Transcript Part 1

CHAPTER 3: Part 1
Structure of the Atom
Electronic Configurations
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
SUBATOMIC PARTICLES (2)
• Proton: positive charge (+e); mass of 1.67E27 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
ATOMIC STRUCTURE (1)
• What about the neutrons? Atoms of the
same element have the same # p+ and #ebut may have a different number of
neutrons. These atoms are called isotopes.
– All carbon atoms have 6 p+ but 12C or carbon12 has 6 n; 13C has 7 n; 14C has 8 n
– All chlorine atoms have 17 p+ but 35Cl has 18 n
and 37Cl has 20 n
– H: normal (1H), deuterium (2H), tritium (3H)
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.
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.
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
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.
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