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

formed by electrons being shared, not completely transferred. 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.

How Covalent Bonds Form 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.

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

Section 3: Covalent Bonds What are the properties of molecular compounds?

Section 3: Covalent Bonds 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

Section 3: Covalent Bonds How does unequal sharing of electrons affect molecules?

Section 3: Covalent Bonds 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 Bonds The 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. Describe how the electron dot configuration helps us see how the valence electrons bond, how many they have and the type of bond 13

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 between carbon dioxide molecules. Describe how the electron dot configuration helps us see how the valence electrons bond, how many they have and the type of bond 14

Section 4: Bonding in Metals How do the properties of metals and alloys compare? 15

Section 4: Bonding in Metals 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. 16

Section 4: Bonding in Metals How do metal atoms combine? 17

Metallic Bonding Metal atoms combine in regular patterns in which the valence electrons are free to move from atom to atom. 18

Section 4: Bonding in Metals How does metallic bonding result in useful properties of metals? 19

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. 20