Please Do Now Get a Book and a Periodic Table Put your name on your periodic table Label GROUPS 1a,2a,3a,4a,5a,6a,7a,8 Label the alkali metals, the alkaline earth metals, the halogens, the noble gases, and the transition metals

Chapter 6

Molecules and Molecular Compounds What does it mean to say that an atom is ‘neutral’? What would happen to the charge of the atom is an electron was removed? Added? What is a molecule?

Although there are only just over 100 elements, there are millions of different compounds! Elements combine! Only the noble gases tend to exist as isolated atoms (think noble = snobby) Monatomic: consist of single atoms (mono = one)

Molecule: the smallest electrically neutral unit of a substance that still has the properties of the substance. Made up of 2 or more atoms that act as a unit Ex: Water, H2O -What is in one molecule of water? 2 hydrogen atoms and 1 oxygen atom

Molecular compounds: compounds composed of molecules. Generally 2 nonmetals Most have low melting or boiling points so most exist in liquid or gas state at room temperature Carbon Monoxide Carbon Dioxide Dihydrogen Monoxide (see a pattern in naming? We’ll get to that later…)

Ions and Ionic Compounds Ions: Atoms or groups of atoms with a positive or negative charge This is where it’s important to know your valence electrons! These are the outermost electrons of an atom Use your periodic table to figure it out! Group 1a has 1 valence electron Group 8 has 8 valence electrons (ex is He=2) Atoms want 8 valence electrons…so, will gain or lose!

Sodium, Na, Group 1a, 1 valence electron Cation: ion with a positive charge (has lost an electron), generally groups 1a, 2a, 3a Sodium, Na, Group 1a, 1 valence electron Remember, atoms want to get to 8 valence electrons Ask yourself: is it easier to lose 1 electron or gain 7? Sodium will generally LOSE one electron= +1 charge Na+1 What about Magnesium? Lithium? What about Hydrogen?

For metallic elements, the name of the cation is the same as the name of the element Sodium atom forms a sodium cation Symbol = Na+1 Metals tend to have very different properties from their cations Sodium metal is explosively reactive with water Sodium cation is in table salt, stable in water

Anions Anions: Atoms that have gained one or more electrons and have a NEGATIVE charge Ex: Chlorine, group 7a, has 7 valence electrons Ask yourself: is it easier to gain one electron or lose 7? Gain 1= Cl-1 Chlorine Ion will gain one electron, -1 charge The name of an ion usually ends in –ide So a chlorine ion will be called chloride

Ionic Compounds Ionic Compounds: Compounds made up of cations and anions Usually composed of metal cations and nonmetal anions Ionic compounds are electrically neutral How Is this possible if they are made up of charged atoms???

Review Molecular compound Ionic Compound Unit: Molecule Formula Unit Type of Elements: Nonmetals Metals + Nonmetals Physical States: Solid/liquids/gases Solid Melting Point: Usually Low High Example: Carbon dioxide Sodium Chloride

Practice: Pg 137 3-9 Pg 166 46-49

PDN 1. Get a book 2. Turn in your ‘Drawing Atoms’ project 3. On a separate sheet of paper: Predict the charge of the ion formed by the following elements and write the complete symbol: Chlorine Sodium Aluminum Potassium Xenon

Chapter 6 Section 2

Representing Chemical Compounds Chemical formula: shows the kinds and numbers of atoms in the smallest representative unit of the substance 2 types: Molecular formulas and Formula Units Molecular Formulas: shows the kinds and numbers of atoms present in a MOLECULE of a compound Think 2 nonmetals! Does not tell you anything about structure Turn to pg 139

Formula Units: lowest whole number ratio of ions in an IONIC COMPOUND Think: metal and nonmetal! Not a molecule. 3 dimensional patterns of ions Think Salt NaCl

The Laws of Definite and Multiple Proportions The law of definite proportions: in samples of any chemical compound, the masses of the elements are always in the same proportion NaCl: One sodium ion, one Chlorine ion. ALWAYS Ratio will always be 1:1 Water? H2O: ratio will always be 2 H : 1 O

The Law of Multiple Proportions: whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers Think Water (H2o) and Hydrogen Peroxide(H2O2) The ratio of oxygens will always be 1:2 because hydrogen peroxide has twice the number of oxygen atoms

Try It! 1. Carbon reacts with oxygen to form two compounds. Compound A contains 2.41 g of carbon for each 3.22 g of oxygen. Compound B contains 6.71 g of carbon for each 17.9 g of oxygen. What is the lowest whole-number mass ratio of carbon that combines with a given mass of oxygen?

How to solve? What do you want to know? Ratio of carbon to oxygen How can you compare? Find out how much carbon for each 1 g of oxygen for each compound (divide) Compound A: 2.41 g C / 3.22 g O= 0.748 g C/ 1.00 g O Compound B: 6.71 g C / 17.9 g O = 0.375 g C / 1.00 g O Compare the masses by dividing again! Compound A carbon / compound B carbon 0.748 g C (compound A)/ 0.375 g Carbon (compound) B Equals 1.99= roughly 2! The ratio of carbon per grams of oxygen in the compounds is 2:1

More Practice! 1. Lead two compounds with oxygen. One compound contains 2.98 g of lead combined with 0.461 g of oxygen. The other compound contains 9.89 g of lead combined 0.763 g of oxygen. What is the lowest whole-number mass ratio of lead in the two compounds that combines with a given mass of oxygen?

Solve 1. What do you want to know? Lead to oxygen… solve for lead! Divide for each compound to figure out how much lead/ 1 g of oxygen Divide the lead values This is your Ratio!

PDN Hand in your Definite Proportions/Multiple Proportions sheet Get a Calculator On a separate sheet of paper: 1. Calculate the % composition by mass for each element in: NaCl (NH4)3PO4 2. Carbon reacts with oxygen to form two compounds. Compound A contains 2.41 g of Carbon for each 3.22 g Oxygen. Compound B contains 6.71 g of Carbon for each 17.9 g of Oxygen. What is the lowest whole number mass ratio of carbon that combines with a given mass of oxygen? Show ALL work

Ionic Charges For monatomic ions, look at the periodic table We know how to do this already! For Transition metals, many have more than one charge! I have to give you the charge Fe(II) ion (Read: “Iron two ion”) Roman numeral gives you the charge You can also use a suffix system ‘-ous’ cation with lower of two charges ‘-ic’ cation with higher of two charges This system does not tell you the charge though!

Polyatomic Ions Poly-many Polyatomic ions: tightly bound groups of atoms that behave as a unit and carry a charge. The names of most of the polyatomic ions end in ‘–ite’ or ‘-ate’ : sulfite (SO3- and SO4-) Charge for each ion is the same, different numbers of O Look at the table on pg 147

Writing Ionic Formulas! (Yay!!!!) Ionic = METAL AND NONMETAL! Ionic bond = swap of electrons Metals lose, nonmetals gain, COMPOUND IS NEUTRAL!!!!! Binary Ionic Compound : (2 elements) 1. Write the symbols 2. Find the charges (periodic table) 3. Criss-Cross 4. Reduce if necessary

Ternary Ionic Compounds: Compound that contains atoms of three different elements Polyatomic Ions! How to write the formula: Write the Symbols Surround the Polyatomic Ion in parentheses (think: KEEP IT TOGETHER) Write charges Criss Cross (charge goes OUTSIDE parentheses

Naming Ionic Compounds Binary: 1. Write the name of the metal (include roman numeral for transition metal) 2. Write the name of the nonmetal ending with –ide Sodium Chloride, Iron (II) Oxide Ternary: Write the name of the cation (usually a metal, but ammonium (NH4) is a cation Write the name of the anion (if polyatomic, just write the name on the chart, if nonmetal, end in –ide)

PDN 1. Turn in your Ionic Compounds Practice sheet On a separate piece of paper: 2. Name the following compounds CrF2 Ga(NO2)3 3. Write the formulas for the following compounds Iron (II) bromide Magnesium acetate

Molecular Formulas YAY!!!! Molecular compounds involve electron SHARING But… they can share in multiple ways! Think of CO and CO2 = both would be named carbon oxide if we used ionic rules Molecular compounds = TWO NONMETALS How can you tell two molecular compounds apart? PREFIXES

Know Your Prefixes!!! Mono = 1 Di = 2 Tri = 3 Tetra = 4 Penta = 5 Hexa = 6 Hepta = 7 Octa = 8 Nona = 9 Deca = 10 You must know these prefixes for the test! I will not give them to you

So, to write the formula of a molecular compound, just decode the prefixes Dihydrogen monoxide Di = 2 hydrogen Mono = 1 oxygen Formula is H2O

Exceptions: If there is only one atom of the first element, you don’t need the prefix ‘mono’ (still need it for the second element, though) If the element starts with a vowel, drop the 2nd ‘o’ on ‘mono’ Monoxide, not monooxide

Naming Molecular Compounds Use prefixes to indicate number of atoms End second element in ‘-ide’ Example: OF2 = oxygen difluoride (no ‘mono’ on first element) Cl2O8 = dichlorine octaoxide

PDN Turn in your Molecular Compounds Practice sheet On a separate piece of paper Name the following compounds CO CO2 Write the formula for the following compounds Dihydrogen monoxide Phosphorus trichloride

PDN Turn in your Drawing Ionic Compounds project On a separate sheet of paper: Name: NaCl, NH4Cl, and PbSO4 Write the formulas: Magnesium Hydroxide Iron (II) Sulfide Ammonium Cyanide

Molecular Compounds Binary molecular compounds 2 NONMETALS How can we tell the different compounds? Prefixes!!! To Name a Molecular compound: Use prefixes to tell me how many of each atom Name end in –ide CO= carbon monoxide CO2= carbon dioxide You can leave the ‘mono’ off of the first element, but not the second

Prefixes Put these on the BACK of your periodic table Mono – 1 Di – 2 Tri – 3 Tetra – 4 Penta – 5 Hexa – 6 Hepta – 7 Octa – 8 Nona – 9 Deca - 10

Molecular formulas Just use the prefixes to tell you how many of each atom! Carbon tetrafluoride = CF4 Dihydrogen monoxide = H2O

The tricky part!!! Ionic : metal and nonmetal, get charges and criss cross, NO prefixes Molecular: two nonmetals, no charges, use PREFIXES

You try it! 1. Identify as ionic or molecular Metal/nonmetal or nonmetal/nonmetal Most on this practice are molecular (so use prefixes)