Chapter 17 - Chemical Bonding
Chapter 17 - Chemical Bonding:
FACTS:
o Charged things interact with other charged things
o If the signs are opposite (protons and electrons),
things attract.
o Three types of bonds: Metallic, Ionic and Covalent
17.1
Metals and Alloys:
Ion-an atom that has either lost or gained one or more
electrons
Metallic Bond: a fluid of electrons holds the positively
charged metal ions together
Alloy- any mixture composed of two or more metallic
elements
E.g.: Steel- iron, manganese and carbon
17.2
Ionic Bonds:
The attraction between two oppositely charged
ions
Ionic Compound – any chemical compound made of
ionically bonded ions
E.g.: Sodium Chloride (Na is + and Cl is -)
♦ A positive superscript means that an electron has
been LOST. (Na+)
♦ A negative superscript means that an electron has
been GAINED. (Cl-)
Ionic Crystal- any array of 2 dimensional ionic
compounds
17.3
Covalent Bonds:
2 elements SHARING valence electrons (co-sharing and valent-valence electrons)
Covalent Compound - any group of atoms held
together by one or more covalent bonds
E.g.: H2
-each H atom shares an electron with the other H
atom
Molecule- a group of atoms held tightly together by
covalent bonds.
17.4
Covalent Polarity:
Dipole- one side of a molecule is slightly positive
one side is slightly negative
Electronegativity- how well atoms are able to pull
electrons toward themselves
E.g.: H and F, Fluorine is more electronegative
holds electrons closer & is
Therefore lightly negative.
Nonpolar: no dipole is formed (E.g. H2)
Polar: Electronegativities are not equal & form a
dipole
Percent Ionic Charter:
o indicates the degree of polarity
o determined by the difference in electronegativity
17.5
Molecular Polarity:
v Polar bonds create polar molecules.
v Chemical bonding is like a tug of war.
v Each atom is pulling on electrons.
v When one atom pulls harder than the other,
the result is a polar molecule.
E.g.: H2O, Oxygen is more electronegative than
hydrogen and therefore “tugs” on
electrons harder.
This ends up forming a polar molecule
The oxygen side is slightly negative.
The hydrogen side is slightly positive.
v Polar molecules attract one another creating
substances with a higher boiling temperature.
E.g.: Liquid Nitrogen is nonpolar and boils at
–196oC.
Water is polar and boils at 100oC.
1