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Dalton’s Atomic Theory (experiment based)
3) Atoms of different elements combine in simple whole-number ratios to form chemical compounds
4) In chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element.
1) All elements are composed of tiny indivisible particles called atoms
2) Atoms of the same element are identical. Atoms of any one element are different from those of any other element.
John Dalton(1766 – 1844)
Sizing up the Atom� Elements are able to be subdivided into
smaller and smaller particles – these are
the atoms, and they still have properties
of that element
�If you could line up 100,000,000
copper atoms in a single file, they
would be approximately 1 cm long
�Despite their small size, individual
atoms are observable with instruments
such as scanning tunneling
microscopes
Subatomic Particles
Nucleus1.67 x 10-240
Neutron
(no)
Nucleus1.67 x 10-24+1
Proton(p+)
Electron cloud
9.11 x 10-28-1
Electron
(e-)
LocationMass (g)ChargeParticle
The Rutherford Atomic Model• Based on his experimental evidence:
–The atom is mostly empty space
–All the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus”
–The nucleus is composed of protons and neutrons
–The electrons distributed around the nucleus, and occupy most of the volume
–His model was called a “nuclear model”
Atomic Number
• Atoms are composed of protons,
neutrons, and electrons
– How then are atoms of one element different from another element?
• Elements are different because they
contain different numbers of PROTONS
• The “atomic number” of an element is
the number of protons in the nucleus
• # protons in an atom = # electrons
Atomic Number
Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.
7979Gold
1515Phosphorus
66Carbon
Atomic # (Z)# of protonsElement
Mass Number
Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p+ + n0
15- 31
4233-
10Oxygen -
Mass #e-n0p+Nuclide
8 8 1818
Arsenic 75 33 75
Phosphorus 15 3116
SymbolsSymbols
�� Find each of these: Find each of these:
a)a) number of protonsnumber of protons
b)b) number of number of
neutronsneutrons
c)c) number of number of
electronselectrons
d)d) Atomic numberAtomic number
e)e) Mass NumberMass Number
Br80
35
Isotopes
• Dalton was wrong about all elements of the same type being identical
• Atoms of the same element canhave different numbers of neutrons.
• Thus, different mass numbers.
• These are called isotopes.
Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.
211Hydrogen-3
(tritium)
111
Hydrogen-2
(deuterium)
011
Hydrogen–1
(protium)
NucleusNeutronsElectronsProtonsIsotope
IsotopesElements occur in nature as mixtures of isotopes.
Isotopes are atoms of the same element that differ in the number of
neutrons.
Atomic Mass� How heavy is an atom of oxygen?
� It depends, because there are different
kinds of oxygen atoms.
� We are more concerned with the average
atomic mass.
� This is based on the abundance (percentage) of each variety of that
element in nature.
� We don’t use grams for this mass because
the numbers would be too small.
Measuring Atomic Mass
• Instead of grams, the unit we use is the Atomic Mass Unit (amu)
• It is defined as one-twelfth the mass of a carbon-12 atom.
– Carbon-12 chosen because of its isotope purity.
• Each isotope has its own atomic mass, thus we determine the average from percent abundance.
To calculate the average:
• Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results.
• If not told otherwise, the mass of the isotope is expressed in atomic mass
units (amu)
Atomic Masses
<0.01%6 protons
8 neutrons
14CCarbon-14
1.11%6 protons
7 neutrons
13CCarbon-13
98.89%6 protons
6 neutrons
12CCarbon-12
% in natureComposition of
the nucleus
SymbolIsotope
Atomic mass is the average of all the naturally occurring isotopes of that element.
Carbon = 12.011
The Periodic Table:
A Preview
� A “periodic table” is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties�The periodic table allows you to easily compare the properties of one element to another
The Periodic Table:
A Preview
� Each horizontal row (there are 7 of them) is called a period�Each vertical column is called a group, or family�Elements in a group have similar chemical and physical properties�Identified with a number and either an “A” or “B”�More presented in Chapter 6
Types of Radioactive Decay
• Alpha Decay (α)
– Alpha particles are just helium nuclei.
– Mass number = 4 (4 amu)
– Charge = 2+
– Low penetration power (Paper & clothing stop
them.)
• Beta Decay (β)
–Beta particles are just electrons.
–Mass number = 0 (1/1837 amu)
–Charge = -1
–Medium penetration power (Metal foil stops them).
• Gamma Decay (γ)
– Gamma radiation is high energy
electromagnetic radiation.
– Mass number = 0
– Charge = 0
– High penetration power (Thick lead shield
stops them.)
• Simulating Radioactive Decay
– You just won $1,000, but…
– …you can only spend half of it in month 1…
– …half of the remainder in month 2, etc.
– After how many months would you be left with less than $1?
– What is the half life for this prize?
Common Half-Lives &
Radiation*
Alpha4.46 X 109 yearsUranium-238
Alpha, gamma7.0 X 108 yearsUranium-235
Beta, gamma24.1 daysThorium-234
Alpha, gamma75,400 yearsThorium-230
Alpha, gamma1,600 yearsRadium-226
Alpha3.8 days Radon-222
Beta, gamma1,25 X 109 years Potassium-40
Beta5,730 yearsCarbon-14
RADIATIONHALF-LIFEISOTOPE
Radiocarbon Dating
• In the upper atmosphere 14C forms at a constant rate:
+→+147N 1
0n 146C
11H
T½ = 5730 Years +→146C 0
-1β147N
• Live organisms maintain 14C/13C at equilibrium.
• Upon death, no more 14C is taken up and ratio changes.
• Measure ratio and determine time since death.
Fission
• splitting a nucleus into two or more
smaller nuclei
• 1 g of 235U =
3 tons of coal
U235
92
Fission• Nuclear chain reaction -
self-propagating reaction, a continuous series of nuclear fission reactions.
• critical mass -the minimum amount of a substance than can undergo a fission reaction and can sustain a chain reaction.
Nuclear Fusion
• Fusion produces the energy of the sun.
• Most promising process on earth would be:
• Plasma temperatures over 40,000,000 K to initiate a self-sustaining reaction (we can’t do this yet).
→H31+ He4
2 + n10H2
1
Fusion
• combining of two nuclei to form one nucleus of larger mass
• thermonuclear reaction – requires temp of 40,000,000 K to sustain
• 1 g of fusion fuel = 20 tons of coal
• occurs naturally in stars
HH3
1
2
1+
Applications of Nuclear
Reactions• Dating of ancient artifacts (Carbon-14).
• Smoke detectors (Americium-241).
• Radioactive tracers in medicine (Iodine-131, barium-140, phosphorus-32).
• Cancer treatment (Cobalt-60).
More Applications of Nuclear
Reactions
• Electricity generation (Uranium-235).
• Artificial (lab-made) elements (beyond Z = 92).
• Bombs (Uranium-235).
• Fusion (Combining two small nuclei to form a large nucleus.)
• Interested in learning more?.
Radioactive Waste Disposal
• Low level waste.
–Gloves, protective clothing,
waste solutions.
• Short half lives.
• After 300 years these materials
will no longer be radioactive.
Radioactive Waste Disposal cont.
• High level waste.
–Long half lives.
• Pu, 24,000 years and extremely
toxic.
• Reprocessing is possible but
hazardous.
–Recovered Pu is of weapons
grade.
Mendeleev’s Periodic Table
• By the mid-1800s, about 70 elements were known to exist
• Dmitri Mendeleev – Russian chemist
• Arranged elements in order of increasing atomic mass
• Thus, the first “Periodic Table”
Mendeleev
• Left blanks for undiscovered elements–When they were discovered, he
had made good predictions
• But, there were problems:
–Co and Ni; Ar and K; Te and I
A better arrangement
• In 1913, Henry Moseley –British physicist, arranged elements according to increasing atomic number
• The arrangement used today
• The symbol, atomic number & mass are basic items included
The Periodic Law says:• When elements are arranged in
order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.
• Horizontal rows = periods– There are 7 periods
• Vertical column = group (or family)– Similar physical & chemical prop.
– Identified by number & letter
Electron Configurations in Groups
1) Noble gases are the elements in Group 8A
• Previously called “inert gases” because they rarely take part in a reaction
• Noble gases have an electron configuration that has the outer s and p sublevels completely full
Electron Configurations in Groups
2) Representative Elements are in Groups 1A through 7A
• Display wide range of properties, thus a good “representative”
• Some are metals, or nonmetals, or metalloids; some are solid, others are gases or liquids
• Their outer s and p electron configurations are NOT filled
1A
2A 3A 4A 5A 6A7A
8A• Elements in the 1A-7A groups
are called the representative elements
outer s or p filling
Valence Electrons in
Representative groups• 1A 1 valence electron
• 2A 2 valence electrons
• 3A 3 valence electrons
• 4A 4 valence electrons
• 5A 5 valence electrons
• 6A 6 valence electrons
• 7A 7 valence electrons
• 8A 8 valence electrons
except He with 2 valence electrons
Memorize this rhyme.
• “1+, 2+, 3+, skip, 3-, 2-, 1-, zip”
• This tells you the Ionic charge and oxidation numbers for the elements in the 8 REPRESENTATIVE GROUPS, 1A-8A, as you count form left to right.
Ions
• Some compounds are composed of particles called “ions”– An ion is an atom (or group of atoms) that
has a positive or negative charge
– Atoms are neutral because the number of
protons equals electrons
– Positive and negative ions are formed when
electrons are transferred (lost or gained)
between atoms
Ions• Metals tend to LOSE electrons,
from their outer energy level
– Sodium loses one: there are now more protons (11) than electrons (10), and thus a positively charged particle is formed = “cation”
– The charge is written as a number followed by a plus sign: Na1+
– Now named a “sodium ion”
Ions
• Nonmetals tend to GAIN one or more electrons
– Chlorine will gain one electron
– Protons (17) no longer equals the electrons (18), so a charge of -1
– Cl1- is re-named a “chloride ion”
– Negative ions are called “anions”
Areas of the periodic table
• Three classes of elements are: 1) metals, 2) nonmetals, and 3) metalloids
1) Metals: electrical conductors, have luster, ductile, malleable
2) Nonmetals: gererally brittle and nonlustrous, poor conductors of heat and electricity
Metals
• Luster – shiny.
• Ductile – drawn into wires.
• Malleable – hammered into sheets.
• Conductors of heat and electricity.
Areas of the periodic table
• Some nonmetals are gases (O, N, Cl); some are brittle solids (S); one is a fuming dark red liquid (Br)
• Notice the heavy, stair-step line?
3) Metalloids: border the line
– Properties are intermediate between
metals and nonmetals
#1. Atomic Size - Group trends
• As we increase the atomic number (or go down a group). . .
• each atom has another energy level,
• so the atoms get
bigger.
HLi
Na
K
Rb
#1. Atomic Size - Period Trends
• Going from left to right across a period, the
size gets smaller.
• Electrons are in the same energy level.
• But, there is more nuclear charge.
• Outermost electrons are pulled closer.
Na Mg Al Si P S Cl Ar
#2. Trends in Electronegativity
• Electronegativity is the tendency for an atom to attract electrons to itself
when it is chemically combined with
another element.
• They share the electron, but how equally do they share it?
• An element with a big electronegativity means it pulls the
electron towards itself strongly!
Electronegativity Group Trend• The further down a group,
the farther the electron is away from the nucleus, plus the more electrons an atom has.
• Thus, more willing to share.
• Low electronegativity.
Electronegativity Period Trend• Metals are at the left of the table.
• They let their electrons go easily
• Thus, low electronegativity
• At the right end are the nonmetals.
• They want more electrons.
• Try to take them away from others
• High electronegativity.
Kinetic Theory
• Kinetic means motion
• Three main parts of the theory
– All matter is made of tiny particles
– These particles are in constant motion and
the higher the temperature, the faster they
move
– At the same temperature, heavier particles
move slower.
States of Matter
• Solid
• Particles are tightly packed
• Stuck to each other in a pattern
• Vibrate in place
• Can’t flow
• Constant volume
States of Matter
• Liquid
• Particles are tightly packed
• Able to slide past each other
• Can flow
• Constant volume
States of Matter
• Gas
• Particles are spread out
• Flying all over the place
• Can flow
• Volume of whatevercontainer their in
#1. Boyle’s Law - 1662
Pressure x Volume = a constant
Equation: P1V1 = P2V2 (T = constant)
Gas pressure is inversely proportional to the volume, when temperature is held constant.
• The combined gas law contains all the other gas laws!
• If the temperature remains constant...
P1 V
1
T1
x=
P2 V
2
T2
x
Boyle’s Law
#2. Charles’s Law - 1787The volume of a fixed mass of gas is
directly proportional to the Kelvin
temperature, when pressure is held
constant.
This extrapolates to zero volume at a
temperature of zero Kelvin.
V
T
V
TP
1
1
2
2
= =( constant)
• The combined gas law contains
all the other gas laws!
• If the pressure remains
constant...
P1 V
1
T1
x=
P2 V
2
T2
x
Charles’s Law
#3. Gay Lussac’s Law -1802•The pressure and Kelvin temperature of
a gas are directly proportional, provided
that the volume remains constant.
2
2
1
1
T
P
T
P=
•How does a pressure cooker affect the time needed to cook food?
•Sample Problem 14.3, page 423
�The combined gas law contains
all the other gas laws!
�If the volume remains
constant...
P1
V1
T1
x=
P2
V2
T2
x
Gay-Lussac’s Law