Transcript The Bonding Continuum - A. Y. Jackson Secondary School

The Bonding Continuum
Ionic
Bonding
Pure
Covalent
Bonding
Ex: Cl2, H2
Pure Covalent
 btwn indentical atoms
Electrons
in orbit
 electrons shared equally
shared
pair of e’s
X
X
Cl
nuclei
Polar Covalent
 unequal sharing of e’s
 shared e’s spend more time near one atom
 Why?
Electronegativity: the relative ability of an atom to attract
an electron
- represented by a number
- a higher number = a greater attraction to a shared pair
 Ex: HCl
- see periodic table at back of text
- Electronegativity - directly under the atomic number
- H = 2.1
- Cl = 3.0
shared pair closer
to Cl
ex. HCl
+
Slight positive
charge
X
X
-
Slight negative
charge
Greek symbol delta = a small difference
(partial)
 Cl has a greater attraction for the bonding e’s
BUT
 the attraction is not strong enough for an electron transfer
(as in an ionic compound)
Ex: HCl
Polar Covalent
Bond
Ionic
Bonding
Pure
Covalent
Bonding
Ex: Cl2, H2
 A polar covalent bond lies between an ionic and a covalent
bond
Predicting type of Bond
 ionic, polar covalent or covalent??
 If difference in electronegativity is great enough,
 an ionic bond is formed
 Ex: Rb and F
Rb = 0.8 and F = 4.0
Absolute difference = 3.2
F “steals” an electron from Rb
(forming two ions and an ionic bond)
Rule
 Difference in electronegativity
 greater than 1.7 = IONIC BOND
do not copy
 This is not a hard and fast rule
 There are many compounds (ex: MgI2) with a smaller
electroneg. difference, but still have ionic properties
 convention used for this course
Ex: HCl
Polar Covalent
Bond
3.3 (F &Fr)
1.7
Ionic
Bonding
Practice
 Page 84 #2,3,4
0
Pure
Covalent
Bonding
Ex: Cl2, H2
Polar Molecules
 a molecule with polar covalent bonds may have
 a slightly positive end and a slightly negative end
 creating a polar molecule
 predict based on chemical or structural formulae
 Hint: symmetrical molecules are usually NOT polar, even
when they contain polar bonds
Guidelines: Predicting Polar and
Non-Polar Molecules (do not copy)
Type
Description
Examples structur
Polar
AB
Diatomic compounds
HAx
molecule with one H
AxOH
with an OH at one end
OxAy
with an O at one end
NxAy
with an N at one end
CO
HCl
C2H5OH
H2O
NH3
Non-polar
Ax
CxAy
Cl2, N2
CO2, CH4
All elements
Most carbon compounds
Practice
 Page 84 #4abc
 Page 85 #6
 Page 88 #8 abcf
 Read p.86-87 and define the words in bold