Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
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Opposites Attract
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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.
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.
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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?
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Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
What properties do most ionic compounds share?• When ions bond, they form a repeating three-
dimensional 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.
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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.
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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.
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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.
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Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
What properties do most ionic compounds share?• 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.
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Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
Let’s Share!
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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.
Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
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.
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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.
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Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
What properties do most covalent compounds share?• 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.
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Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
What properties do most covalent compounds share?• 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.
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Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
What properties do most covalent compounds share?• 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.
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Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
Free to Move
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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.
Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
How does a metallic bond form?
• Copper metal is held together by metallic bonding, in which electrons flow around copper ions.
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Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding
What properties do most metallic compounds share?• 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.
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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.
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Unit 3 Lesson 4 Ionic, Covalent, and Metallic Bonding