CH 18 Properties of Atoms and the Periodic Table

1. CH 18 Properties of Atoms and the Periodic Table

2. Structure of the Atom • Chemical symbol —shorthand way to write element’s name; 1 or 2 letters • 1st letter ALWAYS capitalized and if there is a 2nd it is lowercase • Case sensitive: CO≠Co • Some use Latin names, Ag is silver—Argentum in Latin • System used worldwide

3. Atoms—basic building blocks of all matter • Composed of: • Protons—in nucleus; + • Neutrons—nucleus; neutral • Electrons—around nucleus; - • Nucleus—positively charged center of atom

4. Quarks • Quarks—what protons and neutrons are made of;6 types • Up, down, charm, strange, top & bottom • 3 arranged one way=proton (p+) • 3 arranged another way=neutron (n°)

5. Electron models • Atomic models have changed thru-out history • Models showing where e- is located also changed (pg 548) • Bohr’s model is the one we recognize

6. Electron models • Electron cloud is current model • Cloud is the probable region where you would find an e- • Cloud 100,000 times larger than nucleus! But e- is MUCH smaller than a p+

7. Masses of AtomsSec 2 • Neutral atom— equal # of p+ and e- • Atomic mass unit (amu) used to measure atomic particles • Equal to 1/12th the mass of a carbon atom

8. Masses of Atoms Sec 2 cont. • Atomic # = # of p+ • Atomic mass=# of p+ and n° (# above chem. symbol on your chart—larger #) • Atomic mass – atomic # = # of n° • Isotopes—atoms of the same element that have a different # of n°

9. Sec 3 Periodic Table

10. Dmitri Mendleleev—Russian chemist (late 1800’s) arranged elements in order of increasing atomic mass • Left blank spaces due to undiscovered elements • Vertical columns (18) called groups/families • # of outer e- are the same in each group • Chemical properties are the same for the elements in each group • Horizontal rows called periods

11. Metals—all elements left of the stair step • Properties: solids at room temp (except ?), shiny, good conductors of heat and electricity • Metalloids—elements near the stair step • Have properties of both metals and non-metals • Non-metals—right of stair step • Properties: most are gases, some brittle solids, poor conductors of heat/electricity • Groups 312 called Transition elements: metals, but have properties not found in elements of other groups

12. Energy levels of e- • 1st level, closest to the nucleus, lowest E, only holds 2 e- • 2nd level holds 8 e- • 3rd level holds 18 e- • 4th level holds 32 e-

13. e- dotdiagrams—represents the outermost e- of an element • Called Lewis structures • Chemical symbol and the # of e- in the outer level placed around the chem symbol using dots