AATOMS AND TOMS AND EELEMENTSLEMENTS

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

fact that atoms are made of smaller fact that atoms are made of smaller particles came from the work of particles came from the work of

Marie CurieMarie Curie (1876-1934). (1876-1934). • She discovered She discovered radioactivityradioactivity, ,

the spontaneous disintegration of the spontaneous disintegration of some elements into smaller pieces.some elements into smaller pieces.

ATOMIC COMPOSITIONATOMIC COMPOSITION• ProtonsProtons

– + electrical charge+ electrical charge

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

– relative mass = 1.007 atomic relative mass = 1.007 atomic mass units (amu)mass units (amu)

• ElectronsElectrons– negative electrical chargenegative electrical charge

– relative mass = 0.0005 amurelative mass = 0.0005 amu

• NeutronsNeutrons– no electrical chargeno electrical charge

– mass = 1.009 amumass = 1.009 amu

ATOMATOM COMPOSITIONCOMPOSITION

•protons and neutrons in the nucleus.protons and neutrons in the nucleus.

•the number of electrons is the number of electrons is equalequal to the to the number of protons.number of protons.

•Electrons are extremely small and occupy Electrons are extremely small and occupy the space around the nucleus.the space around the nucleus.

The The atomatom is mostly is mostlyempty spaceempty space

ScientistsScientists

• Chadwich

BecquerelBecquerel

RutherfordRutherford

MillikanMillikan

ThomsomThomsom

CurieCurie

BohrBohr

The modern view of The modern view of

was developed bywas developed by

Ernest Ernest RutherfordRutherford

the “Nuclear Atom”the “Nuclear Atom”

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

Ernest RutherfordErnest Rutherford (1871-1937).(1871-1937).

Screen 2.9Screen 2.9

Atomic Number, ZAtomic Number, Z

All atoms of the same element All atoms of the same element have the same number of have the same number of protons in the nucleus, protons in the nucleus, ZZ

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

Atomic weightAtomic weight

Atomic WeightAtomic Weight• This tells us the mass of one atom This tells us the mass of one atom

of an element relative to one atom of an element relative to one atom of another element.of another element.

• Define one element as the standard Define one element as the standard against which all others are against which all others are measuredmeasured

• Standard = carbonStandard = carbon

• For example, an O atom is For example, an O atom is approximately 16 times heavier than approximately 16 times heavier than an H atom.an H atom.

Mass Number, Mass Number, AA• Mass Number (Mass Number (AA) ) = # p + # n= # p + # n

• C atom with 6 protons and 6 neutrons is C atom with 6 protons and 6 neutrons is the mass standard the mass standard

= 12 atomic mass units= 12 atomic mass units

• For a boron atom For a boron atom

AA = 5 p + 5 n = = 5 p + 5 n =

= 10 amu= 10 amu

A

Z

10

5B

A

Z

10

5B

IsotopesIsotopes

• Atoms of the same element Atoms of the same element

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

Boron-10 has 5 p and 5 nBoron-10 has 5 p and 5 n ((1010B) B)

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

10B

11B

Masses of IsotopesMasses of Isotopesdetermined with a mass determined with a mass

spectrometerspectrometer

IsotopeIsotopess• Because of the existence of isotopes, the Because of the existence of isotopes, the

mass of a collection of atoms has an average mass of a collection of atoms has an average value.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 is B is

80 percent abundant on earth. 80 percent abundant on earth.

• For boron atomic weightFor boron atomic weight

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

10B

11B

Isotopes & Atomic Isotopes & Atomic WeightWeight• Because of the existence of isotopes, the mass Because of the existence of isotopes, the mass

of a collection of atoms has an average value.of a collection of atoms has an average value.

• 66Li = 7.5% abundant and Li = 7.5% abundant and 77Li = 92.5%Li = 92.5%

–Atomic weight of Li = ______________Atomic weight of Li = ______________

• 2828Si = 92.23%, Si = 92.23%, 2929Si = 4.67%, Si = 4.67%, 3030Si = 3.10%Si = 3.10%

–Atomic weight of Si = ______________Atomic weight of Si = ______________

Counting AtomsCounting Atoms

Chemistry is a quantitative Chemistry is a quantitative science—we need a science—we need a “counting unit.”“counting unit.”

1 mole is the amount of 1 mole is the amount of substance that contains as substance that contains as many particles (atoms, many particles (atoms, molecules) as there are in molecules) as there are in 12.0 g of 12.0 g of 1212C.C.

1 mole is the amount of 1 mole is the amount of substance that contains as substance that contains as many particles (atoms, many particles (atoms, molecules) as there are in molecules) as there are in 12.0 g of 12.0 g of 1212C.C.

MOLEMOLE

Particles in a Particles in a MoleMole

6.02214199 x 106.02214199 x 102323

Avogadro’s NumberAvogadro’s Number

There is Avogadro’s number of particles in a mole of any substance.There is Avogadro’s number of particles in a mole of any substance.

Amedeo AvogadroAmedeo Avogadro1776-18561776-1856

Molar MassMolar Mass1 mol of 1 mol of 1212C C

= 12.00 g of C= 12.00 g of C = 6.022 x 10 = 6.022 x 102323 atoms atoms

of Cof C

12.00 g of 12.00 g of 1212C is its C is its

MOLAR MASSMOLAR MASS

Taking into account all Taking into account all

of the isotopes of C, of the isotopes of C,

the molar mass of C is the molar mass of C is

12.011 g/mol12.011 g/mol

One-mole AmountsOne-mole Amounts

PROBLEM: What amount of Mg PROBLEM: What amount of Mg is represented by 0.200 g? How is represented by 0.200 g? How many atoms?many atoms?

PROBLEM: What amount of Mg PROBLEM: What amount of Mg is represented by 0.200 g? How is represented by 0.200 g? How many atoms?many atoms?

Mg has a molar mass of 24.3050 g/mol.

0.200 g • 1 mol

24.31 g = 8.23 x 10-3 mol

8.23 x 10-3 mol • 6.022 x 1023 atoms

1 mol

= 4.95 x 10= 4.95 x 102121 atoms Mg atoms Mg

How many atoms in this piece of Mg?

Periodic TablePeriodic Table• Dmitri Dmitri MendeleevMendeleev developed the developed the

modern periodic table. Argued modern periodic table. Argued that element properties are that element properties are periodic functions of their periodic functions of their atomic atomic weights.weights.

• Today: element properties are Today: element properties are periodic functions of their periodic functions of their

ATOMIC NUMBERSATOMIC NUMBERS..

Periodic Table HistoryPeriodic Table History

Henry Henry Mosley-Mosley- -Grouped elements in order of -Grouped elements in order of

atomic numberatomic number-credited with modern periodic -credited with modern periodic

tabletableCame up with Came up with Period LawPeriod Law--

-physical and chemical properties -physical and chemical properties of elements are a periodic of elements are a periodic function of their atomic numbersfunction of their atomic numbers

Modern Periodic TableModern Periodic Table

Glen Glen Seaborg-Seaborg-

-Grouped elements according to -Grouped elements according to their their electron configurationselectron configurations

-credited with periodic table as -credited with periodic table as it looks todayit looks today

Modern Periodic TableModern Periodic TableGroups (families)Groups (families)

a a verticalvertical column column of elements.of elements.

determined by determined by ## of of

valencevalence electronselectrons

Modern Periodic TableModern Periodic TablePeriodsPeriods ( () )

horizontal rowhorizontal row

of elements.of elements.

-determined by the -determined by the electron’s electron’s energy levelenergy level..

METALSMETALS

METALLOIDSMETALLOIDS

NONMETALSNONMETALS

NOBLE GASESNOBLE GASES

HydrogenHydrogenHydrogenHydrogen

Shuttle main engines Shuttle main engines use Huse H22 and O and O22 The Hindenburg crash, The Hindenburg crash,

May 1939.May 1939.

Group 1A: Alkali MetalsGroup 1A: Alkali MetalsGroup 1A: Alkali MetalsGroup 1A: Alkali Metals

Cutting sodium metalCutting sodium metal

Reaction of potassium + H2O

MagnesiumMagnesium

Magnesium Magnesium oxideoxide

Group 2A: Alkaline Earth MetalsGroup 2A: Alkaline Earth Metals

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

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

AluminumAluminum

Boron halidesBoron halides BF BF33 & BI & BI33

Group 4A: C, Si, Ge, Sn, Group 4A: C, Si, Ge, Sn, PbPb

Group 4A: C, Si, Ge, Sn, Group 4A: C, Si, Ge, Sn, PbPb

Quartz, SiOQuartz, SiO22

DiamondDiamond

Group 5A: N, P, As, Sb, BiGroup 5A: N, P, As, Sb, BiGroup 5A: N, P, As, Sb, BiGroup 5A: N, P, As, Sb, Bi

White and red White and red phosphorusphosphorus

Ammonia, NHAmmonia, NH33

Group 6A: O, S, Se, Te, Group 6A: O, S, Se, Te, PoPo

Group 6A: O, S, Se, Te, Group 6A: O, S, Se, Te, PoPo

Sulfuric acid dripping from Sulfuric acid dripping from snot-tite in cave in Mexicosnot-tite in cave in Mexico

Sulfur from Sulfur from a volcanoa volcano

Group 7A:Group 7A:HALOGENS HALOGENS

F, Cl, Br, I, AtF, Cl, Br, I, At

Group 7A:Group 7A:HALOGENS HALOGENS

F, Cl, Br, I, AtF, Cl, Br, I, At

Group 8A: NOBLE GASESGroup 8A: NOBLE GASESHe, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn

Group 8A: NOBLE GASESGroup 8A: NOBLE GASESHe, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn

• Lighter than air balloons

• “Neon” signs

XeOFXeOF44XeOFXeOF44

Transition ElementsTransition ElementsTransition ElementsTransition Elements

Lanthanides and actinidesLanthanides and actinides

Iron in air gives Iron in air gives iron(III) oxideiron(III) oxide

Colors of Transition Metal Colors of Transition Metal CompoundsCompounds

Iron Cobalt Nickel Copper Zinc

1234567

Peri

ods

Groups/ Families

1A 2A 8A

3A 4A 5A 6A 7A

“B” or

Transition MetalsAlk

ali

Alk

alin

e E

art

h

Halo

gen

sN

oble

Gase

s

Rare LanthanidesEarth Actinides