1. Chapter 19
Chemical Bonds
Lesson 2

2. Gain or Loss of Electrons
Atoms
lose or gain to meet a standard— stability.
Ion
charged particle because it now has either more or fewer electrons than protons.
positive and negative charges are not balanced
electric forces hold compounds together

3. Gain or Loss of Electrons
Common compounds
made by the loss and gain of just one electron.
some examples
sodium chloride, commonly known as table salt;
sodium fluoride, an anticavity ingredient in some toothpastes;
potassium iodide, an ingredient in iodized salt

4. A Bond Forms Potassium Compound with iodine
has one electron in its outer level.
Compound with iodine
potassium loses one electron from its fourth level, and the third level becomes a complete outer level.

5. A Bond Forms Potassium atom The 1+ charge has become an ion
the atom becomes positively charged because there is one electron less in the atom than there are protons in the nucleus
The 1+ charge
shown as a superscript written after the element’s symbol, K+ , to indicate its charge.

6. A Bond Forms The iodine atom undergoes change
has seven electrons in its outer energy level
iodide atom gains an electron, leaving its outer energy level with eight electrons.

7. A Bond Forms
Iodine
no longer neutral because it gained an extra negative particle.
charge of 1− and is called an iodide ion, written as I−.

8. A Bond Forms
Notice that the resulting compound has a neutral charge because the positive and negative charges of the ions cancel each other

9. The Ionic Bond Ionic bond
force of attraction between the opposite charges of the ions in an ionic compound
a transfer of electrons takes place.
one or more elements must gain an equal number of electrons to maintain the neutral charge of the compound.

10. The Ionic Bond Magnesium chloride
MgCl2, is another example of ionic bonding.
magnesium reacts with chlorine, magnesium atom loses two electrons and becomes a positively charged ion, Mg2+.

11. The Ionic Bond Two chlorine atoms
gain one electron each and become negatively charged chloride ions, Cl −

12. Zero Net Charge The result of this bond is a neutral compound.
The compound as a whole is neutral because the sum of the charges on the ions is zero.

13. Zero Net Charge Ionic compound,
electrons are shifted to the other atoms,
the overall number of protons and electrons of the combined atoms remains equal and unchanged.
Ionic bonds usually are formed by bonding between metals and nonmetals.

14. Sharing Electrons Nonmetals Group 4
unlikely to lose or gain electrons.
Group 4
four electrons in their outer levels.
would have to either gain or lose four electrons in order to have a stable outer level
loss of this many electrons takes a great deal of energy

15. Sharing Electrons Covalent bond share electrons
particle forms is a molecule.

16. Single Covalent Bonds Single covalent bond Water molecule Results
made up of two shared electrons.
Water molecule
contains two single bonds.
in each bond, a hydrogen atom contributes one electron to the bond and the oxygen atom contributes the other.
Results
is a stable outer energy level for each atom in the molecule.

17. Multiple Bonds Covalent bond
can contain more than one pair of electrons.
nitrogen (N2).

18. Multiple Bonds Nitrogen atom
has five electrons in its outer energy level
needs to gain three electrons to become stable.
It does this by sharing its three electrons with another nitrogen atom.

19. Multiple Bonds Each nitrogen atom
contributes three electrons to the bond, the bond contains six electrons, or three pairs of electrons.
each pair represents a bond.
three pairs of electrons represent three bonds, or a triple bond.

20. Unequal Sharing Electrons
not always shared equally between atoms in a covalent bond.
elements close together in the upper right-hand corner of the periodic table.
strength of the attraction to electrons related to the size of the atom
charge of the nucleus,
total number of electrons the atom contains.

21. Unequal Sharing Strength of attraction
how far away from the nucleus the electron being shared is.
strength of attraction has to do with the size of the positive charge in the nucleus.

22. Unequal Sharing Unequal sharing Chlorine atoms
found in a molecule of hydrogen chloride, HCl.
Chlorine atoms
stronger attraction for electrons than hydrogen atoms do.

23. Unequal Sharing Electrons shared Polar molecule
spend more time near the chlorine atom than near the hydrogen atom.
Polar molecule
charge is balanced but not equally distributed
slightly positive end and a slightly negative end
water

24. Polar or Nonpolar? Nonpolar molecule
electrons are shared equally in bonds.
does not have oppositely charged ends.
molecules made from two identical atoms or molecules that are symmetric, such as CCl4.

25. The Ionic Bond Attraction between 2 oppositely charged ions
Ions - charged atoms
formed by transferring e- from a metal to a nonmetal

26. Covalent Bond Attraction between neutral atoms
formed by sharing e- between two nonmetals

27. Covalent Bond Nonpolar Covalent Bond e- are shared equally
usually identical atoms

28. + - Covalent Bond Polar Covalent Bond
e- are shared unequally between 2 different atoms
results in partial opposite charges + -

29. Covalent Bond
Nonpolar
Polar
Ionic

30. Comparison Chart IONIC COVALENT transferred from metal to nonmetal
shared between nonmetals
Electrons
Melting
Point
high
low
Soluble in
Water
yes
usually not
Usual state
at room temp
Solids
Liquid or Gas
Smallest Particle
Molecules
Ions