1. Chapter 19: Chemical Bonds
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2. Section 2: Types of Bonds
Gain or Loss of Electrons
ion: an atom that has gained or lost electrons to become more stable
the positive charge of the protons and the negative charge of the electrons is unbalanced
more protons than electrons = positive ion
more electrons than protons = negative ion

3. How do we know how many electrons an atom will lose or gain?
The periodic table tells us!
Group 1: loses 1 electron
Group 2: loses 2 electrons
Group 13: loses 3 electrons
Group 14: shares 4 electrons
Group 15: gains 3 electrons
Group 16: gains 2 electrons
Group 17: gains 1 electron
transition elements vary

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5. The + and – are superscripts, “written above”
A bond forms when elements that need to lose electrons come in contact with atoms that needs to gain electrons to become stable
These are all ions:
Na + sodium ion
Cl - chlorine ion
K + potassium ion
Mg 2+ magnesium ion
Al 3+ aluminum ion
S 2- sulfur ion
The + and – are superscripts, “written above”

6. Example: Potassium Iodide
How many electrons does potassium (K) gain or lose to become stable?
It loses 1 electron
How many electrons does iodine (I) gain or lose to become stable?
It gains 1 electron
Potassium (K+) gives iodine (I-) its lone electron and both are stable
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7. Positive ions and negative ions are always attracted to each other
As a result, they form an ionic bond: the force of attraction between opposite charges of ions
The result of the bond is a neutral compound
Occurs between a metal (+) and a nonmetal (-)
Wait: what if the charges are not the same number of electrons, like Mg 2+ and Cl - ?

8. Example: Magnesium Chloride
Magnesium wants to lose 2 electrons
Chlorine wants to gain only 1 electron
What happens to that extra electron from magnesium?
Another chlorine will take it!
MgCl2 Mg
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10. Sharing Electrons
Some nonmetals are unlikely to lose or gain electrons
Group 14 elements have 4 electrons in their outer energy level: they could gain four or lose four
When it takes more energy to gain or lose electrons rather than just share them, a covalent bond is formed by sharing e-
The new compound is a molecule, and is only formed between nonmetals
Common molecules: SiO2 H2O C12H22O11

11. Sharing Electrons
Some elements can share more than one pair of electrons
CO2 Two pairs shared: double bond O=C=O
N2 Three pairs shared: triple bond N≡N
However, atoms don’t always share nicely
Some atoms “hog” the electrons to themselves, like oxygen
Perfect example: CO2 :O=C=O:
Oxygen pulls the electrons away from carbon

12. Polar or Nonpolar? Remember Mickey Mouse?
Water molecules are polar; the electrons are drawn toward the oxygen, making the oxygen end more negative and the hydrogen end more positive
Nonpolar molecules share electrons equally + -

13. Review Questions, p. 586 Q1-4 Answer these questions for tomorrow:
Why does an atom make an ionic bond only with certain other atoms?
Compare the possession of electrons in ionic and covalent bonds.
What types of particles are formed by ionic bonds? Covalent bonds?
What is the difference between polar and nonpolar molecules?