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Understanding Atoms and Isotopes in Atomic Theory

Explore the structure of an atom, sub-atomic particles, isotopes, atomic number, mass number, and famous scientists in atomic theory like Democritus, Dalton, Thomson, and Rutherford. Understand how isotopes affect the average atomic mass.

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Understanding Atoms and Isotopes in Atomic Theory

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  1. The Atom

  2. Two major parts of an atom Nucleus (not to scale) Electron Cloud

  3. Three Major Sub-Atomic Particles • Protons • Neutrons • Electrons

  4. p+ THE PROTON • Heavy = 1 amu • Positive + 1 charge • Location: Nucleus

  5. N° THE NEUTRON • Heavy = 1 amu • No charge, neutral • Location: Nucleus

  6. e- THE ELECTRON • Very light = 1/2000 amu • Negative  -1 charge • Location: electron cloud

  7. Where are they located? Nucleus:Protons and Neutrons Electron Cloud:Only Electrons

  8. ATOMIC NUMBER (Z) • The # of protons in an atom • Can not change for an element • All atoms are neutral, so Z equals the # of electrons • For an ion – the number of electrons may differ

  9. Example: Sodium Atomic # = # of protons 11 Na

  10. MASS NUMBER (A) • The mass of an atom • A = protons + neutrons • To determine # of neutrons • Neutrons = A - Z

  11. Example • An atom of sodium has a mass of 24 amu, how many protons, electrons and neutrons does it have? 11 p+ 11 e- 24 - 11 = 13 N° 11 Na

  12. ISOTOPES • Atoms of the same element that differ in mass.(They have the same # of p+, but different # of N°)

  13. Isotope Notation Mass # Atomic #

  14. Isotope Notation • Can also be written as ELEMENT – MASS # • Example: Carbon - 12

  15. So, why do the elements on the PT have masses with decimals???

  16. AVERAGE ATOMIC MASS • The weighted average mass of all naturally occurring isotopes of an element.

  17. Example using exam scores! Exam Scores can be weighted higher than homework or quiz grades: What if… And you received: Exam 50% Exam 93 Quizzes 20% Quizzes 82.5 Homework 30% Homework 85 Your grade = (93 x .5) + (82.5 x .2) + (85 x .3) = 88.5

  18. Example • Example: The element hydrogen has three isotopes. It exists in nature 99.41% of the time as Hydrogen-1, 0.4% of the time as Hydrogen-2 and 0.19% of the time as Hydrogen – 3. What is the average atomic mass of hydrogen? 0.9995*1 + 0.004*2 + 0.001*3 = 1.0078 u

  19. Famous Scientists in Atomic Theory

  20. Democritus (400 B.C.) • First to develop the idea of an atom.

  21. DALTON • Dalton created an atomic theory that stated: • All elements are composed of tiny indivisible particles called atoms • Atoms of the same element are identical. The atoms of any one element are different from those of any other element

  22. J.J. Thomson • “Plum Pudding Model” • Solid positively charged sphere • Electrons embedded within

  23. Rutherford’s Gold Foil Experiment

  24. Rutherford • Proved the existence of a tiny, dense, positively charged nucleus. • The rest of the atom is mostly empty space.

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