Chapter 5 Bonding. When atoms combine they form a chemical bond The force of attraction between two...
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- Slide 1
- Chapter 5 Bonding
- Slide 2
- When atoms combine they form a chemical bond The force of
attraction between two or more atoms.
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- Valence Electrons Are the outer most electrons of an atom. They
play a huge role in how an atom bonds.
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- Lewis Structure Is a diagram of atoms that only shows the
valance electrons Ex: ClNaH Ar
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- The Octet Rule The octet rule says that atoms tend to gain,
lose or share electrons so they can have eight electrons in their
outer shell. They do this because they are more stable with a
complete outer shell. There are some situations where it does not
apply. For example, hydrogen wants to take one on to complete its
outer shell with 2 electrons.
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- Oxidation Numbers Oxidation numbers represent the charges that
an ion has when it gains or loses its valence electrons. They are
listed as a + or above each column on the periodic table.
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- Ion An ion is an atom which has lost or gained one or more
electrons, making it positively or negatively charged. A
negatively-charged ion, gains an electrons so it has more electrons
then it has protons. A positively-charged ion, looses electrons so
it has more protons then electrons. A polyatomic ion is an ion that
is made up of more than one atom. Poly= ManyAtomic= Atoms Ex: NH 4
+ is the chemical formula for an ammonium ion. It contains two
elements nitrogen and hydrogen and has a positive charge.
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- Ionic Bonds Bonds that form as a result of the attraction
between positive and negative ions. The atoms are attracted to each
other because of their opposite charges We call the compound that
results from the bond an Ionic Compound. Usually form between a
metal and a nonmetal
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- In an IONIC bond, electrons are lost or gained, resulting in
the formation of IONS in ionic compounds. FK
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- FK
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- FK
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- FK
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- FK
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- FK
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- FK + _ The compound potassium fluoride consists of potassium (K
+ ) ions and fluoride (F - ) ions
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- FK + _ The ionic bond is the attraction between the positive K
+ ion and the negative F - ion
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- Formulas Reminder: A chemical formula is the combination of
symbols that show the elements in the compound. i.e. MgCl 2 If a
molecule contains more than one atom of a particular element, you
indicate it by using a subscript after the chemical symbol (ex: the
2 in MgCl 2 ). It tells you the ratio of atoms in the compound
(MgCl 2 has a 1:2 ratio). If no subscript is written the number 1
is understood( NaCl there is a 1:1ratio). A coefficient acts as a
multiplier for all of the atoms in the entire compound, it is found
in front of the chemical formula Ex: the 5 in 5 MgCl 2
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- Example MgCl 2 Here we have one molecule of magnesium chloride.
The subscript 2 in the formula above only pertains to the chlorine
in the compound. The total number of atoms in the compound is 3.
Now let us put a coefficient in front of the molecule and see how
that changes things. 5 MgCl 2 The coefficient 5 refers to the
entire molecule. It shows that there are 5 compounds of magnesium
chloride. Since each molecule is made up of 3 atoms, the total
number of atoms is now 15. There are 5 magnesium atoms and 10
chlorine atoms. How many atoms are in the following bond 3Na 2 S
Sodium(Na)____ Sulfur(S)____ Sodium Sulfide(3Na 2 S) ____ = total
atoms 6 3 9
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- Naming Ionic Compounds The name of the positive ion comes
first, followed by the name of the negative ion. The metal will be
the positive because it gives away electrons and the nonmetal will
be the negative because it gains electrons. If the negative ion is
a single element the end of its name changes to ide. Ex: NaCl-
Sodium Chloride MgO- Magnesium Oxide If the negative ion is
polyatomic, its name usually ends in ate or ite. Ex: NH 4 NO 3 -
Ammonium nitrate What is the name of the ionic compound with the
formula K 2 S? ______________ Potassium Sulfide
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- Properties of Ionic Compounds Hard Brittle Crystals High
melting points- NaCl melts at 801C= 1473.8 F When dissolved in
water they are electrolytes. An electrolyte solution is one that
can conduct electricity. Ionic bonds in solid from are poor
conductors.
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- Covalent Bonds The chemical bond formed when two atoms share
electrons. Usually form between nonmetals. We call the neutral
group of atoms joined by a covalent bond a molecule.
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- In covalent bonding, atoms still want to follow the octet rule
and have a complete valance shell
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- But rather than losing or gaining electrons, atoms now share an
electron pair. In covalent bonding, atoms still want to follow the
octet rule and have a complete valance shell
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- The shared electron pair is called a bonding pair But rather
than losing or gaining electrons, atoms now share an electron pair.
In covalent bonding, atoms still want to follow the octet rule and
have a complete valance shell
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- Cl 2 Chlorine forms a covalent bond with itself
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- Cl How will two chlorine atoms react?
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- Cl Each chlorine atom wants to gain one electron to achieve a
full outer shell.
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- Neither atom will give up an electron. Whats the solution what
can they do to achieve an octet? Cl
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- complete
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- Cl complete
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- Cl The complete outer shell is achieved by each atom sharing
the electron pair in the middle
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- Cl The complete outer shell is achieved by each atom sharing
the electron pair in the middle
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- Cl This is the bonding pair
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- Cl It is called a SINGLE BOND
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- Cl Single bonds are abbreviated with a dash
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- Cl This is the chlorine molecule, Cl 2
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- O2O2 Oxygen is also one of the diatomic molecules
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- How will two oxygen atoms bond? OO
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- OO Each atom has two unpaired electrons
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- Oxygen atoms want to gain two electrons. OO
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- O O Both electron pairs are shared.
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- 6 valence electrons plus 2 shared electrons = full valance
shell O O
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- 6 valence electrons plus 2 shared electrons = full valance
shell O O
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- two bonding pairs, O O making a double bond
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- O O = For convenience, the double bond can be shown as two
dashes. O O
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- O O = This is the oxygen molecule, O 2
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- Molecular Compounds A compound that is composed of molecules.
Ex: CH 4 - Methane H 2 O- Water Properties: Low melting and boiling
points. Poor conductors
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- Polar Bonds A covalent bond in which electrons are shared
unequally is called a polar bond. ex: water molecules One atom
pulls more strongly on a shared electron causing a slight charge.
Polar molecules tend to pull close together because the negative
end of each molecule is attracted to the positive end of other
molecules.
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- Nonpolar Bonds If the electrons are shared equally it is called
a nonpolar bond. A molecule may contain a polar bond and still be
nonpolar overall. In order for this to happen the molecule must
bond in a straight line with opposite pulling. Ex: carbon dioxide
There is little attraction between non polar molecules
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- Why Doesnt Oil & Water Mix? The molecule in vegetable oil
are nonpolar and have little attraction to other molecule. Water
molecules are polar and are strongly attracted to one another. SO,
the water stays with the water which leave the oil by itself.
Adding soap allows them to mix easily because the soap molecule
contains one end that is an ionic bond and the other end is a
nonpolar covalent bond. The nonpolar end mixes with the oil and the
charge on the ionic end attracts the water
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- Metallic Bonds An attraction between a positive metal ion and
the electrons surrounding it. In other words: Many electrons are
shared by many atoms. A metal consists of positively charged metal
ions embedded in a sea of valence electrons.
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- Metallic Properties The sea of electrons model of solid metals
explains their properties: Heat/electrical conductivity The free
moving valance electrons make it easier for the particles to move
faster. Changes in shape Ductile Malleable This happens because the
ions in the metal are not attracted to each other, instead they are
attracted to the loose electrons all around them. Luster A metals
luster is due to its valance electrons. They absorb and then
reflect the light which we see has shiny.
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