Transcript chemical bonds

p 237
Noble Gas
Halogen
Group
Alkali Metal
Alkali Earth Metal
Period
Chemistry In Action
Natural abundance of elements in Earth’s crust
Natural abundance of elements in human bod
CHEMICAL BONDS
CHAP 9
Homework for Chap 9
Read p 249 - 267
Applying the Concepts: 1 – 14,
16 – 35, 36 – 44, 46 - 50
Compounds and Chemical Change
1. Elements are composed of extremely small particles
called atoms.
2. Compounds are composed of atoms of more than one
element held together by chemical bonds.
3. Molecule – smallest particle of a compound that can
exist and still retain characteristic chemical properties
4. Compounds occur as solids, liquids, and gases
Fig. 9.2 Common gases exist as atoms or molecules
Fig. 9.3
Example of a
chemical reaction
Burning magnesium (Mg)
in air
to produce magnesium oxide
(“milk of magnesia”)
Energy is released
Fig. 9.4 (A) Photosynthesis stores solar energy
Reactants
Products
Fig. 9.4 (B) Combustion releases solar energy
Fig 8.20 Electron dot notation for representative
1
8
elements
2
3
4
5
6
7
Valence electrons – outermost electrons in an atom
Octet rule – atoms attempt to acquire 8 valence electrons
Fig. 9.5
Fig 8.21
energy + Na → Na+ + e−
energy + Ca → Ca2+ + e−
energy + Al → Al3+ + e−
1
2
3 4 5 6 7
8
Three Types of Chemical Bonds
(1) Ionic bonds
•
•
Electrons are transferred from one atom to
another
Occur between a metal atom and a nonmetal
atom
(2) Covalent bonds
•
•
Electrons are shared between two atoms
Occur between two nonmetal atoms
(3) Metallic bonds
•
Metal atoms share many electrons in a “sea” that
is free to move throughout the metal
Formation of an ionic bond
Na
11 protons
11 electrons
Cl
17 protons
17 electrons
Net reaction:
Na+
11 protons
+ e−
10 electrons
Cl-
17 protons
18 electrons
Na + Cl → Na+Cl− + energy
This energy is called the heat of formation
Fig. 9.6 Model of the sodium chloride crystal
No molecules in an ionic compound!
+
−
Formula unit
Na+ ions
Cl− ions
Fig. 9.7 The cubic crystal structure of sodium chloride
• Ionic compounds consist of a combination of
positive ions and negative ions
• Ions are formed as nonmetal atoms gain and
metal atoms lose electrons to achieve stable
noble gas structure
• The sum of the charges on the positive ions
and negative ions in each formula unit must
equal zero
• How do we determine the formula for an ionic
compound?
Formula of Ionic Compounds
2 x +3 = +6
3 x -2 = -6
Al2O3
Al and O
Al3+
Ca and Br
1 x +2 = +2
Ca2+
O22 x -1 = -2
CaBr2
Br-