Ch. 5: Molecules and Compounds Dr. Namphol Sinkaset Chem 152: Introduction to General Chemistry.
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Transcript of Ch. 5: Molecules and Compounds Dr. Namphol Sinkaset Chem 152: Introduction to General Chemistry.
Ch. 5: Molecules and Ch. 5: Molecules and CompoundsCompounds
Dr. Namphol Sinkaset
Chem 152: Introduction to General Chemistry
I. Chapter OutlineI. Chapter Outline
I. IntroductionII. Chemical FormulasIII. Views of Elements/CompoundsIV. Naming “Type I” CompoundsV. Naming “Type II” CompoundsVI. Polyatomic IonsVII. Naming AcidsVIII. Naming “Type III” CompoundsIX. Molecular Masses
I. SugarI. Sugar
• Sugar is composed of carbon, oxygen, and hydrogen atoms.
• Properties of sugar completely different than elements from which it’s made.
I. Elements in CompoundsI. Elements in Compounds
• When an element forms a compound, its properties change completely.
• Generally, properties of the compound have no correlation to the original elements.
• In this chapter, we see how elements become compounds and cover chemical nomenclature.
I. Molecules of a Compound I. Molecules of a Compound Are the SameAre the Same
• Law of Constant Composition: all samples of a given compound have the same proportions of their constituent elements.
• Generally, this is expressed as a mass ratio.
I. Water’s Mass RatioI. Water’s Mass Ratio
• If 18.0 g of water is decomposed into it’s elements O and H, there would be 16.0 g of O and 2.0 g of H.
• The O:H mass ratio is thus 8.0:1.0.
• Any sample of water would have this exact same ratio.
II. Representing CompoundsII. Representing Compounds
• Chemical formulas are used to refer to compounds.
• chemical formula: a way to show the elements present in a compound and the relative numbers of each elemental atom.
• The most common is the molecular formula.
II. Chemical FormulasII. Chemical Formulas• There are three types of
formulas. molecular: gives the actual
number of atoms of each element in a molecule of a compound (e.g. H2O2)
empirical: gives the relative number of atoms of each element in a compound (e.g. HO)
structural: uses lines to represent covalent bonds and shows interconnectivity
II. Writing Molecular FormulasII. Writing Molecular Formulas
• The more metallic element is generally listed first. Metallic character increases to the left and
down on the periodic table.
• Subscripts indicate the number of that type of atom in the compound.
• If groups of atoms behave as an independent entity, parentheses are used.
II. Chemical ModelsII. Chemical Models
• Formulas lead to models which give an idea of the 3-D shape of a molecule.
III. Atomic ElementsIII. Atomic Elements
• If element exists as individual atoms, it is named as “atomic.”
• e.g. atomic mercury
III. Molecular ElementsIII. Molecular Elements
• Some elements occur naturally as groups of two or more atoms.
• These are named “molecular” or “diatomic” (for two).
III. Ionic CompoundsIII. Ionic Compounds
• Comprised of cations and anions.
• A formula unit is the smallest electrically-neutral collection of ions.
IV. Chemical NomenclatureIV. Chemical Nomenclature
• Like any specialized field, chemistry has its own language.
• The ability to name and recognize names of chemical entities is very important.
• The naming system is LOGICAL!!• The periodic table is indispensable
when you are first learning nomenclature.
IV. Type I CompoundsIV. Type I Compounds• Type I compounds are ionics that have a
metal from Groups 1 or 2 and a nonmetal from Groups 14-17.
• Examples: NaCl = sodium chloride MgBr2 = magnesium bromide
K2S = potassium sulfide
IV. Type I CompoundsIV. Type I Compounds
• To get a formula from a name, remember that a compound must be neutral.
• Ion charges can be found by locating the element on the periodic table.
• “The charge on one becomes the subscript of the other.”
IV. Sample ProblemIV. Sample Problem
• Give the correct name or formula for the compounds below.a) sodium nitride
b) CaCl2c) potassium sulfide
d) MgO
V. Transition MetalsV. Transition Metals
• Transition metals are found in the “Valley,” Groups 3-12, of the periodic table.
• Transition metal cations often can carry different charges, e.g. Fe2+ and Fe3+.
• Thus, a name like “iron chloride” is ambiguous.
V. Type II Compounds V. Type II Compounds
• Type II compounds are ionics that have a transition metal (Groups 3-12) and a nonmetal (Groups 14-17).
• Examples: FeCl2 = iron(II) chloride
FeCl3 = iron(III) chloride
V. Sample ProblemV. Sample Problem
• e.g. Give the correct name or formula for the compounds below.
a) MnO2
b) copper(II) chloride
c) AuCl3d) molybdenum(VI) fluoride
e) W2O3
VI. Additional ComplicationsVI. Additional Complications
• To make naming ionic compounds harder, sometimes polyatomic ions are involved.
• polyatomic ion: two or more atoms that are bonded covalently and have a net positive or negative charge
VI. Oxyanion FamiliesVI. Oxyanion Families
• oxyanion: anion containing oxygen
• There are families of oxyanions, and they have a systematic naming system.
• Have either two- or four-member families. e.g. NO2
- and NO3-
e.g. ClO-, ClO2-, ClO3
-, and ClO4-
VI. Two-Member FamiliesVI. Two-Member Families
• For a two-member family, oxoanion with fewer O atoms is given the “–ite” suffix while the one with more O atoms is given the “–ate” suffix. e.g. NO2
- = nitriteand NO3
- = nitrate
VI. Four-Member FamiliesVI. Four-Member Families
• For the four-member families, the prefixes “hypo-” and “per-” are used to indicate fewer or more oxygen atoms.
• e.g. the chlorine oxyanions ClO- = hypochlorite ClO2
- = chlorite
ClO3- = chlorate
ClO4- = perchlorate
VI. Sample ProblemVI. Sample Problem
• e.g. Give names or formulas for the following compounds.
a) Na2CO3
b) magnesium hydroxide
c) potassium nitrate
d) CoPO4
e) nickel(II) sulfate
f) NaClO2
VII. AcidsVII. Acids
• Acids are special ionic compounds that have H+ as the cation.
• There are two categories of acids that have different naming rules.
1) Binary acids contain only hydrogen and a nonmetal.
2) Oxyacids contain hydrogen, a nonmetal, and oxygen.
VII. Naming Binary AcidsVII. Naming Binary Acids
• Examples: HCl = hydrochloric acid HBr = hydrobromic acid H2Se = hydroselenic acid
VII. Naming OxyacidsVII. Naming Oxyacids
• Set 1 HNO3 = nitric acid
H2SO4 = sulfuric acid
HClO3 = chloric acid
HClO4 = perchloric acid
H2CO3 = carbonic acid
H3PO4 = phosphoric acid
• Set 2 HNO2 = nitrous acid
HClO2 = chlorous acid
HClO = hypochlorous acid H2SO3 = sulfurous acid
Examples of oxyacids:
VII. Naming OxyacidsVII. Naming Oxyacids
-ate oxyanions become –ic acids.
-ite oxyanions become –ous acids.
VIII. Type III CompoundsVIII. Type III Compounds
• Type III compounds are covalent (nonmetal bonded to nonmetal).
• Naming rules:1) More metallic element is named 1st using the
normal element name EXCEPT when halogens are bonded to oxygen.
2) Second element is named using its root and the “-ide” suffix.
3) #’s of atoms indicated with Greek prefixes EXCEPT when there is only one atom of the first element.
VIII. Type III CompoundsVIII. Type III Compounds
• Some examples: ClO2 = chlorine dioxide
N2O5 = dinitrogen pentoxide
S2Cl2 = disulfur dichloride
SeF6 = selenium hexafluoride
VIII. Naming PracticeVIII. Naming Practice• e.g. Indicate the “Type” and give the correct
formula or name of the compounds below.a) CoCl3b) dichlorine heptaoxidec) SrOd) magnesium hydroxidee) carbon tetrachloride
f) HF(aq)
g) sodium hydride
h) V2O5
i) Ru(ClO4)3
j) hydrosulfuric acid
k) H2SO4
l) titanium(IV) oxide
m) N2F2
IX. Masses of Compounds IX. Masses of Compounds
• Atomic masses are readily accessible via the periodic table, e.g. H = 1.008 amu.
• Formula masses (a.k.a. molecular masses or molecular weights) are calculated by adding up the masses of each atom in the compound.
IX. Molecular Mass of WaterIX. Molecular Mass of Water
• The formula for water is H2O, so it is comprised of 2 H atoms and 1 O atom.