Topic 2.1: Atomic Structure Honors Chemistry Mrs. Peters 1

Atomic Structure 2.1: The nuclear atom EI: The mass of the atoms is concentrated in its minute, positively charged nucleus. NOS: 1.Evidence and improvements in instrumentation – alpha particles were used in the development of the nuclear model of the atom that was first proposed by Rutherford. (1.8) 2.Paradigm shifts- the subatomic particle theory of matter represents a paradigm shift in science that occurred in the late 1800s (2.3) 2

Atomic Structure 2.1: The nuclear atom Understandings: 1.Atoms contain a positively charged dense nucleus composed of protons and neutrons (nucleons) 2.Negatively charged electrons occupy the space outside the nucleus 3.The mass spectrometer is used to determine the relative atomic mass of an element from its isotopic composition. 3

Atomic Structure 2.1: The nuclear atom Applications and Skills: 1.Use of the nuclear symbol notation A Z X to deduce the number of protons, neutrons, and electrons in atoms and ions. 2.Calculations involving non-integer relative atomic masses and abundance of isotopes from given data, including mass spectra. 4

NOS: Paradigm Shift History behind Atomic Theory Democritus ( 420 BCE ) first proposed the idea that matter may be made up of small, indivisible particles called atoms. Aristotle ( BCE) Greek philosopher; matter composed of earth, air, fire, water. This view dominated thought until 17th century 5

NOS: Paradigm Shift History behind Atomic Theory Atomism developed in Chinese & Arabic cultures during the Dark Ages in Europe. John Dalton ( ) was the first to base atomic theory on scientific evidence. 6

NOS: Paradigm Shift Dalton’s Atomic Theory Elements are made of tiny particles called atoms. All atoms of a given element are identical. The atoms of a given element are different from those of any other element. 7

NOS: Paradigm Shift Dalton’s Atomic Theory Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative number of types of atoms. Atoms cannot be created, nor divided into smaller particles, nor destroyed in the chemical process. A chemical reaction simply changes the way atoms are grouped together. 8

NOS: Paradigm Shift Evidence for sub-atomic particles 1897: J.J. Thomsen: Cathode Ray Tube Evidence for electrons: Bent a stream of rays originating from the negative electrode (cathode). Stream of particles with mass & negative charge. 9

NOS: Paradigm Shift Evidence for sub-atomic particles 1909: Ernest Rutherford: Gold Foil Evidence for protons & nucleus: Alpha particles deflected passing through gold foil 10

NOS: Paradigm Shift Evidence for sub-atomic particles 1932: James Chadwick: Beryllium Evidence for neutrons: Alpha particles caused beryllium to emit rays that could pass through lead but not be deflected, 11

U1. and U2. Atomic Structure Sub-Atomic Particles: Proton: Located in the nucleus Relative charge of +1 Relative mass of 1 amu Neutron: Located in the nucleus Relative charge of 0 Relative mass of 1 amu bp.blogspot.com

U1. and U2. Atomic Structure Sub-Atomic Particles Electron: Located in cloud surrounding the nucleus Relative charge of –1 Relative mass of amu bp.blogspot.com

2.1.1 State the position of protons, neutrons and electrons in the atom State the relative masses and relative charges of protons, neutrons and electrons LocationChargeMassSymbol Proton Electron Neutron 14

U1. and U2. Atomic Structure Nucleus consists of protons and neutrons with the electrons surrounding the nucleus. In a neutral atom, the #protons = # electrons. 15

A1. Nuclear Symbol Notation Atomic Number (Z) The atomic number is the number of protons in the nucleus. It determines the identity of an atom. All calcium atoms have 20 protons in the nucleus All lead atoms have 82 protons in the nucleus 1.What are the atomic numbers for C, H, O, N & P? 2.How many protons does each atom above have? 16

A1. Nuclear Symbol Notation Atomic Number (Z) It also tells us the number of electrons in a neutral atom A neutral sodium atom contains 11 protons and 11 electrons A neutral bromine atom contains 35 protons and 35 electrons 1.How many electrons do neutral atoms of C, H, O, N & P have? 17

A1. Nuclear Symbol Notation Mass Number (A) It is not practical to measure the masses of atoms in grams due to their small size. Scientists devised a measurement called atomic mass units (amu). 18

A1. Nuclear Symbol Notation Mass Number (A) Protons have a mass of 1 amu Neutrons have mass of 1 amu Electrons have mass of 0 amu. Mass Number = # protons + # neutrons 19

A1. Nuclear Symbol Notation Mass Number (A) If… Mass Number = # protons + # neutrons Then… # neutrons = Mass Number – # protons 20

A1. Nuclear Symbol Notation SUMMARY OF SUBATOMIC PARTICLES IN A NEUTRAL ATOM # protons = atomic number (Z) # electrons = # protons = atomic number (Z) # neutrons = mass number (A) – # protons OR mass number (A) – atomic number (Z) 21

A1. Nuclear Symbol Notation Atomic Name: Element Name - A (mass number) Ex: Carbon-12 Nuclear Symbol: 22 X A Z Element Symbol Mass Number (Protons + Neutrons) Atomic Number

How to read the Periodic Table 23 Lithium 3 Li 6.94 Element Name Atomic Number Element Symbol Mass Number

A1. Deduce the symbol given its mass number and atomic number Consider an atom that has an atomic number of 29 and a mass number of 63. What is its name and symbol? Name: Nuclear Symbol: 24

A. Deduce the symbol given its mass number and atomic number Consider an atom that has an atomic number of 29 and a mass number of 63. What is its name and symbol? Atomic number of 29 identifies it as copper Name: Copper-63 Nuclear Symbol: 63 Cu 29 25

A1. Deduce the symbol given its mass number and atomic number Consider an atom that has A=32 and Z=16. What is its name and symbol? Name: Nuclear Symbol: 26

A1. Deduce the symbol given its mass number and atomic number Consider an atom that has A=32 and Z=16. What is its name and symbol? Z=16 identifies it as sulfur Name: Sulfur-32 Symbol: 32 S 16 27

A1. Deduce the symbol given its mass number and atomic number Consider an atom that has an atomic number of 74 and a mass number of 185. What is its name and symbol? Consider an atom that has A=127 and Z=53. What is its name and symbol? 28

A1. Deduce the symbol given its mass number and atomic number Consider an atom that has an atomic number of 74 and a mass number of 185. What is its name and symbol? atomic number of 74 identifies it as tungsten Name: Tungsten-185 Symbol: 185 W 74 Consider an atom that has A=127 and Z=53. What is its name and symbol? Z=53 identifies it as iodine Name: Iodine-127 Symbol: 127 I 53 29

30 Create an Atom Choose any element with atomic number 20 or above. Write the: Element name Nuclear symbol (not JUST the 1-2 letter combo) Atomic number (Z) Atomic mass (A) Number of protons Number of neutrons (show how you determine this) Number of electrons Now draw AND LABEL your atom with the proper number of protons, neutrons and electrons, making sure that the particles are placed in the proper locations.

31 Create an Atom Choose any element with atomic number 20 or above. Now draw AND LABEL your atom with the proper number of protons, neutrons and electrons, making sure that the particles are placed in the proper locations.

Important Terms Isotope Atoms of the same element can have different numbers of neutrons, thus they will have different atomic masses. These are called isotopes of the element. These are the same element, just different numbers of neutrons, which changes the mass. 32

Important Terms Isotope Isotopes are distinguished from each other by adding the mass to the name. For example, carbon-12 and carbon-14 are both isotopes of carbon. Carbon-12 has a mass of 12, while carbon-14 has a mass of

Important Terms Isotope Example There are three isotopes of hydrogen: Hydrogen- 1 has 1 proton, 1 electron, 0 neutrons Aka protium Hydrogen- 2 has 1 proton, 1 electron, 1 neutron Aka deuterium Hydrogen- 3 has 1 proton, 1 electron, 2 neutrons Aka tritium 34

A1. Deduce protons, neutrons, and electrons in atoms and ions from the A, Z, and charge Consider a neutral atom with A=75 and Z=33. How many protons, neutrons, and electrons are in the atom. What is the name and symbol? Consider a neutral atom with A=77 and Z=33. How many protons, neutrons, and electrons are in the atom. What is the name and symbol? 35

A1. Deduce protons, neutrons, and electrons in atoms and ions from A, Z, and charge Consider a neutral atom with A=75 and Z=33. How many protons, neutrons, and electrons are in the atom. What is the name and symbol? Protons = 33Neutrons = 42Electrons = 33 Name: Arsenic-75 Symbol: 75 As 33 Consider a neutral atom with A=77 and Z=33. How many protons, neutrons, and electrons are in the atom. What is the name and symbol? Protons = 33Neutrons = 44Electrons = 33 Name: Arsenic-77 Symbol: 77 As 33 36

A1. Deduce protons, neutrons, and electrons in atoms and ions from the A, Z, and charge Consider two isotopes of carbon: carbon-12 and carbon-14. Find the A, Z, protons, neutrons, electrons, and nuclear symbols for each. 37

A1. Deduce protons, neutrons, and electrons in atoms and ions from the A, Z, and charge Consider the neutral carbon-12 atom. Find the A, Z, protons, neutrons, electrons, and symbol Name is Carbon-12 Atomic mass (A) = 12 Atomic number (Z) = 6 Protons = 6 (atomic number) Neutrons = 6 (mass – protons) Electrons = 6 (neutral atom so same as protons) Nuclear Symbol is 12 C 6 38

A1. Deduce protons, neutrons, and electrons in atoms and ions from the A, Z, and charge Consider the neutral carbon-12 atom. Find the A, Z, protons, neutrons, electrons, and symbol Name is Carbon-12 Atomic mass (A) = 12 Atomic number (Z) = 6 Protons = 6 (atomic number) Neutrons = 6 (mass – protons) Electrons = 6 (neutral atom so same as protons) Nuclear Symbol is 12 C 6 39

Define the terms mass number (A), atomic number (Z), and isotope of an element

A1. Deduce protons, neutrons, and electrons in atoms and ions from the A, Z, and charge Consider an atom that has 9 protons, 9 electrons, and 10 neutrons. What is its atomic number, atomic mass, name and symbol? 41

A1. Deduce protons, neutrons, and electrons in atoms and ions from the A, Z, and charge Consider an atom that has 9 protons, 9 electrons, and 10 neutrons. What is its atomic number, atomic mass, name, and symbol? Z=9 (atomic number = # protons) A=19 (atomic mass = protons + neutrons) Fluorine-19 (name and mass) 19 F (neutral because protons = electrons) 9 42

43 Create an Isotope For the neutral atom you already drew, determine it’s new atomic mass (add or subtract no more than 3). Write the: Isotope name (which should indicate the mass) Nuclear symbol Number of protons Number of neutrons (show how you determine this) Number of electrons Now draw the isotope version of your atom.

2.1.7 Discuss the use of radioisotopes. Radioisotopes: isotopes of elements that have become radioactive because the nucleus is unstable and breaks down spontaneously emitting radiation. Radioisotopes can occur naturally or be created artificially Examples: Carbon-14; Iodine-125; Strontium-90; Cobalt-60, Iodine

2.1.7 Discuss the use of radioisotopes. Uses of Radioisotopes Nuclear power generation Sterilization of surgical instruments Crime detection Food preservation Dating artifacts Treating and diagnosing disease 45

U3. Relative Atomic Mass Relative Atomic Mass Mass numbers (atomic mass) on the periodic table are weighted averages of the isotopes. Based on 12 C. Has 6 protons, 6 neutrons, and 6 electrons Has a relative atomic mass of exactly One amu is exactly 1/12 of the mass of a carbon-12 atom. All other isotopes are measured compared to this value. 46

U3. The Mass Spectrometer Mass Spectrometers: Instruments that measure charge-to-mass ratio of charged particles. Used to measure masses of isotopes as well as isotopic abundance 47

U3. The Mass Spectrometer How a Mass Spec Works: 1. Vaporization: sample is heated to gas state 2. Ionization: sample gas is turned into ions by blasting free electrons to knock electrons off from the gas atoms, creating positive ions 3. Acceleration: increases the speed of particles, using an electric field 48

U3. The Mass Spectrometer How a Mass Spec Works: 4. Deflection: using an electromagnet to create a magnetic field, amount of deflection depends on mass and charge of the ion (think of cars going around a corner) 5. Detection: measures both mass and relative amounts (abundance) of all the ions present 49

U3. The Mass Spectrometer Mass Spectrometer Video wp&v=lxAfw1rftIA&NR=1 wp&v=lxAfw1rftIA&NR=1 50

U3. Relative Atomic Mass A sample of neon is placed in the mass spectrometer The results show the abundance for each isotope of an element o 90.92% is neon-20 o 0.26% is neon-21 o 8.82% is neon-22 51

U3. Relative Atomic Mass Average relative atomic mass: the weighted average for all of the isotopes of a given element, based on the percent abundance of each 52

U3. Relative Atomic Mass Average relative atomic mass: the weighted average for all of the isotopes of a given element, based on the percent abundance of each Need masses of each isotopes Need abundance (percentage) of each isotope o The mass spec is used to determine these values This is the value shown on the periodic table 53

A2. Calculate non-integer relative atomic masses and abundance of isotopes from given data. Relative Atomic Mass RAM = weighted average of all the isotopes of a given element RAM = ∑ mass isotope (ab isotope ) RAM = mass 1 (ab 1 ) + mass 2 (ab 2 ) + (as many isotopes…) 54

A2. Calculate non-integer relative atomic masses and abundance of isotopes from given data. Example % = %= x.955= x.045 = = amu How to Determine Relative Atomic Mass 1. Convert the percent abundance for each isotope into decimal 2. Multiply the mass for each isotope by the abundance 3. Add all product values from step Include amu for the units of the value. 55

U3. Relative Atomic Mass 90.92% is neon % is neon % is neon-22 Average relative atomic mass: AbundanceMass x 20= x 21= x 22= = amu  amu 56

2.2.3 Calculate non-integer relative atomic masses and abundance of isotopes from given data. Three isotopes of magnesium occur in nature. Their abundances and masses, determined by mass spectrometry, are listed in the table on the right. Use this information to calculate the relative atomic mass of magnesium. Isotope% AbundanceMass (amu) 24 Mg Mg Mg

2.2.3 Calculate non-integer relative atomic masses and abundance of isotopes from given data. Three isotopes of magnesium occur in nature. Their abundances and masses, determined by mass spectrometry, are listed in the table on the right. Use this information to calculate the atomic weight of magnesium. Three isotopes: 24, 25, 26 Percentage of each isotope: Given Multiply the percent of each isotope by its mass x.7899 = amu x.1000 = amu x.1101 = amu Add these values = amu Isotope% AbundanceMass (amu) 24 Mg Mg Mg

2.2.3 Calculate non-integer relative atomic masses and abundance of isotopes from given data. Calculate the atomic weight of chromium using the following data for the percent natural abundance and mass of each isotope: 4.35% 50 Cr ( amu); 83.79% 52 Cr ( amu); 9.50% 53 Cr ( amu); 2.36% 54 Cr ( amu) 59

2.2.3 Calculate non-integer relative atomic masses and abundance of isotopes from given data. Calculate the atomic weight of chromium using the following data for the percent natural abundance and mass of each isotope: 4.35% 50 Cr ( amu); 83.79% 52 Cr ( amu); 9.50% 53 Cr ( amu); 2.36% 54 Cr ( amu) Abundance Mass x = 2.17 amu x = amu x = 5.03 amu x = amu amu 60

2.2.3 Calculate non-integer relative atomic masses and abundance of isotopes from given data. 61 Mass Spectrum of Lead

2.2.3 Calculate non-integer relative atomic masses and abundance of isotopes from given data. Determine the atomic weight of lead using the data from the mass spectrum of lead Four isotopes: 204, 206, 207, 208 Percentage of each isotope: Total # isotopes is 10 ( ) 204: 1/10 = 10% 206: 2/10 = 20% 207: 2/10 = 20% 208: 5/10 = 50 % Multiply the percent of each isotope by its mass 204 x.1 = x.2 = x.2 = x.5 = 104 Add these values = Mass Spectrum of Lead

2.2.3 Calculate non-integer relative atomic masses and abundance of isotopes from given data. The atomic weight of gallium is amu. The masses of the naturally occurring isotopes are amu for 69 Ga and amu for 71 Ga. Calculate the percent abundance of each isotope. Let x = % abundance of 69 Ga. Then 1-x = % abundance of 71 Ga x (1-x) = amu x – x = x = x = = decimal value of 69 Ga so 60.0% 69 Ga 1-x = = decimal value 71 Ga so 40.0 % 71 Ga 63

Calculate non-integer relative atomic masses and abundance of isotopes from given data – the reverse method Steps for Calculating Percent Abundance (When given molar masses of each isotope) 1.Because percent abundances will always add up to 100% (1), assign one isotope to have a percentage of “x” and the other isotope to have a percentage of “1-x.” (See chart on next slide) 2.Look up the average atomic mass of the atom on the periodic table, if it is not given in the problem. 3.Set up your problem so it looks like the setup below: Average Atomic Mass = (Mass of Isotope A)x + (Mass of Isotope B)(1-X) 4.Solve for “X.” Multiply this number by 100 to turn it into a percentage. This is the percent abundance of isotope A. 5.The percent abundance of isotope B is 100% minus the percent abundance of isotope A.

Calculate non-integer relative atomic masses and abundance of isotopes from given data – the reverse method IsotopeMassVariableAbundanceFinal Answer Isotope A Given in problem x Solution for x Abundance x 100 = % Isotope B Given in problem 1 – x 100% - IsotopeA%

Calculate non-integer relative atomic masses and abundance of isotopes from given data – the reverse method Example Boron exists as two naturally occurring isotopes 10 5 B (10.1 amu) and 11 5 B (11.01 amu). Calculate the relative abundance of each isotope of boron.

67 Example: Boron exists as two naturally occurring isotopes 10 5 B (10.1 amu) and 11 5 B (11.01 amu) Calculate the relative abundance of each isotope of boron. IsotopeMassVariableAbundanceFinal Answer Boron x Solution for xAbundance x 100 = % Boron – x100% - IsotopeA% Average atomic mass = (from the periodic table) = (10.01)x + (11.01) (1-x) x = Percent abundance of B-10 is , which = 21.98% So, B-11 = 100% % = 78.02%

68 Example: Boron exists as two naturally occurring isotopes 10 5 B (10.1 amu) and 11 5 B (11.01 amu) Calculate the relative abundance of each isotope of boron. IsotopeMassVariableAbundanceFinal Answer Boron x % Boron – xN/A 100% % = 78.02% Answer: 21.98% of the sample is Boron % of the sample is Boron-11

Calculate non-integer relative atomic masses and abundance of isotopes from given data – the reverse method The atomic weight of gallium is amu. The masses of the naturally occurring isotopes are amu for 69 Ga and amu for 71 Ga. Calculate the percent abundance of each isotope.

Calculate non-integer relative atomic masses and abundance of isotopes from given data – the reverse method The atomic weight of gallium is amu. The masses of the naturally occurring isotopes are amu for 69 Ga and amu for 71 Ga. Calculate the percent abundance of each isotope. Let x = the fraction of 69 Ga. Then 1-x = the fraction of 71 Ga x (1-x) = amu x – x = x = x = = fraction of 69 Ga so 60.3% 69 Ga 1-x = = fraction of 71 Ga so 39.7 % 71 Ga

Calculate non-integer relative atomic masses and abundance of isotopes from given data. The atomic weight of copper is amu. The masses of the two naturally occurring isotopes are amu for 63 Cu and amu for 65 Cu. Calculate the percent of 63 Cu in naturally occurring copper. Let x = the fraction of 63 Cu. Then 1-x = the fraction of 65 Cu x (1-x) = amu x – x = x = x = = fraction of 63 Cu so 69.17% 63 Cu

2.2.3 Calculate non-integer relative atomic masses and abundance of isotopes from given data. The atomic weight of copper is amu. The masses of the two naturally occurring isotopes are amu for 63 Cu and amu for 65 Cu. Calculate the percent of 63 Cu in naturally occurring copper. 72

Calculate non-integer relative atomic masses and abundance of isotopes from given data – the reverse method Practice: 1.Hydrogen comes in two stable isotopes, Hydrogen-1 and Hydrogen-2. The molar mass of Hydrogen-1 is g/mol. The molar mass of Hydrogen-2 is g/mol. Determine the percent abundance of each isotope. 2.Oxygen comes in two stable isotopes, Oxygen-16 and Oxygen-18. The molar mass of Oxygen-16 is g/mol. The molar mass of Oxygen-18 is g/mol. Determine the percent abundance of each isotope.

Calculate non-integer relative atomic masses and abundance of isotopes from given data – the reverse method Practice: 1.Hydrogen comes in two stable isotopes, Hydrogen-1 and Hydrogen-2. The molar mass of Hydrogen-1 is g/mol. The molar mass of Hydrogen-2 is g/mol. Determine the percent abundance of each isotope. Hydrogen-1 = 99.78% Hydrogen-2 = 0.22% 2.Oxygen comes in two stable isotopes, Oxygen-16 and Oxygen-18. The molar mass of Oxygen-16 is g/mol. The molar mass of Oxygen-18 is g/mol. Determine the percent abundance of each isotope. Oxygen-16 = 99.75% Oxygen-18 = 0.25%

Important Terms Ion: a charged particle that is formed when an atom loses or gains electron(s) 75

Important Terms Ion: a charged particle that is formed when an atom loses or gains electron(s) o Number of protons ≠ number of electrons o Either positive or negative o A positive ion is formed when an atom loses (an) electron(s) o A negative ion is formed when an atom gains (an) electron(s) 76

Important Terms Cations: Atoms that lose electrons become positively charged Anions: Atoms that gain electrons become negatively charged 77

A1. Nuclear Symbol Notation SUMMARY OF SUBATOMIC PARTICLES IN AN ION # protons = atomic number (Z) # electrons = # protons – charge OR atomic number (Z) – charge # neutrons = mass number (A) – # protons OR mass number (A) – atomic number (Z) 78

Important Terms How many protons, neutrons, and electrons are in an ion of K-39 that has lost one electron? What is the charge of the ion? What is its symbol? Protons = 19 Neutrons = 20 Electrons = 18 Charge = 1+ or +1Symbol is 39 K

A1. Use of Nuclear Symbol Notation Nuclear Symbol: 80 X A Z Element Symbol Mass Number (Protons + Neutrons) Atomic Number + Charge (+, - or nothing) Determined by electrons

A1. Deduce from nuclear symbol notation The symbol of an anion is 31 P 3-. Calculate the number of 15 protons, neutrons, and electrons. What is Z and what is A? What is the symbol of a species containing 26 protons, 30 neutrons, and 23 electrons? What is the symbol of a species with A=56, Z=26, and 24 electrons? 81

A1. Deduce the number of protons, neutrons, and electrons in atoms and ions from A, Z, and charge The symbol of an anion is 31 P 3-. Calculate the number 15 protons, neutrons, and electrons. What is Z and what is A? #P = 15; #N = 16; #E = 18; Z= 15; A = 31 What is the symbol of a species containing 26 protons, 30 neutrons, and 23 electrons? 56 Fe What is the symbol of a species with A=56, Z=26, and 24 electrons? 56 Fe