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AATOMS ANDTOMS AND EELEMENTSLEMENTS

RadioactivityRadioactivity•• One of the pieces of evidence forOne of the pieces of evidence for

the fact that atoms are made ofthe fact that atoms are made of

smaller particles came from thesmaller particles came from the

work ofwork of Marie CurieMarie Curie (1876-(1876-

1934).1934).

•• She discoveredShe discovered radioactivityradioactivity,,

the spontaneous disintegrationthe spontaneous disintegration

of some elements into smallerof some elements into smaller

pieces.pieces.

ATOMIC COMPOSITIONATOMIC COMPOSITION•• ProtonsProtons

 –  –  + electrical charge+ electrical charge

 –  –  mass = 1.672623 x 10mass = 1.672623 x 10-24-24 gg

 –  –  relative mass = 1.007 atomicrelative mass = 1.007 atomicmass units (mass units (amuamu))

•• ElectronsElectrons

 –  –  negative electrical chargenegative electrical charge

 –  –  relative mass = 0.0005relative mass = 0.0005 amuamu

•• NeutronsNeutrons

 –  –  no electrical chargeno electrical charge

 –  –  mass = 1.009mass = 1.009 amuamu

ATOMATOMCOMPOSITIONCOMPOSITION

••protons and neutrons inprotons and neutrons inthe nucleus.the nucleus.

••the number of electrons is equal to thethe number of electrons is equal to the

number of protons.number of protons.

••electrons in space around the nucleus.electrons in space around the nucleus.

••extremely small. One teaspoon of water hasextremely small. One teaspoon of water has

3 times as many atoms as the Atlantic Ocean3 times as many atoms as the Atlantic Ocean

has teaspoons of water.has teaspoons of water.

The atom is mostlyThe atom is mostly

empty spaceempty space

The modern view ofThe modern view ofthe atom wasthe atom wasdeveloped bydeveloped by

ErnestErnestRutherfordRutherford(1871-1937).(1871-1937).

ErnestErnest RutherfordRutherford

CanterburyCanterbury

University inUniversity in

Christchurch, NZChristchurch, NZ

RutherfordRutherford birthplace,birthplace,

Nelson, NZNelson, NZ

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The modern view of the atom was developed byThe modern view of the atom was developed by

ErnestErnest RutherfordRutherford (1871-1937).(1871-1937).The modern view of the atom was developed byThe modern view of the atom was developed by

ErnestErnest RutherfordRutherford (1871-1937).(1871-1937).Atomic Number, ZAtomic Number, Z

All atoms of the same elementAll atoms of the same elementhave the same number ofhave the same number ofprotons in the nucleus,protons in the nucleus, ZZ

13

Al

26.9815

atomic number

symbol

atomic weight

Mass Number, AMass Number, A•• C atom with 6 protons and 6 neutronsC atom with 6 protons and 6 neutrons

is the mass standardis the mass standard

•• = 12 atomic mass units= 12 atomic mass units

•• Mass NumberMass Number = # protons + # neutrons= # protons + # neutrons

•• A boron atom can haveA boron atom can haveA = 5 p + 5 n = 10A = 5 p + 5 n = 10 amuamu

A

Z

10

5B

IsotopesIsotopes•• Atoms of the same element (same Z)Atoms of the same element (same Z)

but different mass number (A).but different mass number (A).

•• Boron-10 (Boron-10 (1010

B) has 5 p and 5 nB) has 5 p and 5 n•• Boron-11 (Boron-11 (1111B) has 5 p and 6 nB) has 5 p and 6 n

10B

11B

Boron in Death ValleyBoron in Death Valley

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Isotopes & Their UsesIsotopes & Their Uses

An MRI image of aAn MRI image of a

guinea pig lungguinea pig lung

done usingdone using

““hyperpolarizedhyperpolarized””

helium-3.helium-3. ArAr-129 is-129 is

also used.also used.

Seewwwcivm.mc.duke.edu/ 

civmProjects

IsotopesIsotopes

•• Because of the existence of isotopes, theBecause of the existence of isotopes, themass of a collection of atoms has an averagemass of a collection of atoms has an averagevalue.value.

•• Average mass =Average mass = ATOMIC WEIGHTATOMIC WEIGHT

•• Boron is 20%Boron is 20% 1010B and 80%B and 80% 1111B. That is,B. That is, 1111B isB is80 percent abundant on earth.80 percent abundant on earth.

•• For boron atomic weightFor boron atomic weight

= 0.20 (10= 0.20 (10 amuamu) + 0.80 (11) + 0.80 (11 amuamu) = 10.8) = 10.8 amuamu

10B

11B Periodic TablePeriodic Table•• Dmitri MendeleevDmitri Mendeleev developeddeveloped

the modern periodic table.the modern periodic table.Argued that elementArgued that elementproperties are periodicproperties are periodicfunctions of their atomicfunctions of their atomicweights.weights.

•• We now know that elementWe now know that elementproperties are periodicproperties are periodicfunctions of theirfunctions of their ATOMICATOMICNUMBERSNUMBERS..

•• See CD-ROM, Screen 2.16.See CD-ROM, Screen 2.16.

PeriodsPeriods in the Periodic Tablein the Periodic Table GroupsGroups in the Periodic Tablein the Periodic TableGroup 1A: Alkali MetalsGroupGroup 1A: Alkali Metals1A: Alkali Metals

Cutting sodium metalCutting sodium metal

Reaction of

potassium + H2O

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MagnesiumMagnesium

MagnesiumMagnesiumoxideoxide

Group 3A: B, Al,Group 3A: B, Al, GaGa, In,, In, TlTl

AluminumAluminum Boron halides,Boron halides,

BFBF33 & BI& BI33

Group 4A: C,Group 4A: C, SiSi,, GeGe,, SnSn,, PbPb

Quartz, SiOQuartz, SiO22

DiamondDiamond

From theFrom theComicComicBookBook

PeriodicPeriodicTableTable

from http://cnst.rice.edu/images Group 5A: N, P, As,Group 5A: N, P, As, SbSb,, BiBi

White and redWhite and redphosphorusphosphorus

Ammonia, NHAmmonia, NH33

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