Periodic Table Trends
Atomic Radius
• Approximate measure of atomic size
• Increases going left and down on the periodic table
• Large increase with additional shells
• The larger the atomic #, the greater the + charge in
the nucleus
• + charge attracts e- more strongly so the atom
becomes smaller
Atomic Radius
Ionization Energy
• Energy required to strip off outermost e- of atom or
molecule
• Increases going right and up on the periodic table
• Noble gases have the highest IE
• Because they have full valence and are very stable
• Valence e- of smaller elements are closer to the
nucleus so there is stronger attraction
• Fewer e- also means less repulsion & shielding
Ionization Energy
Electronegativity
(e
Affinity)
• The attraction of an atom for the electrons in a
chemical bond
• Small IE = less electronegativity: if an atom is not
attracted to its e- then of course it would be easier
to pluck off
• We will revisit electronegativity when we talk about
bonding polarity
Other Properties of Elements
• H: the only element that can act as metal &
nonmetal
• When naming compounds you should’ve noticed that H
could act as either a cation or an anion
• HBr (cation) vs. NaH (anion)
• Elements that form diatomic molecules:
Having, Naps, On, Fluffy, Clouds, Bring, Invigoration
Chemical Bonding
Ionic & Covalent Bonds
• Ionic bonds: cations donate electrons to anions
• Ions interact at a distance
• Not very strong
• Covalent bonds: nonmetals share electrons
• Very strong
• Can form single, double or triple bonds
• Can be represented using Lewis Dot Structures
Bonding & Lewis Structures
• Bonding Models & Lewis Structures
Monatomic Lewis Structures
• Useful for periods 1-3 b/c of octet rule (2, 8, 8)
• To draw a monatomic Lewis structure:
1) Find the number of valence e- of atom or ion
2) Write the element symbol
3) Place dots around the element to represent its
valence e-
Monatomic Lewis Structures
Ionic Lewis Structures
Covalent Lewis Structures
• For a covalent compound:
1) Find total valence e- for compound
2) Draw bonds to connect atoms
3) Each single bond is made of 2 atoms and counts
toward the octet for both atoms
4) Try to satisfy octet rule for all atoms
5) Try to make compound symmetrical
6) If you are short on e-, try double & triple bonds
Covalent Lewis Structures
• Lewis structures with lower formal charges are
favoured
• Formal charge = valence e- - ½(bonding e-) - lone e-
Practice
• Monatomic: He, Li+, C, F• Ionic: KCl, CaCl2
• Covalent: Cl2, H2O, CO2, N2, CH2ClF
Homework
• HW: read p.160-175, 183-188 and try #86
• Review, study and practice Units 1-3
• Be prepared for a Unit 3 test on the 1st week back
• Be prepared for a midterm exam covering Units 1-4
late April
• I will upload answers to old worksheets and new
review packages throughout the break
• Enjoy your break!