organic and Biological Chemistry

Chapter 2 Lecture General, Organic, and Biological Chemistry: An Integrated Approach Chapter 2 Laura Frost, Todd Deal and Karen Timberlake Atoms and Radioactivity by Richard Triplett © 2011 Pearson Education, Inc. Chapter 2

Chapter Outline 2. 1 Atoms and Their Components 2. 2 Atomic Number and Mass Number 2. 3 Isotopes and Atomic Mass 2. 4 Counting Atoms: The Mole 2. 5 Electron Arrangements 2. 6 Radioactivity and Radioisotopes 2. 7 Nuclear Equations and Radioactive Decay 2. 8 Radiation Units and Half-Lives 2. 9 Medical Applications for Radioisotopes © 2011 Pearson Education, Inc. Chapter 2 2

2. 1 Atoms and Their Components Subatomic Particles • An atom is the smallest part of an element. • An atom is made up of three subatomic particles: 1. Electron 2. Proton 3. Neutron • • • An electron is located outside the nucleus of the atom. A proton is located in the nucleus of the atom. A neutron is located in the nucleus of the atom. © 2011 Pearson Education, Inc. Chapter 2 3

2. 1 Atoms and Their Components, Continued Overall charge on an atom is zero

2. 1 Atoms and Their Components, Continued Structure of an Atom • The nucleus is very compact. It contains all the protons and neutrons. • Analogy: If an atom were the size of an enclosed football arena, the nucleus would be about the size of a pea on the 50 -yard line with the electrons occupying the space within the enclosed arena. © 2011 Pearson Education, Inc. Chapter 2 5

2. 1 Atoms and Their Components, Continued • An electron cloud is a space occupied by the electrons. Electrons are constantly moving about this space. • Electrons contribute very little to the mass of an atom. • The majority of the mass of an atom is located in the nucleus and is a result of the relative mass of protons and neutrons. © 2011 Pearson Education, Inc. Chapter 2 6

2. 1 Atoms and Their Components, Continued • The atomic mass unit, or amu, is a unit used by chemists to identify the mass of an atom. • A proton and a neutron have the same mass, so each is defined as weighing 1 amu. • Amu is defined as one-twelfth of a carbon atom containing six protons and six neutrons. Therefore, a carbon atom would be 12 amu. © 2011 Pearson Education, Inc. Chapter 2 7

2. 2 Atomic Number and Mass Number Atomic Number • An atomic number indicates the number of protons in an atom. • The atomic number is located at the top of the element block above the elemental symbol. © 2011 Pearson Education, Inc. Chapter 2 8

2. 2 Atomic Number and Mass Number, Continued • All atoms of an element contain the same number of protons. • All atoms are neutral and therefore, the number of protons equals the number of electrons. Mass Number • To determine the number of neutrons in an atom, we must look at the mass number. © 2011 Pearson Education, Inc. Chapter 2 9

2. 2 Atomic Number and Mass Number, Continued • The mass number, located below the elemental symbol in the element block of the periodic table, is the number of protons plus the number of neutrons. Mass number = number of protons + number of neutrons © 2011 Pearson Education, Inc. Chapter 2 10

2. 2 Atomic Number and Mass Number, Continued © 2011 Pearson Education, Inc. Chapter

2. 2 Atomic Number and Mass Number, Continued • If the mass number and atomic number for a given atom is known, one can determine the number of subatomic particles present. • Symbolic notation is a method used to represent an atom’s atomic symbol, mass number, and atomic number. © 2011 Pearson Education, Inc. Chapter 2 12

2. 3 Isotopes and Atomic Mass • Most atoms of carbon found in nature have a mass number of 12, a few have a mass number of 13, and even fewer have a mass number of 14. • All of these must have the same number of protons to be considered carbon atoms. • The different mass numbers of these carbon atoms are due to a difference in the number of protons. © 2011 Pearson Education, Inc. Chapter 2 13

2. 3 Isotopes and Atomic Mass, Continued • Isotopes are atoms of the same element that have the same number of protons, but different number of neutrons. They have different mass numbers. • Isotopes can be written in symbolic notation as: • Isotopes can also be written by stating the element name followed by the mass number. For example, carbon-12, carbon-13, and carbon-14. © 2011 Pearson Education, Inc. Chapter 2 14

2. 3 Isotopes and Atomic Mass, Continued Atomic Mass • Identification of the common isotope found in an atom is determined from the periodic table. • Carbon has three main isotopes: 1. Carbon-12 2. Carbon-13 3. Carbon-14 • • Review of the periodic table shows the average atomic mass of carbon to be 12. 01 amu. This indicates that the major isotope for carbon is carbon-12. Atomic mass is the average atomic mass weighted for all isotopes of a particular element. © 2011 Pearson Education, Inc. Chapter 2 15

2. 3 Isotopes and Atomic Mass, Continued © 2011 Pearson Education, Inc. Chapter 2

2. 4 Counting Atoms: The Mole • How are atoms counted? • Chemists use a unit called a mole, which relates the mass of an element in grams to the number of atoms it contains. • Molar mass represents the number of grams in one mole of an element and is numerically equal to the atomic mass of the element. • For example, 1 mole of carbon atoms has a molar mass of 12. 01 grams. This can be expressed as 12. 01 g/mole. © 2011 Pearson Education, Inc. Chapter 2 17

2. 4 Counting Atoms: The Mole, Continued • The number of atoms in 1 mole is defined as 602, 000, 000, 000. • Chemists use scientific notation to handle such huge numbers. • The number of atoms in 1 mole can be represented in scientific notation as 6. 02 x 1023 atoms. © 2011 Pearson Education, Inc. Chapter 2 18

2. 4 Counting Atoms: The Mole, Continued Math Matters: Scientific Notation • The general form for scientific notation is C x 10 n where C is called the coefficient and is a number between 1 and 10 and n is the exponent indicating the number of places applying to the coefficient. • A positive coefficient indicates a number greater than 1, and a negative number indicates a number less than 1. © 2011 Pearson Education, Inc. Chapter 2 19

2. 4 Counting Atoms: The Mole, Continued • Only significant figures are shown in scientific notation. • For example, the scientific notation for 3060000 expressed with three significant figures would be 3. 06 x 106, and 0. 000306 would be expressed as 3. 06 x 10 -4. © 2011 Pearson Education, Inc. Chapter 2 20

2. 4 Counting Atoms: The Mole, Continued • Table 2. 3 shows the relationship

2. 4 Counting Atoms: The Mole, Continued Avogadro’s Number • Avogadro’s number (N) is the number of atoms present in 1 mole of atoms. 6. 02 x 1023 atoms = 1 mole of atoms OR N = 6. 02 x 1023 particles/mole • One mole of anything will have 6. 02 x 1023 particles. So 1 mole of eggs will have 6. 02 x 1023 eggs just as 1 mole of carbon will have 6. 02 x 1023 atoms. © 2011 Pearson Education, Inc. Chapter 2 22

2. 5 Electron Arrangements • Electrons of an atom move about the nucleus in an area known as an electron cloud. • Electrons possess energy because they are constantly moving. • Electrons are found in distinct energy levels based on the amount of energy they possess. • Electrons in the same energy level possess similar energies. © 2011 Pearson Education, Inc. Chapter 2 23

2. 5 Electron Arrangements, Continued • Electrons occupy the lowest energy level, first which is closet to the nucleus. • The maximum number of electrons in any energy level can be calculated by the formula 2 n 2, where n is the number of energy level. © 2011 Pearson Education, Inc. Chapter 2 24

2. 5 Electron Arrangements, Continued • The table below shows the electron arrangement of

2. 5 Electron Arrangements, Continued • Elements with the same number of electrons in their highest energy level are in the same group. • The highest energy level containing electrons is known as the valence shell and the electrons are known as the valence electrons. • Valence electrons are furthest from the nucleus and are the electrons responsible for the chemical reactivity of elements. © 2011 Pearson Education, Inc. Chapter 2 26

2. 5 Electron Arrangements, Continued • The group number for an element represents the number of valence electrons each element in the group contains. For example, Group 1 A elements contain one valence electron, Group 2 A elements contain two valence electrons, and so on. • The period number is the outermost energy level containing valence electrons. For example, H and He in Period 1 have their electrons in energy level 1, Period 2 elements have valence electrons in energy level 2, and so on. © 2011 Pearson Education, Inc. Chapter 2 27

2. 6 Radioactivity and Radioisotopes • When energy is given off spontaneously from the nucleus of an atom, it is called nuclear radiation. • Radiation comes in many different types and forms. Cosmic radiation is a natural radiation. It is a major source of radiation to which humans are exposed. • Microwave radiation is an example of humanmade radiation. © 2011 Pearson Education, Inc. Chapter 2 28

2. 6 Radioactivity and Radioisotopes, Continued • Spontaneously emitted radiation from the nucleus of an element is called radioactivity. • Some isotopes of elements are radioactive and are called radioisotopes. © 2011 Pearson Education, Inc. Chapter 2 29

2. 6 Radioactivity and Radioisotopes, Continued Radioisotopes are used for imaging and for diagnosing

2. 6 Radioactivity and Radioisotopes, Continued • Not all naturally occurring radioisotopes are radioactive because they have a stable nucleus. • Isotopes that are not stable become stable by spontaneously emitting radiation from their nuclei. This process is called radioactive decay. © 2011 Pearson Education, Inc. Chapter 2 31

2. 6 Radioactivity and Radioisotopes, Continued Types of Radiation • There are three main types of radiation particles: 1. An alpha particle (α) is a positively charged particle with a 2+ charge. It is also known as a helium particle. 2. A beta particle (β) is a negatively charged particle with a 1 - charge. It is the same as an electron. 3. A gamma particle(γ) is a neutral particle. © 2011 Pearson Education, Inc. Chapter 2 32

2. 6 Radioactivity and Radioisotopes, Continued Types of Radiation Symbols for each type of radiation are shown in the following table. Two additional types of radiation shown are the positron and the neutron. © 2011 Pearson Education, Inc. Chapter 2 33

2. 6 Radioactivity and Radioisotopes, Continued Biological Effect of Radiation • Radiation emissions are dangerous to living organisms because when emitted they interact with any atoms they contact. • Alpha particles, beta particles, and gamma rays are know as ionizing radiation. When they come in contact with atoms, they cause the atoms to lose electrons, which leaves species that are reactive and unstable. © 2011 Pearson Education, Inc. Chapter 2 34

2. 6 Radioactivity and Radioisotopes, Continued Not all ionizing radiation has the same amount of energy, so some are more dangerous than others. This is due to the penetrating power of higher energy radiation like gamma rays. © 2011 Pearson Education, Inc. Chapter 2 35

2. 7 Nuclear Equations and Radioactive Decay • The general form of a nuclear decay equation is: Radioactive nucleus undergoing decay → new nucleus formed + radiation emitted • Uranium-238, a radioactive isotope, emits alpha particles when it undergoes radioactive decay. The nuclear equation for this type of decay is: © 2011 Pearson Education, Inc. Chapter 2 36

2. 7 Nuclear Equations and Radioactive Decay, Continued • In a nuclear decay equation, the mass number of the reactant (238) must equal the total mass number of the products (234 + 4). • In a nuclear decay equation, the atomic number of the reactant (92) must equal the sum of the atomic numbers of the products (90 + 2). © 2011 Pearson Education, Inc. Chapter 2 37

2. 7 Nuclear Equations and Radioactive Decay, Continued Alpha Decay • The alpha particle is a product of alpha decay. • To solve an alpha particle decay equation, remember that the mass and atomic numbers must be equal on both sides of the equation. Then you can look at the periodic table for the element that has the appropriate atomic number. © 2011 Pearson Education, Inc. Chapter 2 38

2. 7 Nuclear Equations and Radioactive Decay, Continued Beta Decay • The high energy electron is emitted from an isotope during beta decay. Remember this particle has no mass and a negative charge. • The product isotope will have the same mass as the reactant, but its atomic number will increase by 1 since the beta particle is negatively charged. © 2011 Pearson Education, Inc. Chapter 2 39

2. 7 Nuclear Equations and Radioactive Decay, Continued Gamma Decay Gamma decay is only energy and will not result in a change of the mass number or atomic number of the product. Remember gamma rays have no mass and no charge. © 2011 Pearson Education, Inc. Chapter 2 40

2. 7 Nuclear Equations and Radioactive Decay, Continued Producing Radioactive Isotopes • Some isotopes are produced in the laboratory by bombarding stable isotopes with fast moving alpha particle, protons, or neutrons. • Some of these isotopes are important in medicine. Technetium-99 m is an example and is produced as follows: © 2011 Pearson Education, Inc. Chapter 2 41

2. 8 Radiation Units and Half-Lives Radioactivity Units • The activity of a radioactive sample is measured in disintegrations/second. • The unit of measuring disintegrations is called the curie (Ci). • The activity of a radioactive isotope defines how quickly it emits radiation. A curie is a unit of activity equal to 3. 7 x 1010 disintegrations/second. © 2011 Pearson Education, Inc. Chapter 2 42

2. 8 Radiation Units and Half-Lives, Continued Half-Life • Each radioactive isotope emits radiation at a different rate. • Emission of radiation can be measure by its half-life. • The half-life of an isotope is the time it takes for 50% of the atoms in a radioactive sample to decay. © 2011 Pearson Education, Inc. Chapter 2 43

2. 8 Radiation Units and Half-Lives, Continued Naturally occurring radioisotopes tend to have long half-lives. Medically important radioisotopes have shorter half-lives to allow radioactivity to be quickly eliminated from the body. © 2011 Pearson Education, Inc. Chapter 2 44

2. 8 Radiation Units and Half-Lives, Continued • The amount of radioactivity left after a given amount of time has passed can be determined if we know the half-life of the sample. • For example, radioactive iodine-131 has a halflife of 8 days. If a dose of 200 µC is given to a patient, how much activity is left after 32 days? • First, we have to know how many half-lives are in 32 days. © 2011 Pearson Education, Inc. Chapter 2 45

2. 8 Radiation Units and Half-Lives, Continued • Now that we have determined 4 half-lives have passed, we can determine how much iodine-131 radioactivity is left after 32 days. © 2011 Pearson Education, Inc. Chapter 2 46

2. 9 Medical Applications for Radioisotopes • Radioisotopes with short half-lives are used in nuclear medicine in order to expose patients with the smallest doses of radiation in the shortest period of time. • Isotopes are used to provide images of specific body tissues. • Iodine, used only by the thyroid gland, can be used to obtain an image of the thyroid gland because radioactive iodine will accumulate in this gland. © 2011 Pearson Education, Inc. Chapter 2 47

2. 9 Medical Applications for Radioisotopes, Continued • A radioisotope used to image specific body tissue is called a tracer. • Iodine-123 is used to diagnose thyroid function. © 2011 Pearson Education, Inc. Chapter 2 48

2. 9 Medical Applications for Radioisotopes, Continued • Radioisotopes are also used to destroy diseased and cancerous tissues. • Emissions from radioactive sources can be used without injecting the patient with radioactive material. • Cobalt-60 can be aimed directly at a cancerous tumor to destroy tissue that affects the diseased area. © 2011 Pearson Education, Inc. Chapter 2 49

Chapter Summary 2. 1 Atoms and Their Components • Atoms consists of three subatomic particles: 1. Electrons (negatively charged) 2. Protons (positively charged) 3. Neutrons (neutral charge) • Mass of an atom is expressed as the atomic mass unit (amu). © 2011 Pearson Education, Inc. Chapter 2 50

Chapter Summary, Continued 2. 2 Atomic Number and Mass Number • Atomic number of an atom is equal to the number of protons in the atom. • Mass number of an atom is equal to the sum of the protons and neutrons in the atom. © 2011 Pearson Education, Inc. Chapter 2 51

Chapter Summary, Continued 2. 3 Isotopes and Atomic Mass • Isotopes of an atom contain the same number of protons, but different number of neutrons so they have a different mass number. • The mass of an element on the periodic table is the average mass of all its isotope. © 2011 Pearson Education, Inc. Chapter 2 52

Chapter Summary, Continued 2. 4 Counting Atoms: The Mole • Chemists use a unit called the mole to relate the number of atoms to an element’s mass. • Avogadro’s number indicates that 1 mole of an element is equivalent to 6. 02 x 1023 atoms. • The atomic mass unit (amu) is equivalent to the number of grams in one mole of atoms, which is known as the molar mass. © 2011 Pearson Education, Inc. Chapter 2 53

Chapter Summary, Continued 2. 5 Electron Arrangements • Electrons exist in distinct energy levels. • Energy levels are referred to as levels n = 1, 2, 3, and so on. • Maximum number of electrons in an energy level is equal to 2 n 2. © 2011 Pearson Education, Inc. Chapter 2 54

Chapter Summary, Continued 2. 6 Radioactivity and Radioisotopes • Energy given off spontaneously from the nucleus of an atom is called nuclear radiation. This process is referred to as radioactive decay. • Three forms of radioactive decay are: 1. Alpha radiation 2. Beta radiation 3. Gamma radiation • Large doses of ionizing radiation cause tissue damage. © 2011 Pearson Education, Inc. Chapter 2 55

Chapter Summary, Continued 2. 7 Nuclear Equations and Radioactive Decay • Radioactive decay can be represented in the form of a nuclear decay equation. • The number of protons and the mass number in the reactant is equal to the number of protons and mass number found in the products. © 2011 Pearson Education, Inc. Chapter 2 56

Chapter Summary, Continued 2. 8 Radiation Units and Half-Lives • Radioactive decay is measured in disintegrations/second. ’ • The curie (Ci) is the standard unit for measuring radioactive decay. • A curie is defined as 3. 7 x 1010 disintegrations/sec. • Half-life is the amount of time it takes for 50% of the radiation of a sample to decay. © 2011 Pearson Education, Inc. Chapter 2 57

Chapter Summary, Continued 2. 9 Medical Applications for Radioisotopes • Radioisotopes are used in imaging body tissues. • Radioisotopes are used in small doses to diagnose disease states. • Radioisotopes are used in high doses to destroy tumors and cancerous tissue. © 2011 Pearson Education, Inc. Chapter 2 58