Chapter 4: Atomic Structure

Early models of the atom:

Have you ever been asked to believe in

something you couldn’t see?

Love, faith, truth… Santa Claus?

Using your unaided eye, you cannot see

the tiny fundamental particles that make

up matter…

atoms.

Add to notes next to defining the atom:

Democritus’s Atomic Philosophy

400 BC

•Atoms are indivisible and

indestructible

•Did not explain chemical behavior

•Lacked experimental support,

because he didn’t use any type of

scientific method

Early philosophers and scientists could not observe

individual atoms, but they were still able to propose

ideas about the structure of atoms.

Dalton’s Atomic Theory (1766-1844) English Chemist and

Schoolteacher

1. All elements are composed

of tiny indivisible particles

called atoms.

2. Atoms of the same element

are identical. Atoms of any

element are different from

atoms of other elements.

3. Atoms of different

elements can chemically

combine in simple whole

number ratios to form

compounds.

4. Chemical reactions

occur when atoms are

separated, joined or

rearranged.

BUT, 1 atom can NOT

change into another.

The smallest particle of an element that

has all the properties of that element

Electron - Negative charge

Proton - Positive charge

Neutron - No charge (neutral)

Nucleus: protons & neutrons

Subatomic Particles: What makes up the atom

Rutherford’s Gold Foil Experiment DO NOT WRITE THIS IN NOTES:

Rutherford aimed his beam of alpha

particles at a sheet of gold foil surrounded

by fluorescent screen

73 through foil

12 deflected

9 bounced back

“ah hah”

LOTS of empty space In an atom!!!

Rutherford’s Gold Foil Experiment

Summarize on your note page.

Rutherford’s Gold Foil Experiment

Current Atomic theory:

•Atoms can be seen with high powered microscope

•Scanning, tunneling microscope

•Generate images of individual atoms

•“Nanoscale” technology = atomic scale

NanoTechnology:

Top: Manganese atom

Bottom:

aligning theoretical

Configuration with

the image

National Institute of Standards and Technology (NIST)

and the Naval Research Laboratory

http://www.sciencecodex.com/nist_researchers_put_a_new_spin_on_atomic_musical_chairs

Summary Time

Up and At ‘em... Atom Ant!

Mystery Box

Activity

Black Box Activity

Obscertainers

Ch 4.3

Distinguishing Among

Atoms

6 protons

=

atomic number of 6

Atomic Number: the number of protons

in the nucleus

Mass Number: The number of protons

and neutrons in the nucleus

6 protons and 6 neutrons

=

mass number of 12

Neutrons: The number of neutrons is the

difference between the mass number and

atomic number

12 items in nucleus

(mass number)

6 Protons (atomic

number)

# Neutrons = 12 – 6 = 6

Electrons: Equal to

the number of

protons

WHY?

ADD THIS ONE TO

YOUR NOTES…

Atoms are always

neutral, so + charges

have to equal - charges

# Protons = 6

SO

# Electrons = 6

Atomic number =

Mass # =

Protons =

Electrons =

Neutrons =

Practice!

Atomic number =

Mass # =

Protons =

Electrons =

Neutrons =

79

Au 197

2

He 4

197-79 = 118

2 4-2 =

79 79

79 197

2

2 4

2

Carbon – 13

Nitrogen – 15

Radium – 226

Practice! • How many neutrons?

16 O 8

32 S 16

108 Ag

47

At. Mass – At # =

16 – 8 = 8 At. Mass – At # =

At. Mass – At # =

At. Mass – At # =

At. Mass – At # =

At. Mass – At # =

226 – 88 = 138

108 – 47 = 61

15 – 7 = 8

32 – 16 = 16

13 – 6 = 7

Atom Electron

Proton Nucleus

# of electrons

= # of protons in neutral atom

Negative

charge Mass:

1200 e- to

equal 1

proton

Neutron

# Neutrons =

Mass Number –

Atomic number

No

Charge

# of Protons

= Atomic

Number

Positive

charge

Summary Time!

Isotopes

• Atoms that have the same

number of protons but

different number of

neutrons

• Because isotopes of an

element have different

number of neutrons

they have different

mass numbers

Isotopes of Carbon

Isotopes of Sodium:

23 Na 11

24 Na 11

Atomic Mass

AMU • Atomic Mass Unit

• 1 amu is defined as

1/12 of the mass of a

carbon-12 atom

Atomic Mass

• The weighted average of all possible masses of 1 kind of atom (isotopes)

• These must occur naturally

• Depends on how many isotopes and abundance of each type

• Chlorine-35 (75%) • Chlorine-37 (25%)

Calculating Atomic Mass

• The number of isotopes

• The mass of each

• The natural percent

abundance of each

What you need to know

Calculating Atomic Mass

Element X has 2 isotopes Isotope 10X mass = 10.012 amu

Relative abundance is 19.91% = 0.1991

Isotope 11X mass = 11.009 amu

Relative abundance is 80.09% = 0.8009

Example

Calculate

isotope mass x abundance 10X: 10.012 amu x 0.1991 = 1.993 amu 11X: 11.009 amu x 0.8009 = 8.817 amu

+

weighted Atomic mass = 10.810 amu

Practice!!

Summary Time!