Transcript Ch. 20 Chemical Bonds

Ch. 20 Chemical Bonds
Stability in Bonding
Ch. 20 Section 1
Bell Work
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Good morning! Today is October 14. I hope you all had a great Fall Break! We
are now on Chapter 20, Section 1 (page 602 in your book). Please get started on
the Bell Work quietly.
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1). Explain why some elements are stable on their own while others are
more stable in compounds?
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2). Describe why chemical bonding occurs. Give two examples of how
bonds can form.
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3). Compare and contrast the properties of the individuals elements that
combine to make salt with the compound salt. (NaCl)
Answers
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1). If an element has eight electrons in its outer electron
energy level, it has a tendency not to react.
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2). Electrons are either gained, lost, or shared between
atoms.
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3). Sodium, as an elements, is a solid metal. Chlorine is
a gas. When the two combine to form sodium chloride,
they form a solid compound.
Warm Up
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Sodium is in group one of the periodic
table. A sodium atom has one valence
electron. Atoms with one electron in their
outer energy levels will bond easily with
atoms having 7 valence electrons. Name
one element sodium could give its one
extra electron to.
Combining Elements
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Many elements exist around you in their
uncombined forms, but elements can unite
chemically to form compounds when
conditions are right
Combining Elements
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Compounds often
have properties unlike
the properties of their
individual elements
Combining Elements
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A Chemical Formula
tells what elements a
compound contains
and the exact number
of atoms of each
element in a unit of
the compound
Combining Elements
A subscript is written after and below the
element’s symbol
 Subscripts tell how many atoms are in
each unit of a compound
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NH3
Atomic Stability
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An atom is chemically stable
when its outer energy level is
complete (like the Noble
Gases)
Other elements are more
stable when they can complete
their outer energy levels by
becoming part of a compound
Atomic Stability
The Octet Rule says that atoms tend to
combine so they have 8 electrons in their
outer energy level
 Atoms can gain, lose, or share
electrons to complete their outer
energy levels and become stable
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Gaining, losing, and
sharing electrons
forms an attraction
between atoms
Atomic Stability
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The attraction is called
a Chemical Bond, and
atoms are pulled
together, forming a
compound
Atomic Stability
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Generally, ionic
bonds are formed
between a metal
and a nonmetal, and
covalent bonds are
formed between two
or more nonmetals
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Electronegativity is the
ability of atoms to attract
electrons within a bond –
this determines the bond
type