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

2 Molecules and Chemical Formulas Molecules and Molecular Compounds 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 Molecular formulas give the actual numbers and types of atoms in a molecule. Examples: Molecules and Molecular Compounds Molecular and Empirical Formulas H 2 O, CO 2, CO, CH 4, H 2 O 2, O 2, O 3, and C 2 H 4. 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: H 2 O, CO 2, CO, CH 4, HO, CH 2.

4 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. Molecules and Molecular Compounds

5 Picturing Molecules Molecules and Molecular Compounds

6 Different representations of methane (CH 4 )

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

8 When an atom or molecule gains electrons, it becomes negatively charged. Ions and Ionic Compounds 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 12p + 12 e - lose 2 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 Mg 2+ Mg atom Mg 2+ ion “magnesium atom” “magnesium ion”

10 16 p + 16 e - gain 2 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 S 2- S atom S 2- ion “sulfur atom” “sulfide ion”

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

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 (Be 2+, Mg 2+ …) Group IIIA elements (B, Al, Ga) form 3+ ions (B 3+, Al 3+, …) Group VA elements (N, P…) form 3 - ions (N 3-, P 3- ) Group VIA elements (O, S,..) form 2- ions (O 2-, S 2- …) Group VIIA elements (F, Cl, Br.) form 1- ions (F -, Cl -, Br - ….) Group VIIIA elements do not form ions. Neither does Group IVA.

13 Ions and Ionic Compounds Na. 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 +. Na + 11 p + 11 e - 11 p + 10 e -

14 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 -. Ions and Ionic Compounds Ionic Compounds The Na + and Cl - ions are attracted to form an ionic NaCl lattice which crystallizes. Cl. Cl - 17 p + 17 e - 17 p + 18 e - (from Na atom)

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

16 Ionic Compounds Consider the formation of Mg 3 N 2 : Mg loses two electrons to become Mg 2+ Nitrogen gains three electrons to become N 3-. 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). Ions and Ionic Compounds

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

18 Naming of compounds, nomenclature, is divided into organic compounds (those containing C) and inorganic compounds (the rest of the periodic table) Naming Inorganic Compounds Names and Formulas of Ionic Compounds 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); Cu 2+ = copper(II).

19 Hydrogen ionH + Cupric ion Co 2+ Lithium ion Li + Cuprous ion Cu + Sodium ion Na + Ferric ion Fe 3+ Potassium ion K + Ferrous ion Fe 2+ Silver ion Ag + Manganous ion Mn 2+ Magnesium ion Mg 2+ Mercurous ion Hg 2 2+ Calcium ion Ca 2+ Mercuric ion Hg 2+ Strontium ion Sr 2+ Nickelous ion Ni 2+ Barium ion Ba 2+ Plumbous ion Pb 2+ Zinc ion Zn 2+ Stannous ion Sn 2+ Cadmium ion Cd 2+ Stannic ion Sn 4+ Aluminum ion Al 3+ Chromic ion Cr 3+

20 Monoatomic anions (with only one atom) are called  ide. Example: Cl  is chloride ion. Exceptions: hydroxide (OH  ), cyanide (CN  ), peroxide (O 2 2  ). Polyatomic anions (with many atoms) containing oxygen end in -ate or -ite. (The one with more oxygen is called - ate.) Examples: NO 3 - is nitrate, NO 2 - is nitrite. Naming Inorganic Compounds Names and Formulas of Ionic Compounds

21 Naming Inorganic Compounds nitrateNO 3 - hydroxide OH - nitriteNO 2 - phosphate PO 4 3- carbonateCO 3 2- ammonium NH 4 + sulfateSO 4 2- perchlorate ClO 4 - sulfiteSO 3 2- chlorate ClO 3 - cyanideCN - chlorite ClO 2 - chromateCrO 4 -2 hypochlorite ClO - dichromateCr 2 O 7 2- carbonate CO 3 2- permanganateMnO 4 - bicarbonate (or hydrogen carbonate) HCO 3 -

22 Hydride H - oxide O 2- fluorideF - peroxide O 2 2- chlorideCl - sulfide S 2- bromideBr - nitrideN 3- iodideI - Monoatomic ions

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: NH 3. If both elements are in the same group, the lower one is written first. Greek prefixes are used to indicate the number of atoms. mono1 di2 tri3 tetra4 penta5 hexa6 hepta7 octa8 nona9 deca10 Name: NO 2 SO 3 N 2 O 4 P 2 O 5 CCl 4 CO CO 2 Nitrogen dioxide Sulfur trioxide Dinitrogen tetroxide Diphosphorus pentoxide Carbon tetrachloride Carbon monoxide Carbon dioxide

24 Naming Organic Compounds Name, formula, bp o C Methane CH Methyl alcohol CH 3 OH, 66 Ethane C 2 H Ethyl alcohol C 2 H 5 OH, 98 Propane C 3 H Propyl alcohol C 3 H 7 OH, 97 Butane C 4 H 10 0 Isopropyl alcohol Pentane C 5 H CH 3 -CH(OH)-CH 3, 82 Hexane C 6 H [Propyl alcohol and isopropyl Heptane C 7 H alcohol are isomers] Octane C 8 H Nonane C 9 H Decane C 10 H