What are compounds and how they form bonds? Octet Rule and Ions An octet is 8 valence electrons. is associated with stability of noble gases. He is stable with 2 valence electrons (duet). valence electrons He 2, 2 Ne 2, 8, 8 Ar 2, 8, 8, 8 Kr 2, 8, 14, 88 1

What are ionic and covalent bonds? Atoms form octets to become more stable. by losing, gaining, or sharing valence electrons. by forming ionic bonds or covalent bonds. 2

Metals Form Positive Ions Metals form positive ions by a loss of their valence electrons. electron configuration of nearest noble gas. have fewer electrons than protons. Group 1A metals  ion 1+ Group 2A metals  ion 2+ Group 3A metals  ion , 8, 1 2, 8 With the loss of its valence electron, sodium ion has a +1 charge. Sodium atom Sodium ion 11p + 11p + 11e - 10e

Formation of Mg 2+ Magnesium achieves an octet by losing its two valence electrons. With the loss of two valence Electrons, magnesium forms a positive ion with a +2 charge. Mg atomMg 2+ ion 12p + 12p + 12e- 10e , 8, 22, 8 charge of a positive ion is equal to its Group number. Group 1A(1) = 1+ Group 2A(2) = 2+ Group 3A(3) = 3+

Formation of Negative Ions In ionic compounds, nonmetals achieve an octet arrangement. gain electrons. form negatively charged ions with 3-, 2-, or 1- charges gaining one electron, chloride ion has a -1 charge. Chlorine atom Chloride ion 17p + 17p + 17e - 18e – 5 2, 8, 72, 8, 8 charge of a negative ion obtained by subtracting 8 or 18 from its Group number. Group 6A = = 2-

What are Ionic Compounds? Ionic compounds consist of positive and negative ions. have attractions called ionic bonds between positively and negatively charged ions. have high melting and boiling points. are solid at room temperature. 6 Sodium chloride or “table salt” is an example of an ionic compound.

How to write Ionic Formulas? An ionic formula consists of positively and negatively charged ions. is neutral. has charge balance. total positive charge = total negative charge In NaCl, a Na atom loses its valence electron. a Cl atom gains an electron. symbol of metal is written first followed by symbol of nonmetal. 7

Examples of charge balances! In MgCl 2, a Mg atom loses two valence electrons. two Cl atoms each gain one electron. In Na 2 S. two Na atoms lose one valence electron each. one S atom gains two electrons. subscripts indicate number of ions needed to give charge balance. 8

Writing Ionic Formulas from Charges using cross your heart method! Charge balance is used to write the formula for sodium nitride, a compound containing Na + and N 3−. Na + 3Na + + N 3− = Na 3 N Na + 3(+1) + 1(3-) = 0 We can also use the “cross your heart” method Where cation and anion ionic charges are crossed to determine the subscript 9

Formula from Ionic Charges Write the ionic formula of the compound with Ba 2+ and Cl . Write the symbols of the ions. Ba 2+ Cl  Balance the charges. Ba 2+ Cl  two Cl - needed Cl  Write the ionic formula using a subscript 2 for two chloride ions that give charge balance. BaCl 2 10

Writing Formulas Write a formula for potassium sulfide. 1. Identify the cation and anion. potassium = K + sulfide = S 2− 2. Balance the charges. K + S 2− K + 2(1+) + 2(1-) = K + and 1 S 2− = K 2 S 11

Naming Ionic Compounds with Two Elements: binary compounds To name a compound that contains two elements, identify the cation and anion. name the cation followed by the name of the anion. 12

Examples of Ionic Compounds with Two Elements Formula IonsName cation anion NaClNa + Cl - sodium chloride K 2 SK + S 2- potassium sulfide MgOMg 2+ O 2- magnesium oxide CaI 2 Ca 2+ I - calcium iodide Al 2 O 3 Al 3+ O 2- aluminum oxide 13

Transition Metals form Positive Ions transition metals and form 2 or more positive ions. use a Roman numeral after name of metal to indicate ionic charge. 14 Lead Pb 2+ lead(II) Pb 4+ lead(IV)

Naming FeCl 2 To name FeCl 2 1. Determine the charge of the cation using the charge of the anion (Cl - ). Fe ion + 2 Cl - = Fe ion + 2- = 0 Fe ion = Name the cation by the element name and add a Roman numeral in parenthesis to show its charge. Fe 2+ = iron(II) 3. Write the anion with an ide ending. FeCl 2 = iron(II) chloride 15

Writing Formulas Write a formula for iron(III) chloride. 1. Identify the cation and anion. iron (III) = Fe 3+ (III = charge of 3+) chloride = Cl − 2. Balance the charges. Fe 3+ Cl − Cl − = (3+) + 3(1-) = 0 Cl − 3. 1 Fe 3+ and 3 Cl − = FeCl 3 16

Ionic compounds containing polyatomic Ions A polyatomic ion group of atoms. has an overall ionic charge. Some examples of polyatomic ions are NH 4 + ammoniumOH − hydroxide NO 3 − nitrateNO 2 − nitrite CO 3 2− carbonatePO 4 3− phosphate HCO 3 − hydrogen carbonate (bicarbonate) 17

Some Names of Polyatomic Ions The names of common polyatomic anions end in ate. NO 3 − nitratePO 4 3− phosphate with one oxygen less end in ite. NO 2 − nitritePO 3 3− phosphite with hydrogen attached use the prefix hydrogen (or bi). HCO 3 − hydrogen carbonate(bicarbonate) HSO 3 − hydrogen sulfite (bisulfite) 18

Naming Compounds with Polyatomic Ions The positive ion is named first followed by the name of the polyatomic ion. NaNO 3 sodium nitrate K 2 SO 4 potassium sulfate Fe(HCO 3 ) 3 iron(III) bicarbonate or iron(III) hydrogen carbonate (NH 4 ) 3 PO 3 ammonium phosphite 19

Writing Formulas with Polyatomic Ions The formula of an ionic compound containing a polyatomic ion must have a charge balance that equals zero (0). Na + and NO 3 −  NaNO 3 with two or more polyatomic ions has the polyatomic ions in parentheses. Mg 2+ and 2NO 3 −  Mg(NO 3 ) 2 subscript 2 for charge balance 20

What are covalent bonds? Covalent bonds form when atoms share electrons to complete octets. between two nonmetal atoms. between nonmetal atoms from Groups 4A, 5A, 6A, and 7A. 21

Forming Octets in Molecules A hydrogen molecule is stable with two electrons (helium). has a shared pair of electrons. In a fluorine, F 2,, molecule, each F atom shares one electron. attains an octet. 22

Carbon forms 4 covalent bonds In a CH 4, methane, molecule a C atom shares 4 electrons to attain an octet. each H shares 1 electron to become stable like helium. 23

Multiple Bonds In nitrogen molecule, N 2, each N atom shares 3 electrons. each N attains an octet. the bond is a multiple bond called a triple bond. the name is the same as the element. 24

Naming Covalent Compounds name covalent compounds STEP 1: =name first nonmetal as an element. STEP 2: name second nonmetal with an ide ending. STEP 3: Use prefixes to indicate number of atoms (subscript) of each element. 25 Table4.12

Naming Covalent Compounds What is the name of SO 3 ? 1. The first nonmetal is S sulfur. 2. The second nonmetal is O named oxide. 3. The subscript 3 of O is shown as the prefix tri. SO 3  sulfur trioxide The subscript 1 (for S) or mono is understood. 26

Naming Covalent Compounds Name P 4 S The first nonmetal P is phosphorus. 2. The second nonmetal S is sulfide. 3. The subscript 4 of P is shown as tetra. The subscript 3 of O is shown as tri. P 4 S 3  tetraphosphorus trisulfide 27

Guide to Writing Formulas The prefixes in the name are used to write the formula. STEP 1: Write the symbols in the order of the elements in the name. STEP 2: Write any prefixes as subscripts. Example: Write the formula for carbon disulfide. STEP 1: Elements are C and S STEP 2: No prefix for carbon means 1 C Prefix di = 2 Formula: CS 2 28

What is electronegativity? Indicates attraction of an atom for shared electrons. increases from left to right going across a period on periodic table. is high for nonmetals with fluorine as highest. is low for metals. 29

Polar and non-polar Covalent Bonds A non-polar covalent bond occurs between nonmetals. is an equal or almost equal sharing of electrons. A polar covalent bond occurs between nonmetal atoms. unequal sharing of electrons 30