CH' 19 Chemical Bonds

1
CH. 19 - Chemical Bonds

• What is a compound?
• Two or more element
• Ex. NaCl
• The chemical formula for any compound tells you
  what elements it contains and ratio or or atoms
  for each element.
• Look at the chemical formulas on table Table 1-
  pg. 575

2

• What causes an atom to be stable?
• An atom is chemically stable if its outer energy
  level is completely filled with electrons.
• Typically, the outer energy level is filled if
  the atom had 8 electrons in it.
• The dot diagram of an atom can be used to show
  the of electrons in the atoms outer energy
  level.

3

• The noble gases (group 18) are the only elements
  to have a full outer energy level.
• All the other elements tend to lose, gain, or
  share electrons with other elements. They tend
  to do this in order to become stable and form a
  chemical bond.
• What is a chemical bond?
• This is where a force holds atoms together.

4

• How would sodium and chlorine bond together?
• How many electrons does Na have in its outer
  energy level?
• 1
• How many electrons does Cl have in its outer
  energy level?
• 7
• Whats going to happen?

5

• If Na got rid of its electron it would have 10
  electrons and 11 protons this would make its
  charge 1 (1 extra proton).
• If Cl gained an electron it would have 18
  electrons and 17 protons this would make its
  charge -1 (1 less proton).
• An ion is an atom that is either positively or
  negatively charged.

6
Two types of chemical bonds

• So, whats an ionic bond?
• The force of attraction between the opposite
  charges of the ions in an ionic compound.
• Ex. Pg. 582
• The other type of bonds is ?
• Covalent bond - the bond between atoms when they
  share electrons.
• Some atoms dont always share their atoms equally
  with each other. Pg. 583

7

• A Polar molecules contain a slightly positive end
  and a slightly negative end. The overall
  molecule is neutral.
• Examples?
• Nonpolar molecules contain electrons that are
  shared equally in bonds.
• Ex. CCl4
• What is the main difference between ionic and
  covalent bonds?
• Forced and shared bonds

8

• Define an oxidation number.
• It is a positive or negative number assigned to
  an element to show its combining ability.
• The oxidation number indicates how many electrons
  an atom would gain, lose, or share when it bonds
  with other atoms.
• Ex. Na is 1
• Ex. O is -2

9

• When an element loses an electron it is positive.
  Ex. 1
• When an element gains an electron it is negative.
  Ex. 1
• Some atoms have several charges. Why?
• Pg. 588?Table 2
• What is a compound called that has just two
  elements?
• Binary compound

10
Rules for writing a formula

• 1. First write the symbol of the element with
  the positive oxidation . Hydrogen and all
  metals have a positive oxidation .
• 2. Next, write the symbol of the element with
  the negative oxidation .
• 3. Finally, add subscripts so that the sum of
  the oxidation numbers of all the atoms in the
  formula is zero.

11
Rules for naming a binary compound

• 1. Write the name of the first element.
• 2. Write the root of the name of the second
  element.
• 3. Add the ending -ide to the root.
• Ex. Table 3 pg. 590
• Polyatomic ions are positively or negatively
  charged groups of atoms.
• More than 2 elements (Table 4) pg. 591

12

• What is a hydrate
• a compound that has water chemically attached to
  its ions.
• Ex. CaSO4 H2O
• So, what is a compound that doesnt have water
  chemically attached?
• Anhydrous compound
• How do you know if a compound has water

13
Know your elements

• Nonmetals are mainly gases at room temperature.
  Right of staircase.
• Most nonmetals do not conduct heat or electricity
  well.
• Metals are mainly solids at room temperature.
  Left of staircase.
• Metalloids are the elements next to the staircase
  line. Have both properties.