A Particulate World – Part I Day 9 Alchemy A Particulate World – Part I Day 9

Catalyst – 9/21 (page 14) What are the five models of atomic theory? (in order)

Agenda Reminders Dead Chemists Lecture Pudding In The Clouds Activity Graphic Organizer Time Line Guided Notes Pudding In The Clouds Activity

Early Theories of Matter Ancient Greeks: All matter consists of 4 elements: Earth, Air, Water, & Fire

It's time for... Dead Chemists Take notes on the Time Line Graphic Organizer

Cast of Characters 1. Democritus 2. Lavoisier 3. Proust 4. John Dalton 5. J.J. Thomson 6. Ernest Rutherford 7. James Chadwick 8. Niels Bohr 9. Robert Millikan 10. Ernst Schrodinger New atomic Model

Democritus (2400 years ago) Greek philosopher (470-380 B.C.) Atomos - “indivisible”. The universe was made up of atoms. Small & indestructible

Antoine Lavoisier (1743 - 1794) Law of Conservation of Mass - 1774 Father of Modern Chemistry

Joseph Proust The Law of Definite Proportions (composition) - 1808 In any compound the elements are present in a fixed proportion by weight.

John Dalton (1766-1844) Atomic Theory Law of Partial Pressures!

Dalton’s Atomic Theory Wrong! Elements are made of tiny particles called atoms that are indivisible.. All atoms of a given element are identical. The atoms of a given element are different from those of any other element. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms. Atoms are indivisible in chemical processes. That is ,atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together. Wrong!

J.J. Thomson (1856-1940) Discovered electrons (cathode ray tube experiment) Developed “plum pudding” atomic model

Thomson’s Cathode Ray Tube Experiment Results: The discovery of the electron! Atoms are divisible! A CRT is an empty glass tube that has an electric current passed through it. Thomson proposed that the mysterious rays in the tubes were pieces of atoms! Remember – up until this point, the atom was it! No protons, neutrons, electrons, quarks, etc.

Thomson’s Plum Pudding Model The atom is divisible! Electrons are suspended in a positively charged electric field Mass of atom due to electrons   Atom mostly "empty" space compared size of electron to size of atom Wrong! Wrong!

Ernest Rutherford (1871-1937) Gold foil experiment Rutherford’s atomic model Discovered the nucleus Atom is mostly space Mass is concentrated in a positively charged nucleus (sort of discovered protons)

Rutherford’s Gold Foil Experiment He bombarded a thin gold foil with alpha particles (He atoms). Although almost all of them went through the gold, 1 in 8000 would "bounce" back. Rutherford said that it was "as if you fired a 15-inch naval shell at a piece of tissue paper and the shell came right back and hit you." He concluded that the atom's mass is concentrated in a small positively-charged nucleus and the electrons inhabit the farthest reaches of the atom.

There are protons and neutrons in Rutherford’s nucleus! James Chadwick (1891-1974) I discovered the neutron! And isotopes!                                             There are protons and neutrons in Rutherford’s nucleus!

Niels Bohr (1885-1962) If electrons are stationary, they would fall into the positively-charged nucleus! The electrons must be moving in planet-like orbits around the nucleus! Wrong!

Bohr’s Atomic Model Electrons orbit in paths around nucleus By assuming electrons orbited in circles with disscrete radii, Bohr could explain the discrete wavelengths in the emission spectrum of H. Big Problem: It only worked for hydrogen! Wrong!

More on the Bohr Model The energy level is the region around the nucleus the electron is likely to be moving. Quantum theory – a quantum of energy is the amount of energy required to move an electron from one energy level to another.

Robert A. Millikan (1868-1953) Millikan found the charge of an electron through his famous oil drop experiment. An electron has a charge of 1.602 x 10-19 coulombs.                                            

Millikan’s Oil Drop Experiment Oil droplets were sprayed into a small hole in a box with a metal top and bottom. The metal was electrified, causing the oil droplet to be suspended in midair. The voltage, speed, and mass of the droplet was used to calculate the electric charge of the electron.

Ernst Schrodinger (1887-1961) Developed the quantum mechanical model of the atom Can only calculate the probability of finding an electron in a certain position around the nucleus (energy levels). Electron clouds are most dense where the probability for finding an electron is high. Particles behave like waves.

Review The 5 Basic Models:

Antiquity Ancient Model through John Dalton

JJ Thomson Plum Pudding Model

Rutherford The nuclear or “nut” model.

Bohr Planetary Model

Schrodinger Quantum Mechanical Model

The Structure of the Atom The Billiard Ball Model Plum Pudding Model Nuclear Atom Bohr Model Electron Cloud (Quantum Mechanical Model)

An Atom

Day 10 Isotopes and Building Atoms

Outside nucleus (electron cloud) Subatomic Particles Charge Location Mass Neutron Nucleus 1 amu Proton +1 Electron -1 Outside nucleus (electron cloud) 1/2000 amu

Nucleus: Atom Marble: Stadium

All about the atom All neutrons are identical All protons are identical Electrons are identical, but have different energy levels The nucleus is dense The electron cloud is mostly empty space In a neutral atom (not an ion): # of electrons = # of protons

Atomic Number The number of protons in the nucleus of an atom is called the atomic number. Protons are what define an atom of an element. So what is going on here?                                                                         Hydrogen Hydrogen (Deuterium) Hydrogen (Tritium)

What does “Carbon-12” mean? Mass Number of an Atom Mass Number = # Protons + # Neutrons Carbon-12 has 6 neutrons and 6 protons, so its mass number is 12 amu. Electrons have a teeny-tiny mass so they are not included in the mass number! What does “Carbon-12” mean?

Building Atoms Complete building atoms activity Questions 1 – 10 found on page 48 of your Alchemy Workbook. Complete on page 16 of your Classwork NB

The Convenient Atomic Mass Unit 1 amu = 1.67 x 10-24 g How did we get it? 1 amu = 1/12 the mass of 1 C-12 atom.

Isotopes An atom that has the same number of protons but a different number of neutrons is an isotope. Example: Carbon will always have 6 protons, but the number of neutrons can change. Carbon-12 (6 protons + 6 neutrons) Carbon-13 (6 protons + 7 neutrons) Carbon-14 (6 protons + 8 neutrons)

Isotopes Lithium-7 3 protons 4 neutrons The 3 protons in the nucleus are what make this atom Lithium! Mass # 7 Li Symbol 3 Atomic # Remember: Atomic # = # of protons

Another Isotope Example ALL Bromine atoms have 35 protons. Some have: 41 neutrons 42 neutrons 44 neutrons 46 neutrons 47 neutrons 48 neutrons Mass # Br Atomic # How would you find the number of neutrons?

Atomic Mass Atomic mass (weight) is the weighted average of the mass numbers of the isotopes of an element. Carbon’s average atomic mass is 12.01

Fill in the table! He 2 4 Mg 12 Br 80 35 Al 13 14 Symbol Atomic # Mass # # Protons # Neutrons # Electrons He 2 4 Mg 12 Br 80 35 Al 13 14

How did you do? He 2 4 Mg 12 24 Br 35 80 45 Al 13 27 14 Symbol Atomic # Mass # # Protons # Neutrons # Electrons He 2 4 Mg 12 24 Br 35 80 45 Al 13 27 14

Ions To be stable, some atoms will gain or lose electrons and become IONS. Cations are positively charged (lose electrons) Anions are negatively charged (gain electrons) Lithium loses one electron to become Li+ Chlorine GAINS one electron to become Cl-