CHEMICAL BONDS

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CHEMICAL BONDS

• Chapter 21.5 Chapter 23

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Elements can combine to form compounds

• When different elements bond together, they make
  a compound
• ie. Sodium and Chlorine combine to form table
  salt
• A compound is represented by its chemical formula
• The chemical formula are the symbols of the
  elements in the compound and the number of each
  atom in the compound

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Elements can combine to form compounds

• Waters chemical formula is H20
• This means water is made of hydrogen and oxygen
• The chemical formula also tells us that there are
  2 hydrogen atoms and one oxygen atom found in
  each molecule of water

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Elements can combine to form compounds

• We use subscripts to show how many atoms of each
  element are in the compound
• Important Note We dont use a subscript 1 if
  there is only one on an atom in a compound
• ie NaCl
• One Sodium Atom
• One Chlorine Atom
• NO SUBSCRIPTS!!!!

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Elements can combine to form compounds
H2O
Hydrogen
Oxygen
2
Atoms
1
Atom
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Elements can combine to form compounds

• We use coefficients to show how many molecules of
  each compound we have
• To figure out how many atom of each element you
  have you must multiply the coefficient by the
  subscript
• Important Note We dont use a coefficient 1 if
  there is only one molecule of the compound
• ie NaCl
• One molecule of Sodium Chloride
• NO COEFFICIENT!!!!

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Elements can combine to form compounds
2H2O
2 molecules of water
coefficient
Hydrogen
Oxygen
2
Atoms
1
Atom
4
2
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Elements can combine to form compounds

• Remember elements lose their properties when they
  are combined in a compound
• Sodium is no longer explosive in salt
• Chlorine is no longer poisonous in salt
• Hydrogen is no longer flammable in water
• Oxygen is no longer flammable in water

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Elements can combine to form compounds

• Review
• A chemical formula is used to represent the
  elements found in compound
• Subscripts are used to show how many atoms of
  each element are in the compound
• Coefficients are used to show how many molecules
  of each compound you have
• Coefficients and subscripts are multiplied
  together to find the total number of atoms of
  each element you have

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TYPES OF BONDS

• IONIC
• COVALENT

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IONIC BONDS

• FORM BETWEEN A METAL A NONMETAL
• USUALLY FORMS SOLIDS

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IONIC BONDS

• TWO ATOMS ARE ATTRACTED TO ONE ANOTHER BECAUSE
  THEY HAVE OPPOSITE CHARGES
• ONE ATOM GAINS ELECTRONS, ONE ATOM LOSES
  ELECTRONS
• USUALLY FORM A BINARY COMPOUND

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BINARY COMPOUNDS

• A binary compound is a compound that is only made
  of two elements
• How do we figure out how to write a binary
  compounds chemical formula?
• First we need to review valence electrons

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Valence Electrons

• Valence electrons are the electrons found in the
  outer energy level of an atom
• These electrons give the atom its unique
  properties
• The elements with the same number of valence
  electrons often have similar properties

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Valence Electrons

• Lewis dot structures show how many valence
  electrons an element has
• Ie. Chlorine has 7 valence electrons

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Valence Electrons

• In a Lewis dot structure the electrons can be
  either paired or unpaired
• Only electrons that are unpaired can take place
  in forming a bond with another atom to form a
  compound

Unpaired electron
Paired electrons
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Atoms can Lose or Gain Valence Electrons

• Atoms like to be full
• It makes them happy!
• To have a filled outer energy level an atom can
  give up its electrons, gain electrons, or share
  electrons with another atom.
• Remember that all atoms start off with the same
  number of electrons as protons
• ie. Chlorine has 17 protons and 17 electrons

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Atoms can Lose or Gain Valence Electrons

• What would make Chlorine have a full outer energy
  level?
• Gaining one electron would make chlorine very
  happy!
• If chlorine now has 17 protons and 18 electrons
  it has one more negative charge than positive
  charge

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Atoms can Lose or Gain Valence Electrons

• When a element gains an electron it is called a
  negative ion or an anion
• Chlorine gained one electron so it now has a
  negative one charge (-1)
• How many electrons does oxygen need to gain to
  become happy
• Hint oxygen has 6 valence electrons

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Atoms can Lose or Gain Valance Electrons

• Oxygen needs to gain 2 electrons to have a full
  valence shell
• What kind of charge would a oxygen ion have?
• Negative 2 (-2)
• What about an element that has one or two
  electrons in its outer energy level

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Atoms can Lose or Gain Valence Electrons

• Lets look at Sodium
• It is easier for Sodium to lose its one valence
  electron to have a full outer energy level.
• Its second energy level is full

.
Na
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Atoms can Lose or Gain Valence Electrons

• If Sodium loses its one valence electron it has
  lost a negative charge.
• A sodium ion has 11 protons and only 10 electrons
• This give sodium a positive one charge (1)
• We call positive ions, cations
• If you like cats, then cats are positively
  positive!

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IONIC BONDS

• The atom that loses electrons is the CATION
• The atom that gains electrons is the ANION

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Atoms can Lose or Gain Valence Electrons

• How do you know if an atom will gain or lose
  electrons?
• If the atoms outer energy level is almost full (4
  or more electrons) it will gain the extra
  electrons it needs.
• Its easier to gain a couple of electrons than to
  lose many
• If the atoms outer energy level is almost empty
  (3 or less) it will lose its electrons leaving
  the energy levels that are left filled
• Its easier to lose a couple of electrons that to
  gain a lot!

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Charge of an Ion

• Represent the number of electrons that an atom
  can gain or lose.

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Charge of an Ion

• The charge of an ion is written as SUPERSCRIPT
  next to the chemical symbol
• Example Ca2

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Charge of and Ion

• If the charge is positive, it LOSES electrons
• METALS
• If the charge is negative, it GAINS electrons
• NONMETALS

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Ion Charges

• GROUP 1 1
• GROUP 2 2
• Group 13 3
• Group 14 4 or 4-

• GROUP 15 3-
• GROUP 16 2-
• GROUP 17 1-
• GROUP 18 0

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Writing Formulas from Names A balanced formula
(compound) means the ions -ions How to
write the formula Ex Lithium sulfide 1. First
look up the charge of each element on
your PTable 2. Then criss-cross the charges
and place as subscripts 3. Remove
superscripts, leave only the subscripts.
Lithium 1 , Sulfur -2 Charge superscript Li
1 S-2 Li 1 S-2 Li2S
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BINARY COMPOUNDS

• Example
• Na Cl-
• Na Cl
• The formula for salt is NaCl

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BINARY COMPOUNDS

• Example
• Ba2 Cl-
• Ba Cl2
• The formula for barium chloride is BaCl2

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BINARY COMPOUNDS

• Example
• Mg2 P3-
• Mg3 P2
• The formula for magnesium phosphide is Mg3P2

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BINARY COMPOUNDS

• Example
• Mg2 O2-
• Mg2 O2
• The formula for magnesium phosphide is MgO

Notice we reduced the subscripts just like
fractions
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NAMINGIONIC BONDS

• Write the ion with the positive charge first
  (metal)
• Write the second ion, but change the end of it to
  ide

• NaCl is
• sodium chloride
• BaCl2 is
• barium chloride

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COVALENT BONDS

• Most compounds form covalent bonds
• Formed when atoms SHARE electrons

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COVALENT BONDS

• Formed between two nonmetals
• Usually form liquids or gases

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COVALENT BONDS
Both chlorine atoms need one electron to become
happy
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COVALENT BONDS
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COVALENT BONDS
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COVALENT BONDS

• Atoms do not always share equally!
• The atom with more protons will pull harder on
  the electrons
• This causes the molecule to become POLAR
• Atoms that do share equally are NONPOLAR

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COVALENT BONDS
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NAMINGCOVALENT BONDS

• The same as ionic compounds...except
• Use prefixes to note the number of atoms of each
  element
• Do not use mono on the first element

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NAMING COVALENT BONDS
1. Use prefixes to note the of atoms for
each element. 2. If there is
only one of the first element do not
use mono carbon dioxide CO2 You do not have
to worry about charges, just use prefixes
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PREFIXES
1. Mono 5. Penta 2. Di 6. Hexa 3. Tri 7.
Hepta 4. Tetra 8. Octo
Examples CO carbon monoxide CO2 carbon
dioxide N2O dinitrogen monoxide
N2O5 dinitrogen pentaoxide