1. Unit 3 Part 1Atomic Structure ICP Mr. Patel SWHS

2. Topic Outline • Learn Major Elements • The Atom • Subatomic Particles • Modern Atomic Theory • Organizing the Elements • Periodic Table • Classifying Elements • Atomic Models

4. Defining the Atom • Atom – the smallest particle of an element that retains its identity • Can not see with naked eye • Nanoscale (10-9 m) • Seen with scanning tunneling electronmicroscope

5. Democritus • Democritus was a Greek to first come up with idea of an atom. • His belief: atoms were indivisible and indestructible. = WRONG! • Atom comes from “atmos” - indivisible

6. Dalton’s Atomic Theory • 2000 yrs later, John Dalton used scientific method to transform Democritus’s idea into a scientific theory • Dalton put his conclusions together into his Atomic Theory (4 parts)

7. Dalton’s Atomic Theory • All elements are composed of indivisible atoms.

8. Dalton’s Atomic Theory • Atoms of the same element are identical. Atoms of different elements are different

9. Dalton’s Atomic Theory • Atoms of different elements can chemically combine in whole number ratios.

10. Dalton’s Atomic Theory • Atoms of one element can never be changed to another element

11. The Electron • Particle with negative charge • Discovered by J.J. Thomson • Used cathode ray (electron) beam and a magnet/charged plate. • Millikan found the charge and mass

13. The Proton and Neutron • An atom is electrically neutral • If there is a negative particle then there must be positive particle • Proton – particle with positive charge • Chadwick discovered neutron – neutral charge

15. Thomson’s Atomic Model • Electrons distributed in a sea of positive charge • Plum Pudding Model

16. Rutherford’s Gold Foil Experiment

17. Rutherford’s Atomic Model • The nucleusis the central part of the atom containing protons and neutrons • Positive charge • Most of the mass • Electrons are located outside the nucleus • Negative charge • Most of the volume

19. Atomic Number • An element is defined only by the number of protons it contains • Atomic Number – number of protons • Number of protons = number of electron • For a neutral element

20. Identify the number of Protons • Zinc (Zn) • Iron (Fe) • Carbon (C) • Uranium (U) • 30 • 26 • 6 • 92

21. Mass Number • Nucleus contains most of the mass • Mass Number – total protons and neutrons Number of neutron = Mass # – Atomic #

22. Identify # of Subatomic Particles • Lithium (MN = 7) • Nitrogen(MN = 14) • Fluorine(MN = 19)**MN = Mass Number • 3 p+ , 3 e-, 4 n0 • 7 p+ , 7 e-, 7 n0 • 9 p+ , 9 e-, 10 n0

23. Differences in Particle Number • Different element: different number of protons • Ions – same number of proton, different number of electrons • Isotope – same number of proton, different number of neutrons • Different Mass Numbers

25. Two Notations for Atoms • Nuclear Notation • Write the element symbol • On left side, superscript = Mass Number • On left side, subscript = Atomic Number • Isotope –Hyphen Notation • Write full name of element • On right side, put a dash • On right side put Mass Number after dash Hydrogen - 3

26. Ex: Three isotopes of oxygen are oxygen-16, oxygen-17, and oxygen-18. Write the nuclear symbol for each.

27. Ex: Three isotopes of chromium are chromium-50, chromium-52, and chromium-53. How many neutrons are in each isotope?

28. Ex: Calculate the number of neutrons for 9942Mo.

29. Atomic Mass • Atomic Mass Unit (amu) – one-twelfth of the mass of the carbon-12 atom • Different isotopes have different amu (mass) and abundance (percentage of total) • Atomic Mass – weighted average mass of the naturally occurring atoms. • Isotope Mass • Isotope Abundance

30. Atomic Mass • Because abundance is considered, the most abundant isotope is typically the one with a mass number closest to the atomic mass. • Example, Boron occurs as Boron-10 and Boron-11. Periodic Table tells us Born has atomic mass of 10.81 amu. • Boron-11 must be more abundant