Chemical Compounds

1. Chapter 3 Chemical Compounds Jons J. Berzelius 1779-1848. Accurately determined atomic weights, used in future Periodic Table. Originated modern chemical formulas, including “K” and “Na” for potassium and sodium.

2. Molecules and Molecular Compounds Molecules and Chemical Formulas Molecules are assemblies of two or more atoms bonded together. • Each molecule has a chemical formula. • The chemical formula indicates: • which atoms are found in the molecule, and • in what proportion they are found. Compounds formed from molecules are molecular compounds.

3. Molecules and Molecular Compounds Molecular and Empirical Formulas • Molecular formulas • give the actual numbers and types of atoms in a molecule. • Examples: • H2O, CO2, CO, CH4, H2O2, O2, O3, and C2H4. • Empirical formulas • give the relative numbers and types of atoms in a molecule. • That is, they give the lowest whole number ratio of atoms • in a molecule. • Examples: H2O, CO2, CO, CH4, HO, CH2.

4. Molecules and Molecular Compounds Picturing Molecules Molecules occupy three dimensional space. However, we often represent them in two dimensions. The structural formula gives the connectivity between individual atoms in the molecule. The structural formula may or may not be used to show the three dimensional shape of the molecule.

5. Molecules and Molecular Compounds Picturing Molecules

6. Different representations of methane (CH4)

7. Ions and Ionic Compounds When an atom or molecule loses electrons, it becomes positively charged. • For example, when Na loses an electron, it becomes Na+. • Positively charged ions are called cations.

8. Ions and Ionic Compounds When an atom or molecule gains electrons, it becomes negatively charged. • For example when Cl gains an electron it becomes Cl-. • Negatively charged ions are called anions. • An atom or molecule can lose more than one electron.

9. lose 2 e- 12p+ 12 e- 12p+ 10 e- Ions and Ionic Compounds When an atom or molecule loses two electrons, it becomes doubly positively charged. For example, when Mg loses two electrons, it becomes Mg2+ Mg2+ion Mg atom “magnesium atom” “magnesium ion”

10. gain 2 e- 16 p+ 16 e- 16p+ 18 e- Ions and Ionic Compounds When an atom or molecule gains two electrons, it becomes doubly negatively charged. For example, when S gains 2 electrons, it becomes S2- S2-ion S atom “sulfur atom” “sulfide ion”

11. Metals tend to form cations whereas non-metals tend to form anions. Ions and Ionic Compounds Predicting Ionic Charge The number of electrons an atom gains or loses is related to its position on the periodic table.

12. Ions and Ionic Compounds What ions do the main group elements (the “A” elements) form? It depends on their grouping. Group IA elements (H, Li, Na..) form 1+ ions (H+,Li+, Na+…) Group IIA elements (Be, Mg, Ca)form 2+ ions (Be2+, Mg2+…) Group IIIA elements (B, Al, Ga) form 3+ ions (B3+, Al3+, …) Group VA elements (N, P…) form 3- ions (N3-, P3-) Group VIA elements (O, S,..) form 2- ions (O2-, S2-…) Group VIIA elements (F, Cl, Br.) form 1- ions (F-, Cl-, Br-….) Group VIIIA elements do not form ions. Neither does Group IVA.

13. . Na. Na+ Ions and Ionic Compounds • Ionic Compounds • The majority of chemistry involves the transfer of electrons between species. • Example: • To form NaCl, the neutral sodium atom, Na, must lose an electron to become a cation: Na+ 11 p+ 10 e- 11 p+ 11 e-

14. . Ions and Ionic Compounds Ionic Compounds • whereas non-metals tend to form anions. • The electron cannot be lost entirely, so it is transferred to a chlorine atom, Cl, which then becomes an anion: Cl-. (from Na atom) Cl- Cl 17 p+ 17 e- 17 p+ 18 e- • The Na+ and Cl- ions are attracted to form an ionic NaCl lattice which crystallizes.

15. Ions and Ionic Compounds Important: note that there are no easily identified NaCl molecules in the ionic lattice. Therefore, we cannot use molecular formulas to describe ionic substances.

16. Ions and Ionic Compounds Ionic Compounds Consider the formation of Mg3N2: Mg loses two electrons to become Mg2+ Nitrogen gains three electrons to become N3-. For a neutral species, the number of electrons lost and gained must be equal. However, Mg can only lose electrons in twos and N can only accept electrons in threes. Therefore, Mg needs to lose 6 electrons (2  3) and N gain those 6 electrons (3  2).

17. Mg2+ N3- Ions and Ionic Compounds Ionic Compounds I.e., 3Mg atoms need to form 3Mg2+ ions (total 3x2+ charges) and 2 N atoms need to form 2N3- ions (total 2x3- charges). Therefore, the formula is Mg3N2. MgO Mg N 3 2 Be careful! what’s the ionic compound formed between magnesium and oxygen?)

18. Naming Inorganic Compounds Names and Formulas of Ionic Compounds Naming of compounds, nomenclature, is divided into organic compounds (those containing C) and inorganic compounds (the rest of the periodic table) • Cations formed from a metal have the same name • as the metal. • Example: Na+ = sodium ion. • If the metal can form more than one cation, then the charge is indicated in parentheses in the name. • Examples: Cu+ = copper(I); Cu2+ = copper(II).

19. Hydrogen ion H+ Cupric ion Co2+ Lithium ion Li+ Cuprous ion Cu+ Sodium ion Na+ Ferric ion Fe3+ Potassium ion K+ Ferrous ion Fe2+ Silver ion Ag+ Manganous ion Mn2+ Magnesium ion Mg2+ Mercurous ion Hg22+ Calcium ion Ca2+ Mercuric ion Hg2+ Strontium ion Sr2+ Nickelous ion Ni2+ Barium ion Ba2+ Plumbous ion Pb2+ Zinc ion Zn2+ Stannous ion Sn2+ Cadmium ion Cd2+ Stannic ion Sn4+ Aluminum ion Al3+ Chromic ion Cr3+

20. Naming Inorganic Compounds Names and Formulas of Ionic Compounds • Monoatomic anions (with only one atom) are called -ide. • Example: Cl- is chloride ion. • Exceptions: hydroxide (OH-), cyanide (CN-), peroxide (O22-). • Polyatomic anions (with many atoms) containing oxygen end in -ate or -ite. (The one with more oxygen is called -ate.) • Examples: NO3- is nitrate, NO2- is nitrite.

21. Naming Inorganic Compounds nitrate NO3- hydroxide OH- nitrite NO2- phosphate PO43- carbonate CO32- ammonium NH4+ sulfate SO42- perchlorate ClO4- sulfite SO32- chlorateClO3- cyanide CN - chlorite ClO2- chromate CrO4-2 hypochlorite ClO - dichromate Cr2O72- carbonate CO32- permanganate MnO4- bicarbonate (or hydrogen carbonate) HCO3-

22. Monoatomic ions HydrideH - oxide O2- fluoride F - peroxide O22- chloride Cl - sulfide S2- bromide Br - nitride N3- iodide I -

23. Names and Formulas of Binary Molecular Compounds Binary molecular compounds have two elements. The most metallic element is usually written first (i.e., the one to the farthest left on the periodic table). Exception: NH3. If both elements are in the same group, the lower one is written first. Greek prefixes are used to indicate the number of atoms. mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 hepta 7 octa 8 nona 9 deca 10 Nitrogen dioxide Name: NO2 SO3 N2O4 P2O5 CCl4 CO CO2 Sulfur trioxide Dinitrogen tetroxide Diphosphorus pentoxide Carbon tetrachloride Carbon monoxide Carbon dioxide

24. Naming Organic Compounds Name, formula, bp oCName, formula, bp oC Methane CH4 -162 Methyl alcohol CH3OH, 66 Ethane C2H6 -89Ethyl alcohol C2H5OH, 98 Propane C3H8 -42 Propyl alcohol C3H7OH, 97 Butane C4H10 0 Isopropyl alcohol Pentane C5H12 36 CH3-CH(OH)-CH3, 82 Hexane C6H14 69 [Propyl alcohol and isopropyl Heptane C7H16 98 alcohol are isomers] Octane C8H18 126 Nonane C9H20 151 Decane C10H22 174