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 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.