Chapter2 notes B and L.ppt

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UNIT 1

Chapter 2: Atoms, Molecules, and Ions

Democritus Laughing Hendrick ter Brugghen, 1628;

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Chemistry Timeline #1

B.C.

400 B.C. Demokritos and Leucippos use the term "atomos”

1500's

_{Georg Bauer: systematic metallurgy}

 Paracelsus: medicinal application of minerals

1600's

Robert Boyle:The Skeptical Chemist. Quantitative experimentation, identification of elements

1700s'

Georg Stahl: Phlogiston Theory

Joseph Priestly: Discovery of oxygen

_{Antoine Lavoisier: The role of oxygen in combustion, law of}

conservation of mass, first modern chemistry textbook

(4)

Chemistry Timeline #2

1800's

_{Joseph Proust: The law of definite proportion (composition)}

 John Dalton: The Atomic Theory, The law of multiple proportions Joseph Gay-Lussac: Combining volumes of gases, existence of diatomic

molecules

Amadeo Avogadro: Molar volumes of gases

_{Jons Jakob Berzelius: Relative atomic masses, modern symbols for the}

elements

 Dmitri Mendeleyev: The periodic table _{J.J. Thomson: discovery of the electron}  Henri Becquerel: Discovery of radioactivity

1900's

_{Robert Millikan: Charge and mass of the electron}

 Ernest Rutherford: Existence of the nucleus, and its relative size  Meitner & Fermi: Sustained nuclear fission

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Dalton

’

s Atomic Theory (1808)

 Atoms cannot be subdivided, created, or destroyed  Atoms of different elements combine in simple

whole-number ratios to form chemical compounds

 In chemical reactions, atoms are combined,

separated, or rearranged

 All matter is composed of extremely

small particles called atoms

 Atoms of a given element are

identical in size, mass, and other properties; atoms of different

elements differ in size, mass, and other properties

(6)

Modern Atomic Theory:

Dalton said:

Modern theory states:

Atoms cannot be subdivided, created, or destroyed

Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these

changes CAN occur in nuclear reactions!

Atoms of a given element are identical in size, mass, and other properties; atoms of different

elements differ in size, mass, and other properties

Dalton said:

Atoms of an element have a characteristic average mass which is unique to that element.

Modern theory states:

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Discovery of the Electron

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Discovery of the Electron

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ELECTRONS!!**

This discovery would alter Dalton

’

s model

of the atom because now we know there

is something inside it – negatively

charged electrons

But, the overall charge of the atom is

neutral, so

what else

must be in it?

(11)

Thomson

’

s Atomic Model

Thomson believed that the electrons were like plums

embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

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Mass and Charge of the Electron

1909 – Robert Millikan determines the mass of the electron using

Thomson’s work

(charge-to-mass ratio).

The oil drop apparatus

Mass is 9.109 x 10 -31 kg

Charge is

1.5924×10−19 C

*within 1% of the currently accepted value of

(14)

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Rutherford

’

s Gold Foil Experiment

 Alpha particles are helium nuclei

 Used polonium to produce alpha particles.

 Particles were fired at a thin sheet of gold foil  Used gold foil because atoms could be made thin.  Particle hits on the detecting screen (film) are

(16)

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Rutherford

’

s Findings

 The nucleus is small  The nucleus is dense

 The nucleus is positively charged  Most of the particles passed right through

 A few particles were deflected  VERY FEW were greatly deflected

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For Discussion Later:

Bohr Model:

Wave (Schrodinger) Model

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Summary of Atomic Particles

Particle Symbol

Mass

(amu)

Location Charge

Proton

p

1

Nucleus

+

Neutron

n

1

Nucleus

No

Charge

Electron

e

-

0

Cloud

(23)

-Atomic Notation

6

C

Carbon

12.011

Atomic #

Symbol

Element

Name

(24)

Isotopes

Isotopes are atoms of the same element having

different masses (due to varying numbers of neutrons).

Isotope Protons Electrons Neutrons Nucleus

Hydrogen–1 (protium)

1 1 0

Hydrogen-2 (deuterium)

1 1 1

Hydrogen-3 (tritium)

(25)

Atomic Masses

Isotope Symbol Composition of

the nucleus % in nature

Carbon-12 12C 6 protons

6 neutrons

98.89%

7 neutrons

1.11%

8 neutrons

<0.01%

(26)

Calculate Average Atomic Mass

As you know, chlorine contains two naturally

occurring isotopes. From the following data,

calculate chlorine’s average atomic mass.

75.4% chlorine – 35

24.6% chlorine – 37

*Formula:

(27)

Atomic Mass

Atomic and

molecular masses

can be measured

with great accuracy

using a mass

spectrometer.

*Watch video online

for a quick

explanation!

(28)

Mass Spectrum Example

• Intensity of the peaks

gives us relative %

abundance.

• Which Cl isotope is

more abundant?

• Cl-35 b/c larger

intensity

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Which of the following elements has the

mass spectrum shown below?

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The mass spectrum of an average sample of a

pure element is shown below. Which of the

following is the identity of the element?

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Atomic number (Z) - The number of p+ in an atom. All atoms of the same element have the same number of p+.

Mass number (A) -The sum of the number of neutrons and p+ for an atom. A different mass number does not

mean a different element--just an isotope.

X

A Z

Mass Number

Atomic Number Element Symbol

(32)

Atomic Number

Atomic number (Z) of an element is the

number of protons in the nucleus of each atom of that element.

Element # of protons Atomic # (Z)

Carbon 6 6

Phosphorus 15 15

(33)

Mass Number

Mass number is the number of protons and neutrons in the nucleus of an isotope.

Mass # = p+_{+ n}0

Nuclide

p

+

n

0

e

-

Mass #

Oxygen - 10

- 33 42

- 31 15

8 8 18

18

Arsenic 75 33 75

(34)

Other Symbols

Find the…



Atomic number



Mass number



Charge



# of protons



# of neutrons



# of electrons

(35)

Other Symbols

Find the…



Atomic number

= 8



Mass number

= 15



Charge

= 0



# of protons

= 8



# of neutrons

= 7



# of electrons

= 8

(36)

How about this one…

Ca

+2

41 20

Find the…



Atomic number



Mass number



Charge



# of protons

(37)

The answers…

Ca

+2

41 20

= 20

= 41

= +2

= 20

= 21

= 18

Find the…



Atomic number



Mass number



Charge



# of protons

(38)

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“Special” Groups

•

Group 1: Alkali metals

•

Group 2: Alkaline earth metals

•

Group 3-12: Transitional elements

•

Group 17: Halogens

•

Group 18: Noble gases

•

Elements 58-71: Lanthanides

(40)

Chemical Bonds

The forces that hold atoms together.

•

Covalent bonding

- sharing electrons.

Makes molecules.

•

Ionic Bonding

– Electrostatic attraction

between opposite charges.

Makes compounds.

•

Metallic Bond

– Sea of free moving

electrons.

(41)

Molecules

Two or more atoms of the same or different

elements, covalently bonded together.

Molecules are discrete structures, and their

formulas represent each atom present in the

molecule.

Benzene, C

₆

H

₆

(42)

Compounds: Made up of ions

 Cation: A positive ion

• Mg2+, NH 4+

 Anion: A negative ion

 _Cl, SO

42

 Ionic Bonding: Force of attraction between

oppositely charged ions.

 Ionic compounds form crystals, so their formulas

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Predicting Ionic Charges

Group 1

:

Lose 1 electron to form

1+

ions

H

++

Li

++

Na

++

K

++

(44)

Predicting Ionic Charges

Group 2

:

Loses 2 electrons to form

2+

ions

Be

2+2+

Mg

2+2+

Ca

2+2+

Sr

2+₂₊

Ba

2+2+

(45)

Group 13

:

Loses 3

electrons to form

3+

ions

B

(46)

Group 15

:

Gains 3

electrons to form

3-

ions

N

3-

3-P

P

3-

3-As

As

3-

(47)

Group 16

:

Gains 2

electrons to form

2-2-

ions

O

2-

2-S

S

2-

2-Se

Se

2-

(48)

Group 17

:

Gains 1

electron to form

1-1-

ions

F

1-

1-Cl

Cl

1-

1-Br

Br

1-

1-Fluoride

Chloride

Bromide

I

1-1- Iodide

(49)

Predicting Ionic Charges

Group 18

:

Stable

Noble gases

do not

form ions!

(50)

Groups 3 - 12

:

Many

transition

elements

have more than one possible oxidation state.

Iron(II) = Fe2+ Iron(III) = Fe3+

(51)

Predicting Ionic Charges

Groups 3 - 12

:

Some

transition

elements

have only one possible oxidation state.

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Naming Ionic Compounds

•

1. Cation first, then anion

•

2. Monatomic cation = name of the element

•

Ca

2+

= calcium

ion

•

3. Monatomic anion =

root

+

-ide

•

Cl



=

chlor

ide

(53)

(continued)



some

metal forms more than one

cation



use

Roman numeral

in name

PbCl

₂

Pb

2+

is the lead(

II

) cation

PbCl

₂

= lead(

II

) chloride

Metals with multiple oxidation states

(54)

Don’t follow the trend:

Zn

2+

, Cd

2+

and Ag

+

Zn and Cd: always 2+ charge,

Ag: always 1+ charge,

*so usually no has Roman numeral

Pb

2+

Sn

2+

Pb

4+

Sn

4+

(55)

Polyatomic Ions

• Groups of atoms covalently

bonded that have a charge.

• See List provided, you

(56)

Writing Ionic Compound Formulas

Example: Barium nitrate

1. Write the formulas for the cation and anion, including CHARGES!

Ba

2+

NO

3

-

-2. Check to see if charges are

balanced.

3. Criss-cross to balance charges using

subscripts. Use parentheses if you

need more than one of a polyatomic ion.

Few more examples: Calcium phosphide lead (IV) sulfide Magnesium phosphate

Not balanced!

( )

(57)

Writing Ionic Compound Formulas

Ammonium sulfate Iron (III) chloride Aluminum sulfide

Magnesium carbonate Zinc hydroxide

Aluminum phosphate

(NH₄)₂SO₄ FeCl₃

(58)

Naming Binary Molecular (Covalent)

Compounds

Naming Binary Molecular (Covalent)

Compounds

 Compounds between two nonmetals

 First element in the formula is named first.

 Second element is named with an ending of -ide.  Use prefixes (mono, di, tri, tetra, etc…)

 Only use mono on second element

P

P₂₂OO₅₅ = = CO

CO₂₂ = = CO =

CO =

N

N₂₂O =O = di

diphosphorus phosphorus pentpentoxideoxide carbon

carbon didioxideoxide carbon

carbon monmonoxideoxide di

(59)

Elements that exist as molecules

HONCl BrIF

Pure hydrogen, nitrogen, oxygen and the halogens [the

“gens” collectively—easier to remember!] exist as DIATOMIC molecules under normal conditions.

MEMORIZE!!!

Be sure you compute their molar masses as diatomics. Others to be aware of, but not memorize:

P₄ - tetratomic form of elemental phosphorous S₈ - sulfur = s elemental form

(60)

HW Word Problem:

2. Aqueous solutions of lead II nitrate and

potassium carbonate are mixed. Aqueous

potassium nitrate and solid lead II carbonate

form.

Rijksmuseum

Discovery of the Electron

Mass and Charge of the Electron

https://www.youtube.com/watch?v=mBT73Pesiog