Unit 1 – Intro to Chemistry: Molecules and Compounds Unit 2: Molecules and Compounds Unit 1 – Intro to Chemistry: Molecules and Compounds

Chemical Formula Indicates: Ex: H2O Unit 2: Molecules and Compounds Chemical Formula Indicates: The elements present The relative number of atoms of each element Ex: H2O The symbols H and O indicate the presence of hydrogen and oxygen, while the number 2 indicates that there are 2 atoms of hydrogen per one atom of oxygen Note: You do not need to write the number “1” if there is only one molecule of an element. If there is no number beside the element, it is assumed there is only one molecule of that element.

How do Atoms Bond? There are two basic types of bonding: Ionic Bonding Unit 2: Molecules and Compounds How do Atoms Bond? There are two basic types of bonding: Ionic Bonding Covalent Bonding

Ionic Bonding Attraction between two oppositely charged ions Unit 2: Molecules and Compounds Ionic Bonding Attraction between two oppositely charged ions Usually between a metal and a nonmetal Atoms of metals tend to lose one or more electrons (Cations), whereas atoms of non metals tend to gain one or more electrons (Anions)

Unit 2: Molecules and Compounds Ionic Bonding Ex: Na+ and Cl- are attracted to each other because they are oppositely charged ions; these two ions give us NaCl (table salt)

Ionic Bonding Continued Unit 2: Molecules and Compounds Ionic Bonding Continued The chemical formula for an ionically bonded molecule is called a Formula Unit, which is the smallest electrically neutral collection of ions Ex: NaCl, MgCl2, Li2O, H3PO4 all represent formula units

How do we know the Charges of Ions? Unit 2: Molecules and Compounds How do we know the Charges of Ions? Remember how elements will lose or gain an electron to become more stable….group 1 elements lose one electron to give them a charge of +1, group 6 gains two electrons to have a charge of -2. Periodic Group Charge Examples 1 +1 H+, Li+, Na+, K+ 2 +2 Be2+, Mg2+, Ca2+ 5 -3 N3-, P3- 6 -2 O2-, S2- 7 -1 F-, Cl-, Br-, I-

Ionic Bonding continued Unit 2: Molecules and Compounds Ionic Bonding continued Monatomic Ion: a single ionized atom Ex: Na+, Cl-, Mg2+, Fe2+, Fe3+ Polyatomic Ion: made up of two or more atoms joined by covalent bonds Ex: NO3-, NH4+ * Notice how some transition metals can have more than one charge *

Unit 2: Molecules and Compounds Oxidation States Oxidation state is the number of electrons that an atom loses or gains when joining with other atoms in compounds (same as charge of ion) When added together, the formula unit of a compound should be 0! Ex: NaCl Na+ is in an oxidation state of +1 and Cl- is in an oxidation state of -1. 1 + (-1) = 0

Unit 2: Molecules and Compounds Naming Compounds Compounds formed by carbon and hydrogen or carbon and hydrogen together with oxygen, nitrogen and a few other elements are organic compounds All other compounds that do not fit this description are inorganic compounds

Name and Formulas of Inorganic Compounds: Binary Compounds Unit 2: Molecules and Compounds Name and Formulas of Inorganic Compounds: Binary Compounds Binary compounds: those formed between two elements To name a binary compound that consists of a metal and nonmetal: Write the unmodified name of the metal Then write the name of the nonmetal, modified to end in “ide” Examples NaCl = Sodium Chloride MgI2 = Magnesium Iodide Al2O3 = Aluminum Oxide Ionic Compounds must be electrically neutral (total charge of the ions in a formula unit must be zero)

Binary compounds: Metal/Nonmetal Unit 2: Molecules and Compounds Binary compounds: Metal/Nonmetal Transition metals form several ions, for example, iron forms two common ions, Fe2+ and Fe3+ Use roman numerals to indicate which one was used (Fe2+ = Iron(II) and Fe3+ = Iron (III) ) Ex: Fe2S3 = Iron(III) Sulfide Note: we looked at the number of S atoms to get Iron(III) Fe2S3 is electrically neutral 2(3) + 3(-2) = 0

Binary compounds: Metal/Nonmetal Unit 2: Molecules and Compounds Binary compounds: Metal/Nonmetal Old system used the words ferrous/ferric instead of Fe2+ and Fe3+ Another example: Cu2O is Copper(I) Oxide or Cuprous oxide, CuO is Copper (II) Oxide or Cupric Oxide.

Binary compounds: Polyatomic Ions Unit 2: Molecules and Compounds Binary compounds: Polyatomic Ions Name of the first element and the name of the polyatomic ion Do not need to change the name to end in “ide”, just keep the name as is. Ex: NaNO3 is Sodium Nitrate NOT Sodium Nitride

Inorganic Compounds: Hydrates Unit 2: Molecules and Compounds Inorganic Compounds: Hydrates Each formula unit of the compound has associated with it a certain number of water molecules To name: write down compound name according to nomenclature rules and then add “prefix” hydrate. Example: CoCl2●6H2O Cobalt(II) chloride hexahydrate

Summary of Naming Unit 2: Molecules and Compounds Inorganic 2 Non Metals Prefixes = # of atoms (1=mono, 2=di, etc.) Last element ends in “ide” Metal/Nonmetal Monoatomic Polyatomic No Different Ending Hydrate Follow other rules, add “prefix”hydrate Summary of Naming

Binary Compounds: Two Nonmetals Unit 2: Molecules and Compounds Binary Compounds: Two Nonmetals Write the element with the positive oxidation state first: HCl not ClH Second element still ends in “ide” but need to use prefixes: Mono = 1 Tetra = 4 Di = 2 Penta = 5 Tri = 3 Hexa = 6 Examples: SO2 = Sulfur Dioxide B2Br4 = Diboron tetrabromide * Need to know these prefixes *

Binary Compounds: Two Nonmetals Unit 2: Molecules and Compounds Binary Compounds: Two Nonmetals More examples: NO = Nitrogen Monoxide (Note that it isn’t mononitrogen monoxide, mono is never used in the first named element) H2O = Dihydrogen monoxide (water)

Ionic vs. Covalent Bonding Unit 2: Molecules and Compounds Ionic vs. Covalent Bonding Ionic: Transfer of electron(s) from one atom to another. Example is Sodium Chloride, NaCl Covalent: The atoms share electrons. Example is Methane, CH4 H H C H H Cl Na H H C H C H Cl Na + - H

Unit 2: Molecules and Compounds

Unit 2: Molecules and Compounds

So what is a Compound? Compounds are pure substances and not mixtures (Examples: Water (H2O), Carbon Dioxide (CO2) ) Compounds are made of atoms of two or more elements