Download 2.1 Atoms and Bonds

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Atoms are the smallest form of matter
Nucleus:
◦ Protons (positive)
◦ Neutrons (neutral)
◦ Protons & neutrons make up most of
the atom’s mass
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Energy levels
◦ “cloud” around nucleus
◦ Contains electrons (negative)
◦ TINY! Only 1/1840th the mass of a proton
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1st energy level:
◦ Holds max 2 electrons (e-)
◦ Electrons fill this energy level FIRST
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2nd energy level:
◦ Holds max 8 electrons
◦ Electrons fill this energy level NEXT!
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3rd energy level:
◦ Holds max 18 electrons (but needs 8 to be stable)
◦ How small is an atom?
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An element:
◦ A substance made up of only 1 type of atom
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Atoms of the same element all have the same
characteristics
Meet the elements
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Each element has a symbol:
◦ Carbon
◦ Oxygen
◦ Hydrogen
◦ Nitrogen
◦ Sulfur
◦ Phosphorus
Non-Metals
Metals
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Atomic Number:
◦ Number of protons in an atom of an element
Atomic symbol
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Atomic Mass:
◦ The mass of one atom of an element
◦ Number of protons + neutrons
 # Neutrons = Atomic Mass - # protons
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Valence electrons are the outermost
electrons of an atom
Tip for calculating valence electrons:
◦ Count the columns on the periodic table from LEFT
to RIGHT (skip the middle)
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Find the number of valence electrons for…
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◦
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Carbon
Hydrogen
Chlorine
Oxygen
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Lewis structures show the number of valence
electrons in an atom
Procedure:
1. Write the atomic symbol
2. Determine the number of valence electrons
3. Place the valence electrons (dots) around all 4
sides of the atomic symbol – not pairing up until
necessary!
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Ex: Carbon (4 valence electrons)
C
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# protons = # electrons
# positive charges = # negative charges
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8 protons
8 electrons
8 neutrons
e-
eee-
8 p+
8n
e-
e-
e-
e-
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Compound
◦ A substance that is composed of two or more
elements that are chemically bonded
◦ Ex: H2O, NaCl, C6H12O6, CO2
◦ The properties of a compound are different than
the properties of the elements in the compound
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Atoms form chemical bonds to become stable
◦ Stable = valence is full of electrons
◦ Row 1 elements need 2 valence electrons to be
stable
◦ The rest of the atoms need 8 valence electrons to
be stable
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Two main types of bonds:
◦ Covalent
◦ Ionic
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Atoms share electrons to complete their
valence
A molecule is formed when atoms share
electrons
Usually formed between two nonmetals
Bonds are represented by lines between
atoms
Covalent bond
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The number of valence electrons needed for
an atom to be stable = how many bonds it
will form
Example: H2
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Example: NH4
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Example: H2O
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Types of covalent bonds
◦ Single bond: share 2 electrons
◦ Double bond: share 4 electrons
◦ Triple bond: share 6 electrons
Double Covalent bond
Single Covalent bond
Triple Covalent bond
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How many of each atom in the following
molecules:
◦ CO2
◦ C6H12O6
◦ H2O
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Atoms transfer valence electrons to become
stable in an ionic bond
Positive
◦ Atoms become ________________ if lose electrons.
Negative
◦ Atoms become ________________ if gain electrons.
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Ionic bonds are the strong attraction between
positive & negative ions
Forms an ionic compound
Often found between metals & nonmetals
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Ex: NaCl
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Ex: MgO
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Attraction between separate molecules
◦ “intermolecular” force
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Not as strong as ionic or covalent bonds!
Uses:
◦ Help keep large molecules (proteins) together
◦ Geckos use to climb glass
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A chemical change occurs when compounds
are formed
Reactants are particles that are present
before the reaction
Products are particles that are present after
the reaction
Of the form: Reactant Products
◦ Ex: 2H2 + O2  2H2O
2H2
+
O2
Number of
Type of compound
compounds Number of atoms
in 1 compound
One atom
 2H2O