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Atomic Theories

Atomic Theories. BrainPOP : Atomic Model. Democritus: 400 B.C. Coined the word “atom” C omes from the Greek a- tomos meaning uncuttable or indivisible. Dalton: Early 1800s. Father of the “Modern Atomic Theory”

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Atomic Theories

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  1. Atomic Theories BrainPOP: Atomic Model

  2. Democritus: 400 B.C. • Coined the word “atom” • Comes from the Greek a-tomosmeaninguncuttable or indivisible

  3. Dalton: Early 1800s • Father of the “Modern Atomic Theory” • All matter is made up of tiny indivisible particles called atoms. • Atoms of the same element have identical properties, including identical mass. • Atoms of different elements have different properties, including different mass. • Atoms combine in fixed whole number ratios to form compounds. • A specific compound is always made up of atoms in a specific proportion.

  4. Dalton: Early 1800s • Determined that each element corresponds to a unique atom • Developed a system of chemical symbols based on atomic mass • Compounds are atoms linked as molecules

  5. Discovery of the Electron • In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. • Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

  6. Thomson: Late 1800s • A neutral atom is made up of an equal number of positive and negative particles. • Electrons were like plums embedded in a positively charged “pudding”, thus it was called the “plum pudding” model.

  7. Rutherford: Early 1900s • Determined that the nucleus of the atom is extremely small and positively charged. • The rest of the atom is mostly empty space and contains electrons. • Rutherford’s Gold Foil Experiment • Using alpha particles as bullets, he knocked hydrogen nuclei out of atoms of 6 elements. • He named them protons, from the Greek word for “first.”

  8. Rutherford’s Gold Foil Experiment  Model of Rutherford’s Atom 

  9. Bohr • RULE 1: Electrons can orbit only at certain allowed distances from the nucleus. • RULE 2: Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. • Also, an atom absorbs energy when an electron gets boosted from a low-energy orbit to a high-energy orbit.

  10. Bohr’s Atomic Model

  11. Quantum Theory • Electrons are distributed around the nucleus in "probability regions" called "atomic orbitals". • Electrons behave like waves and particles.

  12. Atomic Models

  13. Atomic Structure

  14. Intro to Atoms • Matter has mass and takes up space. • Atoms are basic building blocks of matter, and cannot be chemically subdivided by ordinary means.

  15. Composition of Atoms • Atoms are composed of three types of particles: • Protons • Neutrons • Electrons

  16. Protons, Neutrons, and Electrons • Protons and Neutrons are responsible for most of the atomic mass • The mass of an electron is very small • In the nucleus • Protons (positive charge) • Neutrons (no charge) • Outside the nucleus • Electrons (negative charge)

  17. Atomic Number • The number of protons determines the atomic number of an element. • The elements are placed in order by increasing atomic number on the periodic table.

  18. Atomic Mass • The total number of protons and neutrons that make up the nucleus of an atom. • To find the number of neutrons… Mass number – atomic number = # of neutrons • EX: Uranium-235 Mass number – atomic number = neutrons 235 (protons + neutrons) – 92 protons = 143 neutrons

  19. Uh…how is that again? • To find the number of protons, electrons and neutrons in an atom, just follow these easy steps: • Step 1 - Gather Information • Step 2 - The Number of Protons is... • Step 3 - The Number of Electrons is... • Step 4 - The Number of Neutrons is...

  20. Step 1 - Gather Information • Look up the element on the periodic table. • Use the table to find the element’s atomic number and atomic mass (weight). • The atomic number is located at the top, while the atomic mass is located at the bottom.

  21. Step 2 - The Number of Protons is... • The atomic number is the number of protons in an atom of an element. • How many protons are in Krypton?

  22. Step 3 - The Number of Electrons is... • Atoms must have equal number of protons and electrons. • Therefore, in an atom of Krypton, there must be 36 electrons since it contains 36 protons. • An atom can gain or lose an electron, becoming an ion. • Adding or removing electrons does not change what the element is; it just changes its net charge.

  23. Step 4 - The Number of Neutrons is... • Look for the atomic weight/mass on the periodic table. • Round the atomic weight to the nearest whole number to get the mass number. • So for Krypton… • Mass number = # of protons + # of neutrons • 84 = 36 + # of neutrons • 84-36= 48 neutrons!

  24. In summary… For any element… • # of Protons = Atomic # • # of Electrons = # of Protons = Atomic # • # of Neutrons = Mass # - Atomic #

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