Upload
marissa-armstrong
View
243
Download
0
Tags:
Embed Size (px)
Citation preview
Unit II : Atoms, Molecules, Ions and Nuclear Chemistry
Early History of ChemistryBefore 16th Century Alchemy: Attempts (scientific or
otherwise) to change cheap metals into gold
17th Century Robert Boyle: First “chemist” to
perform quantitative experiments
18th Century George Stahl: Phlogiston flows out of a
burning material. Joseph Priestley: Discovers oxygen
gas, “dephlogisticated air.”
Law of Conservation of Mass
-Discovered by Antoine Lavoisier
-Mass is neither created nor destroyed
-Combustion involves oxygen, not phlogiston
Law of Definite Proportions- Sometimes called the law of constant
composition- John Proust (1799)- A given compound always contains exactly the
same proportion of elements by mass.
- Carbon tetrachloride is always 1 atom carbon per 4 atoms chlorine.
Law of Multiple Proportions- When two elements form a series of
compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.
- The ratio of the masses of oxygen in H2O and H2O2 will be a small whole number (“2”).
Dalton’s Atomic Theory
1 Each element is made up of tiny particles called atoms.
2 The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.
3 Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative numbers and types of atoms.
4 Chemical reactions involve reorganization of the atoms - changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.
Avagadro’s Hypothesis (1811)At the same temperature and
pressure, equal volumes of different gases contain the same number of particles.
5 liters of oxygen5 liters of nitrogen
SAME NUMBER OF PARTICLES
Chemical SymbolsThe chemical symbols used today were
developed by Jons Jakob Berzelius.
They consist of one or two letters. The first letter is always capitalized. The second, if there is one, is never
capitalized. The second letter is often a letter prominent in the pronunciation.
Co Cu He H
Early Experiments to Characterize the Atom
DemocritisDaltonThomsonRutherfordBohrSchrodinge
r
Cathode Ray
• Streams of negatively charged particles were found to emanate from cathode tubes.• J. J. Thompson is credited with their discovery (1897).
Deflection of Cathode Ray by an Applied Electric Field
02_21
Metalelectrode
Metalelectrode
(-)
(+)
(+)
(-)
Appliedelectric field
Rutherford Gold Foil Experiment
Ernest Rutherford shot particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.
Rutherford Gold Foil Experiment
02_25
Electrons scatteredthroughout Diffuse
positivecharge
(a) (b)
-
--
-
-
-
--
-
-
-
--
-
-
-
--
--
n+
(a)Expected results if Thomson’s Model was correct
(b)Actual results
Summary of AtomDemocritis - first idea of the atomDalton - ~1807 Atomic Theory (atom = ball)Thomson - Experiment with Cathode Ray
Discovered the electron“Plum pudding model”
Rutherford - Gold Foil ExperimentAtom is mostly empty space with a dense,
positively charged nucleusBohr - “Solar System” Schrodinger - Quantum Mechanical Model
Modern View of Atomic StructureThe atom contains 3 types of subatomic
particles:Electrons
Negatively charged, found outside the nucleus… very small mass… would take ~2000 electrons to equal the mass of 1 of the other subatomic particles
Protons Positively charged, found in the nucleus
Neutrons Found in the nucleus… like a proton but with no
charge
Subatomic Particle Summary
Mass (g)
Charge Atomic Mass Scale
Relative Mass
Relative Charge
Proton (p+) 1.6726x1
0-24
+1.602x10-19 c
1.0073 amu
1 +1
Neutron (n0)
1.6726x10-24
0 1.0087 amu
1 0
Electron (e-) 9.109 x
10-27
-
1.602x10-19 c
5.486 x 10-4 amu
1/1836
-1
Useful UnitsAtomic Diameter:10-10m (1 Å) = 100 pm = 1x10-8cmNuclear Diameter: 10-13cm1 amu (atomic mass unit) = 1.66054 x10-24 kg
Based off of C-12… relative mass of O w/ 8 protons and 8 neutrons is 15.9949
1 picometer (pm) = 1 x 10-12 m
NOTE:Heaviest atom has a mass of only 4.8x10-22g and a diameter of
only 5x10-10mBiggest atom is 240 amu and is 50 Å across.Typical C-C bond length 154 pm (1.54 Å)Molecular models are 1 Å /inch or about 0.4 Å /cm
Atomic Number
K39
19
Element Symbol
Z = atomic number = number of protons
A = mass number = number of protons + number of neutrons
A = Z + NMass number = # p+ + # n0
IsotopesIsotopes are atoms of the same element
with different masses.Isotopes have different numbers of
neutrons.
Carbon has two natural isotopes: 12C and 13C
How does this change things?
IsotopesOn the periodic table the given atomic
mass is the AVERAGE massWe use percentage to help with this math.For Carbon, there is 98.89% 12C and 1.11%
of 13CNow what?
12 (mass of 12C) x 0.9889 = 11.866813 (mass of 13C) x 0.011 = 0.144311.8668 + 0.1443 = 12.0111
IsotopesOn the periodic table the given atomic
mass is the AVERAGE mass
We use percentage to help with this math.
For Carbon, there is 98.89% 12C and 1.11% of 13C
Mass Spectrometer
Used to experimentally determine mass and percent abundances of isotopes
Prentice-Hall © 2002General Chemistry: Chapter 2Slide 23 of 25
The Periodic TableAlkali Metals
Alkaline Earths
Transition Metals
Halogens
Noble Gases
Lanthanides and Actinides
Main Group
Main Group
Periodicity
When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.
The Periodic Table1869- Dmiti Mendeleev organized 1st
periodic table by lining elements up in horizontal rows in order of increasing atomic weightLeft spaces when an element was not
known but should exist and have properties similar to the element about it in his table.Periodicity – periodic repetition of the
properties of elements
1913- H.G.J. Moseley organized elements according to increasing atomic numberLaw of chemical periodicity
The properties of the elements are periodic functions of atomic numbers.
Features of the Periodic TableVertical Columns: Groups or FamiliesA and B groups. “A” main group, “B”
transition elementsHorizontal Rows: called periodsPeriodic Law: when the elements are arranged
in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties
Metals~80% of all elements are
metalsHigh electrical
conductivity and have a high luster when cleaned
Ductile (can be made into wires) and Malleable
Can form alloysAre solid at room
temperature except for one… which one is it?
NonmetalsGenerally
nonlustrous… which means not shiny
Generally poor conductors of electricityWith the
exceptions of carbon (graphite), none conduct electricity
•Allotropes•A particular element can often exist in several different forms
•Carbon as graphite or diamond… oxygen as O2 or O3 (ozone)
MetalloidsSemi-metals
Overview of GroupsGroup 1A
Alkali Metals Metals, solid at room temp, and VERY REACTIVE
Only found in nature combined in compounds
Group 2AAlkaline Earth Metals
Metals, solid at room temp, and also only found in nature in compounds
Except for Be, all react with water to produce alkaline solutions
Overview of GroupsGroup 7A
HalogensAll exist in diatomic moleculesCombine violently with alkali metals to form salts
Group 8ANoble Gases (Inert Gases)
Least reactive elementsAll are gases
Overview of GroupsGroup B Metals (Groups 3-12):
Transition Metals & Inner Transition MetalsLanthanides- shiny metals similar in reactivity to
alkaline earth metalsActinides- unique in nuclear structures – nuclei are
unstable and therefore radioactiveInner Transitions Metals – rare-earth metals
Prentice-Hall © 2002General Chemistry: Chapter 2Slide 33 of 25
The Periodic TableAlkali Metals
Alkaline Earths
Transition Metals
Halogens
Noble Gases
Lanthanides and Actinides
Main Group
Main Group
Chemical FormulasThe subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.
Molecular compounds are composed of molecules and almost always contain only nonmetals.
Chemical Formulas: Diatomic Molecules
These 7 elements occur naturally as diatomic molecules
Types of Formulas
Molecular Formula – CH4
Structural Formula
Ball and Stick Model
Space-Filling Model
Types of FormulasMolecular Formula
Exact number of each type of atomC6H12O6
Empirical FormulaLowest whole number ratio of each type of
atomCH2O