8/12/2019 Introduction to Atomic Structure

1/31

Learning Objectives

Explain the structure of theatom and Bohrs model

Explain the chemistry behind EDX and SEM

Explain the chemistry behind NAA

1

3

Differentiate between emission

and absorption spectroscopy

2

4

8/12/2019 Introduction to Atomic Structure

2/31

What Is It Made Of?

What are the chemical elements present?

Spectroscopy & the structure of atoms

How can we do elemental analysis?

When and why do we want tocarry out elemental analysis?

8/12/2019 Introduction to Atomic Structure

3/31

8/12/2019 Introduction to Atomic Structure

4/31

Examples

Poisoning1

Suspected arsenic, leador chromium poisoning

Analyze body fluids

8/12/2019 Introduction to Atomic Structure

5/31

8/12/2019 Introduction to Atomic Structure

6/31

Poisoning

Determining the time of death

1

2

Elemental analysis of bullets3

Forensic information about firearms u

Examples

8/12/2019 Introduction to Atomic Structure

7/31

Cases

River Thames, London, September 2001

8/12/2019 Introduction to Atomic Structure

8/31

Cases

How many peoplefired at JFK?

John F Ke

8/12/2019 Introduction to Atomic Structure

9/31

Cases

Death of Napoleon

Nap

8/12/2019 Introduction to Atomic Structure

10/31

What is an Element?

Ancient Greeks

4 elements

Concept discarded

8/12/2019 Introduction to Atomic Structure

11/31

What is an Element?

Robert Boyle (16271691)

Elements can neither be

created nor destroyed

Robert

8/12/2019 Introduction to Atomic Structure

12/31

8/12/2019 Introduction to Atomic Structure

13/31

What is an Element?

Common naturally occurring elements

H

O

C

Fe

Ag

Zn

Sn

8/12/2019 Introduction to Atomic Structure

14/31

What is an Element?

Less common naturally occurring elements

U

Ir

Sm

Gd

Kr

Sb

8/12/2019 Introduction to Atomic Structure

15/31

Paper

C, H, O

Burning a piece of paper

C CO2

H H2O

Made of cellulose

8/12/2019 Introduction to Atomic Structure

16/31

Human Body

CO2

H2

O

C, H, O, N, P, S, Ca, Na, K, Fe

N oxides

P oxides

C

H

N

P

8/12/2019 Introduction to Atomic Structure

17/31

Human Body

Au

Au or Hg in teeth

Hg oxides

Au

Hg

8/12/2019 Introduction to Atomic Structure

18/31

The Periodic Table

8/12/2019 Introduction to Atomic Structure

19/31

The Periodic Table

Dmitri Mendeleev

Dmitri Mend

Chemist

Organized the elementsaccording to chemistry

8/12/2019 Introduction to Atomic Structure

20/31

The Periodic Table

Tom Lehrer

Tom L

Mathematician and musician

Organized elements musically

http://www.youtube.com/

watch?v=AcS3NOQnsQM

http://www.youtube.com/watch?v=AcS3NOQnsQMhttp://www.youtube.com/watch?v=AcS3NOQnsQMhttp://www.youtube.com/watch?v=AcS3NOQnsQMhttp://www.youtube.com/watch?v=AcS3NOQnsQM

8/12/2019 Introduction to Atomic Structure

21/31

Bulk composition

What is most of it made of?

What Is It Made Of?

Bu

Lead in bullets

8/12/2019 Introduction to Atomic Structure

22/31

Trace impurities

What is a very smallpart of it made of?

What Is It Made Of?

Bu

Silver and antimony in bullets

8/12/2019 Introduction to Atomic Structure

23/31

Analysis of elements

What Is It Made Of?

Bulk composition1

Trace impurities2 More informative forensic scientists

8/12/2019 Introduction to Atomic Structure

24/31

Chemical Tests

Disadvantages

Large amounts of samples required

Destructive

Subject to interference

8/12/2019 Introduction to Atomic Structure

25/31

Chemical Tests

Advantages

Fast

Easy to do

Simple equipment

8/12/2019 Introduction to Atomic Structure

26/31

Trace Impurities

How small is small?

S. I. prefixes for units

8/12/2019 Introduction to Atomic Structure

27/31

S. I. Prefixes

1 Megagram 1 Mg 1 000 000 g 1 ton1 Kilogram 1 Kg 1 000 g

1 milligram 1 mg 0.001 g 1 / 10

1 microgram 1 g 0.000 001 g 1 / 10

1 nanogram 1 ng 0.000 000 001 g 1 / b1 picogram 1 pg 0.000 000 000 001 g 1/ tril

100 000 000 000 atoms1 picogram

8/12/2019 Introduction to Atomic Structure

28/31

8/12/2019 Introduction to Atomic Structure

29/31

Trace Impurities

5M people in Singapore

1 ppm = 5 people

Singapor

8/12/2019 Introduction to Atomic Structure

30/31

Trace Impurities

Trace elements often measured in ppm

Sometimes measured in ppb

Part per billion 1 per 1 000 000 00

8/12/2019 Introduction to Atomic Structure

31/31

Trace Impurities

7B people in the world

7 000 000 000

World ma

1 ppb = 7 people