Transcript BONDING CHEMCOOL

Bond energy
When a bond is broken, energy is absorbed. When a bond is
formed, energy is released.
Example
Cl2 + 58 Kcal
Cl + Cl (endothermic, ΔH is positive)
Cl + Cl
Cl2 + 58 Kcal (exothermic, ΔH is negative)
Notice that in the potential diagram for the above reactions the
molecule Cl2 is more stable than the 2 atoms of Cl. This is why
chlorine can be found in nature as a diatomic molecule.
Example
H2(g), N2(g), O2(g), F2(g), Cl2(g), Br2(l), and I2(s)
Electronegativity
• Electronegativity indicates how strongly an atom of
an element attracts electrons in a chemical bond.
Electronegativity values are assigned according to
arbitrary scales.
• Example
• In the molecule HCl the atoms are bonded with 2
electrons. Cl attracts electrons in the chemical bond
more strongly than H because the electronegativity
of Cl is 3.2 while H is 2.1. Therefore the electrons are
closer to Cl than H.
Octet rule
Noble gases have stable valence configurations
and tend not to bond.
A stable valence configuration consist of 8
valence electrons. This is called the octet rule.
There are exceptions such as helium that has
only 2 valence electrons.
Noble gases, elements in group 8A, are inert or
unreactive gases and are found in nature as
monatomic molecules (1 atom per molecule).
Example
He(g) and Kr(g)
Electron-dot diagrams (Lewis
structures)
• Electron-dot diagrams (Lewis structures) can
represent the valence electron arrangement
in elements, compounds, and ions.
• Lewis structure of some elements
• Example
• Ne, He, Si, and O
Lewis structure of some ions
• Example
• I-, K+, Mg2+, and Br5+
Lewis structure of some
compounds
• Example
• Cl2 (a molecular or covalent compound) and
NaCl (an ionic compound)
Lewis structure of some
compounds
• Atoms attain a stable valence electron
configuration by bonding with other
atoms.
• Example
• Cl2 and NaCl
Atomic and ionic radius
• When an atom gains one or more
electrons, it becomes a negative ion
and its radius increases.
• Example
Atomic and ionic radius
• When an atom loses one or more
electrons, it becomes a positive ion and
its radius decreases.
• Example