Polyatomic ions Poly = many Atomic = atoms Entire group of atoms is an ion with a positive or negative charge. Examples: Carbonate ion CO3 2- Sulfate ion SO4 2- S C Mullis

Memorize These Polyatomic Ions - 1 charge -2 charge -3 charge nitrate NO3- sulfate SO42- phosphate PO43- nitrite NO2- sulfite SO32- arsenate AsO43- hydroxide OH- carbonate CO32- bromate BrO3- chromate CrO42- perchlorate ClO4- dichromate Cr2O7 2- chlorate ClO3- oxalate C2O42- chlorite ClO2- peroxide O22- hypochlorite ClO- hydrogen phosphate HPO42- cyanide CN- permanganate MnO4- hydrogen sulfate HSO4- hydrogen carbonate HCO3- acetate C2H3O2- or CH3COO- _+ 1 charge +2 charge Ammonium NH4+ dimercury or mercury (I) Hg22+ Mullis

Atoms and Bonding A chemical bond is an attractive force that holds the atoms of a compound together. Atoms of elements with unfilled outer energy levels can form bonds. When atoms form chemical bonds, they fill their outer energy levels with electrons and become more stable. We will study three types of chemical bonds: ionic, covalent and metallic bonds. Mullis

Chemical Bonds Attractive force that holds atoms or ions together. An atom with an unfilled outer electron shell is likely to bond with another atom. Noble gases have filled outer shells. They are unlikely to form bonds readily. Mullis

Stability and Bonding Matter in lowest energy state is more stable than higher energy state. More stable = less likely to change. Filled outer shell = more stable. How can an atom fill its unfilled outer shell? With electrons from another atom Mullis

Three Kinds of Bonds Ionic Covalent Metallic Electrons transferred from atom to atom Example: NaCl Type of bonds in ionic compounds Covalent Electrons are shared. Usually 2 atoms share a pair of electrons. Example: C6H12O6 Type of bonds in molecular compounds. Metallic Electrons are shared between many atoms. Many atoms share many electrons. Example: Pure Ag Mullis

Electronegativity The tendency of an atom to attract an electron to itself when chemically combined with another atom Expressed a numbers on a scale from 0.8 (Fr) to 4.0 (F) Fluorine has the highest electronegativity. Noble gasses are not included in this concept since they are unlikely to form chemical bonds with other elements. Mullis

Electronegativity Difference Predicts Bond Type Subtract the electronegativity values between two atoms in a compound to identify its bond type. Difference in Electronegativities Bond type >1.7 – 4.0 Ionic >0.3 – 1.7 Polar Covalent 0.0 - 0.3 Nonpolar Covalent Mullis

Ionic Bonding Like loaning your friend your extra baseball glove if you want to play ball: The friend is using your glove and you are not, but Both of you benefit. Ionic bonds: One atom uses the electron from another atom. Both benefit because both are more stable. Mullis

More on Ionic bonds The atom that gives up the electron = positive ion. The atom that accepts the electron = negative ion. The ions are attracted to each other because they have opposite charges. AN IONIC BOND IS AN ELECTROSTATIC ATTRACTION BETWEEN OPPOSITELY CHARGED IONS. Mullis

Example of Ionic Bonding Chlorine and sodium Sodium atom Chlorine atom 11 protons = 11+ 17 protons = 17+ 11 electrons = 11 - 17 electrons = 17- Charge 0 Charge 0 Sodium ion Chloride ion 11 electrons = 10 - 17 electrons = 18- Charge 1 + Charge 1- Together, Na and Cl are attracted to each other and they are electrically neutral. Mullis

The Crystal Lattice 3-dimensional pattern that repeats itself over and over again. Each ion is bonded with all oppositely charged ions that directly surround it. NaCl forms a cube shape, called a body-centered-cubic structure. There are 7 crystal shapes, determined by how the ions are arranged in the lattice. Mullis

Crystal growth Crystals grow by adding ions to all sides. They grow equally in all directions from the outside. Crystals form in 2 ways: Solution containing a dissolved ionic compound evaporates. An ionic solid is heated until it melts, then liquid is cooled. (Igneous rocks) Mullis

Ions Positive ions are smaller than atoms of the same element. Alkali metals form ions with + 1 charge since they tend to lose an electron. Halogens tend to form ions with –1 charge since they tend to gain an electron. Positive ions are smaller than atoms of the same element. Nucleus holds on to the remaining electrons (existing happily in their filled outer shell). Negative ions are larger than atoms of the same element. More electrons means more repulsion . Cl- has radius of almost 2x the radius of Cl atom. Na - 1 electron Na+ + 1 electron Cl Cl- Mullis

Ions, Continued When an ionic compound dissolves in water, each ion is surrounded by water molecules. Living things take up the ions dissolved in water to use as nutrients. Water softeners replace Ca and Mg ions in hard water with Na ions. Mullis

19.2 Ionic Bonds An ionic bond forms when electrons are transferred from one atom to another. An ionic bond is an electrostatic attraction between ions that have opposite charges. Ionic bonds form between the atoms of metallic and nonmetallic elements. The ions that make up ionic solids are arranged in a three-dimensional structure called a crystal lattice. Mullis

A shared pair of electrons makes up a covalent bond between two atoms. 19.3 Covalent Bonds A shared pair of electrons makes up a covalent bond between two atoms. Covalently bonded atoms form either molecules or network solids. Polyatomic ions, such as ammonium and sulfate ions, are groups of covalently bonded atoms with an overall charge. Metallic bonds occur in metals, where a sea of shared electrons surrounds positive metal ions arranged in a lattice structure. Mullis

Covalent Bonds shared pair of electrons Between 2 or more nonmetals Nonmetals have outer shells that are at least ½ full. Molecules are formed with covalent bonds ( …molecular compounds). Mullis

Covalent Bonds again Molecules have definite size; they do not keep growing like ionic solids. Example: Br H + H Br H Br Mullis

8 Octet Rule 8 Chemical compounds tend to form so that each atom has an octet of electrons in its highest occupied energy level. s orbital = 2 electrons when full p orbital = 6 electrons when full Orbitals which overlap for sharing feel full, since they have 8 electrons. (6 + 2 = 8) Example: O (8 total electrons, 6 valence electrons) O ___ ___ ___ ___ ___ 1s 2s 2p O2 is O O 4 shared electrons = 2 pairs = 2 bonds Mullis

Bond energy Bond energy is the energy required to break a chemical bond and form neutral isolated atoms. Units are kilojoules/mole (kJ/mol). Higher bond energy = shorter bond length H—F length is 92 pm, energy is 569 kJ/mol F—F length is 141 pm, energy is 159 kJ/mol Mullis

Lewis structure and structural formula Lewis structures represent molecules with dots and dashes Atomic symbol represents nucleus + inner electrons Dots represent electrons A dash represents a shared electron pair, or single bond. A structural formula shows the kind of bonds, but not unshared pairs of electrons. H—S—H H—S—H Mullis

Resonance structure Resonate: To bounce, or alternate, back and forth The structure switches from one Lewis structure to another One Lewis structure is not entirely accurate. O O O O O O Mullis

Metallic Bonds The valence electrons make up a “sea” of electrons. Valence electrons do not belong to individual atoms, so charge is positive. (It’s like living in a commune.) Metals have high density because lattice is tightly packed atoms. Metals conduct electricity because electrons move freely. Mullis