The Periodic Table and Chemical Bonding Lesson 4 UNIT VIII The Periodic Table and Chemical Bonding Lesson 4

Review Going DOWN a FAMILY ----- size of atom increases and distance between valence electrons and nuclei increase   Going ACROSS a PERIOD ----- properties are affected by differing valence, nuclear charge and charge on the species One more piece of info on trends…Electronegativity!

Hey! I find your electrons attractive! Electronegativity Electronegativity – the tendency of an atom to attract electrons from a neighbouring atom. Get lost, loser! Hey! I find your electrons attractive!

VIII.3 CHEMICAL BONDING ELECTRONEGATIVITY --- tendency of the atom to attract electrons from a neighbouring atom   Going from left to right across the periodic table the electronegativity of the atoms will __________________ Going down a family of the periodic table the electronegativity of the atoms will _____________________

Electronegativity increases as you move from left to right. Electronegativity decreases as you move down each column.

Ex: Which is more electronegative: K or Br? Pb or S?

Electronegativity & Ionization Energy(IE) If an atom has high electronegativity, it strongly attracts e- from a neighbouring atom (also difficult to remove its own e- so it has high IE) If an atom has low electronegativity, it has little attraction to the electrons of neighbouring atoms (easy to remove e- so low IE) Electronegativity and IE have the same trend on PT!

SUMMARY OF PERIODIC TABLE TRENDS:

Size of ions vs size of a neutral atom

SIZE OF IONS vs NEUTRAL atoms  Li → e- + Li+ 1 valence e- closed shell Positive ions are smaller than the corresponding neutral atom Why?? (fewer electrons, so less repulsion between them).

SIZE OF IONS vs NEUTRAL atoms Cl + e- → Cl- 7 valence e- closed shell Negative ions are larger than the corresponding neutral atom Why?? (more electrons, so more repulsion between them).

Types of chemical bonds Ionic and covalent

Types of Chemical Bonds A. Ionic Bonding:   Ionic Bond –

VIII.3 CHEMICAL BONDING Ex: Na + Cl Ex: Ca + O *The greater the distance between the charges, the smaller the attraction!

NaCl Crystal Lattice

Li F An F Atom A Li Atom - + Li F A Li+ Ion An F- Ion

The melting points of some Ionic Compounds are as follows: NaF 993 oC KCl 770 oC LiCl 605 oC These high melting points are experimental evidence that Ionic Bonds are VERY STRONG. (Hard to break just by heating).

Ionic Bonds IONIC BONDS are VERY STRONG, so compounds held together by ionic bonds have HIGH MELTING TEMPERATURES Think about it… *When there is a smaller radius, there is a stronger/weaker bond *When there is a larger charge, there is a stronger/weaker bond

Covalent Bonds

Covalent Bonds b. Covalent Bonding:  Covalent Bond: Octet Rule:

In Covalent bonds, electrons are Shared

VIII.3 CHEMICAL BONDING Ex: Cl – Cl   Non-mental bonds to a nonmetal (SHARE e-) Covalent bonds are STRONG, but the bonds between molecules are WEAK ex: Cl2 molecules bonded together

Covalent Bonds Polar Covalent Non-polar Covalent HCl Cl2

Diamonds are “forever”! diamond structure Diamonds are “forever”!

Covalent bonds are also very strong! Some melting points of Network Solids: Diamond (Carbon) 3550 oC Silicon Carbide (SiC) 2700 oC Boron Nitride (BN) 3000 oC Covalent bonds are also very strong!

HOWEVER LOOK AT THESE MELTING POINTS… CH4 -182 oC O2 -218 oC F2 -220 oC How come they are so low??

Third type of chemical bonding… “Van der waals Forces” The sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or the electrostatic interaction of ions with one another.

Third type of chemical bonding… “Van der waals Forces” INTRAmolecular INTERmolecular (within/inside the molecule) (between) COVALENT BONDS Van Der Waals

The covalent intramolecular bond in I2 is very strong. There are weaker intermolecular forces which hold covalent molecules together in a molecular solid. I I I I

Intra Vs Inter molecular forces

2 types of Van der Waals London forces Dipole-dipole forces London Forces are weak attractive forces which exist between atoms as a result of temporary dipoles Dipole-dipole forces A permanent dipole So what are dipoles??????

What are dipoles? Dipole –

Polarization causes dipoles!

LONDON FORCES London Forces –  

London Forces London Forces: The WEAKEST TYPE of bonding force ALWAYS present, even in species which have covalent or ionic bonding IMPORTANT??? when they are the only force of attraction.... adjacent noble gas atoms adjacent covalently-bonded molecules The greater the atomic number, the stronger the London forces it experiences

homework P172 #57 P173 #59,60 P 175 #62,63,64 P177 #68, 69 P 179 #72 from a to k P 181 #74,76,78 Read summary on page 182 and try to solve the summary exercises if you have time.