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Atomic Structure

Atomic Structure. Chemistry Timeline #1. B.C. 400 B.C. Demokritos and Leucippos use the term "atomos” .  2000 years of Alchemy . 1500's George Bauer: systematic metallurgy Paracelsus: medicinal application of minerals. 1600's

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Atomic Structure

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  1. Atomic Structure

  2. Chemistry Timeline #1 B.C. 400 B.C. Demokritos and Leucipposuse the term "atomos” 2000 years of Alchemy • 1500's • George Bauer: systematic metallurgy • Paracelsus: medicinal application of minerals 1600's Robert Boyle:The Skeptical Chemist.Quantitative experimentation, identification of elements • 1700s' • Georg Stahl: Phlogiston Theory • Joseph Priestly: Discovery of oxygen • Antoine Lavoisier: The role of oxygen in combustion, law of conservation of mass, first modern chemistry textbook

  3. Chemistry Timeline #2 • 1800's • Joseph Proust: The law of definite proportion (composition) • John Dalton: The Atomic Theory, The law of multiple proportions • Joseph Gay-Lussac: Combining volumes of gases, existence of diatomic molecules • Amadeo Avogadro: Molar volumes of gases • Jons Jakob Berzelius: Relative atomic masses,modern symbols for the elements • Dmitri Mendeleev: The periodic table • J.J. Thomson: discovery of the electron • Henri Becquerel: Discovery of radioactivity • 1900's • Robert Millikan: Charge and mass of the electron • Ernest Rutherford: Existence of the nucleus, and its relative size • Henry Moseley: Organizes Periodic Table by Atomic Number • Chadwick: Discovery of Neutron • Meitner & Fermi: Sustained nuclear fission • Ernest Lawrence: The cyclotron and trans-uranium elements

  4. Dalton’s Atomic Theory (1808) • All matter is composed of extremely small particles called atoms • Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties John Dalton • Atoms cannot be subdivided, created, or destroyed • Atoms of different elements combine in simple whole-number ratios to form chemical compounds • In chemical reactions, atoms are combined, separated, or rearranged

  5. Modern Atomic Theory Several changes have been made to Dalton’s theory. Dalton said: Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties Modern theory states: Atoms of an element have a characteristic average mass which is unique to that element.

  6. Modern Atomic Theory #2 Dalton said: Atoms cannot be subdivided, created, or destroyed Modern theory states: Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions

  7. 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.

  8. Thomson’s Atomic Model J.J. Thomson Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

  9. Mass of the Electron 1909 – Robert Millikan determines the mass of the electron. Mass of the electron is 9.109 x 10-31 kg The oil drop apparatus

  10. Conclusions from the Study of the Electron • Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons. • Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons • Electrons have so little mass that atoms must contain other particles that account for most of the mass

  11. Rutherford’s Gold Foil Experiment • Alpha particles are helium nuclei • Particles were fired at a thin sheet of gold foil • Particle hits on the detecting screen (film) are recorded

  12. Rutherford’s Findings • Most of the particles passed right through • A few particles were deflected • VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions: • The nucleus is small • The nucleus is dense • The nucleus is positively charged

  13. Atomic Particles

  14. The Atomic Scale Helium-4 • Most of the mass of the atom is in the nucleus (protons and neutrons) • Electrons are found outside of the nucleus (the electron cloud) • Most of the volume of the atom is empty space Image: User YzmoWikimedia Commons.

  15. Noble Gas Halogen Alkali Earth Metal Period Alkali Metal Group

  16. Isotopes Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.

  17. Atomic Masses Atomic mass is the average of all the naturally isotopes of that element. Carbon = 12.011

  18. Atomic Number Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

  19. Mass Number Mass number (A) is the number of protons and neutrons in the nucleus of an isotope. Mass # = p+ + n0 18 8 8 18 Arsenic 75 33 75 Phosphorus 16 15 31

  20. A X Mass Number Element Symbol Z Atomic Number 1 3 2 H (D) H (T) H 1 1 1 235 238 U U 92 92 Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei

  21. ? ? How many protons, neutrons, and electrons are in How many protons, neutrons, and electrons are in 14 11 C C 6 6 Do You Understand Isotopes? 6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons

  22. Ions • Not only can atoms have a different number of neutrons but they can also have a different number of electrons. • When they have more or less electrons they are called ions.

  23. 11 protons 11 electrons 11 protons 10 electrons Na+ Na 17 protons 18 electrons 17 protons 17 electrons Cl- Cl An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion.

  24. Determining the Electrons • In a neutral atom the number of electrons is the same as the number of protons. • When an atom becomes an ion to calculate the number of electrons you can use the following equation: Ion charge = p+ - e-

  25. Determining the Electrons (Cont.) • So for the following ion: N-3 the charge is -3 which means… Ion charge = p+ - e- -3 = 7 – (# electrons) … or there are 10 electrons.

  26. 27 3+ Al ? How many protons, and electrons arein 13 ? 78 2- How many protons and electrons are in Se 34 Do You Understand Ions? 13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons

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