2-1 CHEM 100, Fall 2014 LA TECH Instructor: Dr. Upali Siriwardane e-mail: upali@latech.edu Office:...

2-1CHEM 100, Fall 2014 LA TECH

Instructor: Dr. Upali Siriwardane

e-mail: upali@latech.edu

Office: CTH 311

Phone 257-4941

Office Hours: M,W, 8:00-9:30 & 11:30-12:30 a.m

Tu,Th,F 8:00 - 10:00 a.m.   Or by appointment

Test Dates:

Chemistry 100(02) Fall 2014

September 29, 2014 (Test 1): Chapter 1 & 2

October 20, 2014 (Test 2): Chapter 3 & 4

November 12, 2014 (Test 3) Chapter 5 & 6

November 13, 2014 (Make-up test) comprehensive: Chapters 1-6 9:30-10:45:15 AM, CTH 328

2-2CHEM 100, Fall 2014 LA TECH

REQUIRED :

Textbook:  Principles of Chemistry: A Molecular Approach, 2nd Edition-Nivaldo J. Tro - Pearson Prentice

Hall and also purchase the Mastering Chemistry

Group Homework, Slides and Exam review guides and sample exam questions are available online:

http://moodle.latech.edu/ and follow the course information links.

OPTIONAL :

Study Guide: Chemistry: A Molecular Approach, 2nd Edition-Nivaldo J. Tro 2nd Edition

Student Solutions Manual: Chemistry: A Molecular Approach, 2nd Edition-Nivaldo J. Tro 2nd

Text Book & Resources

2-3CHEM 100, Fall 2014 LA TECH

2.1 Imaging and Moving Individual Atoms…………….. 43

2.2 Early Ideas about the Building Blocks of Matter……. 45

2.3 Modern Atomic Theory and the Laws That Led to It… 45

2.4 The Discovery of the Electron……………………….. 49

2.5 The Structure of the Atom……………………………. 51

2.6 Subatomic Particles: Protons, Neutrons, and Electrons

in Atoms……………………………………………… 53

2.7 Finding Patterns: The Periodic Law and the

Periodic Table…………………………………………. 58

2.8 Atomic Mass: The Average Mass Of an Element’s Atoms. 64

2.9 Molar Mass: Counting Atoms by Weighing Them……… 66

Chapter 2. Atoms and Elements

2-4CHEM 100, Fall 2014 LA TECH

Chapter 2. KEY CONCEPTS

• Atom Imaging• Radioactivity • Subatomic Particles • Electrons • Electronic Charge • Nuclear atom Protons • Neutrons • Atomic number (Z) • Size of Atoms • Three chemical Laws• Dalton's atomic theory • Interpreting chemical formulas

and chemical reaction.

• Isotopes • Isotopic symbols • Atomic Mass Units • Mass Spectrometer • isotope masses and %

composition? • Average atomic weights • Periodic Table • Abundance of Elements • Earth's Atmosphere• Concept of mole• Gram to mole conversion

2-5CHEM 100, Fall 2014 LA TECH

1) What are following experimental techniques that are being used to image individual atoms?

a) STM (SPM) b) AFM (SPM) c) SEM (e-beam)

d) TEM (e-beam)

2-6CHEM 100, Fall 2014 LA TECH

Scanning Tunneling Microscope

2-7CHEM 100, Fall 2014 LA TECH

Microscopes

1) Optical Microscopes

2) SPB-Scanning Probe Microscopy

a)STM-Scanning Tunneling Microscope

b) Atomic Force Microscope

3) Electron beam Techniques

a) SEM-Scanning Electron Microscope

b) TEM-Transmission Electrum Microscope

Microscopy

2-8CHEM 100, Fall 2014 LA TECH

Alchemist: Discovery of Elements

Early scientist observed chemical changes of matter. They called these changes chemical reactions when there are changes in substances or the physical & chemical properties of the matter. They also observed a pattern or a repeatable observation during chemical reactions.

2-9CHEM 100, Fall 2014 LA TECH

Law of the Conservation of Matter

Lavoisier proposed from his experimental evidence the following law:

Matter is neither created nor destroyed in a chemical reaction.

• Total mass of used reactants = Total mass of products produced• Total number of reactant atoms = Total number of product atoms

2-10CHEM 100, Fall 2014 LA TECH

•Law of Conservation of Mass:

•Law of Constant Proportions:

•Law of Multiple Proportions:

Three Observed Chemical Laws:

2-11CHEM 100, Fall 2014 LA TECH

Early scientist observed changes of matter

 They called these changes chemical reactions when there are changes in substances or the chemical properties of matter. They also observed a pattern or a repeatable observation in chemical reactions. They observed that Mass was neither destroyed nor created (E.g. Hydrogen (4g) + oxygen (32g) gives water 36g

after the reaction),

and elements combine in Constant Proportions (E.g. 36g of water contains 4g of hydrogen and 32g of

oxygen) and in compounds in 1:8

Multiple Proportion (E.g. In CO, 1g C contains 1.33 g of O and In CO2 1g C

contains 2.66 g of O).

2-12CHEM 100, Fall 2014 LA TECH

Law of multiple proportions:

• Two elements A and X can form different compounds by combining in different proportions.

– These combinations can be represented as a ratio. • For example:

– A molecule of carbon dioxide (CO2) has a ratio of 1 C atom to every 2 atoms of oxygen, or 1:2.

– A molecule of hydrogen peroxide (CO) has a ratio of 1 C atom to 1 atom of oxygen, or 1:1.

Law of Multiple Proportions

2-13CHEM 100, Fall 2014 LA TECH

 2) What are the patterns of observations in conducting chemical reactions by early chemists?

a)

b)

c)

2-14CHEM 100, Fall 2014 LA TECH

 3) What theory John Dalton came up with to explain the body of chemical observations and laws?

2-15CHEM 100, Fall 2014 LA TECH

Dalton’s atomic theoryAll matter is composed of atoms -- the smallest

particle of an element that takes part in a chemical reaction.

All atoms of an element are alike.

Compounds are combinations of atoms of one or more elements. The relative number of atoms each element is always the same.

Atoms cannot be created or destroyed by a chemical reaction. They only change how they combine with each other.

2-16CHEM 100, Fall 2014 LA TECH

4) What are the postulates of Dalton’s atomic theory?

a)

b)

c)

d)

2-17CHEM 100, Fall 2014 LA TECH

5) How was Dalton’s atomic theory modified based on new experimental observations leading to the discovery of the electron, nucleus, protons and neutrons? Reword Dalton’s postulates to accommodate new observations and particles.

a)

b)

c)

d)

2-18CHEM 100, Fall 2014 LA TECH

Radioactivity

•Becquerel (1896)

–Uranium ore emits rays that “fog” a photographic plate.

•Marie and Pierre Curie (1898)

–Isolated 2 new elements (Po and Ra) that did the same.

–Marie Curie called the phenomenon radioactivity.

2-19CHEM 100, Fall 2014 LA TECH

6) What is radioactive decay?

2-20CHEM 100, Fall 2014 LA TECH

RadioactivityTypes of RadiationAlpha ray α (positive charge)

Beta ray β (negative charge)

Gamma ray γ (no charge)

Electrical behavior: + attracted to - (opposites attract)

(like charges repel)

Radioactive material

Electrically

Charged plates

screen

+

−

Beam of α, β, and γ

αγ

β

2-21CHEM 100, Fall 2014 LA TECH

7) What are following radiation?

a) a

 b) b

 c) g

2-22CHEM 100, Fall 2014 LA TECH

8) Which of the following radiation, , ,a b and g is most harmful?

2-23CHEM 100, Fall 2014 LA TECH

ElectronsThomson (1897) studied cathode rays and

discovered the electron:

•Beam travels from the cathode (-) to the anode (+).

–the beam flies through a ring anode and hits a fluorescent screen.

•The cathode rays come from the cathode metal.

•They are negative particles – electrons (e

−).

fluorescent

screen

– high voltage + cathode ray

2-24CHEM 100, Fall 2014 LA TECH

ElectronsThomson showed that electric and magnetic

fields deflect the beam.

–– high voltage +

+

From the deflections, Thomson calculated the mass/charge ratio for an

e-:

= −5.60 x 10-9

g/C

(Coulomb (C) = the SI unit of charge)

2-25CHEM 100, Fall 2014 LA TECH

The Discovery of the Electron, Nucleus

Subatomic Particles: Protons, Neutrons, and Electrons in Atoms

9) How did Thompson know that every element has electrons?

10) How did Thompson know that an electron has a negative charge?

2-26CHEM 100, Fall 2014 LA TECH

11) In the Millikan’s oil drop experiment, how did he remove electrons from atoms?

12) In the Millikan’s oil drop experiment, where did some of the electrons removed from atoms ended up?

 13) In the Millikan’s oil drop experiment, why was some oil drops had multiples (1,2,3 of −1.60 x 10-19 ) of charges?

2-27CHEM 100, Fall 2014 LA TECH

14) Thomson calculated the mass/charge (m/e) ratio for an e- to be = −5.60 x 10-9 g/C. and then Millikan found the charge on an e- to be −1.60 x 10-19 C. What is the mass on an electron?

2-28CHEM 100, Fall 2014 LA TECH

15) In the Rutherford’s experiment, what caused a few α’s were deflected through large angles and some came almost straight back!

2-29CHEM 100, Fall 2014 LA TECH

Electronic ChargeRobert Millikan (1911) studied electrically-

charged oil drops.

• For a single charged drop, he measured:

– the time to fall a fixed distance, and

– to rise the same distance in an electric field.

•He showed that each drop had a charge that was an integer multiple

of −1.60 x 10-19

C.

(The charge of an electron. )

•The modern value is −1.602176462 x 10

-19 C.

(Often written in “atomic units” as charge = −1).

2-30CHEM 100, Fall 2014 LA TECH

Millikan’s Experiment

2-31CHEM 100, Fall 2014 LA TECH

Mass of an Electron

The experiments by Thomson and Millikan gave the mass/charge ratio and charge of an e−.

The modern value is:

me = 9.10938188 x 10-28

g

= (−1.60 x 10-19

C)/(−5.60 x 10-9

g/C)

= 8.96 x 10-28

g

me = charge xmass

charge

2-32CHEM 100, Fall 2014 LA TECH

• J. J. Thomson (plum-pudding model)

- The atom is composed of a positive cloud of matter in which electrons are embedded.

• Explains the positive (+), negative (-) charged behavior of matter

Atomic Structure: Plum-Pudding Model

2-33CHEM 100, Fall 2014 LA TECH

Nuclear Atom

•Thompson thought it was a ball of uniform

positive charge, with small negative dots (e-)

stuck in it. However “plum pudding” model was

short lived and was changed to Nuclear model.

2-34CHEM 100, Fall 2014 LA TECH

Gold foil experiment:

Could not explain Thomson’s plum-pudding atom model.

Led to the discovery of the atom’s nucleus.

Rutherford’s Gold Foil

Experiment Setup

2-35CHEM 100, Fall 2014 LA TECH

From the gold foil experiment, the following conclusions were proposed:• The atom contains a tiny, dense center called the nucleus.• The nucleus has essentially the entire mass of the atom.

– The electrons weigh so little they give practically no mass to the atom.• The nucleus is positively charged.

– The amount of positive charge balances the negative charge of the electrons.

– The electrons are dispersed in the empty space of the atom surrounding the nucleus.

Rutherford & the Nucleus: Gold Foil Experiment

2-36CHEM 100, Fall 2014 LA TECH

•Rutherford estimated that the charge of the nucleus of an atom was

about one half of the atomic mass.

•Moseley, while working for Rutherford, developed a more accurate

measurement.

•While working with cathode rays on metal targets, he measured the

wavelength of the X-rays produced.

•He found that a direct relationship exists between the metal’s

atomic number and the square root of the frequency.

Determination of nuclear charge

2-37CHEM 100, Fall 2014 LA TECH

Moseley, Henry & Gwyn Jeffreys

1887–1915, English physicist.

•studied the relations among x-ray spectra of different elements.

•concluded that the atomic number is equal to the charge on the nucleus based

on the x-ray spectra emitted by the element.

•explained discrepancies in Mendeleev’s Periodic Law.

Discovery of Protons and Atomic Number

2-38CHEM 100, Fall 2014 LA TECH

Moseley concluded that

the charge of the nucleus

was an integer.

Further, it was the same

as the number of electrical

units (electrons) but of

opposite charge.

Moseley concluded that

the charge of the nucleus

was an integer.

Further, it was the same

as the number of electrical

units (electrons) but of

opposite charge.

Ato

mic

nu

mb

er

X-Ray Frequency1/2

Determination of nuclear charge

2-39CHEM 100, Fall 2014 LA TECH

Summary of Subatomic Particles

Particle Charge Mass (g) Mass (amu)Proton

Neutron

Electron

+1.6 x 10-19 C

zero

-1. 6 x 10-19 C

1.7 x 10-24 g

1.7 x 10-24 g

9.1 x 10-28 g

1.0073

1.0087

5. 5x 10-4

Remember: Atoms are usually electrically neutral, Indicating equal numbers

of protons and electrons!

2-40CHEM 100, Fall 2014 LA TECH

Atomic number, Z

• The number of protons in the nucleus• The number of electrons in a neutral

atom• The integer on the periodic table for each

element

2-41CHEM 100, Fall 2014 LA TECH

Relative size of atom and atomic nucleus

2-42CHEM 100, Fall 2014 LA TECH

Ions

Charged single atomCharged cluster of atoms•Cations: positive ions

•Anions: negative ionsIonic compounds: combination of cations and

anions with zero net charge

2-43CHEM 100, Fall 2014 LA TECH

Nuclear NotationX = atomic symbol

A = mass number

Z = atomic number

C-12, carbon-12

XA

C12

ZXA

6C12

2-44CHEM 100, Fall 2014 LA TECH

Mass Number, Ainteger representing the approximate mass of an

atom

equal to the sum of the number of protons and neutrons in the nucleus