chapter 2: atoms, molecules, and ions the atomic theory of matter john dalton (1766-1844): elements...

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

The Atomic Theory of Matter

John Dalton (1766-1844): • Elements are made of tiny particles called atoms

• atoms of different elementscan combine to form compounds

• atoms are not created nor destroyed in chemical processes

• all atoms of one element are identical

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

The Discovery of Atomic Structure

J.J. Thomson (1856-1940): • discovered the electron

• electron: negatively chargedparticles of very small mass

• atoms of all elements containelectrons

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

R. Millikan (1868-1953):

• measured electron charge (oil-drop experiment)

electron charge = 1.60×10−19 C

The Discovery of Atomic Structure

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Ernest Rutherford (1871-1937):

(a) the atom has a positive charge concentrated in the nucleus

(b) the electrons orbit around the positive nucleus

(c) that the atom is mostly emptyspace

The Discovery of Atomic Structure

Gold-foil experiment:

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

+

Rutherford's Model:

The Discovery of Atomic Structure

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

The nucleus is structured:

PROTONS: positively charged (+1)

NEUTRONS: no charge

The Modern View of Atomic Structure

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

The mass of an atom is concentrated in its nucleus:

•proton: 1 atomic mass unit (1amu) +1

•neutron: 1 amu 0

•electron: negligible mass -1 (5.486 x 10-4 amu) (1.6 x 10-19C)

MASS Charge

The Modern View of Atomic Structure

1 amu = 1.66054 x 10-24 g

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Elements differ in their number of protons:

Hydrogen:1 proton

H1

the atomic number counts the number of protons

1

the mass number counts protons and neutrons

Helium:2 protons

2 neutrons

He24

Lithium:3 protons

4 neutrons

Li37

Beryllium:4 protons

5 neutrons

Be49

The Modern View of Atomic Structure

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

The Modern View of Atomic Structure

How about the neutrons?

• an element is defined by the number of protons

• atoms of one element can exist in different 'versions' :

all atoms must still have the same number of protons

but they may have a different number of neutrons

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

The Modern View of Atomic Structure

H1

1H3

1H2

1

Hydrogen or Protium

Deuterium Tritium

Isotopes of an element:

same number of protons but different number of neutrons

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Periodic Table

Elements are sorted according to atomic number

C6

12.01

Atomic Number

Atomic weight

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Periodic Table

Elements with similar properties fall in vertical groups

A row in the periodic table is called a period

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Average Atomic Mass = Atomic Weight

Average Mass = fraction of heavy x mass of heavy + fraction of light x mass of light

= 3/4 x 70amu + 1/4 x 30amu

= 0.75 x 70amu + 0.25 x 30amu = 60amu

30amu

70amu

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Average Atomic Mass = Atomic Weight

7Li

For example: Lithium AW = 6.939 amu

6Li Exact mass: 6.015 amu

Exact mass: 7.016 amu

Do the two isotopes exist in equal amounts ?

No, because the simple average of the isotope masses is:

(6.015 + 7.016) / 2 =

0.5 x 6.015 + 0.5 x 7.016 = 6.516

which is not the correct atomic weight

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Average Atomic Mass = Atomic Weight

7Li

For example: Lithium AW = 6.939 amu

6Li Exact mass: 6.015 amu

Exact mass: 7.016 amu

Which isotope is more abundant?

It must be 7Li because the average massIs closer to the mass of the 7Li isotope

The average is weighted in favor of the more abundant isotope

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Average Atomic Mass = Atomic Weight

7Li

For example: Lithium AW = 6.939 amu

6Li Exact mass: 6.015 amu

Exact mass: 7.016 amu

What are the fractions of the individual isotopes ?

X 6.015 + Y 7.016 = 6.939 X + Y = 1

X 6.015 + (1-X) 7.016 = 6.939

6.015 X + 7.016 – 7.016 X = 6.939

- 1.001 X = - 0.077

X = -0.077/ -1.001 = 0.0769

7.69% 6Li

92.31 % 7Li

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

number of electrons = number of protons = atomic number

Hydrogen:1 proton

H11

Helium:2 protons

2 neutrons

He24

Lithium:3 protons

4 neutrons

Li37

Beryllium:4 protons

5 neutrons

Be49

1 electron 2 electrons 3 electrons 4 electrons

How can you tell how many electrons an element has?

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

number of electrons number of protons number of neutrons

80Br-

40Ca2+

32S 16 32 – 16 = 1616

35 + 1 = 36

20 - 2 = 18

35

20

80 – 35 = 45

40 – 20 = 20

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Periodic Table

Most elements are metals

Alkali Metals

Alkaline Earth Metals

Noble Gases

Halogens

I A II A

III A IV A VA VI A VIIA

VIII A

Transition metals

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Molecules and Molecular Compounds

Some elements exist as diatomic molecules at room temp.

H2 N

2 O

2 F

2 Cl

2Br

2 I

2

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Molecules and Molecular Compounds

The periodic table helps predict how elements combine

Empirical Formulas Molecular Formulas

Only gives relative number of atoms in compound

Subscripts are smallestwhole-number ratios

Show actual number and types of atoms in a molecule

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Hydrogen peroxide

Empirical Formulas Molecular Formulas

H2O

2HO

Butane

C4H

10C2H

5

Propane

C3H

8C3H

8

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Drawing Molecules: methane

Space-filling model

Ball-and-Stick model

Structural formula

Perspectivedrawing

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Ions and Ionic Compounds

Ions are formed when a neutral atom

- gains electrons or- loses electrons

Li Li+

e-

Cation

BrBr

-Anion

e-

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

How can you tell how many electrons an element will gain/lose?

NOBLE GASES

Atoms tend to gain/lose the number of electrons neededto achieve the electron configuration of the closest noble gas

X1

Nb

X1 would lose 2 e- to get to the Nb configuration: X12+

X2

X2 would gain 3 e- to get to the N

b configuration: X23-

X3

Na

Nc

Nd

Ne

Nf

X3 would gain 1 e- to get to the N

e configuration: X3-

X4 would lose 1 e- to get to the N

c configuration: X4+

X4

Metals tend to form Cations Nonmetals tend to form Anions

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Li Li+

e-

Cation

BrBr

-Anion

Cations and Anions can combine to from Ionic Compounds

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Cations and Anions can combine to from Ionic Compounds

Ionic Crystal – not a discrete molecule

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Empirical Formulas for Ionic Compounds:

(A) determine charge of ions formed

(B) add ions so that compound is neutral overall

Na, O =>

Na+

2+ 2-

0

Na2O

Al, O =>

O2-Al3+

O2-

6+ 6-

0

Al2O

3

Na+ Al3+O2- O2-

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Li+

Br-

LiBr

Mg2+

Cl-

MgCl2

Li, Br =>

1+ 1-

0

Mg, Cl =>

2+ 2-

0

Cl-

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Empirical Formulas for Ionic Compounds:

Mg2+ MgCl

2

Al O3+ 2-Al

2O

3

O 2-

Ca2+ Ca

2O

2

CaO

smallest possible ratio!

Cl-1

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds: cations come first

(Ia) Monoatomic Cations:

Metal cations keep the name of the element:

Na+ Sodium ion Li+ Lithium ion Zn2+ Zinc ion

If a metal can form different kinds of cations (transition metals),the charge is indicated by a Roman Numeral:

Fe2+ Iron(II) ionFe3+ Iron(III) ionCo2+ Cobalt(II) ion

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds

(Ib) Cations formed from Nonmetals:

end in -ium:

NH4+ Ammonium ion H

3O+ Hydronium ion

+ +

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds

(IIa) Monoatomic and Simple Polyatomic Anions

Are derived from the element name by replacing the ending with -ide

N3- Nitride ion

O2- Oxide ion CN-

OH- Hydroxide ion

Cyanide ion

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds

(IIb) Oxyanions (polyatomic anions containing oxygen)

The most common oxyanion of an element ends in -ate One more oxygen: per-.....-ate One fewer oxygen: -ite Two fewer oxygen: hypo-.....-ite

Chlorate ClO3-

Perchlorate ClO4-

Chlorite ClO2-

Hypochlorite ClO-

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds

(IIb) Oxyanions (polyatomic anions containing oxygen)

The most common oxyanion of an element ends in -ate One more oxygen: per-.....-ate One fewer oxygen: -ite Two fewer oxygen: hypo-.....-ite

Sulfate SO42-

Sulfite SO32-

Hyposulfite SO22-

[ Persulfate SO52-, S

2O

82-

]

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds

Common Oxyanions:

SulfateSO

42-

Phosphate PO

43-

ChlorateClO

3-

BromateBrO

3-

IodateIO

3-

Nitrate NO

3-

Carbonate CO

32-

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds

You must know these!

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds

You must know these!

HCO3¯ Hydrogen carbonate ion

or Bicarbonate ion

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds: chemical formula → name

Identify the ions

Cation Anion

Transition metal ?Element name

Element name and charge in

Roman numerals

Group 1A, 2A, 3A metal?

Nonmetal ion?

-ide

monoatomic orsimple polyatomic

anion? oxyanion?

per ... ate... ate... ite

hypo ... iteMemorizee.g. Ammonium

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds: chemical formula → name

MgSO4

Mg2+

SO4

2-

→ simple cation: magnesium

→ oxyanion: sulfateMagnesium sulfate

FeCl3

Fe3+

3 Cl-

→ transition metal cation: Iron(III)

→ monoatomic anion: chlorideIron(III) chloride

NaClONa+

ClO-

→ simple cation: Sodium

→ oxyanion: hypochloriteSodium hypochlorite

NH4OH

NH4

+

OH-

→ cation: Ammonium

→ anion: hydroxideAmmonium hydroxide

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds: name → chemical formula

Identify the ions

CationAnion

Transition metal ?

Group 1A, 2A, 3A metal?

Charge is given in Roman numerals

Polyatomiccation?

Determine charge fromPeriodic Table

(Slide #25)Memorize...

Ammonium: NH4+

Determine charge

Polyatomicanion?

Memorize...Hydroxide: OH-

Cyanide: CN-

Oxyanions!

Determine charge

Monoatomic,nonmetal?

Determine charge fromPeriodic Table

(Slide #25)

combine cations & anions so that overall compound is neutral!

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Ionic Compounds: name → chemical formula

Iron(II) chlorideFe2+

Cl- FeCl2

Remember to balance charge!

Potassium cyanideK+

CN-KCN

Magnesium hydroxideMg2+

OH- Mg(OH)2

More than onepolyatomic anion

(or cation)=> in parantheses!

Sodium sulfiteNa+

SO3

2-Na

2SO

3

x 2

x 2

x 2

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

What ions does ClO2 dissociate into?

(A) Cl- and 2 O2-

(B) Cl- and O22-

(C) Cl+ and O2-

(D) doesn’t form ions

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Molecular Compounds

ClO2

does not dissociate into ions!

Metal cations + Nonmetal anions => ionic compoundsNonmetal cations + Nonmetal anions => ionic compounds(e.g. NH

4+)

Nonmetal + Nonmetal => molecular compounds

Before you start naming, determine what kind of compound you have!

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Binary Molecular Compounds

ClO2

Name of the element farther to the left in the P.T. comes first- except oxygen, which is usually named last

If both elements are from the same group, the heavier one is named first

The second element is given an -ide ending

Greek prefixes indicate number of atoms of each element involved

Chlorine dioxide

[mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona- , deca-]

[mono-prefix is never used with 1st element]

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Compounds

NiO 1) Ionic or molecular?

2 a) Ionic: what are the ions? b) molecular: how many atoms?

=> ionic

=> Ni2+ and O2-

=> Nickel(II) oxide

SO => molecular

=> Sulfur monoxide

KMnO4 => ionic

=> K+ and MnO4-

=> Potassium permanganate

BF3 => molecular

=> Boron trifluoride

Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions

Naming Compounds

Ca(BrO3)2

BrO3-

Calcium bromate Ionic or molecular compound?

Empirical formula?

Ions:

SO3

Sulfur trioxide

Ionic or molecular compound?

Name?

Charge on oxygen?

You can only assign “real” charges to ions in ionic compounds

You cannot determine the empirical formula of a molecularcompound simply by consulting the periodic table

SO3SO SO2

Ca2+

N/A