Chapter 10 Section 1 (pgs. 282-285)
Ionic and Covalent Compounds
-Chemical bond- interaction that holds atoms and ions together
-Valence electrons- are outermost energy level of electrons in atoms
-The properties of ionic compounds are different from the properties of covalent compounds
Ionic Compounds and Their Properties
-Ionic bond is an attraction between oppositely charged ions
-Metal atoms become positively charged ions when electrons are transferred
-Ionic compounds they are compounds that have ionic bonds
-Ionic compounds are formed by a reaction between metals and nonmetals
-Sodium chloride is salt
A. Brittleness
-Ionic compounds are very brittle at room temp.
-Crystal lattice is repeating 3d pattern
- In a crystal lattice ions are bonded with surrounding ions of opposite charge
-They break because their ions are arranged in a repeating 3d pattern (crystal lattice)
B. High Melting Points
-Sodium chloride must be heated at 801 degrees Celsius before it will melt
-high melting bc of the strong bonds holding them together
-high melting points are the reason that most ionic compounds are solid at room temp
C. Solubility and electrical conductivity
-Many ionic compounds are highly soluble in water
-The solution (ionic compounds that dissolve in water) can conduct an electric current bc
the ions are charged and are able to move freely past one another
-An undissolved crystal of an ionic compound does not conduct an electric current
-Water molecules attract each of the ions of an ionic compound and pull the ions away
from one another
Covalent Compounds and Their Properties
-covalent compounds are compounds that form when atoms share electrons
-a molecule is the smallest particle into which a covalently bonded compound can be divided and still
be the same compound
A. Solubility
-Some covalent compounds are not soluble in water
-They are not soluble bc the molecules are not attracted to the water molecules
-They do not dissolve well in water
B. Low Melting Points
-Covalent compounds have weak bonds which is why they have low melting points
-Less heat is need to separate the molecules of covalent compounds
C. Electrical conductivity
-most covalent compounds that dissolve in water form solutions with uncharged
molecules
-Sugar is a covalent compound that dissolves in water but it does not form ions, so a
solution of sugar and water does not conduct an electrical current
-acidic solutions conduct an electric current
Section Review
1. Use ionic compound, covalent compound and chemical bond in separate sentences.
Ionic compounds are useful because they balance things with the opposite charge ions. Some
covalent compounds are not soluble in water. Chemical bonds hold atoms together. Ionic
compounds can be formed from a metal and a nonmetal. A covalent compound is a chemical
compound that is formed by sharing electrons. A chemical bond is an interaction that holds
atoms and ions together.
2. Why do ionic compounds tend to be brittle?
When an ionic compound is hit, ions that have the same charge line up and repel one another,
causing the crystal to break.
3. List two properties of covalent compounds.
2 properties of covalent compounds are not soluble in water and have a low melting point,
usually no electrical conductivity in solution
4. Solid crystals of ionic compounds do not conduct an electric current. But when the crystals
dissolve in water, the solution conducts an electric current. Explain.
In solution, ionic compounds exist as charged ions that can move freely past one another. Ions
in crystals cannot move freely and therefore cannot conduct an electric current.
5. A compound is composed of 39.37% chromium, 38.10% oxygen and potassium. What
percentage of the compound is potassium?
100-39.37-38.10=22.53%
6. Solid crystals are dissolved in water. If the solution does not conduct an electric current, is the
solid an ionic compound or a covalent compound? Explain.
The solid is a covalent compound. A soluble ionic compound would conduct an electric current