chapter 5 atoms and bonding section 3: covalent bonds

Chapter 5 Atoms and Bonding

Section 3:Covalent Bonds


Key Terms•Covalent Bond – formed when two atoms share electrons•Molecule – a neutral group of atoms joined by covalent bonds•Double Bond – when two atoms share two pairs of electrons•Triple Bond – when atoms share three pairs of electrons•Molecular Compound – a compound that is composed of molecules•Polar Bond – a covalent bond in which electrons are shared unequally•Nonpolar Bond – a covalent bond in which electrons are shared equally


Covalent Bonds

• formed by electrons being shared, not completely transferred.

• The attractions between the nucleus and the shared electrons holds the atoms together as a compound. This type of bond is not as strong as an ionic bond.


How Covalent Bonds Form

The force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons.



The oxygen atom in water and the nitrogen atom in ammonia each have eight valence electrons as a result of forming covalent bonds with hydrogen atoms.



Double and triple bonds can form when atoms share more than one pair of electrons.



What are the properties of molecular compounds?



What are the properties of molecular compounds? (as compared to ionic compounds)

• Lower melting point• Lower boiling point• Doesn’t conduct electricity when melted or dissolved in water



How does unequal sharing of electrons affect molecules?



How does unequal sharing of electrons affect molecules?

Unequal sharing of electrons causes the bonded atoms to have slight electrical charges.


Unequal Sharing of Electrons

Fluorine forms a nonpolar bond with another fluorine atom. In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does, so the bond formed is polar.


Unequal Sharing of Electrons

A carbon dioxide molecule is a nonpolar molecule because of its straight-line shape. In contrast, a water molecule is a polar molecule because of its bent shape.


Polar BondsThe unequal sharing of electrons because one atom is stronger than the other atom. It makes the atom with the stronger pull slightly negative and the atom with the weaker pull slightly positive. When this happens a polar bond forms.

When polar bonds form in molecules one end will become more positive, while the other end becomes more negative. The water has one end that has a more positive charge and one end that has a more negative charge. The water molecules are pulled towards each other.


Non-Polar Bonds

-If the electrons are shared equally, then a nonpolar bond is formed.

-As in the picture, the carbon dioxide is a nonpolar molecule, having no positive or negative end.

-Because of this, the there is little attraction betweencarbon dioxide molecules.


Section 4:Bonding in Metals

How do the properties of metals and alloys compare?



How do the properties of metals and alloys compare?

Alloys are mixtures made of two or more elements, at least one of which is a metal. Alloys are generally stronger and less reactive than the pure metals from which they are made.



How do metal atoms combine?


Metallic Bonding

Metal atoms combine in regular patterns in which the valence electrons are free to move from atom to atom.



How does metallic bonding result in useful properties of metals?


Metallic Properties

The “sea of electrons” model of solid metals explains their ability to conduct heat and electricity, the ease with which they can be made to change shape, and their luster.

chapter 5 atoms and bonding section 3: covalent bonds

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