< backnext >previewmain chemical bonding preview section 1 electrons and chemical...

< Back Next > Preview Main

Chemical Bonding

Preview

Section 1 Electrons and Chemical Bonding

Section 2 Ionic Bonds

Section 3 Covalent and Metallic Bonds

Chapter 13

Concept Mapping



Bellringer

Look at these chemical formulas:

C6H1206 C2H5OH

C6H8O6 C6H8O7

Identify the elements in these compounds and predict whether the compounds are similar to each other. Explain your reasoning.

Chapter 13



Objectives

• Describe chemical bonding.

• Identify the number of valence electrons in an atom.

• Predict whether an atom is likely to form bonds.

Chapter 13



Combining Atoms Through Chemical Bonding

• Chemical bonding is the joining of atoms to form new substances.

• An interaction that holds two atoms together is called a chemical bond. When chemical bonds form, electrons are shared, gained, or lost.

Chapter 13



Combining Atoms Through Chemical Bonding, continued

• Discussing Bonding Using Theories and Models We cannot see atoms and chemical bonds with the unaided eye.

• So, the use of models helps people discuss the theory of how and why atoms form bonds.

Chapter 13



Electron Number and Organization

• The number of electrons in an atom can be determined from the atomic number of the element.

• Electrons in an atom are organized in energy levels.

• The next slide shows a model of the arrangement of electron in an atom. This model and models like it are useful for counting electrons, but do not show the true structure of an atom.

Chapter 13


Section 1 Electrons and Chemical BondingChapter 13



Electron Number and Organization, continued

• Outer-Level Electrons and Bonding Most atoms form bond using only its valence electrons, the electrons in an atom’s outermost energy level.

Chapter 13



Electron Number and Organization, continued

• Valence Electrons and the Periodic Table You can use the periodic table to determine the number of valence electrons for atoms of some elements, as shown on the next slide.

Chapter 13


Section 1 Electrons and Chemical BondingChapter 13



To Bond or Not to Bond

• The number of electrons in the outermost energy level of an atom determine whether an atom will form bonds.

• Atoms that have 8 electrons in their outermost energy level do not usually form bonds. The outermost energy level is considered to be full if it contains 8 electrons.

Chapter 13



To Bond or Not to Bond, continued

• Filling the Outermost Level An atom that has fewer than 8 valence electrons is more likely to form bonds than at atom that has 8 valence electrons is. Atoms bond by gaining, losing, or sharing electrons to have a filled outermost energy level.

Chapter 13



To Bond or Not to Bond, continued

• Is Two Electrons a Full Set? Not all atoms need 8 valence electrons to have a filled outermost energy level. Helium atoms need only 2 valence electrons because the outermost level is the first energy level.

• Atoms of hydrogen and lithium form bonds by gaining, losing, or sharing electrons to achieve 2 electrons in the first energy level.

Chapter 13



Bellringer

Salts are ionic compounds. Brainstorm uses for salts, things that contain salts, and words and phrases containing the term salt.

Write your responses in your science journal.

Chapter 13



Objectives

• Explain how ionic bonds form.

• Describe how positive ions form.

• Describe how negative ions form.

• Explain why ionic compounds are neutral.

Chapter 13



Forming Ionic Bonds

• An ionic bond is a bond that forms when electrons are transferred from one atom to another atom.

• Charged Particles An atom is neutral because the number of electrons in an atom equals the number of protons. So, the charges cancel each other out.

• But when an atom gains or loses electrons, it becomes a charged particle called an ion.

Chapter 13



Forming Positive Ions

• Metal Atoms and the Loss of Electrons Atoms of most metals have few valence electrons and tend to lose these valence electrons and form positive ions.

• The Energy Needed to Lose Electrons Energy is needed to pull electrons away from atoms. The energy needed comes from the formation of negative ions.

Chapter 13



Forming Negative Ions

• Nonmetal Atoms Gain Electrons The outer energy level of nonmetal atoms is almost full. So, nonmetal atoms tend to gain electrons and become negative ions.

• The Energy of Gaining Electrons Energy is given off when nonmetals gain electrons. An ionic bond will form between a metal and a nonmetal if the nonmetal releases more energy than is needed to take electrons from the metal.

Chapter 13


Section 2 Ionic BondsChapter 13



Ionic Compounds

• When ionic bonds form, the number of electrons lost by the metal atoms equals the number gained by the nonmetal atoms.

• The ions that bond are charged, but the compound formed is neutral because the charges of the ions cancel each other.

Chapter 13



Ionic Compounds, continued

• When ions bond, they form a repeating three-dimensional pattern called a crystal lattice, such as the one shown below.

Chapter 13

• Properties of ionic compounds include brittleness, high melting points, and high boiling points.



Bellringer

Take a minute or two to brainstorm a list of things made of metal. Then, use your list to describe three properties of metals.

Write your responses in your science journal.

Chapter 13



Objectives

• Explain how covalent bonds form.

• Describe molecules.

• Explain how metallic bonds form.

• Describe the properties of metals.

Chapter 13



Covalent Bonds

• A covalent bond forms when atoms share one or more pairs of electrons.

• Substances that have covalent bonds tend to have low melting and boiling points and are brittle in the solid state.

• Covalent bonds usually form between atoms of nonmetals, such as the atoms shown on the next slide.

Chapter 13


Section 3 Covalent and Metallic BondsChapter 13



Covalent Bonds, continued

• Covalent Bonds and Molecules Substances containing covalent bonds consist of particles called molecules. A molecule usually consists of two or more atoms joined in a definite ratio.

• The models on the next slide show two ways to represent the covalent bonds in a water molecule.

Chapter 13


Section 3 Covalent and Metallic BondsChapter 13



Covalent Bonds, continued

• One way to represent atoms and molecules is to use electron-dot diagrams. An electron-dot diagram shows only the valence electrons in an atom.

Chapter 13



Covalent Compounds and Molecules

• A molecule is the smallest particle into which a covalently bonded compound can be divided and still be the same compound.

• The Simplest Molecules are made up of two bonded atoms. Molecules made up of two atoms of the same element are called diatomic molecules.

Chapter 13



Covalent Compounds and Molecules, continued

• More-Complex Molecules Carbon atoms are the basis of many complex molecules.

Chapter 13

• Each carbon atom can form four covalent bonds. These bonds can be with atoms of other elements or with other carbon atoms, as shown at right.



Metallic Bonds

• A metallic bond is a bond formed by the attraction between positively charged metal ions and the electrons in the metal.

• Movement of Electrons Throughout a Metal Bonding in metals is a result of the metal atoms being so close to one another that their outermost energy levels overlap. This overlapping allows valence electrons to move throughout the metal.

Chapter 13



Metallic Bonding

Chapter 13

Click below to watch the Visual Concept.

Visual Concept



Properties of Metals

• Conducting Electric Current Metallic bonding allows metals to conduct electric current.

• Electric current is conducted when valence electrons move within a metal. These electrons are free to move because the electrons are not connected to any one atom.

Chapter 13



Properties of Metals, continued

• Reshaping Metals Because the electrons swim freely around the metal ions, atoms in metals can be rearranged. The properties of ductility and malleability describe a metal’s ability to be reshaped.

• Ductility is the ability to be draw in to wires.

• Malleability is the ability to be hammered into sheets.

Chapter 13



Properties of Metals, continued

• Bending Without Breaking When a piece of metal is bent, some of the metal ions are forced closer together.

• But the metal does not break because the positive metal ions are always surround by and attracted to the electrons in the metal.

Chapter 13


Chemical Bonding

Use the terms below to complete the Concept Mapping on the next slide.

Chapter 13

Concept Mapping

covalent bonds

ions

molecules

electrons

metallic bonds

chemical bonds


Chemical BondingChapter 13

< backnext >previewmain chemical bonding preview section 1 electrons and chemical...

Documents

chemical bonding section

chemical bonding chapter

number of electrons

chemical bonding bellringer

chemical bonding objectives

number of valence electrons

backnext previewmain

chemical bonds form