Chapter 23 Chemical Bonding Electrons can be described as occupying a series of shells. Electrons in the outermost shell are called valence electrons and the shell they are in is called the valence shell.

Chapter 23 Chemical Bonding

Chapter 23 Chemical Bonding We represent valence electrons in an electron dot diagram. Chlorine has three nonbonding pairs and one unpaired electron which will tend to want to bond.

Chapter 23 Chemical Bonding

Chapter 23 Chemical Bonding Ion Formation: When an atom has the same number of protons and electron, it is electrically neutral. When atoms lose or gain electrons they form ions. Ions are written as follows: Fˉ, Ca²+, Clˉ, O²ˉ Atoms tend to lose or gain electrons so that they end up with the outermost occupied shell filled and stable.

Chapter 23 Chemical Bonding Ion Formation: Group 1: likes to become +1 (Cations are +) Group 2: likes to become +2 Transition metals usually +2 or +3 Group 13: can become +3, but usually covalently bond Group 14: Covalently bond Group 15: N and P can become -3 Group 16: likes to become -2 (Anions are -) Group 17: Likes to become -1 Group 18: Not reactive (outer shell full)

Chapter 23 Chemical Bonding

Chapter 23 Chemical Bonding Ionic bonding: When a bond is formed due to the electrical attraction after one atom loses an electron to another atom forming two oppositely charged ions.

Chapter 23 Chemical Bonding Realistically, ionic bonds are formed as a highly ordered, three-dimensional grouping (Ionic crystal) like the above pictures, not one at a time like on the previous slide.

Chapter 23 Chemical Bonding Ionic bonds are usually made from a metal and a non-metal Metals like to become positive ions and nonmetals (if not sharing electrons to form covalent bonds), will gain electrons to become negative ions.

Chapter 23 Chemical Bonding

Chapter 23 Chemical Bonding Naming Ionic Compounds: The cation (the positive one) always goes first The anion (the negative one) goes second and usually ends in -ide Add subscripts to make sure the positive and negative charges cancel out to zero. Examples: Ca²+ and Iˉ gives us CaI2 and is called Calcium Iodide Fe ³+ and O²ˉ gives us Fe2O3 and is called Iron (III) Oxide

Chapter 23 Chemical Bonding 3. K+ and S²ˉ gives us K2S and is called potassium sulfide 4. Ca²+ and O²ˉ gives us CaO and is called calcium oxide 5. Cu²+ and Clˉ gives us CuCl2 and is called copper (II) chloride When cations have multiple charges (like transition metals), you designate the charge with a roman numeral after it.

Chapter 23 Chemical Bonding Covalent Bonding: Atoms held together by their mutual attraction for shared electrons. Covalent bonds are formed by two atoms that tend to gain electrons come into contact with each other. They can’t effectively take an electron from one another so they share. These are primarily nonmetals in the upper right-hand corner of the periodic table.

Chapter 23 Chemical Bonding

Chapter 23 Chemical Bonding single covalent bond Double covalent bond

Chapter 23 Chemical Bonding Triple covalent bond

Chapter 23 Chemical Bonding Naming Covalent Compounds: We use prefixes to designate the number of atoms of each element we have. mono = 1 hexa = 6 di = 2 hepta = 7 tri = 3 octa = 8 tetra = 4 nona = 9 penta = 5 deca = 10

Chapter 23 Chemical Bonding Examples: SiO2 is called Silicon dioxide N2O3 is called dinitrogen trioxide CF4 is called carbon tetrafluoride Cl2O7 is called dichlorine heptoxide P4S3 is called tetraphosphorus trisulfide PCl5 is called phosphorus pentachloride S2F10 is called disulfur decafluoride

Chapter 23 Chemical Bonding Polar Covalent Bonding: Uneven sharing of electrons between two atoms. In a molecule like H2, the two atoms share the electrons evenly. In HF, the fluorine atoms pull the electrons closer to its side given the molecule a slightly negative charge on that side. The hydrogen side becomes slightly positive. This separation of charge that happens in a polar covalent molecule is called a dipole.

Chapter 23 Chemical Bonding This is a polar covalent bond Notice the larger cloud around the fluorine atom because it has a greater need for that electron they share. Why?

Chapter 23 Chemical Bonding Electronegativity – How strongly an atom is able to tug on bonding electrons . It can be measured. The range of electronegativity is from 0.7 to 3.98 Electronegativity is greatest for elements in the upper right hand corner of the periodic table. When two elements have the same electronegativity (usually the same element) it forms a nonpolar bond because the electrons are shared evenly.

Chapter 23 Chemical Bonding Notice that the further apart two elements are on the table, generally the greater the difference in their electronegativities.

Chapter 23 Chemical Bonding In Summary: Ionic bonds have great differences in electronegativities to the point that one atom takes the other’s electrons. (metal/nonmetal) Nonpolar covalent bonds have similar electronegativities and share evenly. (two nonmetals) Polar covalent bonds have noticeable differences in electronegativities where one atom holds the electrons closer creating a dipole. (two nonmetals)

Chapter 23 Chemical Bonding Water is a polar covalent molecule that has about a 105° bond angle allowing the oxygen to pull much of the charge away from the two hydrogen atoms. This creates a highly polar and “sticky” water molecule. This is why a belly flop hurts as well as water being able to dissolve many different substances

Chapter 23 Chemical Bonding

Bonding Covalent Compounds Gases, liquids, or solids (made of molecules) Low melting and boiling points Poor electrical conductors in all phases Many soluble in nonpolar liquids but not in water

Bonding Ionic Compounds Crystalline solids (made of ions) High melting and boiling points Conduct electricity when melted or in solution Many soluble in water but not in nonpolar liquid