I. Elements combine to form compounds

1
I. Elements combine to form compounds

• A. Compounds have different properties from the
  elements that make them.
• 1. A compound is a substance made of atoms
• 2. A compound is made of two or more different
  elements.

2
I. Elements combine to form compounds

• 3. All compounds are held together by chemical
  bonds.
• a. Bonds can hold atoms together in large
  networks
• b. Small groups
• Bonds help determine the properties of a
  compound.
• 4. Properties of a compound depend not only on
  which atoms the compound contains
• 5. Also depend on how the atoms are arranged.
• a. Example would be carbon and hydrogen
• b. Arrangement and amount of each element
  determines what gets created

3
I. Elements combine to form compounds

• c. List 3 examples in the text of items made of
  carbon and hydrogen
• _______________________
• ________________________
• _______________________

4
I. Elements combine to form compounds
5
I. Elements combine to form compounds

• B. Atoms combine in predictable numbers
• 1. A given compound always contains atoms of
  elements in a specific ratio or combination.
• 2. The arrangement and amount gives the compound
• a. Ammonia has three hydrogen to one nitrogen
• b. Hydrazoic acid contains one hydrogen to three
  nitrogen
• C. Chemical Formulas
• 1. A chemical formula uses chemical symbols from
  the periodic table to represent the atoms of the
  elements and their ratios in a chemical
  compound.

6
I. Elements combine to form compounds

• a. Carbon dioxide is a compound consisting of
  one atom carbon
• b. This is connected to two atoms of oxygen.
• 2. To write this as a chemical formula you
  follow the steps.
• a. Find the symbols for carbon and oxygen and
  write them side by side
• b. Indicate that there are 2 oxygen atoms for
  every carbon atom and place the subscript 2 to
  the right of the oxygens atoms symbol
• c. A subscript is the number written to the
  right of the chemical symbol and dropped down, or
  slightly below it.
• 3. Notice the charge on page 44. If there are
  more then one for the same atom, that is when you
  use a subscript.

7
I. Elements combine to form compounds

• D. Same Elements, Different compounds.
• 1. The arrangement and number determines what
  gets created.
• 2. Compounds with the same elements can be very
  different based on their combination and amounts
  of these elements.

8
II. Chemical bonds hold compounds together

• A. Chemical bonds between atoms involve
  electrons
• 1. Chemical bonds are the glue that holds the
  atoms of elements together in compounds.
• 2. Chemical bonds are what make compounds more
  than just mixtures of atoms.
• 3. Atoms have a positively charged nucleus
  surrounded by a cloud of electrons
• 4. Chemical bonds form when the electrons in the
  electron clouds around two atoms interact.

9
II. Chemical bonds hold compounds together

• 5. How the electron clouds interact determines
  the kind of chemical bond that is formed.
• 6. Chemical bonds have a great effect on the
  chemical and physical properties of compounds.
• Chemical bonds also influence how different
  substances interact.
• B. Atoms can transfer electrons.
• 1. Ions are formed when atoms gain or lose
  electrons
• 2. Gaining electrons changes an atom into a
  negative ion

10
II. Chemical bonds hold compounds together

• 3. Losing electrons changes the atom into a
  positive ion
• 4. Ions typically form in pairs when one atoms
  transfers one or more electrons to another atom.
• 5. Elements location on the periodic table
  gives clues as to what type of ions the atoms of
  that element will form.
• 6. All metals lose electrons to form positive
  ions
• a. Group 1 metals usually lose electron to form
  ions with a single positive charge. (Li, Na,
  K, Rb, Cs, Fr )
• Group 2 metals commonly lose 2 electrons to form
  ions with a positive 2 charge. (Be2, Mg2, Ca2,
  Sr2, Ba2, Ra2,)
• Transition meals, always form a positive ion, but
  the number of electrons they may lose varies

11
II. Chemical bonds hold compounds together

• 7. Nonmetals form ions by gaining electrons
• a. Group 17 nonmetals gain one to form a -1
  charge. ( F-, Cl-, Br-, I-)
• b. Group 16 gain 2 electrons to form a -2 charge
  (O-2, S-2, Se-2)
• C. Ionic bonds
• a. When group 1 reacts with group 17, an
  electron moves from one atom (sodium) to another
  atom (chlorine)
• b. Force of attraction between a positive and
  negative ion is called an ionic bond.

12
II. Chemical bonds hold compounds together

• 2. Electrical forces act in all directions, each
  ion, therefore attracts all other nearby ions
  with the opposite charge.
• 3. These interactions make ionic compounds very
  stable and their crystals very strong.
• D. Names of Ionic Compounds
• 1. The name for a positive ion is the same as
  the name of the atom from which it is formed.
• 2. The name of a negative ion is formed by
  dropping the last part of the name of the atom
  and adding the suffix ide.

13
II. Chemical bonds hold compounds together

• 3. To name an ionic compound the name of the
  positive ion is placed first
• 4. Next comes the name fo the negative ion.
• a. Sodium and Chlorine
• b. Na and Chlorine-
• c. Sodium chloride
• 5. BaI2
• a. Barium and iodide
• b. Barium iodide

14
II. Chemical bonds hold compounds together

• E. Atoms can share electrons
• 1. An ionic bond forms between atoms that lose
  electrons and gain electrons
• 2. Another way is when bonds are held together
  by sharing electrons.
• F. When bonds are held together by sharing, they
  are called Covalent Bonds
• 1. Neither atom gains or loses electrons
• 2. Shared electrons are attracted to both
  positively charged nuclei.
• 3. Electron clouds overlap.
• 4. Often represented by a line between two atoms
  

15
II. Chemical bonds hold compounds together

• 5. Number of covalent bonds that can form
  depends on the number or electrons that it has
  available for sharing.
• a. Halogen groups (17) and hydrogen can
  contribute only one electron to a covalent bond
• b. Group 17 can form 2 covalent bonds
• c. Atoms of group 15 can form 3
• d. Carbon and silicon can form 4 bonds
• 1.) Example CH4 , Methane gas
• 2. )Carbon forms 4 covalent bonds with four
  hydrogen

16
II. Chemical bonds hold compounds together

• 6. Sometimes atoms may share more than one pair
  of electrons with another atom
• a. Carbon in CO2 ( carbon dioxide) forms double
  bonds with each of the oxygen atoms.
• b. A double bond consists of four (2 pair of)
  shared electrons
• c. Two nitrogen atoms form a triple bond,
  meaning they share six (three pairs of )
  electrons
• 7. A group of atoms held together by a covalent
  bond is called a molecule
• 8. Most molecules can contain the atoms of two
  or more elements

17
II. Chemical bonds hold compounds together

• G. Polar Covalent Bonds
• 1. A covalent bond which the electrons are
  shared unequally is called a polar covalent bond.
• 2. The word polar refers to anything that has
  two extremes, like a magnet with 2 opposite
  poles.

18
III. Substances properties depend on their bonds

• A. Metals have unique bonds
• 1. Metal atoms bond together by sharing
  electrons with one another
• 2. The atoms share the electrons equally in all
  directions
• 3. The equal sharing allows the electrons to
  move easily among the atoms of the metal
• 4. This special type of bond is called a
  metallic bond
• 5. Properties of metals determined by metallic
  bonds

19
III. Substances properties depend on their bonds

• 6. Being good conductors, electrons in metals
  flow through the material, carrying the electric
  current as well as making them good conductors of
  heat too.
• 7. Except for mercury, all metals are solids at
  room temperature.
• 8. The metallic bond, atoms can slide past one
  another. This allows them to be drawn into wire
  as well as pounded into metals sheets.
• 9. The atoms can simply slide into other
  positions .

20
III. Substances properties depend on their bonds

• B. Ionic and covalent bonds give compounds
  certain properties
• 1. Ionic compounds have extremely high melting
  and boiling points
• 2. These points require a lot o energy to break
  all the bonds among the ions in a crystal.
• 3. The crystal network also makes ionic
  compounds the following
• a. ) Hard
• b. )Brittle
• c.) Poor conductors of electricity

21
III. Substances properties depend on their bonds

• 4. Ionic compounds dissolve easily in water
  separating into positive and negative ions.
• 5. The separation makes them good conductors of
  electricity
• 6. Yellowstone mineral hot springs are also ionic
  solutions.
• 7. Covalent compounds have almost exact opposite
  properties.
• 8. Covalent compounds have lower melting and
  boiling points
• 9. Covalent compounds are poor conductors of
  electricity and stay together when dissolved in
  water

22
III. Substances properties depend on their bonds

• C. Bonds can makes the same element look
  different
• 1. Carbon can exist as different properties
  based on how the atoms are bonded.
• a. Diamonds- carbon forms covalent bonds with
  four other atoms in a three dimensional pattern
  giving it its strength.
• b. Graphite- forms covalent bonds with there
  other atoms to make 2dimensional layers.
• c. Fullerene- has a molecule shaped like a
  soccer ball.