atomic structure what does the atom look like??? chapter 3 part i
TRANSCRIPT
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.
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. 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”
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.)
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 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.
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.
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
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
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 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 Sodium
Protons
Neutrons
Electrons
Sodium has eleven electrons, eleven protons and twelve neutrons.