Notes 5-1 Atoms, Bonding and the Periodic Table Key Ideas: How is the reactivity of elements related to valence electrons in atoms? What does the periodic table tell you about the atoms of elements?

Valence Electrons and Bonding Valence electrons are the electrons in the highest energy level and are held most loosely to the atom. The number of valence electrons determines many properties of that element, including the ways the atom can bond with other atoms. Each element has a specific number of valence electrons from 1-8. Electron Dot Diagrams: A model that represents how many valence electrons are in an element Includes a symbol and dot/s representing valence electrons Chemical Bonds and Stability Noble gases most nonreactive since they have 8 electrons in their outer shell Small atoms like helium are stable with just two valence electrons When atoms give up their valence electrons are accept valence electrons from other atoms, they become chemically combined forming a chemical bond. This is due to the rearrangement of their electrons. Chemical Bonds and Chemical Reactions Electrons can be transferred forming a bond but they can also be shared forming a bond (more to come on covalent bonding) In either case, the change results in a chemical reaction forming a new substance

How the Periodic Table Works Relating Periods and Groups: As atomic number increases, number of valence electrons increase; Periods end when valence electrons reach 8; Elements within a group always have the same number of valence electrons with similar properties Inert Gases: Group 18=Inert gases, 8 valence electrons except with helium which has 2 Reactive Nonmetals and Metals: Group 17=Halogens with 7 valence electrons; Group 1=Alkali metal family with 1 valence electron Other Metals: Groups 2 through 12, most have 1-3 valence electrons, Reactivity increases from top to bottom in Groups 1 and 2 Other Nonmetals: All nonmetals have 4 or more valence electrons (Groups 14-17) Semimetals: fall on zigzag line(Groups 13—16), from 3 to 6 electrons, can lose or share electrons, can behave like metals or nonmetals Hydrogen: In (Group I), 1 valence electron, not a metal

Notes 5-2 Ionic Bonds Key Ideas: How do ions form bonds? How are the formulas and names of ionic compounds written? What are the properties of ionic compounds?

Ions An atom that has an electric charge is an ion. How Ions Form Lose a valence electron = gain a positive charge = cation Gain a valence electron = gain a negative charge = anion Polyatomic Ions Ions made of several atoms Ammonium ion / 1+ / NH4+ Bicarbonate ion / 1- / HCO3- Ionic Bond (the attraction between two oppositely charged ions) Ionic bonds form as a result of the attraction between positive and negative ions. NA+ Cl- → NaCl

Chemical Formulas and Names A chemical formula is a combination of symbols that show the ration of elements in a compound. Example: MgCl2 What does this mean? Formulas of Ionic Compounds When ions come together to form a compound, the charges cancel out. Mg 2+, + Cl 1- + Cl 1- → MgCl2 The subscript 2 tells you the ratio of magnesium to chloride. Naming Ionic Compounds For an ionic compound, the name of the positive ion comes first, followed by the name of the negative ion.

Properties of Ionic Compounds Generally, ionic compounds are hard, brittle solids with high melting points. They conduct electricity when melted or dissolved in water. Ionic Crystals Ionic compounds form solids by building up a repeating pattern of ions known as crystals. These crystals have an orderly, three dimensional arrangement. High Melting Points When you hear NaCl, its energy increases and the ionic crystal melts into a liquid. A lot of energy is needed to break the bonds therefore, ionic compounds have high melting points. (For NaCl the melting point is 801C.) Electrical Conductivity Ionic compounds dissolved in water conduct electricity. Ionic compounds dissolved due to melting into a liquid conduct electricity. Ionic compounds in a solid do NOT conduct electricity well because the ions are so tightly bound together.

Notes 5-3 Covalent Bonds Key Ideas: What holds covalently boned atoms together? What are the properties of molecular compounds? How does unequal sharing of electrons affect molecules?

COVALENT BOND A force that bonds two atoms together by a sharing of electrons Each pair of shared electrons creates a bond Usually occurs between atoms of non-metals Example – Water (H 2 O)Water (H 2 O) OHH

How Covalent Bonds Form

The oxygen atom in water and the nitrogen atom in ammonia each have eight valence electrons as a result of forming covalent bonds with hydrogen atoms.

How Covalent Bonds Form Double and triple bonds can form when atoms share more than one pair of electrons.

Types of Covalent Bonds Different covalent bond types share a different number of electrons Single Bonds Share 2 Electrons Double Bonds Share 4 Electrons Triple Bonds Share 6 Electrons Water (H 2 O)Carbon Dioxide (CO 2 )Nitrogen (N 2 )

Unequal Sharing (Polar Covalent Bond) Why do you think the two Hydrogen atoms share equally, but the Hydrogen and fluorine do not? Bonded hydrogen atoms showing equal sharing of electrons Hydrogen and fluorine bond with an unequal sharing of electrons The unequal sharing of electrons between two atoms that gives rise to negative and positive regions of electric charge Results from an atom’s electronegativity – the ability to attract electrons to itself Electron Cloud

Unequal Sharing of Electrons Fluorine forms a nonpolar bond with another fluorine atom. In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does, so the bond formed is polar.

Unequal Sharing of Electrons A carbon dioxide molecule is a nonpolar molecule because of its straight-line shape. In contrast, a water molecule is a polar molecule because of its bent shape.

Results of Bonding Molecule A neutral group of two or more non-metal atoms held together by covalent bonds Type: Diatomic - molecules consisting of two atoms of the same element bonded together Examples: H 2, F 2, O 2, N 2 Compound A pure substance composed of two or more different elements (atoms) that are chemically combined Examples: CO, NO 2, NaCl

Molecule, Compound, or Both? H 2 Hydrogen NO 2 Nitrogen Dioxide Cl 2 Chlorine O 2 Oxygen NO Nitric Oxide CO 2 Carbon Dioxide N 2 Nitrogen H 2 O Water CH 4 Methane

Notes 5-4 Bonding in Metals Key Ideas: How do the properties of metals and alloys compare? How do metal atoms combine? How does metallic bonding result in useful properties of metals?

Metals and Alloys An alloy is a mixture made of two or more elements, at least one of which is a metal. They are generally stronger and less reactive than the pure metals from which they are made. Physical Properties Pure gold= shiny and soft Gold alloys = still shiny but much harder (mixed with copper or silver) Chemical Properties Pure iron = rusts when exposed to air and water Iron alloy = stronger, resists rust (mixed with one or more other elements to make steel)

Metallic Bonding and Metallic Properties Bonds: Metal atoms combine in regular patterns in which the valence electrons are free to move from atom to atom (think of metal atoms floating in a sea of electrons). Each metal ion is held in place by a metallic bond - an attraction between a positive metal ion and the many electrons surrounding it. (The more valence electrons, the stronger the bond.) Properties: Malleability = easily rolled into sheets or made into complex shapes Ductility = easily bent or pulled into wires Luster = shiny and reflective Electrical Conductivity = conduct electricity easily (because electrons move freely) Thermal Conductivity = conduct heat easily (because electrons move freely)