Chapter 18 Chemical Bonds

18-1 – Electrons and Bonding Combined Elements Atoms bond with other atoms to become stable Elements combine to form compounds and molecules

18-1 – Electrons and Bonding Remember Periodic Trends Number of valence electrons increases as you move left to right All elements in the same column have the same number of valence electrons Number of valence electrons determines how atom will react with other atoms

18-1 – Electrons and Bonding Remember Lewis Structures to represent valence electrons

18-1 – Electrons and Bonding Stability of an Atom Depends on how full the outer energy level is Filled energy levels = stable Unfilled energy levels = unstable Octet Rule 8 is the number toward stability Exceptions to the octet rule is hydrogen and helium

18-2 – Ionic and Covalent Bonds Atoms are electrically neutral Why? Ions are not electrically neutral Can be negative or positive Atoms tend to lose or gain electrons so they end up with an outermost occupied shell that is filled to capacity The Periodic table can be used to determine the type of ion that an atom tends to form

18-2 – Ionic and Covalent Bonds Positive Ion (cation) Negative Ion (anion)

Ionic Bonds Result from an Transfer of Valence Electrons 18-2 – Ionic and Covalent Bonds Ionic Bonds Result from an Transfer of Valence Electrons Result of transfer of electrons forms a positive ion and a negative ion Ionic Bond – Ionic Compounds – Characteristics of Ionic Bonds –

18-2 – Ionic and Covalent Bonds

18-2 – Ionic and Covalent Bonds Ionic Bonds: One big greedy thief dog! Ionic bonding can be best imagined as one big greedy dog steeling the other dog's bone.  If the bone represents the electron that is up for grabs, then when the big dog gains an electron he becomes negatively charged and the little dog who lost the electron becomes positively charged.  The two ions (that's where the name ionic comes from) are attracted very strongly to each other as a result of the opposite charges.

18-2 – Ionic and Covalent Bonds Properties of Ionic Compounds Solids at room temperature High melting and boiling points Dissolve in water and separates into ions Conducts electricity

Covalent Bonds Result from a Sharing of Valence Electrons 18-2 – Ionic and Covalent Bonds Covalent Bonds Result from a Sharing of Valence Electrons Covalent bond – Covalent Compound – Molecule – Characteristics of Covalent Bonds – Can be single, double, or triple

18-2 – Ionic and Covalent Bonds

18-2 – Ionic and Covalent Bonds

18-2 – Ionic and Covalent Bonds Covalent Bonds: Dogs of equal strength. Covalent bonds can be thought of as two or more dogs with equal attraction to the bones.  Since the dogs (atoms) are identical, then the dogs share the pairs of available bones evenly.  Since one dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs.  The molecule is not "polar" meaning one side does not have more charge than the other.

18-2 – Ionic and Covalent Bonds Properties of Covalent Compounds Exist as solids, liquids, or gases Molecules in covalent compounds easy to separate Lower melting and boiling points Generally, do not dissolve in water Do not conduct electricity

H2O C6H12O6 NaCl O2 CO2 18-3 – Chemical Formulas Chemical Formulas The symbols of each element in a molecule of the substance A number indicating how many atoms of each element are in each molecule of the substance H2O C6H12O6 NaCl O2 CO2

18-3 – Chemical Formulas Subscripts Small numbers to the right of the symbol Subscripts of 1 are not written

18-3 – Chemical Formulas Prefixes Indicate the number of atoms in a molecule of the compound (covalently bonded compounds) Prefix Meaning Example di– two sulfur dioxide (SO2) tri– three nitrogen trifluoride (NF3) tetra– four carbon tetrachloride (CCl4) penta– five phosphorus pentachloride (PCl5) hexa– six sulfur hexafluoride (SF6)

18-3 – Chemical Formulas Names of some of the elements in these compounds are slightly different from their regular element names. For example, the symbol O by itself represents the element oxygen, but when oxygen combines with carbon to form CO2, its name changes to oxide. In a compound made up of two elements, the name of the first element stays the same. The ending of the second element changes to –ide.

(NH4)3PO4 Fe(OH)2 18-3 – Chemical Formulas Some of the compounds above contain parentheses in their chemical formulas. Parentheses are used for grouping. (NH4)3PO4 Fe(OH)2

18-3 – Chemical Formulas Writing formulas for Ionic Compounds Use oxidation numbers from the periodic table Use oxidation numbers to write formulas

18-3 – Chemical Formulas

18-3 – Chemical Formulas Naming Ionic Compounds Write name of positive ion Check oxidation number of positive ion Write root name of negative ion Add ending “-ide”

18-3 – Chemical Formulas

18-3 – Chemical Formulas Naming Covalent Compounds Use element name Add prefixes to designate number of atoms

18-3 – Chemical Formulas

18-3 – Chemical Formulas Writing formulas for Covalent Compounds Think about valence electrons and how atoms will share electrons Use element name Add prefixes to designate number of atoms

18-3 – Chemical Formulas