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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!
Electronegativity Electronegativity – the tendency of an atom to attract electrons from a neighbouring atom.
Hey! I find your electrons attractive!
Get lost, loser!
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.
Electron
egativity decreases as you move dow
n each column
.
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!
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).
VIII.3 CHEMICAL BONDING
Ex: Na + Cl
Ex: Ca + O
*The greater the distance between the charges, the smaller the attraction!
The melting points of some Ionic Compounds are as follows:
NaF 993 oCKCl 770 oCLiCl 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
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
Some melting points of Network Solids:
Diamond (Carbon) 3550 oCSilicon Carbide (SiC) 2700 oCBoron Nitride (BN) 3000 oC
Covalent bonds are also very strong!
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
I
I
The covalent intramolecular bond in I2 is very strong.
I
I
I
I
I
I
I
I
I
IThere are weaker intermolecular forces which hold covalent molecules together in a molecular solid.
2 TYPES OF VAN DER WAALS
London 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??????
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 atomsadjacent covalently-bonded molecules
The greater the atomic number, the stronger the London forces it experiences