1. CHAPTER 3: Part 1 Structure of the Atom Electronic Configurations

2. SUBATOMIC PARTICLES (1) The atom consists of a massive and compact nucleus and electrons moving about the nucleus. The nucleus contains protons and neutrons. The atom's identity is uniquely defined by the number of protons (Z = atomic number) in the nucleus

3. SUBATOMIC PARTICLES (2) Proton: positive charge (+e); mass of 1.67E- 27 kg; located in nucleus Neutron: zero charge; mass of 1.67E-27 kg; located in nucleus Electron: negative charge (-e); mass of 9.1E-31 kg; moves in space around nucleus In a neutral atom #p+ = #e- If Z = 11, atom = Na. If Z = 80, atom = Hg

5. ATOMIC STRUCTURE (1) What about the neutrons? Atoms of the same element have the same # p+ and #e- but may have a different number of neutrons. These atoms are called isotopes. –All carbon atoms have 6 p+ but 12 C or carbon- 12 has 6 n; 13 C has 7 n; 14 C has 8 n –All chlorine atoms have 17 p+ but 35 Cl has 18 n and 37 Cl has 20 n –H: normal ( 1 H), deuterium ( 2 H), tritium ( 3 H)

6. ATOMIC STRUCTURE (2) Given that atom consists of positive and negative particles, what holds it together? Ans: A balance of electrostatic and centrifugal forces. Nucleus consists of about 99.9%= of mass of atom but only about 1E-13% of volume. Recall atom diameter = 1E-10 m and nucleus diameter = 1E-15 m.

7. ELECTRON CONFIGURATION (1) How are the electrons (e-s) actually arranged around the nucleus? It turns out that e-s occupy shells around the nucleus with e-s in the shell closest to the nucleus being held most tightly. The e-s in the shell farthest from the nucleus are held most loosely. We call the latter e-s valence electrons.

8. ELECTRON CONFIGURATION (2) Valence electrons are the outermost e-s and are most involved in chemical bonding. They also determine the size of the atom. As Z increases, more shells are filled and the larger the atom. The group number above a column on the Periodic Table is equal to the number of valence electrons in the atom

9. ELECTRON CONFIGURATION (3) The occupancy numbers for these shells are 2, 8, 18 (T3.1) How do the electrons fill these shells? They fill from the innermost shell (closest to the nucleus) to the outermost shell until all of the e-s are placed around the nucleus.

11. OCTET OF ELECTRONS Atoms with 8 electrons in the valence shell are extra stable meaning that they do not react readily with other elements. Group VIIIA atoms have an octet of e-s. These are the Noble Gases and are found in nature as single atoms (unreactive) He (duet of electrons), Ne, Ar, Kr, Xe Uses: lighting, fireworks