Chapter 6 – Chemical Bonds

6.1 Ionic Bonding• When the highest occupied energy level of

an atom is filled with electrons, the atom is stable and not likely to react.

• Electron dot diagram – symbol represents the nucleus and each dot represents a valence electron (also called Lewis Dot Diagram or Lewis Dot Structure)

Ionic Bonds

• Elements achieve stable e- config. through the transfer of e-

• Form between a metal and a nonmetal

• Metal gives up e-; nonmetal gains e-

• Ions (atoms with charges) are formed

• Metal becomes + ion, nonmetal becomes a neg. ion

• Opposite charges attract each other

Sodium Chloride

• Chemical bond – the force that holds atoms or ions together

• Cation – positive ion• Anion – negative ion

• Ionic bond – the force that holds ions together

• Ionization energy – the amount of energy used to remove an e-

• Lower ionization energy = easier to remove an electron

Ionic Compounds

• Chemical Formula – shows which elements are in a compound and the ratio – Ex. NaCl, MgCl2

• Crystal lattices – ions are arranged in an orderly, 3-D structure

• Crystals – solids whose particles are arranged in a lattice structure

• Properties of ionic compounds– High melting points– Poor conductors in solid form– Good conductors when melted– Brittle (shatter when struck by a hammer)

When an ionic crystal is struck, ions are moved from their fixed positions. Ions with the same charge repel one another and the crystal shatters.

6.2 Covalent Bonds

• Form when two or more atoms SHARE e-

• Form between two or more nonmetals

• Can be polar or nonpolar– Polar – e- are NOT shared equally– Nonpolar – e- ARE shared equally

• Form molecules (neutral group of atoms that are joined by covalent bonds)

• Atoms may share 1, 2, or 3 prs. of e-

Many nonmetals exist as diatomic molecules. Diatomic means “two

atoms”

Polar Covalent Bonds

• One atom has a greater attraction for the e-, making one end of the molecule have a partial neg. charge. The other end has a partial pos. charge.

Water is a polar molecule. The e- spend most of their time with the Oxygen atom, making the O end of the molecule slightly negative and the H end slightly positive.

Nonpolar Covalent Bond

Both atoms have an equal attraction for the electrons, so they share them equally.

Attraction Between Molecules

• Attractions between polar molecules are stronger than between nonpolar molecules.

6.3 Naming Compounds and Writing Formulas

• Binary Ionic Compounds– 1st word – name of metal– 2nd word – name of nonmetal ending in –ide– If the metal is a transition metal, a roman

numeral is placed between the metal and nonmetal to indicate which ion.

• Ex. Sodium Chloride, Copper (II) Chloride

Polyatomic Ions

• Covalently bonded group of atoms with a charge.

• Polyatomic ions act like single atoms when forming chemical bonds.

• Polyatomic ions are COVALENTLY bonded to each other, but as a group they bond IONICALLY to another ion.

Writing Formulas for Ionic Compounds

• Symbol of cation is written first, followed by the symbol of the anion

• Use subscripts to show the ratio of ions

• Parentheses are used to enclose polyatomic ions

Naming Molecular Compounds

• MOST metallic element appears first in the name (the one closer to the left on the periodic table)

• If both elements are in the same group, the one closer to the bottom is listed first

• Use prefixes to indicate the number of atoms

• The prefix “mono-” is not used in the first element name.

Writing Molecular Formulas

• Write the symbols for the elements in the order that they appear in the name

• Use the prefixes to determine the number of atoms

• Use subscripts to show how many atoms of each element are in a molecule

6.4 The Structure of Metals

• Metallic Bonds– Form between two or more metal atoms– Attraction between the metal cation and the

shared electrons that surround it– “sea of electrons”

• Metals are malleable and are good conductors because of metallic bonds.

• Alloys– Mixture of two or more elements at least one

of which is a metal– Can be designed with specific properties by

varying the types and amounts of elements in them.

Bronze is a common alloy made usually of copper and tin.

Steel is an alloy of iron that contains small quantities of iron.