Chapter 4: Atomic Structure

1. Chapter 4: Atomic Structure Subatomic Particles Symbol Notation Isotopes Average Atomic Mass

2. Democritus • Atom: smallest part of an element that retains the identity of that element. • Democritus (460-370 B.C.): believed in tiny, indivisible, indestructible particles he called “atomos.” • He had NO experimental proof!

3. John Dalton’s Atomic Theory (1803-1807) • All elements are composed of tiny indivisible particles called atoms. • Atoms of the same element are identical; atoms of different elements are different. • Atoms of different elements can mix in whole number ratios to form compounds. • Chemical reactions cause atoms to separate and recombine, NOT change into different atoms.

4. Subatomic Particles

5. Comparing Subatomic Particles The proton gives identity to an atom, the electron gives personality.

6. Mass Number & Atomic Number Mass Number = Number of protons + neutrons Atomic Number = Number of protons

7. Complete the Table

8. Mass of Atoms • Mass of atom is very small! • Heaviest atom is 4 x 10-22g. • Diameters of atoms: 100-500 pm (1-5 angstroms) • 1 A = 10-10m • Both pm and A are commonly used for diameters.

9. Isotopes Have the Same… • Number of protons • Atomic Number • Number of electrons

10. Isotopes Have Different… n0 • Number of neutrons • Mass Number • Mass

12. Isotopes of Hydrogen Hydrogen-3 Hydrogen-1 Hydrogen-2 Protium Deuterium Tritium

14. Atomic Mass Unit (amu) • carbon-12 isotope used as standard • 1 atom of carbon-12 = 12 amu • carbon-12 has 12 particles with mass • mass of proton = 1 amu • mass of neutron = 1 amu 12 C 6

15. Average Atomic Mass • Weighted average of all isotopes • Seen as mass number on periodic table • Units in amu

16. To Calculate Average Atomic Mass You Need…

17. Calculating Average Atomic Mass Isotope A Isotope B