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Atomic Structure

Atomic Structure. Stepwise Timeline of Atomic Theory. Rutherford 1911. Dalton 1803. Modern Theory. Thomson 1897. Bohr 1913. Chadwick 1932. Democritus ~ 460 B.C. to 360 B.C. Who Greek Philosopher What Atoms cannot be created, destroyed or divided. How Observing nature.

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Atomic Structure

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  1. Atomic Structure

  2. Stepwise Timeline of Atomic Theory Rutherford 1911 Dalton 1803 Modern Theory Thomson 1897 Bohr 1913 Chadwick 1932

  3. Democritus ~ 460 B.C. to 360 B.C. Who Greek Philosopher What • Atoms cannot be created, destroyed or divided. How • Observing nature

  4. Dalton’s Atomic Theory • Who • John Dalton (1766-1844), an English schoolteacher and chemist • What • proposed his atomic theory of matter in 1803. • Although his theory has been modified slightly to accommodate new discoveries, Dalton’s theory was so insightful that it has remained essentially intact up to the present time.

  5. Dalton • What ( write this outside the text box) • Cannot be created or destroyed. • All atoms of one element are exactly alike, (same size, mass, properties) but different from atoms of other elements • Combine in whole number ratios to form compounds. • How- • work with gases

  6. J.J. Thomson -1903 • Who • a British physicist. • What • Plum Pudding model (or Chocolate Chip Cookie model) Discovered electrons Model • Atom was a positively charged sphere with negative electrons in it like chips POSITIVE CHARGE ELECTRONS

  7. J. J. Thomson • How • discovered that cathode rays are made up of invisible, negatively charged particles referred to as electrons. • http://tinyurl.com/cathodert

  8. Ernest Rutherford • What • Found nucleus (1911) • Occupies a small volume of the atom • Contains almost all the mass of the atom • Electrons orbit around nucleus • Discovered proton • Who • British chemist and physicist.

  9. Ernest Rutherford • How • Gold Foil Experiment Alpha particles which are positively charged pass through unmolested most of the time. Occasionally they would bounce off when they hit something (proton) that was also positively charged.

  10. Niels Bohr - 1913 • What • Planetary Model • Electrons (e-) have definite path around the nucleus (orbit) • e- arranged around the nucleus according to energy level • e- with lowest energy level are closest to nucleus • How • Spectral emission lines • Who • Danish Physicist

  11. Chadwick • What • Discovered the neutron in 1932 • How • Used alpha particles Who British Scientist

  12. Modern Atomic Theory 1. All matter is made up of very tiny particles called atoms. 2. Atoms of the same element are chemically alike. 3. Individual atoms of an element may not all have the same mass. However, the atoms of an element have a definite average mass that is characteristic of the element. 4. Atoms of different elements have different average masses. 5. Atoms are not subdivided, created, or destroyed in chemical reactions.

  13. Atom and Elements • Element - a substance that is composed of a single type of atom. • Atom - the smallest particle of an element that retains the properties of that element. • The diameter of an atom is measured in nanometers • 1 nm = 1 x 10-9 m = 0.000000001 m • Atoms are composed of sub-atomic particles.

  14. Proton • Discovered by John Dalton in early 1800’s • Determines the identity of an atom • Relative mass of 1 atomic mass unit • Part of the nucleus of an atom • Positive charge If you change only the # of protons, you change the element being described.

  15. Neutron • Discovered by James Chadwick in 1932 • Determines the isotope of an atom • Relative mass of 1 atomic mass unit • Part of the nucleus of an atom • No charge (neutral) If you change only the # of neutrons, you have a new isotope (variety) of the element .

  16. Changing the number of neutrons • creates isotopes • The same element but a different number of neutrons. • Isotopes of an element have nearly identical chemical properties

  17. Electron • Discovered by J. J. Thomson in 1903 • Determines the charge of an atom (charged atoms are called ions) • Relative mass of 0 (~1/1836) atomic mass unit • Make up the electron cloud of an atom • Negative charge

  18. Changing the number of electrons • When an atom loses electrons, it results in a net positive charge and is called a CATION • ions are I itive

  19. Example of a cation Neutral potassium (K) has 19 protons and 19 electrons. 19 protons = +19 19 electrons = -19 0 If potassium (K) loses an electron, it only has 18 electrons. 19 protons = +19 18electrons = -18 +1 This is written as K+1 and is called a cation

  20. Changing the number of electrons • When an atom gains electrons, it results in a net negative charge and is called an ANION

  21. Example of an anion Neutral bromine (Br) has 35 protons and 35 electrons. 35 protons = +35 35 electrons = -35 0 If bromine (Br) gains an electron, it has 36 electrons. 35 protons = +35 36 electrons = -36 -1 This is written as Br -1 and is called an anion

  22. Gained electron Lost electron anion cation

  23. Describing an atom • ATOMIC NUMBER • Equals the number of protons in an element. • In a neutral atom, the atomic number also equals the number of electrons. • All atoms of the same element have the same number of protons. • The smaller of the two numbers in the periodic table square, always a whole number

  24. Describing an atom • ATOMIC MASS • A weighted average of the mass of all the isotopes (varieties) of an atom • Each element has only one atomic mass • Also called “average atomic mass” • The larger of the two numbers in the periodic table square • Always a decimal number

  25. Describing an atom • MASS NUMBER • Equals the # protons + # neutrons in an atom • Not always the same for atoms of an element  isotopes • Not listed on the periodic table • Always a whole number

  26. APE MAN A = Atomic Number P = Number of Protons E = Number of Electrons M= Mass number A = Atomic Number (again) N = Number of Neutrons Always the same number in a neutral atom Mass Number minus Atomic number equals Number of neutrons

  27. Isotope Name • name of the elementdashmass number • Example: Carbon -14 is the isotope name for a carbon atom with a mass number of 14

  28. C 12 6 Isotope Notation mass number element symbol atomic number

  29. C 14 6 Isotope Notation mass number element symbol atomic number number of neutrons = mass number – atomic number. How many protons and neutrons in this isotope?

  30. Practice

  31. Determining Atomic Mass • To determine the atomic mass you must know what percent of each isotope of the element is found in nature. This is called the relative abundance. • Example: There are 2 common isotopes of Chlorine. 25% is chlorine - 37 75% is chlorine – 35 Calculate the atomic mass of chlorine.

  32. Average Atomic Mass • Neon in nature is 90.5% Neon-20, 0.3% Neon-21, and 9.2% Neon-22. What is the average atomic mass of Neon?

  33. REACTIONS CHEMICAL NUCLEAR involve the absorption or emission of particles by the nucleus of an atom • involve the transfer or sharing of electrons

  34. Nuclear Chemistry Vocabulary • Nuclide- General name given to the nucleus of an atom • Parent nuclide- initial nucleus • Daughter nuclide- the nucleus after the decay has occurred

  35. Nuclear Chemistry Vocabulary • Radiation - energy that is emitted from a source and travels through space. • Ionizing Radiation- Has enough energy to change atoms and molecules into ions; examples: X-rays and gamma rays. • Nonionizing Radiation- Does not have enough energy to ionize matter; examples: radio waves, microwaves • Accidentally discovered by Henri Becquerel in 1896 when he was performing a lab with fluorescent screens. • Radioactivity is the spontaneous emission of radiation from the nucleus of an atom.

  36. Types of Ionizing Radiation

  37. penetrating ability

  38. Why decay happens • To become more stable. • Large atoms are stable when the neutron: proton ratio is 1.5:1 • Decay happens when the nucleus when the neutron: proton ratio is too high.

  39. Alpha decay

  40. Alpha Decay • Occurs when an alpha particle leaves the nucleus - alpha particle = Helium nucleus • Parent  daughter: mass decreases by 4 and atomic number decreases by 2 Example: Thorium-230 undergoes alpha decay. Write the decay reaction. Th ------> He + Ra

  41. Alpha decay practice Write the decay reaction for alpha decay of Uranium-238.

  42. Beta decay

  43. Beta Decay • occurs when a beta particle e is emitted from the nucleus • Parent  daughter: equal mass but atomic number increases by 1. • a neutron becomes a proton. Example: Carbon-14 undergoes beta decay. Write the decay reaction. C -----> e + N

  44. Beta decay practice Write the decay reaction showing beta decay of Thorium-234.

  45. Fission and Fusion

  46. Fission Reaction • Nuclear reaction • Splitting an atom’s nucleus • Releases energy • Alpha, beta are examples • Used in nuclear reactors • Causes a chain reaction • Problem: produce radioactive waste; storage of fuel is dangerous

  47. chain reaction

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