chapter2-part 1(3).ppt

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Atoms, Molecules and Ions

Chapter 2

Part 1

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Chapter outline Introduction

Laws pertaining to chemical reactions DALTON ATOMIC THEORY The structure of the atom Nuclide symbol and Isotopes. The periodic Table Molecules &Ions Chemical formula

Naming Simple Compounds

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Part 1Outline

Introduction Laws pertaining to chemical reactions

DALTON ATOMIC THEORY The structure of the atom Nuclear structure; Isotopes.

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The Early History of Chemistry500 BCE-1000 CE: Ancient Greek tried to understand the nature

of properties of matter. They made use of some properties ofmater that were useful in their every day life:

Extracted metals from oresEmbalming (preserving) fluids

Then, they tried to come with theories to explain the behavior ofmatter:

First theory: mater is composed of four elements: Fire, water,earth and air. This theory explaned some behavior of matter

Second theory: Nature of matter. There was a dispute.Aristotle view: Matter is continuous. Can be divided to infinitenumberDemocritus view: Matter is composed of small indivisible

particles. He called them atomos. (No experiments weredone to solve this dispute till 16 th century)


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The Early History of Chemistry-continued

1000 CE-1600 CE Alchemy : Attempts (scientific or otherwise) tochange cheap metals into gold and discover the exereof life. (Eternal life )

17th CenturyRobert Boyle : First chemist to perform quantitativeexperiments

18th CenturyGeorge Stahl : Phlogiston flows out of a burning material.

Joseph Priestley : Discovers oxygen gas,

dephlogisticated air. 6


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7

Law of Conservation of Mass

Discovered by Antoine Lavoisier

Mass is neither created nor destroyedCombustion involves oxygen, not

phlogiston


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8 X 2 Y16 X 8 Y+

Law of Conservation of Mass


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Other Fundamental Chemical Laws

A given compound always contains exactly

the same proportion of elements by mass.Carbon tetrachloride is always 1 atomcarbon per 4 atoms chlorine.

Copper carbonate is always 5.3 partscopper, 4 parts oxygen, and 1 part carbon

by mass.

1- Law of Definite ProportionDiscovered by Proust


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2- Law of Multiple ProportionsDiscovered by Dalton

If two elements cancombine to form morethan one compound,the masses of one

element that combinewith fixed mass of theother element are inratios of small whole

numbers.CO: 1 g C: 1.33 g OCO2: 1 g C: 2.66 g OThe ratio of O in the second compound to that in

the first compound per 1 g C is 2:1


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Atomic Theory of Matter

1- Elements are composed of small particles called atomsproved to be wrong by radioactivity

2- All atoms of a given element are identical,having the same size, mass and chemical

properties. The atoms of one element aredifferent from atoms of all other elements.

proved to be wrong by the discovery of isotopes

In order to explain the three scientific laws,Dalton came up with first scientific theory. It ismade of different hypothesis called postulates.

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Postulates of Daltons Atomic Theory


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3- Compounds are composed of atoms of more thanone element. In any compound, the ration of thenumber of atoms of any two of the elementspresent is either an integer or a simple fraction.

Atomic Theory of Matter

4- A chemical reaction involves only the separation,combination, or rearrangement of atoms; it does not

result in their creation or destruction.Nuclear reactions results in changing the identity ofatoms

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2.2 The structure of the atom

Thomson Millikan Radioactivity Rutherford

Chadwick

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Early Experiments toCharacterize the Atom

J. J. Thomson - postulated the existence ofelectrons using cathode ray tubes.(-ve

charge, mass= 9.11x 10 -31Kg)Proton was postulated to exist based on theemission of particles from anodes (+ve

charge, mass = 1.67x 10-27

Kg, Goldstein) Neutrons: neutral, same mass as proton(Chadwick)


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J.J. Thomson, measured charge/mass of e -

(1906 Nobel Prize in Physics) 15-1.76 x 10 8 C/g


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Cathode Ray Tube

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e - charge = -1.60 x 10 -19 C

Thomsons charge/mass of e - = -1.76 x 10 8 C/g

e- mass = 9.10 x 10

-28

g

Measured mass of e -

(1923 Nobel Prize in Physics)

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Radioactivity

Some elements emit spontaneously highenergy radiation. (Madam Curie).

Three types of radiations:a- Gamma rays (High energy light)

b- Beta particles (High energy electron)c- Alpha particles (Particles with +2 charge

and m = 7300 x m e)


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1. atoms positive charge is concentrated in the nucleus2. proton (p) has opposite (+) charge of electron (-)3. mass of p is 1840 x mass of e - (1.67 x 10 -24 g)

particle velocity ~ 1.4 x 10 7 m/s

(~5% speed of light)

(1908 Nobel Prize in Chemistry)

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atomic radius ~ 100 pm = 1 x 10 -10 m

nuclear radius ~ 5 x 10 -3 pm = 5 x 10 -15 m

Rutherfords Model ofthe Atom

If the atom is the Houston Astrodome, then

the nucleus is a marble on the 50- yard line. 22


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Chadwicks Experiment (1932) (1935 Noble Prize in Physics)

H atoms - 1 p; He atoms - 2 p

mass He/mass H should = 2

measured mass He/mass H = 4

+ 9Be 1n + 12 C + energyneutron (n) is neutral (charge = 0)

n mass ~ p mass = 1.67 x 10 -24 g24


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Conclusion

Electrons

Protons: found in the nucleus, they have a positive charge equal in magnitude to theelectrons negative charge.

Neutrons: found in the nucleus, virtuallysame mass as a proton but no charge.

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mass p = mass n = 1840 x mass e - 26


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A t o m i c n u m b er (Z) = number of protons in nucleus

Mass n um ber (A) = number of protons + number of neutrons= atomic number (Z) + number of neutrons

Isotopes are atoms of the same element (X) with differentnumbers of neutrons in their nuclei

Nuclide symbol:

X AZ

H11 H (D)21 H (T)

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U235

92 U238

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Mass Number

Atomic NumberElement Symbol

Atomic number, Mass number and Isotopes

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The Isotopes of Hydrogen

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Example: Write the nuclide symbol for theatom that has 19 protons and 20 neutrons.

K3919

Atomic number: Z = 19

The element is potassium, K.Mass number: A = 19 + 20 = 39

The nuclide symbol is


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6 protons, 8 (14 - 6) neutrons, 6 electrons

6 protons, 5 (11 - 6) neutrons, 6 electrons

Do You Understand Isotopes?

How many protons, neutrons, and electrons are in C14

6 ?

How many protons, neutrons, and electrons are in C11

6 ?

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2.1

Give the number of protons, neutrons, and electrons in each ofthe following species:

(a)

(b)

(c)

(d) carbon-14


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The Modern Periodic Table

Period

Gr o

u p

A l k

al i M

e t al

N o b

l e G a s

H al o

g en

A l k

al i E

ar t h M

e t al

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