Warmup 11/10/15 Which of the following statements about density is true? Density depends on mass and volume. Density is weight per unit volume. Density is measured in milliliters. Density is a chemical property. Which change of state is exothermic? Sublimation Melting Condensation Freezing

12.1 Atomic theory

Close reading First Read Through Look at pictures only. What do you think the pictures represent? Second Read Through Only skim and highlight all of the names you find.

Atomic Theory A scientific theory is a unifying explanation for a broad range of hypothesis and observations supported by testing. Democritus proposed the first “uncuttable” particle. Called atom from Greek atomos meaning indivisble.

Image taken from: www.ldeo.columbia.edu/.../v1001/geotime2.html Antoine Lavoisier Known as the “Father of Modern Chemistry” Was the first person to generate a list of thirty-three elements in his textbook. Devised the metric system. Was married to a 13-year old Marie-Anne Pierette Paulze; she assisted him with much of his work Image taken from: www.ldeo.columbia.edu/.../v1001/geotime2.html

John Dalton In 1803, proposed an Atomic Theory which states: 1. All substances are made of atoms; 2. Atoms of the same element are exactly alike, and atoms of different elements are different 3. Atoms join with other atoms to make new substances Calculated the atomic weights of many various elements

Close reading Third Read through Read first two paragraphs aloud to your partner. One paragraph each. Underline or bracket the main idea in each paragraph.

Image taken from: www.wired.com/.../news/2008/04/dayintech_0430 J.J. Thomson Proved that an atom can be divided into smaller parts While experimenting with cathode-ray tubes, discovered corpuscles, which were later called electrons. Stated that the atom is neutral In 1897, proposed the Plum Pudding Model. Image taken from: www.wired.com/.../news/2008/04/dayintech_0430

Ernest Rutherford In 1909, performed the Gold Foil Experiment and suggested the following characteristics of the atom: It consists of a small core, or nucleus, that contains most of the mass of the atom This nucleus is made up of particles called protons, which have a positive charge The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space Image taken from: http://www.scientific-web.com/en/Physics/Biographies/ErnestRutherford.html

NielS Bohr This model was introduced in 1913 Proposed that electrons move in set paths around the nucleus. These levels are a set distance from the nucleus Electrons can jump levels but not stay between. NOTE: It is inaccurate but still widely used as a basis for understanding.

Draw this nitrogen atom

Modern Theory Many scientists have since added to the theory and model of the atom. Schrödinger and Heisenberg discovered that the path is not exact and can only be predicted. Electron clouds are the regions inside an atom where electrons are likely to be found.

James Chadwick Realized that the atomic mass of most elements was double the number of protons → discovery of the neutron in 1932 Worked on the Manhattan Project Worked with Ernest Rutherford Won a Nobel Prize

History of the Atom - Timeline Antoine Lavoisier makes a substantial number of contributions to the field of Chemistry J.J. Thomson discovers the electron and proposes the Plum Pudding Model in 1897 Niels Bohr proposes the Bohr Model in 1913 James Chadwick discovered the neutron in 1932 1766 – 1844 1871 – 1937 1887 – 1961 460 – 370 BC 1700s 1800s 1900s Erwin Schrodinger describes the electron cloud in 1926 Democritus proposes the 1st atomic theory John Dalton proposes his atomic theory in 1803 Ernest Rutherford performs the Gold Foil Experiment in 1909 1891 – 1974 1743 – 1794 1885 – 1962 1856 – 1940 Click on picture for more information

Democritus & John Dalton + - The structure of an atom, according to: Democritus & John Dalton James Chadwick J.J. Thomson Neils Bohr Ernest Rutherford Erwin Schrodinger

Review In what part of the atoms is most of the mass located? What are two differences between the atomic theory described by Thomson and that described by Rutherford? Identify the difference in how Bohr’s theory and the modern theory describe the location of electrons.

Warmup Which of the following determines the identity of an atom? Atomic number Mass number Atomic mass Overall charge How many protons does an atom of Iron (Fe) have? 55.8 9 26 Unknown

Warmup 11/5/14 In what part of the atom is most of the mass located? Electron cloud Electrons Neutrons Nucleus Electrons have a __________ charge. Positive Negative Neutral Infinite