4.3 Distinguishing Among Atoms > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 4 Atomic Structure 4.1 Defining the Atom 4.2 Structure of the Nuclear Atom 4.3 Distinguishing Among Atoms

4.3 Distinguishing Among Atoms > 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Number and Mass Number What makes one element different from another? Atomic Number and Mass Number  Elements are different because they contain different numbers of protons. An element’s atomic number is the number of protons in the nucleus of an atom of that element. The atomic number identifies an element.

4.3 Distinguishing Among Atoms > 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Number and Mass Number Mass Number The total number of protons and neutrons in an atom is called the mass number.  If you know the atomic number and mass number of an atom of any element, you can determine the atom’s composition… the # of p, n and e. Number of neutrons = mass number – atomic number

4.3 Distinguishing Among Atoms > 4 Mass Number Mass Number = Protons + Neutrons Always a whole number! (Round the value under the symbol to the closest whole number) NOT listed on the Periodic Table! Nucleus Electrons Nucleus Neutron Proton Carbon-12 Protons 6 Neutrons 6 Electrons 6 e-

4.3 Distinguishing Among Atoms > 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Number and Mass Number Remember that atoms are electrically neutral. Thus, the number of electrons (negatively charged particles) must equal the number of protons (positively charged particles). Atoms of the First Ten Elements NameSymbolAtomic number ProtonsNeutronsMass number Electrons BoronB CarbonC NitrogenN OxygenO FluorineF NeonNe

4.3 Distinguishing Among Atoms > 6 Atomic Notation: A E Z Atomic Number Mass Number Element Symbol Z E XXX.XX (Av. Atomic Mass) Periodic Table Info

4.3 Distinguishing Among Atoms > 7 Atomic Notation Practice If an element has an atomic number of 23 and a mass number of 51, determine the… –number of protons –number of neutrons –number of electrons –Write the Atomic Notation V = 23 = 28 = 23

4.3 Distinguishing Among Atoms > 8 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What information is used to determine the composition of a neutral atom of any element? How is it used? The atomic number and mass number are needed to determine an atom’s composition. The atomic number gives the number of protons, which equals the number of electrons. The number of neutrons is the difference between the mass number and the atomic number.

4.3 Distinguishing Among Atoms > 9 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Specialized Atoms Consider three different kinds of neon atoms… what is the difference? Specialized Atoms: Isotopes Isotopes have the same number of protons but different numbers of neutrons.

4.3 Distinguishing Among Atoms > 10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Because isotopes of an element have different numbers of neutrons, they also have different mass numbers. Specialized Atoms Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons, which are the subatomic particles responsible for chemical behavior.

4.3 Distinguishing Among Atoms > 11 Specialized Atoms Mass # Atomic # Atomic Notation: Courtesy Christy Johannesson U Isotope Notation: Uranium-235  To write this isotope in atomic notation, simply write the mass number in the appropriate location & determine the #p, n and e as usual. How would things change if it was Uranium-238?

4.3 Distinguishing Among Atoms > 12 Specialized Atoms Specialized Atoms: Ions  Ions are atoms with different numbers of electrons than expected, based on atomic number.  This changes the electrical balance of an atom, so (+) and (-) signs are used. Ion is positive when electrons are lost Ion is negative when electrons are gained  Ion Notation: 235 U  To find the number of electrons, do the OPPOSITE math operation that is indicated by the charge. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved Ion Charge

4.3 Distinguishing Among Atoms > 13 Specialized Atoms Use the atomic notation box to find the… number of protons number of neutrons number of electrons Atomic number Mass number Na Sodium ion = 11 = 12 = 10 = 11 = 23

4.3 Distinguishing Among Atoms > 14 Atomic Mass Nucleus Electrons A Standard for Measuring Atomic Particles… Neutron Proton Carbon-12 Protons 6 Neutrons 6 Electrons 6 Carbon-12 is used as a standard because it has exactly 12 atomic mass units. An atomic mass unit (amu) is defined as one- twelfth of the mass of a carbon-12 atom. Therefore, the standard mass of a single proton or a single neutron is about one-twelfth of 12 amu, or about 1 amu.

4.3 Distinguishing Among Atoms > 15 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Mass Average Atomic Mass How do you calculate the average atomic mass of an element? In nature, most elements occur as a mixture of two or more isotopes. Each isotope of an element has a fixed mass and a natural percent abundance.

4.3 Distinguishing Among Atoms > 16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Interpret Data Natural Percent Abundance of Stable Isotopes of Some Elements NameSymbol Natural Percent Abundance Mass (amu)Atomic mass Hydrogen HHHHHH negligible Helium He Carbon CCCC Oxygen OOOOOO Chlorine Cl

4.3 Distinguishing Among Atoms > 17 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Mass The average atomic mass reflects both the mass and the relative abundance (percent) of the isotopes as they occur in nature. Weighted Averages Just as your final average grade in Chem reflects the subtotal for each category and percentage that each category is worth … To calculate the atomic mass of an element: 1.) Turn the % abundance into a decimal value 2.) Multiply the mass of each isotope by the decimal value & note products (subtotals) 3.) Add the subtotals & round to the hundredths place

4.3 Distinguishing Among Atoms > 18 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Mass Carbon has two stable isotopes: carbon-12, which has a natural abundance of %, and carbon-13, which has a natural abundance of 1.11 %. The mass of carbon-12 is amu; the mass of carbon-13 is amu. The atomic mass of carbon is calculated as follows: Atomic mass of carbon = ( amu x ) amu x ) = ( amu) + (0.144 amu) = amu Calculating Atomic Mass 1) Turn the percent into decimal form ! 2) Multiply the atomic mass by the decimal value 3) Add each product together to obtain the AAM

4.3 Distinguishing Among Atoms > 19 Average Atomic Mass Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Oxygen OOOOOO ?? NameSymbol Natural Percent Abundance Mass (amu)Atomic mass

4.3 Distinguishing Among Atoms > 20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 4.5 Evaluate: Does the result make sense? The calculated value is closer to the mass of the more abundant isotope, as would be expected.

4.3 Distinguishing Among Atoms > 21 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Understanding Relative Abundance of Isotopes If the average atomic mass is closer to a given mass number, that isotope must be more abundant than the others. Ex: The average atomic mass of copper is amu. Which of copper’s two isotopes is more abundant: copper-63 or copper- 65? Sample Problem 4.4

4.3 Distinguishing Among Atoms > 22 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.  Compare the atomic mass to the mass of each isotope. The atomic mass of amu is closer to 63 than it is to 65. Because the atomic mass is a weighted average of the isotopes, copper-63 must be more abundant than copper-65. Sample Problem 4.4 1

4.3 Distinguishing Among Atoms > 23 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Why is the atomic mass of an element usually not a whole number? The atomic mass of an element is usually not a whole number because it is a weighted average of the masses of the naturally occurring isotopes of the element.

4.3 Distinguishing Among Atoms > 24 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Key Concepts Elements are different because they contain different numbers of protons. Because isotopes of an element have different numbers of neutrons, they also have different mass numbers. To calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.

4.3 Distinguishing Among Atoms > 25 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Key Equation number of neutrons = mass number – atomic number Average atomic mass: 1.Convert % to decimal equivalent 2.Multiply decimal equivalent by amu or mass number, as given. 3.Add subtotals. Round to nearest hundredth place.

4.3 Distinguishing Among Atoms > 26 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary Terms atomic number: the number of protons in the nucleus of an atom of an element mass number: the total number of protons and neutrons in the nucleus of an atom isotopes: atoms of the same element that have the same atomic number but different atomic masses due to a different number of neutrons

4.3 Distinguishing Among Atoms > 27 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary Terms atomic mass unit (amu): a unit of mass equal to one-twelfth the mass of a carbon-12 atom atomic mass: the weighted average of the masses of the isotopes of an element

4.3 Distinguishing Among Atoms > 28 Thank you for your attention! Complete Pkt. Pages for next class! Review for QOD next class! Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.