CHEMICAL BOND

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.

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.

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.

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.

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.

Ionic Compounds

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

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

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.

Covalent Bonds

• 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.

Covalent Bonds

• 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.

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.

Covalent Compounds and Molecules

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

• 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.