Chapter 23
Chemical Bonding
Presented by April Senger
Valence Shells & Lewis Dot Structures
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The valence electrons are the outermost electrons
that are available for bonding
For the purpose of understanding how atoms bond,
we can ignore the inner electrons
To draw the model more simply we use a dot
structure as shown on page 389 for groups 1, 2, 13,
14, 15, 16, 17 & 18
Electrons shown side by side are bonding pairs and
single dots are unpaired electrons available for
bonding
Presented by April Senger
Concept Check
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What is a valance electron?
Any electron in the outermost shell that is
available for chemical bonding with another
atom
Presented by April Senger
Ions
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Ionization is the process of adding electrons to or
removing electrons from an atom or groups of atoms
Atoms like to have 8 electrons. If it doesn’t it will try
to add or lose electrons to get there
When an atom gains or loses electrons it becomes
an ion…these have electrical charges
If you gain an electrons you are negative called
anion
If you lose electrons you are positive called cations
If unstable Li loses one electron, it will only have 2
like He and that is stable
Presented by April Senger
Ions & More Ions
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If unstable Ca loses two electrons, it will only have
18 and can act like stable Ar
If unstable Br takes an electron it becomes negative
and can act like stable Kr
Anions are written like FCations are written like Ca 2+
Metals that form + and nonmetals – bond together
The Alkali and Halogens commonly bond
Presented by April Senger
Concept Check
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What type of ion does t he magnesium atom,
Mg, tend to form?
Mg forms 2+
Presented by April Senger
Ionic Bonds
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Ionic Bonds are a bond formed by the
attraction between oppositely charged ions.
When a positive and negative ion are
attracted together
Nonmetals and Metals!!!
Presented by April Senger
Ionics are Ornery
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Atoms do not always share electrons equally
and transfer them to one atom more than
another
Chlorine is the greediest-it steals the Sodium
electrons in salt to its side a little more.
The Na becomes a little more positive
because it loses electrons and Cl becomes a
little more negative with extra electrons
Presented by April Senger
Facts Continued…
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The positives and negatives are attracted to form a
bond to form a NETWORK called salt
Salt is a series of NaCl molecules in a ratio of 1:1
We call the NaCl a formula unit
CaF2 is a ratio of 1:2 to even the charges
Ionic bonds are held in place and can’t conduct
electricity unless dissolved in water where they can
move freely
The NETWORKS make them strong and have high
melting points
Presented by April Senger
Concept Check
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Is the transfer of an electron from a sodium atom to a
chlorine atom a physical or chemical change?
Electron transfer results in the formation of a new
substance and therefore is a chemical change
What is the chemical formula for the ionic compound
magnesium oxide?
MgO
Presented by April Senger
Metallic Bonds
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Metallic bonds are a bond formed by the
attraction between positively charged metal
ions and the electrons around them.
Bonds between positive metal ions and
electrons in the environment
Presented by April Senger
Metal Facts
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Metals have unique properties
such as bending, stretching,
flexibility, etc
A metal is attracted to
another’s electrons and draws
them very close together
When this close together, the
orbits overlap and electrons
can flow from atom to atom
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Electricity is flowing
electrons so metals
naturally allow electricity
to flow
Metals are flexible
because the atoms can
slide past each other
Presented by April Senger
Covalent Bonds
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Covalent bonds are a kind of bond formed when
atoms share one or more pairs of electrons.
A bond where the electrons are shared
Nonmetal and Nonmetal bond
Don’t Forget!!! Hydrogen is a nonmetal on the
metal side
An atom can have single, double or triple covalent
bonds
Presented by April Senger
Caring Is Sharing
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Examples of covalent bonds are sugar, water, and
networks like silicon dioxide
Covalent bonds only occur between nonmetals
Covalent bonds can be solids, liquids or gases
They do not conduct electricity or have a charge
They dissolve easily in water, can move freely if
melted, and have low melting points
The molecules themselves are strong but the
attractions between the molecules is what gives
them the low melting point
All gases are in 2-packs & are covalently bonded
Presented by April Senger
Nonpolar & Polar Covalent Bonds
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Nonpolar covalent bonds are when the electrons
are shared evenly like in Cl-Cl gas
Polar covalent bonds are when the electrons are
not shared evenly.
Elements to the right and closer to the top “want”
the electrons more = electronegativity
They pull the shared electrons closer giving a
slightly negative charge. The other element
becomes slightly positive. Ex: Water
Presented by April Senger
Concept Check
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How many electrons make up one covalent
bond?
Covalent bonds share 2 electrons
Why do polar covalent bonds have a slightly
higher boiling point than nonpolar bonds?
They have more attraction which means they
require more energy to break them apart
Presented by April Senger
Polyatomic Ions
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Polyatomic ions are an ion made of two or more
atoms that are covalently bonded and that act like
a single ion.
It is a group of atoms with covalent bonds that act
as an ion (have a charge)
An example is Sodium hydrogen carbonate or
NaHCO3
Positive ions are attracted to negative ions
Ammonium likes to be with Nitrate or Sulfate
Presented by April Senger
Hurray For Facts!
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Parentheses are used to remind you that they act as
a single ion
Without parentheses the numbers of atoms can
become incorrect such as (NH4)2SO4
-ate is used for ions with the most oxygen atoms
-ite is used for ions that have the least oxygens
Presented by April Senger