Chapter 2: Atoms, Molecules, & Ions Law of Conservation of Mass Antoine Lavoisier (late 1700’s) Mass cannot be created or destroyed, merely converted from one form into another. mass before rxn = mass after rxn example: 10.62 g mercury is allowed to react with oxygen gas resulting in the formation of 11.47 g of mercury oxide. Determine the mass of oxygen gas consumed in this reaction. Law of Definite Proportions Joseph Proust (late 1700’s - early 1800’s) A given compound always consists of the same proportion of its constituent elements by mass. example: sodium chloride (salt) 1.00g salt ! 0.394 g Na & 0.606 g Cl 100 g salt ! 39.4 g Na & 60.6 g Cl Law of Multiple Proportions John Dalton (late 1700’s - early 1800’s) When 2 elements form a series of compounds, the ratio of the mass of the 2 nd element that combines with 1 g of the 1 st element is a small whole number ratio. example: Consider three different compounds composed of sulfur and fluorine: mass of sulfur mass of fluorine compound A 1.000 g 1.188 g compound B 1.000 g 2.375 g compound C 1.000 g 3.563 g
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Chapter 2:Atoms, Molecules, & Ions
Law of Conservation of Mass
Antoine Lavoisier (late 1700’s)
Mass cannot be created or destroyed, merely converted from one form into another.
mass before rxn = mass after rxn
example: 10.62 g mercury is allowed to react with oxygen gas resulting in the formation of 11.47 g of mercury oxide.
Determine the mass of oxygen gas consumed in this reaction.
Law of Definite Proportions
Joseph Proust (late 1700’s - early 1800’s)
A given compound always consists of the same proportion of its constituent elements by mass.
example: sodium chloride (salt)
1.00g salt ! 0.394 g Na & 0.606 g Cl
100 g salt ! 39.4 g Na & 60.6 g Cl
Law of Multiple Proportions
John Dalton (late 1700’s - early 1800’s)
When 2 elements form a series of compounds, the ratio of the mass of the 2nd element that combines with 1 g of the 1st element is a small whole number ratio.
example: Consider three different compounds composed of sulfur and fluorine:
mass of sulfur mass of fluorinecompound A 1.000 g 1.188 gcompound B 1.000 g 2.375 gcompound C 1.000 g 3.563 g
Dalton’s Atomic Theory - 4 basic statements:1. All matter is composed of atoms.
2. Atoms of the same element are identical; atoms of different elements are distinct.
- with respect to physical and chemical properties
3. A compound is a specific combination of atoms of 2 or more elements bonded together in a specific ratio.
4. In a chemical reaction atoms are neither created or destroyed, merely rearranged into new substances.
- Law of Conservation of Matter
In 1808, John Dalton published A New System of Chemical Philosophy.
Early Experiments to Establish Atomic Structure:
J.J.Thomson and Cathode RaysRobert Millikan and the Oil Drop Experiment
Ernest Rutherford and the Nuclear Structure of the Atom
J.J. Thomson and Cathode Rays (1897)
Thomson’s Conclusions:
negatively charged particles (electrons, e!) are common to the internal structure of atoms of all elements
charge to mass ratio of electron: e/m = 1.76 x 108 C/g
Millikan’s Oil Drop Experiment (1909)
Millikan determined the charge of a single electron:1 e! = 1.6 x 10 −19 C
coupled with Thomson’s results: mass of e− = 9.1 x 10−28 g
Ernest Rutherford and α-Rays (1911)
● beam of alpha-particles shot at thin gold film
● Rutherford expected to see very little or no deflection of particle beam
● approximately 1 in 20,000 particles were deflected sharply backward
Rutherford: the Nuclear Structure of the Atomthe nucleus: center of mass and positive charge
very small relative to the whole atom
Atomic Structure: Protons, Neutrons, & Electrons
note: an atom is charge neutral when number protons = number electrons
Individual atoms identified by:name and symbol
atomic number (Z)mass number (A)
atomic number, Z:
Z = number of protons in the nucleus
Z does not change for a given element
mass number, A:
A = number protons + number neutronsor equals total number of nucleons
number of protons is constant for atoms of the same element, but the number of neutrons is variable
Isotopes - atoms with the same number of protons but differing numbers of neutrons
same atomic number ∴ same elementdifferent mass numbers
consider 2 atoms (atom A and atom B are isotopes of one another):
atom A atom Bnumber protons 50 50number neutrons 69 73number electrons 50 50atomic numbermass number
symbol
Elements and the Periodic Tableelements:
◆ pure substances◆ only one type of matter◆ cannot be broken down into simpler substances◆ 118 known; 112 named
each element has a name and a symbol:
◆ an element’s name should not be capitalized unless it is the 1st word in a sentence
◆ for elemental symbol - 1st letter is always capitalized, 2nd letter is never capitalized
★★★ In Chem 1711 you need to know the names (correctly
spelled) and symbols for elements 1 - 56 plus W, Pt, Au, Hg, Pb, & Bi
Periodic Table of the ElementsOrganization of the Periodic Table:
Periods and Groups
horizontal rows: periods
vertical columns: groups or families
numbering of groups - IA to VIIIA; 1A to 8; 1 to 18groups with special names -
naming type II metal cations: use stock system to indicate charge on cationCr3+ chromium (III) ionCr6+ chromium (VI) ionSn2+ tin (II) ion Sn4+ tin (IV) ion
Naming Monatomic Anionsnonmetals tend to form anions
monatomic anions: primarily nonmentals in groups VA, VIA, and VIIA
◆ name the elements in the order that they appear◆ add suffix !ide to stem of 2nd element name◆ use prefixes to indicate how many atoms of each element are presentexamples:
Give the name for each of the following:
SiO2 PCl3 XeF6
Give the chemical formula for each of the following:
◆ Acids - one or more H+ with an anionnumber of H+’s in acid formula = charge on anion
◆ binary acids - anion is a monatomic anion; only 2 elements present
to name a binary acid: hydro-______-ic acid
examples: HI hydrosulfuric acid
Naming Acids
◆ oxoacids - anion is an oxoanion
◆ the name of an oxoacid is determined based on the name of the oxoanion:
if oxoanion name ends in -ate: ______-ic acid
if oxoanion name ends in -ite: ______-ous acid
examples: HClO4 HNO2
acetic acid carbonic acid sulfurous acid
Naming Hydrated Metal Salts
◆ ionic compounds (aka salts) that have one or more water molecule associated per formula unit
◆ “waters of hydration”
name these in the following way:
ionic compound name + ______ - hydrate
examples:
Mg(NO3)2•4H2O magnesium nitrate tetrahydrate
CoSO4•7H2O cobalt (II) sulfate heptahydrate
Writing and Balancing Chemical EquationsReactants ! Products
substances consumed substances formed
chemical equations provide qualitative information:◆ identity of reactants and products; chemical formulas◆ physical states; s, l, g, aq◆ reaction conditions
chemical equations provide quantitative information:◆ stoichiometric coefficients◆ numbers of particles that combine◆ ratio of how reactants combine and products form
Writing and Balancing Chemical Equations
Chemical equations must be balanced before they can provide quantitative information.
◆ atom book-keeping . . . must have equal numbers of atoms of each element of both sides of the arrow
Law of Conservation of Matter - matter cannot be created or destroyed, merely converted from one form into another
Writing and Balancing Chemical Equations
to balance a chemical equation:1. write the skeletal equation
◆ chemical formulas of reactants and productsnote: there are 7 elements that exist as diatomic molecules in their element form:
H2, N2, O2, F2, Cl2, Br2, I2
2. adjust the stoichiometric coefficients until the equation is balanced
◆ do not change subscripts in chemical formulas◆ trial and error
3. DOUBLE CHECK!
4. add details if you know them◆ physical states; reaction conditions
Writing and Balancing Chemical Equations
examples:
Molten aluminum metal and solid barium oxide are combined and heated resulting in the formation of elemental, liquid barium and solid aluminum oxide.