10/26/2015 Today I will discuss the early models of the atom. Warm Up – What do you already know about atoms?

Chapter 3 – Atomic Structure Chemistry

Early Models of the Atom Atom – smallest part of an element that retains the chemical properties of that element.

Early Models of the Atom Greek philosophers – around 400 BC Democritus – “atomos” Aristotle – Earth, Air, Fire, Water

Early Models of the Atom Antoine Lavoisier – late 1700s Law of Conservation of Matter – matter can be neither created nor destroyed. Starting = Ending

Early Models of the Atom Joseph Proust Law of Definite Proportions – a given compound always contains the same elements in the same proportions by mass. 88.9% of mass is oxygen and 11.1% of mass is hydrogen

Early Models of the Atom John Dalton – 1803 Dalton’s Atomic Theory Each element is composed of extremely small, indivisible particles called atoms. All atoms of a given element are the same, atoms of different elements are different. Atoms are neither created nor destroyed. A given compound always has the same relative numbers and kinds of atoms. Democritus Not always true! Lavoisier Proust

Early Model of the Atom Notice it has been over 2000 years since Democritus first introduced the idea of the atom. Science now relies on observations and experiments rather than just thoughts.

Early Models of the Atom Dalton - “Billiard Ball” Model

Early Models of the Atom Michael Faraday – 1839 Atom structure contain particles that have electrical charge. Elektron From Greek word for Amber Describes static electricity (charges not in motion) Benjamin Franklin Called charges positive (+) and negative (-)

Early Models of the Atom Why don’t we know for sure? Different Worlds – Macroscopic – ordinary-sized objects Microscopic – seen through a microscope Sub-microscopic – cannot be seen through a microscope (chemistry)

Early Models of the Atom Scanning Tunneling Microscope

Cool Down Question How has your idea of an atom changed since the beginning of class?

10/27/15 Today I will discuss the early figures involved in modern atomic theory Warm up – Discuss the events in early Greece that set science back thousands of years.

Atomic Structure J.J. Thomson – 1869 Cathode Ray Tube Named negative particles “electrons” Negatively charged plate Positivelycharged plate

Atomic Structure J.J Thomson – 1869 Plum-pudding model Charge to mass ratio Coulomb (C) – SI unit of charge 1.76 x 108 Coulombs per gram

Atomic Structure Robert Millikan Oil Drop Experiment Determined charge on an electron 1.60 x 10-19C (Coulomb – SI unit of charge) Calculated mass using charge to mass ratio 9.11 x 10-28g

Nuclear Atom Ernest Rutherford – 1909 Gold foil Experiment Alpha particle – large positive particle Composed of two protons

Nuclear Atom Ernest Rutherford – 1909 Gold foil Experiment – If Thomson is correct:

Nuclear Atom Ernest Rutherford – 1909 Gold foil Experiment Nucleus – small positive center of an atom that contains most of its mass

Nuclear Atom Rutherford’s Model

Cool Down Question How has your idea of the atom changed even further today?

10/28/2015 Today I will explain protons, neutrons and electrons and determine the number of each in an atom. Warm Up – What are protons, neutrons & electrons? *Staple Lab reports and make a pile by the window!

Modern Atomic Theory Atoms are composed of: Protons, neutrons, electrons Particle Location Charge Mass (g) Rel Mass Rel Charge proton Inside nucleus +1.6x10-19 1.673x10-24 neutron 1.675x10-24 electron Outside nucleus -1.6x10-19 9.109x10-28

Modern Atomic Theory Atomic Mass Units 1/12 the mass of a carbon-12 atom (so basically the relative mass of a proton or neutron)

Modern Atomic Theory (Protons) Moseley - An element is defined by the number of protons in it’s atoms. Atomic Number - # of protons in an atom How many protons are in each atom of nitrogen?

Modern Atomic Theory (Protons) How many protons? Copper Sodium Helium

Modern Atomic Theory (Electrons) In an electrically neutral atoms, the number of electrons must equal the number of protons. How many electrons are in each atom of nitrogen?

Modern Atomic Theory (Electrons) How many electrons? Copper Sodium Helium

Modern Atomic Theory (Electrons) Ions An atom that has an electrical charge due to gaining or losing electrons Gaining electrons makes the atom negative overall (more negatives than positives) Losing electrons make the atom positive overall (more positives)

Modern Atomic Theory (Electrons) Ions An atom that has an electrical charge due to gaining or losing electrons How many electrons in a chlorine atom that has a -1 charge?

Modern Atomic Theory (Electrons) How many electrons? Copper (+2) Sodium (-1) Helium (+2)

Modern Atomic Theory (Electrons) Finding Charge Remember: More electrons makes overall negative More protons makes overall positive Find the charge & write the symbol: 34 protons, 36 electrons 13 protons, 10 electrons

10/29/15 Today I will explain isotope and count the number of neutrons in an atom. Warm up – How many protons and electrons in an atom of sulfur with a -2 charge?

Modern Atomic Theory (Neutrons) Neutrons add stability to a nucleus Only the protons and the neutrons have mass (for practical purposes). Protons + Neutrons = Mass Number What is the mass number of chlorine if it has 18 neutrons?

Modern Atomic Theory (Neutrons) Isotopes An atom that has the same number of protons but different numbers of neutrons Same protons, means it’s the same element Different neutrons changes the mass!

Modern Atomic Theory (Neutrons) Mass number = protons + neutrons How many neutrons does Cl have if its mass number is 36?

Modern Atomic Theory Mass Number Notation Symbolic Notation Name-mass number Symbolic Notation Mass number   Charge Atomic number 

Cool Down Question How many protons, neutrons and electrons? 53 55 54 Protons Neutrons Electrons 53 55 54 12 13 10 8 10 8

10/30/15 Today I will practice finding the number of protons, neutrons and electrons in atoms, ion sand isotopes. Warm Up – How many protons neutrons and electrons in Bromine – 74 Sodium - 24

11/2/15 Objective – to calculate average atomic mass Warm Up – How many protons neutrons and electrons in Oxygen – 18 Lithium-8

Atomic Mass Atomic Mass – The average mass of all the isotopes of an atom Shown below the symbol on the periodic table.

Modern Atomic Theory You get the following grades: A,A,A,A,C,A,A,A,A,A. Can we average the A’s and the C’s to get a B average? No! We have to take into account the percent of your grade that are A’s and the percent that are C’s You could do: 4+4+4+4+2+4+4+4+4+4/10 = 3.8

Modern Atomic Theory You get the following grades: A,A,A,A,C,A,A,A,A,A. You could also find your average grade by Percent Abundance! You have 90% A’s and 10% C’s. So… (.9)(4) = 3.6 (.1)(2) = 0.2 3.8

Modern Atomic Theory Average Atomic Mass The average mass of an atom would be the mass of all the atoms in the world averaged. Can we count up the masses of all the atoms and divide by the number? Percent Abundance! – we can calculate average atomic mass based on the known percents of each isotope.

Modern Atomic Theory What is the average atomic mass of Nitrogen? Fractional abundance – percent abundance as a decimal mass number exact mass percent abundance 14 14.003 99.63 15 15.000 0.37 mass number exact mass Fractional abundance 14 14.003 0.9963 15 15.000 0.0037

Modern Atomic Theory AAM = (mass)(fractional abundance) + (mass)(fractional abundance) + … What is the average atomic mass of Nitrogen? mass number exact mass percent abundance 14 14.003 99.63 15 15.000 0.37 (14.003) (0.9963) + (15.000) (0.0037) = (14.007) Average Atomic Mass of Nitrogen is 14.007 amu.

Cool Down Question What element is represented below? (27.977) Mass number Exact mass Percent abundance 28 27.977 92.23 29 28.976 4.67 30 29.973 3.10 (27.977) (0.9223) + (28.976) (0.0467) + (29.973) (0.0310) = (28.086) Average Atomic Mass is 28.086 amu. From periodic table, it must be silicon!

11/4/15 Today I will write nuclear equations Warm up – Calculate the average atomic mass for Magnesium: mass number exact mass percent abundance 24 23.985 78.99 25 24.985 10.00 26 25.982 11.01

Early Models of the Atom Henri Bequerel - 1896 Uranium exhibits radioactivity Radioactivity changes the properties of an atom.

Changes in the Nucleus If all atoms of the same element have the same properties, how can they change? Nuclear reactions – radioactive changes that alter the composition of the nucleus. Therefore, they change their identity!

Changes in the Nucleus How can these positive protons live together if like charges repel? Strong Nuclear Force – attractive force that overcomes the repulsion of the protons. Neutrons help stabilize! - The larger the nucleus, the greater the neutron to proton ratio.

Changes in the Nucleus At some point, there can be too much repulsion to overcome & nucleus becomes unstable. All elements above atomic number 83 are unstable or radioactive! Some isotopes of smaller elements can be radioactive too if they have too many neutrons!

Changes in the Nucleus Radioactive decay – spontaneous emission of radioactive particles from the nucleus. Radioactive Particles: Alpha – 2 protons & 2 neutrons Beta – electron from the nucleus (1 neutron becomes 1 electron and 1 proton) Gamma – energetic form of light

Medium, stopped by heavy clothing Changes in the Nucleus Radioactive Particles: Particle Symbol Equation symbol Charge Penetrating ability Energy Danger alpha α +2 Low, stopped by paper Low beta β -1 Medium, stopped by heavy clothing Medium gamma ɣ none High, stopped by lead High

Changes in the Nucleus Alpha Decay – emission of an alpha particle +

Changes in the Nucleus Beta Decay – emission of a beta particle +

Cool Down Question Write the nuclear equation for the beta decay of Bismuth-209

11/5/15 Today I will demonstrate the idea of average atomic mass. Warm Up – Why do we use an average of atomic mass rather than the actual mass?

Pennium Lab What is an isotope? Pretend each penny is an atom. How can we tell if there are different isotopes in our sample of Pennium?

11/6/15 Objective – to review chapter 3 Warm up – Calculate the average atomic mass for Magnesium: mass number exact mass percent abundance 24 23.985 78.99 25 24.985 10.00 26 25.982 11.01

11/9/15 Warm Up – How many protons, neutrons and electrons: Objective –to review for the chapter 3 exam Warm Up – How many protons, neutrons and electrons: A. selenium – 70 B. curium - 244 Write the equations for the following: A. The beta decay of selenium- 70 B. The alpha decay of curium - 244

How many protons, neutrons and electrons: A. selenium – 70 P = 34 N = 36 E = 34 B. curium - 244 P = 96 N = 148 E = 96 Write the equations for the following: A. The beta decay of selenium- 70 B. The alpha decay of curium - 244

Symbolic Form Mass Form Atomic # Mass # Protons Neutron Electron Atomic Mass Iron - 56 13 14 10