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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.