Opposites Attract What is an ion? Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding Opposites Attract What is an ion? An atom has a neutral charge because it has an equal number of electrons and protons. An ion is a particle with a positive or negative charge. An ion forms when an atom gains or loses electrons from its outer, or valence, shell. Copyright © Houghton Mifflin Harcourt Publishing Company

How does an ionic bond form? Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding How does an ionic bond form? An ionic bond is a force that brings oppositely charged ions together. Ionic bonds form when electrons are transferred from a metal atom to a nonmetal atom. In the process of ionic bonding, valence electrons move from the outer shell of the metal atom to the outer shell of the nonmetal atom. Copyright © Houghton Mifflin Harcourt Publishing Company

How does an ionic bond form? Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding How does an ionic bond form? How are the sodium and chlorine atoms held together in the compound sodium chloride? Copyright © Houghton Mifflin Harcourt Publishing Company

What properties do most ionic compounds share? Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding What properties do most ionic compounds share? Sodium chloride consists of sodium and chloride ions held together in a crystal lattice structure. Copyright © Houghton Mifflin Harcourt Publishing Company

What properties do most ionic compounds share? Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding What properties do most ionic compounds share? The crystals of ionic compounds are hard and brittle. Striking a crystal of an ionic compound with a hammer will likely shatter the crystals in many places. Most ionic compounds dissolve in water. Copyright © Houghton Mifflin Harcourt Publishing Company

What properties do most ionic compounds share? Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding What properties do most ionic compounds share? Solid ionic compounds are poor conductors of electric current, because the ions are held tightly in place. Melting an ionic solid, however, allows the individual ions to move around. Melted ionic compounds can conduct an electric current. Ionic compounds dissolved in water can also conduct an electric current. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding What is a covalent bond? A covalent bond forms when atoms share one or more pairs of electrons. When two nonmetal atoms bond, a large amount of energy is needed for either atom to lose an electron. So they bond by sharing electrons. In a covalent bond, the shared electrons fill empty spaces in the outermost electron shell of each atom. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding What is a molecule? In a water molecule, two hydrogen atoms form covalent bonds with a central oxygen atom. A molecule is the smallest unit of a compound that can be identified as that compound. Copyright © Houghton Mifflin Harcourt Publishing Company

What properties do most covalent compounds share? Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding What properties do most covalent compounds share? They tend to have lower melting and boiling points than ionic compounds. Some covalent compounds dissolve in water. Other covalent compounds do not. Most covalent compounds are poor conductors of electric current in both solid and liquid form. Copyright © Houghton Mifflin Harcourt Publishing Company

Free to Move How does a metallic bond form? Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding Free to Move How does a metallic bond form? A metallic bond forms between metal atoms when their outermost energy levels overlap. Metallic bonding is weak compared to ionic or covalent bonding. You can think of a metal as being made up of positive metal ions with enough valence electrons “swimming” around to hold the ions together. Copyright © Houghton Mifflin Harcourt Publishing Company

What properties do most metallic compounds share? Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding What properties do most metallic compounds share? Due to their free-moving electrons, metals have two properties that allow them to be reshaped. Malleability is the ability to be hammered into sheets. Ductility is the ability to be formed into long, thin wires. Because the electrons in a metal can move freely, most metals are good conductors of electric current. Copyright © Houghton Mifflin Harcourt Publishing Company