Atoms, Ions and Molecules - PowerPoint Presentation

Slide1

Atoms, Ions and MoleculesThe Building Blocks of Matter

Chapter 2Slide2
Slide3

Chapter Outline

2.1 The

Rutherford Model of Atomic Structure

2.2

Nuclides and Their Symbols

2.3

Navigating the Periodic Table

2.4 The

Masses of Atoms, Ions, and Molecules

2.5

Moles and Molar Mass

2.6

Making Elements

2.7

Artificial NuclidesSlide4

Experiments in Atomic Structure

J. J. Thompson (1906 Nobel Prize in Physics)

- cathode ray tube experiments; discovery of the electron; measurement of the charge-to-mass ratio.

Robert Millikan (1923 Nobel Prize in Physics)

- oil-drop experiments; measured the mass of the

electron, therefore calculate the charge

Ernest Rutherford (1908 Nobel Prize in Physics)

- gold-foil

experiments; the nuclear atomJames Chadwick (1935 Nobel Prize in Physics) - discovery of the neutronSlide5

J.J.

Thomson Cathode Ray Tube Experiments

- Electrons Slide6

Results of “Cathode Ray” Experiments

Travel in straight lines

invisible

independent of cathode composition

bend in a magnetic field like a negatively-charged particle would

charge/mass = -1.76 x 10

8

C/gSlide7

Thompson’s “Plum Pudding” Model of the Atom

electrons distributed throughout a diffuse, positively charged sphere.Slide8

Robert

Millikan’s oil drop Experiment - measured the mass of the electron

Slide9

Millikan’s Results

The air molecules in the chamber were ionized by a beam of X-rays, producing electrons and positively-charged fragments

Fine mist of oil introduced into chamber; electrons adhere to the droplets

Negatively-charged droplets settle to bottom of chamber under influence of gravity

Charged repeller plates adjusted until droplets were suspended in mid-air

From the physics and knowledge of the size of the gravitational and electrostatic forces, the charge on each droplet could be calculated

Discovered that each droplet was a whole-number multiple of 1.60 X 10

-19

C, so the mass = 9.11 X 10-28

gSlide10

Radioactivity and the Nuclear Atom

Spontaneous emission of particles and/or radiation from a decaying, unstable nucleus

-particles =

-particles =

-rays =Slide11
Slide12

Ernest Rutherford - the nuclear atom

Slide13

Rutherford's Observations

the majority of particles penetrated

undeflected

some particles were deflected at small angles

occasionally

-particles scattered back at large angles

b) Expected results from

“

plum pudding

”

model.

c) Actual results

.Slide14

Rutherford’s Conclusions

The atom is mainly empty space because most of the

-particles passed through undeflected

The nucleus is very dense and positively charged because some of the

-particles were repulsed and deflected

Electrons occupy the space around the nucleus

The atom is electrically neutralSlide15

atomic radius ~ 100 pm = 1 x 10

-10

mnuclear radius ~ 5 x 10

-3

pm = 5 x 10

-15

m

Rutherford’s Model of

the Atom

If the nucleus was the size of an orange, then the radius of the atom would be 2.5 milesSlide16

mass p

 mass n = 1840 x mass e

-Slide17

Chapter Outline

2.1 The

Rutherford Model of Atomic Structure2.2

Nuclides and Their Symbols

2.3

Navigating the Periodic Table

2.4 The

Masses of Atoms, Ions, and Molecules2.5 Moles and Molar Mass2.6

Making Elements2.7 Artificial NuclidesSlide18

Atomic Mass Units

Atomic Mass Units (

amu

)

Comprise a relative scale to express the masses of atoms and subatomic particles.

Scale is based on the mass of 1 atom

of carbon:

6 protons + 6 neutrons = 12

amu

.

1

amu

= 1 Dalton (Da)Slide19

Isotopes: Experimental EvidenceSlide20

Atomic number

(Z)

= number of protons in nucleusMass

number

(A

)

=

number of protons + number of neutrons

= atomic number (Z) + number of neutronsIsotopes (nuclides) are atoms of the same element with different numbers of neutrons in the nucleus

X

A

Z

Mass Number

Atomic Number

Element Symbol

U

235

92

U

238

92

H

1

1

H (D)

2

1

H (T)

3

1Slide21

Use the format A

X to write the symbol for the nuclides having 28

protons and 31 neutrons.

Practice: Isotopic Symbols

Collect and Organize:

Analyze

:

Solve

:

Think

about It:Slide22

Complete the missing information in the table.

Practice: Identifying Atoms and Ions

Collect and Organize:

Analyze

:

Solve

:

Think

about It:Slide23

Chapter Outline

2.1 The

Rutherford Model of Atomic Structure2.2

Nuclides and Their Symbols

2.3

Navigating the Periodic Table

2.4 The

Masses of Atoms, Ions, and Molecules

2.5 Moles and Molar Mass2.6 Making Elements

2.7 Artificial NuclidesSlide24

Mendeleev’s Periodic Table

Dmitrii

Mendeleev (1872):Ordered elements

by atomic mass.

Arranged elements in columns based on similar chemical and physical properties.

Left open spaces in the table for elements not yet discovered.

The Periodic Table of the ElementsSlide25

The Modern Periodic Table

Also based on a classification of elements in terms of their physical and chemical properties.

Horizontal rows: called periods (1 → 7).

Columns: contain elements of the same family or

group

(1

→

18).

Several groups have names as well as numbers.Slide26

Navigating the Modern Periodic Table – Groups and FamiliesSlide27
Slide28

Groups of Elements (cont.)Slide29

These 7 elements occur naturally as diatomics (memorize) -

H

2

N

2

F

2

O

2

I

2

Cl2

Br

2Slide30

Metals

found to the left of the “diagonal line”lose electrons in chemical reactions

solids (except for Hg, Cs, and Fr)conduct electricityductile (draw into a wire)malleable (roll into sheets)form alloys ("solid-solution" of one metal in another)Slide31

Nonmetals

found to the right of the “diagonal line”like to gain electrons from metals, or share electrons among themselves

found as solids, liquids (Br), and gases (Inert gases, and H, N, O, F, Cl)“diatomics

” - H

2

, N

2

, F

2, O2 ,I2, Cl2, Br2oxygen also exist as ozone, O3insulators (except for graphite or C)

Helium-Neon lasersSlide32

Metalloids

elements next to the “diagonal line”B, Si, Ge, As, Sb, and Tephysical properties of a metal (can be “convinced” to conduct electricity) and chemical properties of a nonmetal

Elemental Si is used in the semiconductor industrySlide33

Chapter Outline

2.1 The

Rutherford Model of Atomic Structure2.2

Nuclides and Their Symbols

2.3

Navigating the Periodic Table

2.4 The

Masses of Atoms, Ions, and Molecules2.5 Moles and Molar Mass2.6

Making Elements2.7 Artificial NuclidesSlide34

AM

= (mass 1)(abn) + (mass 2)(abn

) + (mass 3)(abn) +………

Average Atomic Mass

Weighted average mass

of natural sample of an element, calculated by multiplying the natural abundance of each isotope by its exact mass in

amu’s

and then summing up these products.Slide35

Molecular Mass – the sum of the average atomic masses of the atoms in it.

NOTE

: the terms mass and weight are used interchangeably, e.g. molecular weight (MW) or atomic weight (AW

)

Molecular Mass

e.g. H

2

SO

4Slide36

Formula Units

– for ionic compounds, the smallest electrically neutral unit in an ionic compound

Formula Mass – the sum of the average atomic masses of the cations

and anions that make up a neutral formula unit

Formula

Units and

Formula Mass

e.g. NaClSlide37

Chapter Outline

2.1 The

Rutherford Model of Atomic Structure2.2

Nuclides and Their Symbols

2.3

Navigating the Periodic Table

2.4 The

Masses of Atoms, Ions, and Molecules

2.5 Moles and Molar Mass2.6 Making Elements

2.7 Artificial NuclidesSlide38

The Mole -

The mole is the

Chemist’s

counting unit

Avogadro’s Number (N

A

) = 6.022 X 10

23

= 1 mole of atoms, molecules, ions, etc.

pair = 2

dozen = 12

gross = 144

ream = 500Slide39

One Mole of:

C

S

Cu

Fe

HgSlide40

Experiment

–

how many atoms must be added together so that the mass in grams = mass in

amu’s

?

Analogy using coins:

Mass ratio = 1 : 5 : 25Slide41

Significance of the Mole

N

A

of carbon atoms weighs __________

N

A

of iron atoms weighs __________

Mass in amu’s

Mass in grams/mole

Equivalent toSlide42

To convert between number of particles and an equivalent number of moles.

Moles, Mass, and ParticlesSlide43

Sample Exercise 2.5

The silicon used to make computer chips has to be extremely pure.

Fpr example, it must contain less than 3 x 10-10

moles of phosphorus (a common impurity in Si) per mole of silicon. What is this level of impurity expressed in atoms of phosphorus per mole of Si?Slide44

e.g. carbon

e.g. H

2

SO

4

sulfuric acid

Using the Molar Mass as a Conversion Factor for Atoms & Molecules

 Slide45

Moles, Mass, and Particles

grams of atoms or molecules

moles of atoms or molecules

Numbers of atoms or moleculesSlide46

How

many moles of K atoms are present in

19.5 g of potassium?

How many atoms of K are there?

Practice: Mole Calculations #1Slide47

How

many moles are present in 58.4 g of

chalk (CaCO3)?

Practice: Mole Calculations #2Slide48

The uranium used in nuclear fuel exists in nature in several minerals. Calculate how many moles of uranium are found in 100.0 grams of

carnotite, K

2(UO2

)

2

(VO

4

)

2•3H2O.Practice: Mole Calculations #3Slide49

Practice: Mole Calculations #4

Convert 2.45 x 10

18

molecules of

KCl

to grams