8th Grade Science
© Fall 2005, Pflugerville ISD, 8th Grade
Chapter 4- Chemical Compounds
Section 1: Ionic Compounds
Section 2: Covalent Compounds
Section 3: Acids, Bases, & Salts
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is a chemical compound?
What Do You Think?
Imagine that you need to attach two
pieces of paper together. What are
three ways you might do this?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Chemical Bonds
Terms to Know:
• Valence Electrons
• Ionic Compounds
-Ions
-Crystal Lattice
• Covalent Compounds
-Molecule
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Ionic Bonding
• Ionic bonds are
the forces of
attraction between
positive and
negative ions
• They are formed
when atoms lend
or borrow
electrons from
each other
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Ionic Bonding
• Metals lend
electrons
• Nonmetals borrow
electrons
• Ionic compounds
usually involve a
metal and a
nonmetal
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Na & Cl bond to form NaCl, or salt
• Na has 1
valence
electron in
its outermost
energy level
• Cl has 7
valence
electrons
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Na & Cl bond to form NaCl, or salt
• Na lends one
electron to Cl
• Na becomes
positive and
Cl becomes
negative
• Salt ions are
formed!
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Metal and Nonmetal Ions bond to
form a Crystal Lattice
• A crystal lattice is
a 3-D, repeating
pattern of ions
• Ions are arranged
by alternating
positive and
negative charges
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Properties of Ionic Compounds
• Very high melting
points
• Brittle– break along
planes of cleavage
• Dissolve well in water
• Water solution will
conduct electricity
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Ionic bonds, revisited
• Charged ions bond to form a
neutral compound
• Ionic bonds are the strongest
type of bond
• The number of valence
electrons in an atom determines
its reactivity with other elements
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Covalent Bonding
• Covalent bonds
are formed
between
nonmetals only
• In a covalent
bond, atoms
share valence
electrons
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Covalent Bonding
• Valence electrons
are weakly bonded
to the nucleus
• This weak
attraction between
the nuclei and the
shared electron(s)
binds the molecule
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
O and H bond to form H2O
• Oxygen has
6 valence
electrons
• Hydrogen
has 1
valence
electron
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
O and H bond to form H2O
• Oxygen needs
2 valence
electrons for a
stable shell
• Hydrogen
needs 1 valence
electron for a
stable shell
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
O and H bond to form H2O
• 1 Oxygen bonds
with 2 atoms of
Hydrogen and all
3 share the
electrons
• As long as the
electrons are
shared, valence
shells are full
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Nonmetals bond to form Molecules
• The simplest type of molecule
is diatomic, meaning it is
made of only 2 atoms
• There are only seven
elements that are diatomic:
Hydrogen, Oxygen,
Nitrogen, Fluorine,
Chlorine, Bromine, and
Iodine
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Nonmetals bond to form Molecules
Caffeine Molecule
© Fall 2005, Pflugerville ISD, 8th Grade
• Molecules can get
more complex,
involving many
different elements
• Remember, covalent
compounds contain
only nonmetals
Unit A : Chapter 1 : Section 1
Properties of Covalent Compounds
• Low melting points
• Most covalent
compounds do not
dissolve in water (oil &
water don’t mix)
• If it can dissolve, the
solution does not
conduct electricity
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Covalent bonds, revisited
• Nonmetals only
• Form uncharged
molecules, not charged
ions
• Covalent bonds are the
weakest type of bond
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Bonding & Compounds- Quick Quiz
• How does a molecule form?
• Which is stronger, an ionic or a
covalent bond?
• What is an ion?
• Which type of bond typically has a
higher melting point?
• Which type of bond involves only
nonmetals?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is a chemical compound?
What Do You Think?
Lemons and tomatoes have a tangy
taste because they contain citric acid.
What are some other foods that might
be flavored by acids?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is an Acid?
All of these products contain Acids
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is an Acid?
•HCl dissolves
in water
because it is an
ionic compound
•HCl breaks
apart to form H+
ions and Cl- ions
HCl is added to H2O
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is an Acid?
•The H+ ions
bond with H2O
to form H3O+,
a hydronium
ion
HCl is added to H2O
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is an Acid?
•An acid is any compound that
increases the number of H+ ions
when dissolved in water
•These H+ ions bond with the water
to create H3O+, the hydronium ion
•Strong acids are corrosive,
meaning they can destroy clothing
and body tissues
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is a Base?
All of these products contain Bases
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is a Base?
•Like other
bases, NaOH is
an ionic
compound
NaOH is added to H2O
© Fall 2005, Pflugerville ISD, 8th Grade
•NaOH dissolves
in H2O and
breaks apart to
form Na+ ions
and OH- ions
Unit A : Chapter 1 : Section 1
What is a Base?
•Strong bases
will break apart
completely to
form lots of
OH- ions,
which are
corrosive
NaOH is added to H2O
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is a Base?
•A base is any compound that
increases the number of OH-, or
hydroxide, ions when dissolved
in water
•Strong bases, like strong acids,
are corrosive, meaning they can
destroy clothing and body tissues
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is a Salt?
All of these products contain a Salt
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is a Salt?
•When you hear the
word salt, you probably
think of table salt
NaCl, or Salt Crystals
© Fall 2005, Pflugerville ISD, 8th Grade
•But salts are any ionic
compounds formed
from the positive ion of
a base and the
negative ion of an acid
Unit A : Chapter 1 : Section 1
What is a Salt?
•The
from the base
and the Cl from the acid
bond to form NaCl, salt
+
Na
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is a Salt?
•The
from the acid
and the OH from the
base bond to form H2O,
water
+
H
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
What is a Salt?
•A salt is an ionic compound formed
from the positive ion of a base and
the negative ion of an acid
•Salts are used to season our foods,
make soap, treat our pools, and settle
our stomachs
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Let’s Review!
-1-
What is the difference
between ionic compounds
and covalent compounds?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Let’s Review!
-2-
What is an acid?
What is a base?
What is a salt?
How are they all related?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Chemical Compounds
•http://www.ausetute.com.au/namiform.html
•http://www.elmhurst.edu/~chm/vchembook/144
Acovalent.html
•http://www.sciencebyjones.com/acids_bases_s
alts.htm
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1
Pre-AP Extensions
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 1 : Section 1