Chapter 3: Molecules, compounds, and chemical equations

Molecules Combining two or more atoms forms a molecule Combining two or more elements forms a compound The composition and structure determine the physical and chemical properties of an element or compound Molecules

Chemical formula – tells you the elements and relative atoms in a compound 2 types, molecular and empirical formula Molecular formula give the actual number of atoms of each element in a compound H2O2 = two H atoms and two O atoms Empirical formula – gives the relative atom to atom ratio with whole numbers H2O2 , greatest common factor is 2 so in empirical form H2O2 = HO C6H12 = CH2 Chemical formulas

Structural formula A structural formula uses lines to represent covalent bonds between atoms in a molecule

Molecular Models Ball and stick molecular model – each colored ball represents a atom and the sticks represent the bonds between atoms CH4 Space filling molecular model – size of each atom reflected in size of each sphere Larger spheres have larger atomic radii Model gives best 3-D image

Element and compound definitions Atomic elements – elements that exist as single atomic units Molecular elements – elements that exist as diatomic or polyatomic molecular units Formula unit – basic unit of an ionic compound Polyatomic ions – an ion composed of two or more atoms PO43-

Ionic compounds vs Covalent compounds

Ionic bonding Ions: atoms that have a charge due to gain or loss of electrons Anion: (-) charged atom – gained electron(s) Cation: (+) charged atom – lost electron(s) Ionic Bond - a bond formed through the transfer of one or more electrons from one atom or group of atoms to another atom or group of atoms

Oxidation state NaCl Formula Unit

Oxidation state MgF2

Ways to make an ionic compound Metal + Non-metal NaCl Metal + Polyatomic Ion NaNO3 Polyatomic Ion + Non-metal NH4Cl Polyatomic Ion + Polyatomic Ion NH4NO3 Net charge on compound equal to zero

Oxyanions SO42- Sulfate SO32- Sulfite PO43- Phosphate PO33- Phosphite NO3- Nitrate NO2- Nitrite ClO4- Perchlorate ClO3- Chlorate ClO2- Chlorite ClO- Hypochlorite

Covalent bond – a bond formed through two atoms sharing electrons Covalent bonding or H-H or

Ways to make a covalent compound Covalent compound - two or more nonmetals sharing electrons to make bonds create a covalent compound or molecular compound nonmetal + nonmetal

Nomenclature (naming compounds)

Naming ionic compounds Name the cation by its elemental or polyatomic name If the metal is a transition metal with a variable charge, use a roman numeral in parentheses for its charge Next, name the anion and change its ending to “-ide” If the anion is polyatomic, do not change the ending to “-ide” NaBr cation is Na+ = sodium anion is Br- = bromine  bromide sodium bromide FeCO3 Transition metal cation is Fe2+ = iron(II) Polyatomic anion is CO32- = carbonate Iron(II) carbonate

Iron (III) Chloride Iron (II) Chloride FeCl3 FeCl2

Hydrated ionic compounds Hydrates – contain a specific number of water molecules associated with each formula unit The waters can typically be removed with heating Ionic compound naming is the same, just add in hydrate and the prefix for the amount of waters

Naming covalent compounds Name the first non-metal by its elemental name Add a prefix to indicate how many If only one atom, don’t put mono 4) Name the 2nd non-metal and change its ending to “-ide” 5) Add a prefix to indicate how many Naming covalent compounds 1 mono 6 hexa 2 di 7 hepta 3 tri 8 octa 4 tetra 9 nona 5 penta 10 deca CO2 First nonmetal C = carbon Second nonmetal O = oxygen  oxide Carbon dioxide

Naming acids (acids w/o oxygen) Acids contain hydrogen atoms that can be donated to other molecules, indicated by being at the front of a chemical formula Begin the name with “hydro” Name the anion, but change the ending to “-ic” Add “acid” on the end The anion is Br = bromine  bromic Hydrobromic acid HBr

Naming acids (acids with oxygen) Begin the name with the anion If the anion has the ending “-ate,” change this to “-ic acid” If the anion has the ending “-ite,” change this to “-ous acid” HNO3 The anion is NO3- = nitrate  nitric nitric acid

EXCEPTION, if in the gas phase, treat like a regular covalent compound for naming with no prefixes HF(g) = hydrogen fluoride Naming gas phase acids

The Mole

1 dozen eggs = 12 eggs 1 pair of kings = 2 kings 2 dozen eggs = 24 eggs 2 pairs of kings = 2 x 2 kings = 4 kings

The Mole 1 mole = 6.022 x 1023 things Avogadro’s number Abbreviation: “mol” 1 mol = The number of carbon atoms in 12g of C-12

Moles to atoms or molecules 1 mole C = 6.022 x 1023 C atoms 1mol H2O = 6.022 x1023 H2O molecules If you have moles of something, you can convert to atoms or molecules of that something Moles to atoms or molecules

Molar mass moles to grams The mass, in grams, of one mole of any element or compound Unit = grams/mole = g/mol Gives us a way to go from grams to moles 1 𝑚𝑜𝑙𝑒 𝐴 𝑥 𝑔𝑟𝑎𝑚𝑠 𝑜𝑓 𝐴

Molar Masses for elements and molecules Use periodic table to figure out Molar mass for each element. Carbon 1 atom of carbon is 12.01 amu 1mole of carbon is 12.01 grams Molar Mass = 12.01 g/mol H2O Made of 2 hydrogen atoms and 1 oxygen atom Molar mass of each hydrogen is 1.008 g/mol Molar mass of each oxygen is 16.00 g/mol 2×1.008 + 1×16.00 =𝟏𝟖.𝟎𝟏𝟔 𝒈 𝒎𝒐𝒍 Molar mass of H2O

Problems You have 145.9 g Hg. How many moles are in the sample? b. How many atoms of Hg are in the sample? 2) What is the molar mass for C3H8 (propane)? 3) What is the amount of grams in 3.57 moles of iron(III) chloride (FeCl3)?

Composition of compounds Mass percent – the percentage of mass of an element in a compound (keep units consistent since it is a ratio) Mass percent of H in H2O 1.008 amu per H atom x 2 H atoms = 2.016 amu 18.016 amu for H2O Mass percent of element X= mass of element X in 1 mol of compound mass of 1 mol of the compound ×100% Mass% H= 2.016amu 18.016amu ×100%=11.19%H in H 2 O

Practice If you have 55.4 grams of H2O, how many grams of that sample is hydrogen?

Chemical formula from empirical data Decomposing a compound can give you the grams of each of the constituent elements of that compound The grams can be converted into moles of each element The whole numbered mole ratio between the elements gives the empirical formula

Grams to chemical formula 25.0 g gas decomposes into 18.75 g of carbon and 6.25 g of hydrogen. What is the chemical formula of the original gas? 18.75𝑔 𝐶 1𝑚𝑜𝑙 𝐶 12.01𝑔 𝐶 = 1.561 mol C 6.25𝑔 𝐻 1𝑚𝑜𝑙 𝐻 1.008𝑔 𝐻 = 6.200 mol H 𝐶 1.561 𝐻 6.200 = 𝐶 1.561 1.561 𝐻 6.200 6.200 = 𝐶 1 𝐻 3.971 = 𝐶 1 𝐻 4 = C 𝐻 4

Mass percent to chemical formula Given the mass percentages of elements in a compound you can determine in a 100g sample, how much grams of each element would be present C 60.00%, H 4.48 %, O 35.52 % In 100g sample – C 60.00g, H 4.48g, O 35.52g Once you have the grams, continue the rest of the steps from previous slide

Mole ratios of a molecule The atoms of an element in a molecule can be represented as a mole ratio 2 atoms of H in 1 molecule of H2O 2 mol of H in 1 mol of H2O 2:1 H:O ratio 3 mol of Cl in 1 mol FeCl3 3:1 Cl:Fe ratio Mole ratio gets you from moles of one element to moles of another element

Grams of molecule Moles of molecule Moles of element Grams of element 55.40 grams H2O Use Molar Mass of H2O Moles of molecule 3.075 mol H2O Use Mole ratio between H2O and H Moles of element 6.150 mol H Use Molar Mass of H Grams of element 6.199 grams H

Chemical equations H2 (g) + Cl2(g)  2 HCl (g) Reactants Product(s) Coefficient Physical State Subscript H2 (g) + Cl2(g)  2 HCl (g) Reactants Product(s)

Law of conservation of Mass Matter is neither created, nor destroyed, but is merely rearranged The mass of the reactants must equal the mass of the products Atoms in the reactants must equal atoms in the products H2 (g) + Cl2(g)  2 HCl (g)

Balancing Chemical Equations Write the unbalanced equation Balance the atoms of one element (saving single elements for last) Choose another element and balance it Continue until all elements have the same number of atoms on both sides of the equation Check yourself __Zn(s) + __HCl(aq)  __H2(g) + __ZnCl2(aq)

Problems __ N2(g) + __ H2(g)  __ NH3(g) __ Fe(s) + __ Cl2(g)  __ FeCl3(s) __NH3(g) + __O2(g)  __NO(g) + __H2O(g) __C5H12(l) + __O2(g)  __CO2(g) + __H2O(g)

Organic molecules Living organisms are comprised primarily of organic molecules Composed of carbon mainly, but also hydrogen, nitrogen, oxygen, and sulfur Methane, CH4, is the simplest organic molecule

Hydrocarbons and functional groups Hydrocarbons – major class of organic molecules containing carbon and hydrogen Octane C8H18 Benzene C6H6 Functional group – a characteristic atom or group of atoms Commonly found attached to hydrocarbons Organic chemistry focuses on chemistry with organic molecules Reactions transform one functional group into another, changing the connectivity of the atoms to produce new products Hydrocarbons and functional groups

Functional groups

Chapter 3…all done