Atoms and Elements:The Atoms and Elements:The Nature of MatterNature of Matter

Atoms and Elements:The Atoms and Elements:The Nature of MatterNature of Matter

Chemists are interested in the Chemists are interested in the nature of matternature of matter and and how this is related to its atoms and molecules.how this is related to its atoms and molecules.

GoldGold MercuryMercury

“It’s easier to break an atom than a prejudice” A. Einstein

The red compound is The red compound is composed ofcomposed of• • nickel (Ni) (silver)nickel (Ni) (silver)• • carbon (C) (black)carbon (C) (black)• hydrogen (H) (white)• hydrogen (H) (white) • • oxygen (O) (red)oxygen (O) (red)• • nitrogen (N) (blue)nitrogen (N) (blue)

The red compound is The red compound is composed ofcomposed of• • nickel (Ni) (silver)nickel (Ni) (silver)• • carbon (C) (black)carbon (C) (black)• hydrogen (H) (white)• hydrogen (H) (white) • • oxygen (O) (red)oxygen (O) (red)• • nitrogen (N) (blue)nitrogen (N) (blue)

CHEMICAL COMPOUNDSCHEMICAL COMPOUNDS are composed of atoms and so can are composed of atoms and so can be decomposed to those atoms.be decomposed to those atoms.

Nature of Matter, cont’dNature of Matter, cont’d

A A MOLECULEMOLECULE is the smallest unit is the smallest unit of a compound that retains the chemical of a compound that retains the chemical characteristics of the compound.characteristics of the compound.Composition of molecules is given by aComposition of molecules is given by a MOLECULAR FORMULAMOLECULAR FORMULA

HH22OO CC88HH1010NN44OO22 - caffeine - caffeine

Nature of Matter, cont’dNature of Matter, cont’d

STATES OF MATTERSTATES OF MATTERSTATES OF MATTERSTATES OF MATTER•SOLIDSSOLIDS — have rigid shape, fixed — have rigid shape, fixed

volume. External shape can reflect the volume. External shape can reflect the atomic and molecular arrangement.atomic and molecular arrangement.

–Reasonably well understood.Reasonably well understood.

•LIQUIDSLIQUIDS — have no fixed shape and — have no fixed shape and may not fill a container completely. may not fill a container completely.

–Not well understood.Not well understood.

•GASESGASES — expand to fill their container. — expand to fill their container.

–Good theoretical understanding.Good theoretical understanding.

Nature of Matter, cont’dNature of Matter, cont’d

Kinetic Nature of MatterKinetic Nature of MatterKinetic Nature of MatterKinetic Nature of MatterMatter consists of atoms and molecules Matter consists of atoms and molecules

in motion.in motion.

Nature of Matter, cont’dNature of Matter, cont’d

Copper Copper atoms on atoms on silica silica surface.surface.

See CD-See CD-ROM ROM Screen 1.4Screen 1.4

• An An atomatom is the smallest particle of an is the smallest particle of an element that has the chemical element that has the chemical properties of the element.properties of the element.

Distance across = 1.8 nanometer (1.8 x 10-9 m)

Nature of Matter, cont’dNature of Matter, cont’d

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

Nature of Matter, cont’dNature of Matter, cont’d

An atom consists of a An atom consists of a

• nucleus nucleus – (of (of protonsprotons and and neutronsneutrons) )

• electronselectrons in space about the nucleus. in space about the nucleus.

The The AtomAtom

Electron cloudElectron cloud

NucleusNucleus

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.

ATOM ATOM COMPOSITIONCOMPOSITION

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

•the number of electrons is equal to the the 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.

•Atoms are extremely small: One teaspoon Atoms are extremely small: One teaspoon of water has 3 times as many atoms as the of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of waterAtlantic Ocean has teaspoons of water..

The atom is mostlyThe atom is mostlyempty spaceempty space

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 of an This tells us the mass of one atom of an

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

• OR — the mass of 1000 atoms of one relative OR — the mass of 1000 atoms of one relative to 1000 atoms of another.to 1000 atoms of another.

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

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

• Standard = carbonStandard = carbon

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

is the mass standard is the mass standard

• = 12 atomic mass units= 12 atomic mass units

• Mass NumberMass Number (A) (A)= # protons + # neutrons= # protons + # neutrons

• A boron atom can have A boron atom can have A = 5 p + 5 n = 10 amuA = 5 p + 5 n = 10 amu

A

Z

10

5B

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 (1010B) 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

Isotopes Isotopes & Their & Their

UsesUsesBone scans with Bone scans with radioactive radioactive technetium-99. technetium-99.

Isotopes & Their Isotopes & Their UsesUses

The The tritiumtritium content of ground water is content of ground water is used to discover the source of the water, used to discover the source of the water, for example, in municipal water or the for example, in municipal water or the source of the steam from a volcano. source of the steam from a volcano.

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 of a Because of the existence of isotopes, the mass of a

collection of atoms has an average value.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 Counting AtomsAtoms

Mg burns in air (OMg burns in air (O22) to ) to produce white produce white magnesium oxide, MgO. magnesium oxide, MgO.

How can we figure out how How can we figure out how much oxide is produced much oxide is produced from a given mass of Mg?from a given mass of Mg?

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 C atoms in molecules) as C atoms 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 C atoms in molecules) as C atoms 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 Mendeleev developed the Dmitri Mendeleev developed the

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

• We now know that element We now know that element properties are periodic functions properties are periodic functions of their of their ATOMIC NUMBERS.ATOMIC NUMBERS.

PeriodsPeriods in the Periodic in the Periodic TableTable

Regions of the Periodic Regions of the Periodic TableTable

http://www.webelements.com/webelements/elements/text/Si/geol.html

Element AbundanceElement Abundance

FeC AlO Si

HydrogenHydrogenHydrogenHydrogen

Shuttle main engines use HShuttle main engines use H22 and O and O22

What was the cause of the What was the cause of the Hindenburg fire while landing in Hindenburg fire while landing in New Jersey in May 1939 ?New Jersey in May 1939 ?

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

Cutting sodium metalCutting sodium metal

Reaction of potassium + H2O

Solids at room temperature, react with water

What are the characteristic properties of a metal ?

MagnesiumMagnesium

Magnesium Magnesium oxideoxide

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

Occur naturally only in compounds,except for Be they also react with water. Mg and Ca are the most abundant

Calcium Carbonate—Calcium Carbonate—LimestoneLimestone

The Appian Way, ItalyThe Appian Way, Italy Champagne cave carved into Champagne cave carved into chalk in Francechalk in France

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

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

Aluminum, the mostAluminum, the mostabundant metal in theabundant metal in theearth’s crustearth’s crust

Boron halidesBoron halides BF BF33 & BI & BI33

Gems & MineralsGems & Minerals

• Sapphire:Sapphire: Al Al22OO33 with Fewith Fe3+3+ or Ti or Ti3+3+ impurity gives impurity gives blueblue whereas V whereas V3+3+ gives gives violetviolet..

• Ruby:Ruby: Al Al22OO33 with with CrCr3+3+ impurity impurity

What determines the colors of precious stones ?

Colors of Transition Metal Colors of Transition Metal CompoundsCompounds

Iron Cobalt Nickel Copper Zinc

Relative Densities of the ElementsRelative Densities of the Elements

Transition ElementsTransition ElementsTransition ElementsTransition Elements

Lanthanides and actinidesLanthanides and actinides

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

They are all metals, Ag, Au and Pt are the less reactiveStructural materials, paints, catalytic converters, batteries

They play important biological roles, e.g., Fe.

Glenn Glenn SeaborgSeaborg

(1912-1999 )(1912-1999 )• Discovered 8 Discovered 8

new elements.new elements.

• Only living Only living person for person for whom an whom an element was element was named.named.

What is a synchrotron ? What is a synchrotron ? How does it work?How does it work?

Group 4A: Group 4A: CC, , Si, GeSi, Ge, , Sn, Sn, PbPb

Group 4A: Group 4A: CC, , Si, GeSi, Ge, , Sn, Sn, PbPb

Quartz, SiOQuartz, SiO22

DiamondDiamond

GraphiteGraphite — layer — layer structure of structure of carbon atoms carbon atoms reflects reflects physical physical properties.properties.

DiamondDiamond

““Buckyballs”Buckyballs”

AllotropesAllotropes: distinct forms of : distinct forms of nonmetals, also called allomorphic nonmetals, also called allomorphic

formsforms

C60:buckminsterfullerene

Group 5A: N, P, Group 5A: N, P, As, SbAs, Sb, , BiBiGroup 5A: N, P, Group 5A: N, P, As, SbAs, Sb, , BiBi

White and red White and red phosphorusphosphorus

Ammonia, NHAmmonia, NH33

How does nature break atmospheric N2 and transform it into compounds such as chlorophyll, proteins and DNA ?

PhosphorPhosphorusus• Phosphorus is essential

to life, important constituent of bones and teeth, first isolated by Brandt from urine, 1669. Both white and red P ignite spontaneously in air to form P4O10, which then transforms into H3PO4

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

Group 6A: O, S, Se, Group 6A: O, S, Se, TeTe, , 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

What allotropes of oxygen do you know ?What is sulfuric acid most commonly used for ?

Group Group 7A:7A:halohalogensgens F, Cl, Br, I, AtF, Cl, Br, I, At

Group Group 7A:7A:halohalogensgens F, Cl, Br, I, AtF, Cl, Br, I, At

salt

Group 8A: Group 8A: He, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn

Group 8A: Group 8A: He, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn

• Lighter than air balloons

• “Neon” signs

XeOFXeOF44XeOFXeOF44

Gases at room temperature Until 1962 they were considered chemically unreactive

SummaryHistorical experiments that motivated the

development of the modern view of matter (Thompson, Rutherford, M. Curie).

Description of elementary particles (electrons, protons, neutrons).

Isotopes, Atomic number (Z), Mass number (A), Atomic Weight.

Molar mass, Avogadro’s number.Periodic Table, groups, periods, metals, metalloids, nonmetals, halogens, noble gases, transition elements.