Presentation on theme: "Molecules, Compounds, and Chemical Equations. Compounds When two or more elements are combined chemically, they are called a compound. Just like letters."— Presentation transcript:
Compounds When two or more elements are combined chemically, they are called a compound. Just like letters of the alphabet can be combined to form an endless number of words, elements can be combined to form an endless number of compounds. Life would not possible without the diversity of compounds.
Compounds Hydrogen, a diatomic and colorless gas Oxygen, a diatomic and colorless gas Water, a clear liquid which is essential for most life forms
Most elements are not found by themselves in nature, rather they occur in compounds like NaCl or MgO Some occur as diatomic molecules: N 2, O 2, F 2, Cl 2, Br 2, and I 2. Others like P and S are polyatomic. Only the metals of Gold, Copper, and Silver can sometimes be found in their pure state.
Chemical Bonds Compounds are held together by one of two types of bonds. Ionic bonds are the electrostatic attraction between cations and anions. Covalent bonds are when two atoms share at least a pair of electrons.
Compounds A chemical formula is used to describe our compounds. Uses subscripts after each element in the formula. Subscript of “1” is implied if no subscript. Empirical formula = simplest whole number ratio of the elements in compound. Molecular formula = actual number of atoms bonded together. Structural formula = shows how the atoms are bonded together with lines representing the bonds.
Molecular Models A model may be used to represent a molecule. Ball-and-stick Space-filling No model is completely accurate!
Classifying Elements & Compounds Atomic elements = elements whose particles are single atoms Molecular elements = elements whose particles are multi-atom molecules Molecular compounds = compounds whose particles are molecules made of only nonmetals Ionic compounds = compounds whose particles are cations and anions
Ionic vs. Molecular Propane – contains individual C 3 H 8 molecules Table salt – contains an array of Na + ions and Cl - ions
Learning Check Classifying each as either an Atomic element, Molecular element, Molecular compound, or Ionic compound. A) Formaldehyde, CH 2 O B) Red phosphorous, P 4 C) Cobalt, Co D) Magnesium chloride, MgCl 2
Ionic Compounds Ionic compounds – are substances that contain both cations and anions. Formulas are always empirical – lowest whole number ratio of cations and anions. Writing ionic formulas – charges must cancel to yield a neutral species. Most common charges for cations = +1, +2, or +3 Most common charges for anions are -1, -2, or -3.
Ionic Compounds Learning Check Write the correct formula between the ions of… A) Ca and Br B) K and S C) Li and N D) Al and O E) Mg and P
Naming Inorganic Compounds Chemical Nomenclature ‑ the systematic method of naming chemical compounds. Different system for naming Ionic and Molecular compounds. Ionic = cation (usually a metal) with an anion (usually a non-metal. Molecular = two or more non-metals or metalloid with a non-metal. Identify compound BEFORE going to the rules!!!
Ionic or Molecular Learning Check… Identify as Ionic or Molecular A) Na 2 S B) PCl 3 C) SiH 4 D) FeBr 3 E) ZnO F) CCl 4
Polyatomic Ions An ion composed of two or more elements with a net charge. Only one is a cation – NH 4 + = ammonium ion. All the rest are anions. Any time a polyatomic ion is present, then the compound is ionic. Ex) Na 2 SO 4, MgCO 3, NH 4 Cl When more than one polyatomic ion is needed to balance charges, then use (poly) x. Ex) Al(NO 3 ) 3, (NH 4 ) 2 S
Naming Ionic Compounds Two subcategories: Metals with only one valence (mostly the main group metals) Metals with more than one possible valence charge. Metals with only one valence 1. Name the metal first 2. Name the non-metal second and change its suffix to ide. For polyatomic ions, they ALWAYS keep their same name – DO NOT CHANGE TO ide ending.
Learning Check What is the name of… A) NaBr B) MgSO 4 C) K 2 S D) Li 3 PO 4
Naming Ionic Compounds Metals with more than one valence 1. Name metal first followed by its valence in Roman Numerals and in ( ). This means that you will have to figure out the charge for that metal based on what it is bonded to. 2. Name the non-metal second and change the suffix to ide. As before, polyatomics remain the same.
Learning Check What is the name of… A) Cu 2 O B) Fe 2 S 3 C) Mn(NO 3 ) 2 D) Co 3 (PO 4 ) 2
Naming Molecular Compounds Remember, these contain only non-metals or a metalloid with a non-metal. 1. Name the first non-metal in the formula. 2. Name the second non-metal in the formula and change the suffix to ide. 3. Add prefixes for all subscripts - except if the first one is a “1”. 1 = mono, 2 = di, 3 = tri, 4 = tetra, 5 = penta, and 6 = hexa.
Learning Check What is the name of… A) CS 2 B) PCl 5 C) AsBr 3 D) N 2 O 4 E) N 2 O
Nomenclature Overview Compound Ionic or Molecular? Ionic Metal Fixed charge Metal Variable Charge Molecular
Learning Check What is the name of… A) NiCl 2 B) K 2 CrO 4 C) Cl 2 O D) SF 4 E) (NH 4 ) 2 SO 4
Naming Acids Acids are molecular compounds that release an H + when added to water. Formula starts with an “H”. Binary acids = H with one other element. Hydro + base name of non-metal + ic + acid HCl = hydrochloric acid Oxoacids = HXO y Polyatomic ion ends in –ate, then suffix changes to –ic Polyatomic ion ends in –ite, then suffix changes to -ous
Learning Check What is the name of… A) HBr B) HNO 3 C) H 2 SO 3 D) H 3 PO 4
Quantitative Aspect A chemical formula also has a quantitative aspect. A Formula Weight for an element or compound is found using the periodic table. Formula weights can refer to a single element’s weight or an ionic compound. Molecular weight refers to a molecular compound’s weight. Weights from periodic table should be rounded to the nearest 0.1 amu at the bare minimum!
Molar Mass The molar mass of any compound is equal to the sum of the atomic weights expressed in grams. Ex) The molar mass of CO2 is 44.0 grams. Thus, one mole of CO2 = 44.0 grams. 1 mol CO2 = 6.02 x 10 23 molecules. Calculate the molar mass for… A) PCl 3 B) C 6 H 12 O 6 C) Fe 2 (SO 4 ) 3
Using Molar Masses A molar mass can be used to convert grams to moles or moles to grams. Calculate: A) the moles present in 2.85g of CO 2 B) the grams present in 0.552 moles of NH 3 C) the number of molecules present in 0.255g of H 2 O D) the number of O atoms in 3.00g of C 6 H 12 O 6
Percent Composition A formula weight can be used to calculate the mass percentage of any element in the formula by: This is one place to also test nomenclature! Find the mass percent of each element in the compound Calcium nitrate.
Empirical Formulas We can use moles to find an empirical (simplest) formula from mass percentages by: 1. Assume a 100 gram sample (% grams). 2. Convert grams of each element to moles use the formula weights. 3. Divide each mole amount by the smallest one. 4. Using a multiplier to eliminate fractions like: 0.25, 0.33, 0.50, 0.67, and 0.75.
Empirical Formulas A compound contains 17.6% Na, 39.7% Cr, and 42.7% O by mass. What is its empirical formula?
Molecular Formulas An empirical formula may not be the actual formula since molecular formulas do not have to be the lowest whole number subscripts. The multiplier, n, can be found if we know the overall molecular weight of the compound. A compound is contains 40.9% C, 4.6% H, and 54.5% O by mass with a molecular weight of about 176g/mol. What is the molecular formula for this compound?
Combustion Analysis 38 Tro: Chemistry: A Molecular Approach, 2/e
Combustion Analysis Combustion of a 0.8233 g sample of a compound containing only carbon, hydrogen, and oxygen produced the following: CO 2 = 2.445 g H 2 O = 0.6003 g Determine the empirical formula of the compound
Chemical Equations Chemical reactions are represented in a concise method by a chemical equation. Ex) 2 H2(g) + O2(g) 2 H2O(l) Reactants Products
Balancing an Equation A subscript in a chemical formula tells us how many of each type of atom are in the compound. Ex) C 6 H 12 O 6 Subscripts cannot be altered!!! Atoms can be created nor destroyed in a chemical reaction. Thus, we balance a reaction by adding coefficients in front of each substance.
Balancing an Equation Balance by inspection. Use a tally sheet. Start with elements that occur once on each side. Combustion – do C, then H, then O. Balance each reaction… __ Al + __ Cl 2 __ AlCl __ H 3 PO 3 __ H 3 PO 4 + __ PH 3
Balancing an Equation __ Na 3 PO 4 + __ CaBr 2 __ Ca 3 (PO 4 ) 2 + __ NaBr __ C 3 H 8 + __ O 2 __ CO 2 + __ H 2 O __ C 4 H 8 O + __ O 2 __ CO 2 + __ H 2
Classifying Compounds Organic vs. Inorganic In the 18 th century, compounds from living things were called organic; compounds from the nonliving environment were called inorganic Organic compounds easily decomposed and could not be made in the 18 th -century lab Inorganic compounds very difficult to decompose, but able to be synthesized 45 Tro: Chemistry: A Molecular Approach, 2/e
Modern Classifying Compounds Organic vs. Inorganic Today we commonly make organic compounds in the lab and find them all around us Organic compounds are mainly made of C and H, sometimes with O, N, P, S, and trace amounts of other elements The main element that is the focus of organic chemistry is carbon 46 Tro: Chemistry: A Molecular Approach, 2/e
Carbon Bonding Carbon atoms bond almost exclusively covalently compounds with ionic bonding C are generally inorganic When C bonds, it forms four covalent bonds 4 single bonds, 2 double bonds, 1 triple + 1 single, etc. Carbon is unique in that it can form limitless chains of C atoms, both straight and branched, and rings of C atoms
48 Carbon Bonding Tro: Chemistry: A Molecular Approach, 2/e
Classifying Organic Compounds There are two main categories of organic compounds, hydrocarbons and functionalized hydrocarbons Hydrocarbons contain only C and H When all C-C bonds are single bonds, they are called alkanes. Formula for any alkane is: C n H 2n+2.