Atomic Structure

What does the atom look like???

Chapter 3 Part I

3-1 Early Models of the Atom

• Democritus: c. 400 BC matter is composed of tiny indivisible particles called atoms.

• An atom is the smallest part of an element that retains the chemical properties of that element.

Antoine Laurent Lavoisier: A.D. 1780

•Law of Conservation of Matter states that matter is neither created nor destroyed.

•Lavoisier is known as the Father of Chemistry.

• In 1771, at age 28, Lavoisier married the 13-year-old Marie-Anne Pierrette Paulze.

• Over time, she proved to be a scientific colleague to her husband.

• She translated documents and chemistry books from English.

• She created many sketches and carved engravings of the laboratory instruments he used.

• She also edited and published Lavoisier’s memoirs after his death.

• She hosted parties at which eminent scientists discussed ideas and problems related to chemistry.

Engravings of Lavoisier’s Equipment by his wife

Lavoisier was Guillotined May 8, 1794

• An appeal to spare his life so that he could continue his experiments was cut short by a judge saying: "The Republic needs neither scientists nor chemists; the course of justice cannot be delayed.”

• One and a half years following his death, Lavoisier was exonerated by the French government.

• When his private belongings were delivered to his widow, a brief note was included reading "To the widow of Lavoisier, who was falsely convicted."

Joseph Louis Proust: A.D. 1799

•Law of Constant Composition states that compounds always have the same elements in the same

proportion by mass. Ex) the ratio of H:O in water is always 2:16.

John Dalton A.D.1766-1844

• Some of the original chemical symbols from his book:

John Dalton: A.D. 1803

• Four Part Atomic Theory:1. All elements are made of atoms.2. All atoms in an element are identical.3. Atoms are neither created nor destroyed in chemical reactions.

4. Compounds have definite proportions

of elements.His model of the atom was like “Billiard Balls”

Benjamin Franklin: 1706-1790

Ben’s lightning rod in the Franklin Institute

In 1752 Benjamin Franklin

• Was the first person to suggest the structure of the atom was related to electricity.

• He found that there were two types of charge and that:

negative and negative: repelnegative and positive: attractpositive and positive: repel

Cathode Rays and Electrons

• Cathode Ray Tube: An evacuated glass tube where a beam of electrons flows from the

cathode (negative electrode) to the anode (positive electrode.)

Effect of a magnet on a cathode ray

Cathode Ray Tube

J.J. Thomson: 1897• English Physicist

who said a cathode ray is made of electrons, they

have mass (9.1 x 10-28g)

and are negatively charged particles. Thus he

is credited with “discovering” electrons.

Henri Becquerel: 1896

• Becquerel “discovered” radioactivity using pitchblende, a uranium ore (a rock that has a metal in it.)

A rock, a drawer and a tired chemist

on a Friday afternoon…

Radioactivity

• Radioactivity is the spontaneous emission of matter & energy from a sample. It exposed the film in Becquerel’s drawer and left an image.

Marie & Pierre Curie: 1903• Shared the Nobel

Prize in Chemistry with Becquerel.

• They discovered 2 new radioactive elements, Radium and Polonium.

• Marie called Radium the “Radiant” element and Polonium she named for her native Poland.

• How do you think Marie & Pierre died???

1867-1934

1859-1906

What happened to The Curies?

• Pierre was run over by a horse-drawn wagon in Paris and killed in 1906. Marie was left alone with two daughters, aged 2 and 9.

• In 1911 she went on to win a second Nobel Prize in chemistry.

• In 1934, Marie died of leukemia brought on by radiation exposure one year before her daughter and son-in-law won the Nobel Prize for Chemistry.

Ernest Rutherford: 1903

• Rutherford studies under Thomson.

• He found that there was 3 types of natural radiation or radioactive decay.

α - Alpha Particlesβ - Beta Particles

γ - Gamma Rays

high energy X-rays

Rutherford’s 1st Experiment 1903

What can we tell about α, β, & γ?

Rutherford’s Conclusions:

• α is drawn slightly toward the negative plate so it must be large & positive.

• β is drawn a lot toward the positive plate so it must be small & negative.

• γ is not deflected at all so it is neutral –and has no mass.

View of the atoms in the Gold Foil Experiment

• Rutherford's Gold Foil Experiment

Rutherford’s Gold Foil Experiment 1909

• This experiment showed the atom has a small, central positive nucleus and that most of the atom is empty space.

Positive Protons are compacted in the Nucleus

J.J. Thomson: 1897• Thought the atom looked like

“plum pudding” with negative charges distributed throughout:

Rutherford: 1909• After his Gold Foil Experiment,

Rutherford modifies his model of the atom to contain a small dense positive nucleus (protons) with electrons outside.

Neils Bohr: 1913• Thought the atom was like the solar system (planetary model).• It was eventually

shown to be inaccurate and too simplistic. • He wins the Nobel Prize for this model in 1922.• What happened to his medal?

Wave (electron cloud) Model:1924 to Present

• Using Quantum Mechanics, the electron can be found in a probability region.

Evolution of the Atomic Model

Progression of the Atomic Model

James Chadwick: 1932

• Studied under Rutherford. • He determined that the atom

also contained a neutron which had approximately the same mass as a proton, but had a neutral charge (it was actually a proton and an electron together – so its mass was slightly larger than a proton.)

• Chadwick won the Nobel Prize for his work in 1935.

• This discovery made it possible to develop the Nuclear Bomb.

Therefore: • There are 3 subatomic particles: protons, neutrons

and electrons. These are measured in “atomic mass units” (amu) as their mass is so small.

SubatomicParticle

Mass (amu) Location Charge

Proton ( p+ ) 1 (1.673 x 10-27 kg) In the nucleus +

Neutron ( n0 ) 1 (1.675 x 10-27 kg) In the nucleus 0

Electron ( e- ) 0 (9.1x 10-31 kg) Outside the nucleus -

John Moseley: 1914• Worked under Rutherford.• He determined that each

atom has a different number of protons (Atomic Number). Each atom is electrically neutral and therefore has an equal number of electrons.

• Killed by a sniper at Gallipoli in WWI…what else might he have done?

Atomic Number and Mass Number

• Atomic Number = the number of protonsIn a neutral atom, the number of protonsequal the number of electrons. Ex) carbon =

6

• Mass Number equal to the total number of protons + neutrons in the nucleus of an atom.Ex) carbon-12 has 6 protons and 6 neutrons

Ions

• Formed when an atom gains or loses an electrona. Charge = # of protons - # of electrons

Ex) Mg +2 = lost 2 electrons # of protons: 12 # of electrons: 10

Charge: +2

Ex) N-3 = gained 3 electrons # of protons: 7 # of electrons: 10

Charge: -3

IsotopesAtoms that have the same number of protons but a different number of neutrons (mass.)

Isotopic NotationShorthand way of representing an isotope of

an element.

Ex) top number is the mass number (#p + #n)

bottom number is the atomic number (#p)

May also be written: chlorine-37 or Cl-37

The actual average atomic mass for all chlorine isotopes is 35.45 amu

3717 Cl

Isotopes of Hydrogen

a. hydrogen (hydrogen – 1) 1p+ 0n0 b. deuterium (hydrogen – 2) 1p+ 1n0 c. tritium (hydrogen – 3) 1p+ 2n0

11H21H31H

Two Isotopes of Sodium

Isotopes of Carbon

Isotope ProtonsNeutro

nsMass

NumberElectro

ns

Isotopic Notatio

n

Carbon-12 6 6 12 6

Carbon-13 6 7 13 6

Carbon-14 6 8 14 6

126C

146C

136C

Atomic Mass of Li = 6.94 amu

• How are the 2 isotopes of Li the same?same # of protons

• How are the 2 isotopes of Li different?

Li-6 has 1 fewer neutron

Atomic Mass:• The mass of an atom expressed in amu (atomic mass units.)

• One amu is equal to 1/12 the mass of a carbon-12 atom.

Average Atomic Mass:• The weighted average of all an element’s isotopes.

• This is the number shown in the box on the Periodic Table.

• It is calculated by: (mass1 x %1) + (mass2 x %2) + …

Weighted Average Grade Example:

Straight Class

93% Tests90% HW70%

Participation

84.3% Average

Weighted Class

x 70% = 65.1

x 20% = 18x 10% = 7

Weighted Average:

90.1%

Ex) carbon

C-12C-13C-14 ? Straight

Average 13???Actual

AverageAtomic Mass

= 12.011 amu

Ex) hydrogen

H-1H-2H-3 ? Straight Average 2???Actual

AverageAtomic Mass

= 1.0079 amu

Isotopes of Hydrogen

The Atom Hydrogen

Proton Electron

Hydrogen has one proton, one electron and NO neutrons

The Atom Helium

ElectronProton

Neutron

Helium has two electrons, two protons and two neutrons

The Atom Lithium

Protons

Neutrons

Electrons

Lithium has three electrons, three protons and four neutrons

The Atom Beryllium

Protons

Neutrons

Electrons

Beryllium has four electrons, four protons and five neutrons.

The Atom Boron

Protons

Neutrons

Electrons

Boron has five electrons, five protons and six neutrons.

The Atom Carbon

Protons

Neutrons

Electrons

Carbon has six electrons, six protons and six neutrons.

The Atom Nitrogen

Protons

Neutrons

Electrons

Nitrogen has seven electrons, seven protons and seven neutrons.

The Atom Oxygen

Protons

Neutrons

Electrons

Oxygen has eight electrons, eight protons and eight neutrons.

The Atom Fluorine

Protons

Neutrons

Electrons

Fluorine has nine electrons, nine protons and ten neutrons.

The Atom Neon

Protons

Neutrons

Electrons

Neon has ten electrons, ten protons and ten neutrons.

The Atom Sodium

Protons

Neutrons

Electrons

Sodium has eleven electrons, eleven protons and twelve neutrons.