Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding. Copyright Houghton Mifflin Harcourt Publishing Company

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2 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.

3 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.

4 How does an ionic bond form? How are the sodium and chlorine atoms held together in the compound sodium chloride?

5 What properties do most ionic When ions bond, they form a repeating threedimensional pattern called a crystal lattice. Each ion has many oppositely charged ions around it, and every ion is held firmly in place with strong bonds. It takes a lot of energy to separate these ions from one another. So most ionic compounds have high melting and boiling points.

6 What properties do most ionic Sodium chloride consists of sodium and chloride ions held together in a crystal lattice structure.

7 What properties do most ionic 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.

8 What properties do most ionic 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.

9 What properties do most ionic Solubility is the ability to dissolve in liquid. Most ionic compounds dissolve in water. When salt is added to water, water molecules attract the positive and negative salt ions. Water molecules surround each ion, and move the ions apart from each other. The separated ions dissolve in water.

10 Let s Share! 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.

11 What is a molecule? Substances that have covalent bonds are made of individual particles called molecules. A molecule is a group of atoms held together by chemical bonds. A molecule is the smallest unit of a compound that can be identified as that compound.

12 What is a molecule? In a water molecule, two hydrogen atoms form covalent bonds with a central oxygen atom.

13 What properties do most covalent Some covalent compounds dissolve in water. Other covalent compounds do not. Wax molecules have a stronger attraction to other wax molecules than they have to water molecules. This is why wax does not dissolve in water.

14 What properties do most covalent When a covalent compound melts or boils, the covalent bonds holding the molecules together do not break as ionic bonds in an ionic compound do. Instead, one molecule separates from another. Because molecules separate easily from other molecules, they tend to have lower melting and boiling points than ionic compounds.

15 What properties do most covalent Most covalent compounds are poor conductors of electric current in both solid and liquid form. Unlike ions, which are charged, molecules are neutral. So, even in a liquid in which molecules can move around, the compound cannot conduct electric current.

16 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.

17 How does a metallic bond form? Copper metal is held together by metallic bonding, in which electrons flow around copper ions.

18 What properties do most metallic Because the electrons in a metal can move freely, most metals are good conductors of electric current. When you turn on a lamp, valence electrons move through the copper wire that connects the light bulb to the electrical outlet. The valence electrons in the copper atoms are free to move because they are not connected to any one atom.

19 What properties do most metallic 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.