LIFE IS A SERIES OF THINGS YOU’RE NOT QUITE READY FOR.

REVIEW

1. What are the main subatomic particles that make up the atom?

2. What is the charge on each of the particles?

3. Which of the particles is most massive? Least massive?

4. What isotope is used as the standard in establishing the atomic mass scale?

5. The atomic weight of chlorine is reported as 35.5, yet no atom of chlorine has this mass. Explain.

6. How many protons, neutrons, and electrons are in the following atoms?

a. 28Si

b. 60Ni

c. 85Rb

d. 128Xe

7. Write the electron configuration for the following atoms:

a. Boron, B

b. Sodium, Na

c. Silicon, Si

d. Calcium, Ca

8. How many valence electrons does each atom in #7 have?

IONS AND IONIC COMPOUNDS

One way atoms can form chemical compounds is through the loss and gain of electrons.

Note: “the nucleus of an atom is unchanged in chemical processes, but atoms can readily lose or gain electrons.”

- Brown and LeMay-

If an atom is neutral to begin with, it becomes electrically charged if it loses or gains electrons.

The resulting charged particles are called ions.

Keep in mind the “octet rule” when talking about bonding. A full outer shell represents a stable configuration. If the first shell is the outer shell, it can hold 2 electrons. In any other shell, 8 is the maximum number of electrons that can exist in the outer shell.

Let’s consider the reaction between sodium and chlorine:

Na + Cl --> Na+Cl-

Sodium loses and electron to become a sodium ion with a positive charge.

Na (1s22s22p63s1) --> Na+ (1s22s22p6) + e-

Positive ions are called cations.8 electrons in outer shell

Chlorine gains an electron.

Cl (1s22s22p63s23p5) + e- --> Cl- (1s22s22p63s23p6)

Note: negative ions are called anions.

Or

Na --> Na+ + e-

Cl + e- --> Cl-

Adding the two equations

Na + Cl --> Na+Cl-

Note: the net charge on an ion is represented with a superscript.

8 electrons inouter shell

Give the chemical symbols, including mass numbers for the following ions:

a. An ion with 22 protons, 26 neutrons, and 19 electrons.

b. The ion of sulfur that has 16 neutrons and 18 electrons.

c. The ion of selenium with 34 protons and 36 electrons

In predicting the charge on a simple ion, a good rule of thumb is that atoms gain or lose electrons to end up with the same number of electrons as the nearest noble gas on the periodic table.

a. Group I ions (alkali metals) have +1 charges.b. Group 2 ions (alkaline earth metals) have +2 charges.c. Group 6 ions (nonmetals) have -2 charges.d. Group 7 ions (halides) have -1 charges.e. There is no simple way to predict the charges of the transition metals.

Another way of expressing the rules is that metals will usually react by losing electrons, and nonmetals will react by gaining electrons.

Although we write the formulas for ionic compounds as the simple formulas, for example, NaCl (the simplest whole number ratio), ionic compounds usually exist as three dimensional solids.

Using sodium chloride as an example

Some characteristics of ionic compounds:

1. They are solids at room temperature.

2. They are held together by electrostatic forces of attraction between oppositely charged ions.

3. They have very high melting points.

4. All ionic compounds form crystals.

5. Ionic substances are hard, brittle solids.

6. When dissolved in water, the solutions are good conductors of electricity.

Ions in water.

NAMING IONIC COMPOUNDS

Cations formed from metal atoms take the name of the metal.

Na+ - sodium ion

Ca+2 - calcium ion

Al+3 - aluminum ion

In the case of transition metal ions that can form ions of different charges, the charge is given as a Roman numeral.

Fe+2 - iron (II) ion

Fe+3 - iron (III) ion

Anions formed from single nonmetal ions have names formed by replacing the ending of the name of the element with -ide.

Br- - bromide ion

Cl- - chloride ion

S-2 - sulfide ion

N-3 - nitride ion

A few simple polyatomic anions also take the -ide ending.

OH- - hydroxide ion

CN- - cyanide ion

O2-2 - peroxide ion

To name compounds, you combine the name of the cation (first) with the name of the anion, dropping “ion”.

Examples:

NaCl sodium chloride

BaF2 barium fluoride (note: charges have to balance)

NaCN sodium cyanide

KOH potassium hydroxide

AgCl silver chloride

FeCl2 iron (II) chloride

FeCl3 iron (III) chloride

There are some polyatomic anions that you will just have to learn the names.

NO3- nitrate ion

NO2- nitrite ion

SO4-2 sulfate ion

SO3-2 sulfite ion

CO3-2 carbonate ion

PO4-3 phosphate ion

There is one polyatomic cation you need to know the name.

NH4+ ammonium ion

We would use the names of these polyatomic anions in naming our compounds.

Na2SO4 - sodium sulfate (again, charges have to balance)

NaHCO3 - sodium hydrogen carbonate

KNO3 - potassium nitrate

BaSO4 - barium sulfate

Ca(NO2)2 - calcium nitrite

Li3PO4 - lithium phosphate

NH4Cl - ammonium chloride

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