From Atoms to Compounds (Chapters 7-9) Dr. Walker

Objectives Determine valence electrons and ionic charge of elements based on placement on the periodic table Determine names and formulas of compounds using IUPAC naming rules Differentiate between ionic and covalent compounds based on elemental composition and physical properties

More on Electrons Valence Electrons Electrons in the outer shell of an atom Determines chemical properties

Determining Valence Electrons How do we determine valence electrons? Valence electrons = last number of group number Examples Sodium – Group 1 = 1 valence electron Boron – Group 13 = 3 valence electrons Chlorine – Group 17 = 7 valence electrons Nitrogen – Group 15 = 5 valence electrons

Determining Valence Electrons We can also get valence electrons from the electron configuration Examples Sodium – 1s22s22p63s1 = 1 valence electron There is one electron in the third energy level Boron – 1s22s22p1 = 3 valence electrons There are three electrons in the second energy level Chlorine – 1s22s22p63s23p5 = 7 valence electrons There are seven electrons in the third energy level The electrons in s and p subshells of a given energy level are valence electrons

Determining Valence Electrons What about the transition metals, actinides, and lathanides? We don’t worry about these elements These elements can use electrons from d and f orbitals, which we won’t deal with

The Octet Rule Every main group element wants to have eight valence electrons Main groups = 1-2, 13-18 Not transition metals, inner transition metals Can lose d or f electrons to gain stability

But wait… Not all elements have eight valence electrons Only the noble gases (group 18) has eight valence electrons So how does an element obey the octet rule?

From Atoms to Ions Ion An atom that has gained or lost one or more electrons This species is now charged Cation – positively charged (loses electrons) Anion – negatively charged (gains electrons)

From Atoms to Ions Atoms will gain or lose electrons to obey the octet rule Example Sodium has 1 valence electron in level 3 It can either gain 7 electrons to fill level 3 or lose the electron in level 3, making level 2 the valence shell.

From Atoms to Ions The second energy level is now the valence shell for sodium

From Atoms to Ions Notice sodium started with 11 protons (+) and 11 electrons (-). This was a neutral atom. After losing an electron, the sodium ion has 11 protons (+) and 10 electrons (-). There is one extra proton, so the charge is +1.

From Atoms to Ions Chlorine has 7 valence electrons. It can either gain 1 electron or lose 7 electrons. It is easier to gain 1 electron

From Atoms to Ions Chlorine starts with 17 protons (+) and 17 electrons (-) and was neutral When chlorine gains an electron, it has 17 protons (+) and 18 electrons (-) Chlorine now has an extra electron, giving it a charge of -1.

Valence Electrons and Charge Group 1 2 13 14 15 16 17 18 Valence Electrons 3 4 5 6 7 8 Lose or Gain Lose 1 Lose 2 Lose 3 Either/or Gain 3 Gain 2 Gain 1 Neither Charge +1 +2 +3 +4 or -4 -3 -2 -1 Keep in mind: -Losing electrons gives you a positive charge because you are losing negative charges. -Gaining electrons gives you a negative charge This is the concept that confuses students the most! -Only electrons will EVER be gained or lost!!!

Exercises How many valence electrons are in nitrogen? What will its charge be? How many protons and electrons will be present at this time?

Exercises How many valence electrons are in nitrogen? 5 (group 15) What will its charge be? It must gain 3 electrons, so it will be -3 How many protons and electrons will be present at this time? 7 protons (atomic # = 7) 10 electrons (had 7, gained 3, 7 + 3 = 10)

Exercises How many valence electrons are in calcium? What will its charge be? How many protons and electrons will be present at this time?

Exercises How many valence electrons are in calcium? 2 (group 2) What will its charge be? Needs to lose two electrons, so +2 How many protons and electrons will be present at this time? 20 protons (atomic #) 18 electrons (had 20, lost 2, 20 – 2 = 18)

Notice the trend? When atoms gain or lose electrons, they will have the same number of electrons as one of the noble gases and will have a noble gas electron configuration Losing or gaining electrons changes the electron configuration Sodium (neutral): 1s22s22p63s1 Sodium (cation, +1 charge): 1s22s22p6 Notice the sodium has 10 electrons now, which is the same number of electrons as neon

Summary Valence electrons are determined by the group number and electron configuration Octet Rule: All main group elements want eight valence electrons Atoms gain or lose electrons to obey the octet rule. This results in a charge. A charged atom is known as an ion.

A question…. If cations lose electrons, where do they go? Don’t’ write!! A question…. If cations lose electrons, where do they go? If anions gain electrons, where do they come from?

Ionic Bonding Ionic bonds are formed when ions transfer electrons to obey the octet rule Ionic bonds between elements result in the formation of compounds The net charge of all compounds is zero

Ionic Bonding Ionic bonding occurs between elements that form opposite charges upon bonding These atoms will be on opposite sides of the periodic table staircase One atom from the left, one from the right One metal, one nonmetal

Ionic Bonding This diagram shows the transfer of an electron from sodium to chlorine A sodium cation and chloride anion are formed in this process The two ions together form a neutral compound http://eweb.furman.edu/~wworthen/bio111/2ionic.gif

Ionic Bonding This shows an example of multiple electrons being transferred Each chlorine needs to gain one electron Calcium loses two electrons, donating one to each chlorine http://www.geo.arizona.edu/xtal/nats101/9_3.jpg

Rule stating everyone wants Eight valence electrons Atoms lose electrons to form __________ Atoms gain electrons to form __________ Combines To form _________ bonds Results from the __________ of electrons

Rule stating everyone wants Eight valence electrons Octet rule Atoms lose electrons to form cations Atoms gain electrons to form anions Combines To form Ionic bonds Results from the transfer of electrons

What is a Formula? A chemical formula shows the numbers of atoms of each element in the smallest representative unit of a substance. Formulas are used to represent compounds Examples NaCl (1 sodium, 1 chlorine) H2O (2 hydrogens, 1 oxygen) C6H12O6 (6 carbons, 12 hydrogens, 6 oxygens)

Formula Unit Chemical formula of an ionic compound Ionic compounds exist in networks Formula unit shows the lowest number ratio Example: LiCl – Li loses 1 electron, Cl gains 1 electron, formula unit is LiCl Diagram shown is the crystal structure which shows a large network Lithium and chlorine still have 1:1 ratio

Ionic Formulas You can figure out the formula for an ionic compound by criss-crossing charges to subscripts and reducing subscripts if possible The formulas are determined so that (+) charge = (-) charge The overall charge MUST be zero!!!!!

Ionic Formulas You figure out the formula for an ionic compound by criss-crossing charges to subscripts and reducing subscripts if possible. Na+1 Cl-1 K+1 O-2 Mg+2 P-3

Ionic Formulas You figure out the formula for an ionic compound by criss-crossing charges to subscripts and reducing subscripts if possible. Na+1 Cl-1 NaCl K+1 O-2 K2O Mg+2 P-3 Mg3P2

More Ionic Examples Give the formula for the following Ca+2 and N-3 Mg+2 and F-1 Li+1 and S-2 Al+3 and O-2

More Ionic Examples Give the formula for the following Ca+2 and N-3 Ca3N2 Mg+2 and F-1 MgF2 Li+1 and S-2 Li2S Al+3 and O-2 Al2O3

Polyatomic Ions Group of atoms that are covalently bound with a singular charge Makes ionic bonds like any other ion Ones to know Nitrate, NO3- Ammonium, NH4+ Hydroxide, OH- Sulfate, SO4-2 Carbonate, CO3-2 Phosphate, PO4-3

Polyatomic Examples Na+1 and CO3-2 NH4+1 and Cl-1 Ca+2 and PO4-3 Al+3 and SO4-2

Polyatomic Examples Na+1 and CO3-2 NH4+1 and Cl-1 Ca+2 and PO4-3 Na2CO3 NH4+1 and Cl-1 NH4Cl Ca+2 and PO4-3 Ca3(PO4)2 Al+3 and SO4-2 Al2(SO4)3 Need parentheses around multiple polyatomic ions

Naming Ionic Compounds Rules for naming made by IUPAC International Union of Pure and Applied Chemistry Write the name of the cation. If the anion is an element, change its ending to -ide; if the anion is a polyatomic ion, simply write the name of the polyatomic ion. Ca3N2 MgF2 Na2CO3 Al2(SO4)3

Naming Ionic Compounds Write the name of the cation. If the anion is an element, change its ending to -ide; if the anion is a polyatomic ion, simply write the name of the polyatomic ion. Ca3N2 = Calcium nitride MgF2 = Magnesium fluoride Na2CO3 = Sodium carbonate Al2(SO4)3 = Aluminum Sulfate

Transition Metals Transition metals do not follow the octet rule Transition metals can have multiple charges The charge of a transition metal is designated by a roman numeral Reverse the arrows to determine the charge on the metal, then name accordingly Examples FeCl2 FeCl3 Cu2O CuO

Transition Metals Transition metals do not follow the octet rule Transition metals can have multiple charges The charge of a transition metal is designated by a roman numeral Reverse the arrows to determine the charge on the metal, then name accordingly Examples FeCl2 = Iron (II) chloride FeCl3 = Iron (III) chloride Cu2O = Copper (I) oxide CuO = Copper (II) oxide

From Name to Formula Determine charges on ions Reverse arrows accordingly Name doesn’t tell you how many atoms are present Example Potassium sulfide

From Name to Formula Determine charges on ions Reverse arrows accordingly Name doesn’t tell you how many atoms are present Example Potassium sulfide K+1 S-2 K2S

From Name to Formula More Examples Aluminum hydroxide Lithium nitride Magnesium sulfate Calcium chloride

From Name to Formula More Examples Aluminum hydroxide Lithium nitride Al(OH)3 Lithium nitride Li3N Magnesium sulfate MgSO4 Calcium chloride CaCl2

From Name to Formula Lead (IV) oxide Copper (I) sulfate Iron (II) chloride Potassium phosphate

From Name to Formula Lead (IV) oxide PbO2 Copper (I) sulfate Cu2SO4 Iron (II) chloride FeCl2 Potassium phosphate K3PO4

More Examples

More Examples

Covalent Bonding Covalent bonding results from the sharing of electrons Forms molecular compounds Ionic bonding occurs from the transfer of electrons Ionic bonding occurs between ions with opposite charges Covalent bonding occurs between atoms that need electrons to fill their octets

Covalent Bonding Naming covalent compounds: Use prefixes

Covalent Bonding Name to Formula Give the formula for the following compounds: Carbon tetrachloride Dinitrogen tetroxide Nitrogen monoxide Phosphorous trifluoride

Covalent Bonding Naming Molecular Compounds Give the formula for the following compounds: Carbon tetrachloride CCl4 Dinitrogen tetroxide N2O4 Nitrogen monoxide NO Phosphorous trifluoride PF3

Covalent Bonding Formula to Name: SO2 N2O3 SiBr4 NCI3

Covalent Bonding Formula to Name: SO2 N2O3 SiBr4 NCl3 Sulfur dioxide Dinitrogen trioxide SiBr4 Silicon tetrabromide NCl3 Nitrogen trichloride

Compare and Contrast Ionic Bonding Elements have opposite charges One element gains electrons, one loses electrons Found on opposite sides of the staircase of the periodic table Includes transition metals and polyatomic ions Large electronegativity difference between atoms

Compare and Contrast Covalent Bonding Both elements found on right side of “the staircase” (exception: Hydrogen uses covalent bonds) No metals!!! Remember, hydrogen is a gas, NOT a metal! Small electronegativity difference between atoms

Compare and Contrast Ionic Covalent Mostly crystalline solids at room temperature (very high melting points) Ionic salts dissolved in water conduct electricity Covalent Can be liquids or gases at room temperature Poor or non-conducting

Rule stating everyone wants Eight valence electrons Valence shell filled by transfer Valence shell filled by sharing Elements Used Elements Used How to name How to name Includes Which one conducts electricity? ___________ Ends in ________ _________ shows charge

Rule stating everyone wants Eight valence electrons Octet rule Valence shell filled by transfer Valence shell filled by sharing ionic covalent Elements Used Elements Used How to name How to name Metal + nonmetal No prefixes Use prefixes Nonmetals only Includes Which one conducts electricity? ___ionic_ Polyatomic ions Transitional metals Roman numeral shows charge Ends in –ate or -ite

Review Electronegativity The tendency of an atom to attract electrons to itself when chemically combined with another element Increases to the right on the Periodic Table Increases going up on the Periodic Table Most electronegative elements: F, O, Cl

http://www. cusd. chico. k12. ca http://www.cusd.chico.k12.ca.us/~rbarber/chem/chem/page57_files/electronegativity_table_bw.jpg

Ionic or Covalent? Are the following compounds ionic or covalent? What are they called? KCl H2O Fe(OH)2 MgBr2 P2O5

Ionic or Covalent? Are the following compounds ionic or covalent? What are they called? KCl Ionic; Potassium chloride H2O Covalent; Dihydrogen monoxide (aka water) Fe(OH)2 Ionic; Iron (II) hydroxide MgBr2 Ionic; Magnesium bromide P2O5 Covalent; Diphosphorous pentoxide

Review How many valence electrons does nitrogen have? When it ionizes, what is its charge? After it ionizes, how many protons and electrons does it have? What is the formula for calcium hydroxide? What is the name of P2O4? Is Iron (III) sulfate an ionic or covalent compound?

Review How many valence electrons does nitrogen have? 5 When it ionizes, what is its charge? -3 After it ionizes, how many protons and electrons does it have? 7 protons, 10 electrons What is the formula for calcium hydroxide? Ca(OH)2 What is the name of P2O4? Diphosphorous tetroxide Is Iron (III) sulfate an ionic or covalent compound? Ionic; it involves a transition metal and a polyatomic ion

Terms to Know Valence Electrons Octet Rule Cation Anion Chemical Formula Formula Unit Ionic Bond Covalent Bond Polyatomic Ion Electronegativity

Skills To Master Determining Valence Electrons From the periodic table From electron configuration Determining charge From numbers of subatomic particles Determine the formula of a compound from its name Differentiate ionic and covalent compounds from name or formula Determine the name of a compound from its formula based on its bonding type (ionic or covalent)