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Sometimes, people are beautiful. Not in looks. Not in what they say. Just in who they are. -Markus Zusak. IT IS USEFUL WHEN WE WRITE EQUATIONS FOR REACTIONS THAT OCCUR IN AQUEOUS SOLUTION TO INDICATE IF THE REACTANTS AND PRODUCTS ARE IONS OR MOLECULES OR IONIC SOLIDS. - PowerPoint PPT Presentation
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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. 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
9. Write the electron configuration for the following atoms:
a. Boron, B
b. Sodium, Na
c. Silicon, Si
d. Calcium, Ca
10. How many valence electrons does each atom in #9 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 (1st 2, 2nd 8, 3rd 1) --> Na+ (1st 2, 2nd 8) + e-
Positive ions are called cations.8 electrons in outer shell
Chlorine gains an electron.
Cl (1st 2. 2nd 8, 3rd 7) + e- --> Cl- (1st 2, 2nd 8, 3rd 8)
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. 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
COMMON LAB EQUIPMENT
BeakerErlenmeyer flask
Graduated cylinder
FunnelFilter paper
Test tube
Test tube
clamp
Ring stand
Ring support Wire gauze
Evaporating
dish
Volumetric flask