COVALENT BONDS Chapter 5 Section 3

Covalent bonds are usually formed between atoms of nonmetals. The force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons. A molecule is a neutral group of atoms joined by covalent bonds.

If the atom shares one pair of electrons they make a single bond. If the atom shares two pairs of electrons they make a double bonds. If the atom shares three pairs of electrons they make a triple bonds.

Molecular Compound- is a compound composed of molecules, that are covalently bonded. Compared to ionic compounds, molecular compounds generally have lower melting points and boiling points. And, unlike ionic compounds, molecular compounds do not conduct electric current when melted or dissolved in water.

Unequal sharing of electrons- atoms of some elements pull more strongly than do atoms of other elements. Unequal sharing of electrons causes the bonded atoms to have slight electric charges. Polar bond is a covalent bond in which electrons are shared unequally. Nonpolar bond is a covalent bond in which electrons are shared equally.

Questions 1. What is an ion? 2. Contrast sodium and chloride ions, including how they form. Write the symbol for each ion. 3. What holds the ions together in sodium chloride? Indicate the specific charges that are involved. 4. Write the formula for calcium chloride 5. List three properties of ionic compounds.

1. An ion is an atom or group of atoms that has an electric charge. 2. A sodium ion (Na+) forms when a sodium atom loses one electron and becomes positively charged. A chloride ion (Cl-) forms when a chloride atom gains one electron and becomes negatively charged. 3. Attraction between positive and negative ions; a sodium ion has a charge of 1+, and a chloride ion has a charge of 1-.

4. CaCl2 5.Ionic compounds are hard, brittle crystals that have high melting points and can conduct electric current when melted or in solutions.