Unit 1: Structure of Matter Sections: 1.4, 2.5, 2.6, 3.1-3.6 urea Chalcopyrite. Elemental sulfur (S8) consists of eight S atoms joined in a ring. A scientific research helium balloon. Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

Classifications of Matter

Chemistry is the study of matter and the changes it undergoes. Matter is anything that occupies space and has mass. A substance is a form of matter that has a definite composition and distinct properties. liquid nitrogen gold ingots silicon crystals

An element is a substance that cannot be separated into simpler substances by chemical means. 114 elements have been identified 82 elements occur naturally on Earth gold, aluminum, lead, oxygen, carbon, sulfur 32 elements have been created by scientists technetium, americium, seaborgium

Atomic mass is the mass of an atom in atomic mass units (amu) Micro World atoms & molecules Macro World grams Atomic mass is the mass of an atom in atomic mass units (amu) By definition: 1 atom 12C “weighs” 12 amu On this scale 1H = 1.008 amu 16O = 16.00 amu

The average atomic mass is the weighted average of all of the naturally occurring isotopes of the element.

3.1 Copper, a metal known since ancient times, is used in electrical cables and pennies, among other things. The atomic masses of its two stable isotopes, (69.09 percent) and (30.91 percent), are 62.93 amu and 64.9278 amu, respectively. Calculate the average atomic mass of copper. The relative abundances are given in parentheses.

Average atomic mass (63.55)

Avogadro’s number (NA) The Mole (mol): A unit to count numbers of particles Dozen = 12 Pair = 2 The mole (mol) is the amount of a substance that contains as many elementary entities as there are atoms in exactly 12.00 grams of 12C 1 mol = NA = 6.022 x 1023 Avogadro’s number (NA)

Molar mass is the mass of 1 mole of in grams marbles atoms eggs shoes Molar mass is the mass of 1 mole of in grams marbles atoms 1 mole 12C atoms = 6.022 x 1023 atoms = 12.00 g 1 12C atom = 12.00 amu 1 mole lithium atoms = 6.941 g of Li For any element atomic mass (amu) = molar mass (grams)

One Mole of: S C Hg Cu Fe

1 12C atom 12.00 amu 12.00 g 6.022 x 1023 12C atoms = 1.66 x 10-24 g 1 amu x 1 amu = 1.66 x 10-24 g or 1 g = 6.022 x 1023 amu M = molar mass in g/mol NA = Avogadro’s number

3.2 Helium (He) is a valuable gas used in industry, low-temperature research, deep-sea diving tanks, and balloons. How many moles of He atoms are in 6.46 g of He?

3.3 Zinc (Zn) is a silvery metal that is used in making brass (with copper) and in plating iron to prevent corrosion. How many grams of Zn are in 0.356 mole of Zn?

3.4 Sulfur (S) is a nonmetallic element that is present in coal. When coal is burned, sulfur is converted to sulfur dioxide and eventually to sulfuric acid that gives rise to the acid rain phenomenon. How many atoms are in 16.3 g of S?

A compound is a substance composed of atoms of two or more elements chemically united in fixed proportions. Compounds can only be separated into their pure components (elements) by chemical means. lithium fluoride quartz dry ice – carbon dioxide

Molecular Compound H2O NH3 CO2 HCl CO Binary Molecular Compound

2.8 Write chemical formulas for the following molecular compounds: carbon disulfide (b) disilicon hexabromide

Ionic compounds consist of a combination of cations and anions. The formula is usually the same as the empirical formula. The sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero.

cation – ion with a positive charge An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. Na 11 protons 11 electrons Na+ 11 protons 10 electrons anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Cl- 17 protons 18 electrons Cl 17 protons 17 electrons

A monatomic ion contains only one atom: Na+, Cl-, Ca2+, O2-, Al3+, N3- A polyatomic ion contains more than one atom: OH-, CN-, NH4+, NO3-

Formulas of Ionic Compounds 2 x +3 = +6 3 x -2 = -6 Al2O3 Al3+ O2- 1 x +2 = +2 2 x -1 = -2 CaBr2 Ca2+ Br- 2 x +1 = +2 1 x -2 = -2 Na2CO3 Na+ CO32-

The most reactive metals (green) and the most reactive nonmetals (blue) combine to form ionic compounds.

Common Ions Shown on the Periodic Table

2.4 Write the formula of magnesium nitride, containing the Mg2+ and N3− ions.

2.6 Write chemical formulas for the following compounds: mercury(I) nitrite cesium sulfide calcium phosphate

formula mass (amu) = molar mass (grams) Formula mass is the sum of the atomic masses (in amu) in a formula unit of an ionic compound. NaCl 1Na 22.99 amu 1Cl + 35.45 amu NaCl 58.44 amu For any ionic compound formula mass (amu) = molar mass (grams) 1 formula unit NaCl = 58.44 amu 1 mole NaCl = 58.44 g NaCl

Concept Review Identify whether the following diagrams represent (a) an element or (b) a compound? Each color sphere (or truncated sphere) represents an atom.

A diatomic molecule contains only two atoms: A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical forces. H2 H2O NH3 CH4 A diatomic molecule contains only two atoms: diatomic elements H2, N2, O2, Br2, HCl, CO A polyatomic molecule contains more than two atoms: O3, H2O, NH3, CH4

Molecules Diatomic HCl CO

Molecules Polyatomic O3 H2O CO2 NH3

molecular mass (amu) = molar mass (grams) Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. SO2 1S 32.07 amu 2O + 2 x 16.00 amu SO2 64.07 amu For any molecule molecular mass (amu) = molar mass (grams) 1 molecule SO2 = 64.07 amu 1 mole SO2 = 64.07 g SO2

3.5 Calculate the molecular masses (in amu) of the following compounds: sulfur dioxide (SO2), a gas that is responsible for acid rain caffeine (C8H10N4O2), a stimulant present in tea, coffee, and cola beverages

3.6 Methane (CH4) is the principal component of natural gas. How many moles of CH4 are present in 6.07 g of CH4?

3.7 How many hydrogen atoms are present in 25.6 g of urea [(NH2)2CO], which is used as a fertilizer, in animal feed, and in the manufacture of polymers? The molar mass of urea is 60.06 g.

Percent composition of an element in a compound = n x molar mass of element molar mass of compound x 100% n is the number of moles of the element in 1 mole of the compound %C = 2 x (12.01 g) 46.07 g x 100% = 52.14% C2H6O %H = 6 x (1.008 g) 46.07 g x 100% = 13.13% %O = 1 x (16.00 g) 46.07 g x 100% = 34.73% 52.14% + 13.13% + 34.73% = 100.0%

3.8 Phosphoric acid (H3PO4) is a colorless, syrupy liquid used in detergents, fertilizers, toothpastes, and in carbonated beverages for a “tangy” flavor. Calculate the percent composition by mass of H, P, and O in this compound.

3.10 Chalcopyrite (CuFeS2) is a principal mineral of copper. Calculate the number of kilograms of Cu in 3.71 × 103 kg of chalcopyrite.

Formulas and Models

A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance. An empirical formula shows the simplest whole-number ratio of the atoms in a substance. H2O molecular empirical H2O CH2O C6H12O6 O O3 NH2 N2H4 C2H5 C4H10 Butane

2.2 Write the molecular formula of methanol, an organic solvent and antifreeze, from its ball-and-stick model, shown below.

2.3 Write the empirical formulas for the following molecules: acetylene (C2H2), which is used in welding torches glucose (C6H12O6), a substance known as blood sugar nitrous oxide (N2O), a gas that is used as an anesthetic gas (“laughing gas”) and as an aerosol propellant for whipped creams.

Percent Composition and Empirical Formulas Steps: Percent to mass Mass to moles Divide by small Multiply ‘til whole

3.9 Ascorbic acid (vitamin C) cures scurvy. It is composed of 40.92 percent carbon (C), 4.58 percent hydrogen (H), and 54.50 percent oxygen (O) by mass. Determine its empirical formula.

Combustion Analysis g CO2 mol CO2 mol C g C 6.0 g C = 0.5 mol C g H2O Combust 11.5 g ethanol Collect 22.0 g CO2 and 13.5 g H2O g CO2 mol CO2 mol C g C 6.0 g C = 0.5 mol C g H2O mol H2O mol H g H 1.5 g H = 1.5 mol H g of O = g of sample – (g of C + g of H) 4.0 g O = 0.25 mol O Empirical formula C0.5H1.5O0.25 Divide by smallest subscript (0.25) Empirical formula C2H6O

Hydrate Steps: Find the mass of water or mass of anhydrate Turn mass of water and mass of anhydrate into moles (individually) Find the mole ratio; mole of anhydrate mole of water mole of anhydrate mole of anhydrate Write the formula of the hydrate :

Example A calcium chloride hydrate has a mass of 4.72 g. After heating for several minutes the mass of the anhydrate is found to be 3.56 g. Use this information to determine the formula for the hydrate.

Molecular Formula Steps: Find empirical formula Determine the molar mass of the empirical formula Find multiplier (molar mass given/empirical molar mass) Multiply empirical formula subscripts by the multiplier

3.11 A sample of a compound contains 30.46 percent nitrogen and 69.54 percent oxygen by mass, as determined by a mass spectrometer. In a separate experiment, the molar mass of the compound is found to be between 90 g and 95 g. Determine the molecular formula and the accurate molar mass of the compound.

Allotrope one of two or more distinct forms of an element. different number of atoms of the element different properties physical and chemical properties

A mixture is a combination of two or more substances in which the substances retain their distinct identities. Homogenous mixture – composition of the mixture is the same throughout soft drink, milk, solder Heterogeneous mixture – composition is not uniform throughout cement, iron filings in sand

Mass Spectrometry Heavy Light Mass Spectrum of Ne

Light Mass Spectrum of Ne Heavy