2-1 THE NATURE OF MATTER:
CHEMICAL COMPOUNDS
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CHEMICAL
COMPOUNDS
Chemical Compounds
• In nature, most elements are found combined
with other elements in compounds.
• A chemical compound is a substance formed
by the chemical combination of two or more
elements in definite proportions.
• The physical and chemical properties of a
compound are different from the elements
from which it is formed.
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CHEMICAL COMPOUNDS
Scientists show the composition of compounds by a kind of
shorthand known as a chemical formula.
A chemical formula is a way of naming a compound using
symbol (letters and numbers)
Water, H2O, contains two atoms of hydrogen for each atom of
oxygen.
The formula for table salt, NaCl, indicates that sodium and
chlorine combine in a 1 : 1 ratio.
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WHITEBOARD
Given:
Glucose: C6H12O6
1. How many types of atoms are
in glucose?
2. How many Carbon atoms?
3. How many Hydrogen atoms?
1. 3
2. 6
3. 12
4. 24
4. What is the total number of
atoms?
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CHEMICAL BONDS
Chemical Bonds
• The atoms in compounds are held
together by chemical bonds.
• Bond formation involves the
electrons that surround each
atomic nucleus.
• The electrons that are available to
form bonds are called valence
electrons.
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CHEMICAL BONDS
•Ionic Bonds
• An ionic bond is formed when one or
more electrons are transferred from
one atom to another.
• An atom that loses electrons has a
positive charge.
• An atom that gains electrons has a
negative charge.
• These positively and negatively
charged atoms are known as ions.
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CHEMICAL BONDS
Sodium atom (Na)
Sodium ion (Cl-)
Sodium ion (Na+)
Protons
Electrons
Charge
+11
- 11
0
Sodium atom (Cl)
Protons
Electrons
+17
18
- 17
Charge
-10
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CHEMICAL BONDS
•Covalent Bonds
• Sometimes electrons are shared
by atoms instead of being
transferred.
• Sharing electrons means that the
moving electrons actually travel in
the orbitals of both atoms.
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CHEMICAL BONDS
A covalent bond forms when electrons are
shared between atoms.
• When the atoms share two electrons,
the bond is called a single covalent
bond.
• When atoms share four electrons it is
called a double bond.
• When atoms share six electrons it is
called a triple bond.
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CHEMICAL BONDS
The structure that results when atoms
are joined together by covalent bonds
is called a molecule.
A molecule is the smallest unit of
most compounds.
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CHEMICAL BONDS
In a water
molecule, each
hydrogen atom
forms a single
covalent bond
with the oxygen
atom.
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CHEMICAL BONDS
•Van der Waals Forces
• When molecules are close together, a
slight attraction can develop between
the oppositely charged regions of
nearby molecules.
• Chemists call such intermolecular
forces of attraction van der Waals
forces, after the scientist who
discovered them.
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CHEMICAL BONDS
Although van der Waals forces are not as strong
as ionic bonds or covalent bonds, they can hold
molecules together, especially when the molecules
are large.
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CHEMICAL BONDS
For example, van der Waals forces
form between the molecules on the
surface of a gecko’s foot and the
molecules on the surface of the wall.
The combined strength of all the van
der Waals forces allows the gecko to
grip the wall.
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WHITE BOARD
1. Which kind of bond
shares electrons?
1. Covalent
2. During Ionic
bonding, an electron is
taken by one atom from
another. The resulting +
and – charged atoms
are called ______.
2. Ions
3. What type of bonding
occurs between close
molecules.
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3. van der Waals
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