Chemical Bonds

1
Chemical Bonds
2
Chapter
Sections
6.1 - Ionic Bonding 6.2 - Covalent Bonding 6.3 -
Naming of Compounds and Writing Formulas 6.4 -
The Structure of Metals
3
Why is Neon (a noble gas) inert, and Oxygen
isnt??????
4
Stable Electron
Configurations

• When the highest energy level of an atom is
  filled, the atom is stable and is not likely to
  react
• Noble gases are stable because they have 8
  valence electrons (octet rule)
• Valence electrons determine chemical properties

5
Electron Dot
Diagram

• A model of an atom in which each dot represents
  a valence electron

O



Electron dot diagram for Oxygen (6 valence
electrons)

• Symbol in the center represents the nucleus
• Figure 2 (p. 159)

6
Transfer of Electrons

• Atoms react in order to achieve a stable
  configuration (a stable octet)
• Some elements achieve an octet by transferring
  electrons
• By transferring electrons an atom become an ion
• Ion An atom that has a positive or negative
  charge

7
continued . . .

• Anion An ion with a negative charge
  (non-metals form anions)
• Named by adding ide to the beginning of the
  element name (i.e. Chloride)
• Cation An ion with a positive charge (metals
  form cations)
• Named by placing the word ion after the element
  name

8
Ionic Bonds

• Anions and cations are attracted to one another
• When an anion and cation are close to one
  another, a chemical bond is formed
• An ionic bond holds cations and anions together
• Remember!! - it happens because electrons are
  transferred!!!!

9
Ionization Energy

• Cations form when electrons escape from the
  nucleus
• The energy needed to do this is ionization
  energy
• Ionization energy decreases going down a group
  because atomic radius increases
• Ionization energy increases going across a
  period because atomic radius decreases

10
Ionic Compounds

• Ionic compounds contain ionic bonds
• A chemical formula shows what a compound
  contains and the ratio of the elements in the
  compound.
• NaCl (contains 1 Na ion 1 chloride ion)
• MgCl2 (contains 1 Mg ion 2 chloride ions)

11
Crystal Lattices

• Ionic compounds have an atomic structure called
  a crystal lattice
• These substances are then considered crystals
• Refer to p. 162

12
Properties of Ionic Compounds

• High strength of ionic bonds
• High melting point
• Conduct electricity as a liquid or when
  dissolved
• Brittle

13
Sharing of Electrons

• Non-metals share electrons with one another
• A covalent bond is a chemical bond in which two
  atoms share electrons
• Covalent bonding forms molecules a neutral
  group of atoms covalently bonded together
• Electrons are attracted to the other atoms
  nucleus

14
Molecules continued . . .

• Molecules are written with chemical formulas as
  well
• H2 two hydrogen atoms bonded together
• H2O two hydrogen atoms bonded to one oxygen
  atom
• Covalent bonds may be single, double, or triple
  bonds

15
Polar Covalent Bonds

• Unequal sharing of electrons result in unequal
  distribution of charge
• A polar covalent bond is the result (a end and
  a end)
• The atoms with a greater attraction to the
  electrons receive a partial negative charge
• The other atom a partial positive charge

16
Polar and Non-Polar Molecules

• A polar bond doesnt necessarily mean a molecule
  is polar
• Molecular shape determines this

17
Molecular Attractions

• Molecular attractions hold molecular compounds
  together (weaker than ionic and covalent bonds)
• 3 types of molecular attractions
• Dipole-dipole forces (polar)
• Dispersion forces (non-polar)
• Hydrogen bonds (H to F, O, N)

18
Describing Ionic Compounds

• Ionic compounds are named based on their
  composition
• A binary compound contains only two elements
  (bi- means two)
• The name consists of the name of the cation
• followed by the name of the anion with the
  suffix -ide

19
Naming continued

• Some examples

NaCl -
Sodium Chloride
LiF -
Lithium Fluoride
KI -
Potassium Iodide
MgO -
Magnesium Oxide
FeCl3 -
Iron Chloride
20
Metals with Multiple Ions

• Many metals for ions with positive charges equal
  to the group number (i.e. Group 1, Group 2, and
  Aluminum)
• p. 172 Figure 17 shows some metals form more
  than one kind of ion.
• Cu2O copper(I) oxide
• CuO copper(II) oxide

Roman numeral indicates the charge
21
Polyatomic Ions

• A covalently bonded group of atoms that has a
  charge
• poly- means many (polyatomic ion ion of many
  atoms)
• OH- CO32- SO42- are a few examples (p.
  173 for others)

22
Formulas for Ionic Compounds

• If you know the name, you can write the formula
• Place the symbol of the cation first and then
  the symbol of the anion second

Sodium Chloride -
NaCl
Lithium Fluoride -
LiF
Calcium Oxide -
CaO
23
Formulas for Ionic Compounds continued

• Use subscripts to show the ration of ions in the
  compound

Calcium Chloride -
CaCl2
Sodium Oxide -
Na2O
Copper(II) Chloride -
CuCl2

• Page 174 (Math Skills) discusses this topic
  perfectly

24
Formulas for Ionic Practice
Calcium oxide -
CaO
Copper(I) sulfide -
Cu2S
Lithium oxide -
Li2O
Iron(III) oxide -
Fe2O3
Sodium sulfate -
Na2SO4
Sodium hydroxide -
NaOH
25
Describing Molecular Compounds

• The compound name is the name of the first
  element followed by the name of the second
  element, ending in ide, however.
• Prefixes are used to indicate the number of each
  element present.

Carbon tetrachloride
CO2 -
CCl4 -
Carbon dioxide
Dinitrogen tetraoxide
Dihydrogen monoxide
N2O4 -
H2O -
26
Prefixes
Mono-
Di-
Tri-
Tetra-
Penta-
Hexa-
Hepta-
Octa-
Nona-
Deca-
27
Writing Molecular Formulas

• Write the symbols for the elements in the order
  they appear in the name
• Prefixes appear as subscripts

Diphosphorus tetrafluoride -
P2F4
Carbon monoxide -
CO
Dihydrogen sulfide -
H2S
28
Metallic Bonds

• In a metal, valence electrons are free to move
  among the atoms
• Metal ions can be considered a cation surrounded
  by a pool of electrons (electrons are free to
  move about)
• Metallic bond the attraction between a metal
  cation and the shared electrons around it.

29
Explaining Properties of Metals

• The mobility of the electrons explains some of
  the properties
• Electrical conductivity
• Malleability
• Ductility

30
Alloys

• Alloy A mixture of two or more elements, at
  least on of which is a metal
• Have characteristic properties of metals
• Copper Alloys
• Steel Alloys
• Other Alloys