Chemistry SM-1131Week 4 Lesson 2

Dr. Jesse ReichAssistant Professor of Chemistry

Massachusetts Maritime AcademyFall 2008

Class Today• Test in 1 Week• Atomic Theory• Protons, Neutrons, and Electrons• Elements by the protons• Periodic Table• Gaining and losing electrons• Isotopes• Atomic Mass

Democritus The material cause of all things that exist is the coming

together of atoms and void. Atoms are too small to be perceived by the senses. They are eternal and have many different shapes, and they can cluster together to create things that are perceivable. Differences in shape, arrangement, and position of atoms produce different things. By aggregation they provide bulky objects that we can perceive with our sight and other senses.

We see changes in things because of the rearrangement of atoms, but atoms themselves are eternal. Words such as ‘nothing’, ‘the void’, and ‘the infinite’ describe space. Individual atoms are describable as ‘not nothing’, ‘being’, and ‘the compact’. There is no void in atoms, so they cannot be divided. I hold the same view as Leucippus regarding atoms and space: atoms are always in motion in space.

(www.humanistictexts.org)

~460, Greece-371 BCE

His Buddy Aristotle• Aristotle emphasized that nature consisted of

four elements: air, earth, fire, and water.

The Greek GodsEmpedocles associates the Elements with four Gods: Hera (Earth), Persephone (Water), Zeus (Air) and Hades (Fire),

Fast Forward to DaltonSept. 6, 1766, England-July 27, 1844

 Dalton's Atomic Theory

1) All matter is made of atoms. Atoms are indivisible and indestructible.2) All atoms of a given element are identical in mass and properties3) Compounds are formed by a combination of two or more different kinds of atoms.4) A chemical reaction is a rearrangement of atoms.

Dalton’s Creek, err, element set

So what changed?

abyss.uoregon.edu

Crooks TubeCurrent moved from the cathode to the anode through a vacuum

It moved in lines similar to light

But magnets could deflect the current

The new path could be used to calculate a mass to charge ratio but couldn’t calculate mass or charge

J. J. ThompsonDec. 18, 1856, England - Aug. 30, 1940

Wilhelm Conrad Röntgen

March 27, 1845, Germany - Feb. 10, 1923 “On the evening of November 8, 1895, he found that, if the discharge tube is enclosed in a sealed, thick black carton to exclude all light, and if he worked in a dark room, a paper plate covered on one side with barium platinocyanide placed in the path of the rays became fluorescent even when it was as far as two metres from the discharge tube. During subsequent experiments he found that objects of different thicknesses interposed in the path of the rays showed variable transparency to them when recorded on a photographic plate. When he immobilised for some moments the hand of his wife in the path of the rays over a photographic plate, he observed after development of the plate an image of his wife's hand which showed the shadows thrown by the bones of her hand and that of a ring she was wearing, surrounded by the penumbra of the flesh, which was more permeable to the rays and therefore threw a fainter shadow. This was the first "röntgenogram" ever taken. In further experiments, Röntgen showed that the new rays are produced by the impact of cathode rays on a material object. Because their nature was then unknown, he gave them the name X-rays. Later, Max von Laue and his pupils showed that they are of the same electromagnetic nature as light, but differ from it only in the higher frequency of their vibration.” (nobelprize.org)

Henri BecquerelDec. 15, 1952, France – Aug. 25, 1908

Following a discussion with Henri Poincaré on the radiation which had recently been discovered by Röntgen (X-rays) and which was accompanied by a type of phosphorescence in the vacuum tube, Becquerel decided to investigate whether there was any connection between X-rays and naturally occurring phosphorescence. He had inherited from his father a supply of uranium salts, which phosphoresce on exposure to light. When the salts were placed near to a photographic plate covered with opaque paper, the plate was discovered to be fogged. The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom. Later, Becquerel showed that the rays emitted by uranium, which for a long time were named after their discoverer, caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields. For his discovery of spontaneous radioactivity Becquerel was awarded half of the Nobel Prize for Physics in 1903, the other half being given to Pierre and Marie Curie for their study of the Becquerel radiation. (nobelprize.org)

A Nobel Next to Socks

Pause for Dramatic EffectWhat We Know Up to Now!

• There are different elements• Elements are made up of atoms• Atoms have positive and negative components• Some elements are radioactive

Anyone for a CurieNovember 7, 1867, France – July 4, 1934

She helped to discover Polonium and Radium. To do this she and her husband took Pitchblend, which contained the radioactive element Uranium by the ton and carefully isolated the radioactive components over several years. What they found was that there were more than one radioactive element in it because they found an element that was far more radioactive than the element uranium.

She got a Nobel in Physics for radioactivity.She got a Nobel in chemistry for discovering two new elements.

Raw Materials

Pitchblende Radium

There is 1 gram of radium in 7 tons of pitchblende

“It therefore appeared probable that if pitchblende, chalcolite, and autunite possess so great a degree of activity, these substances contain a small quantity of a strongly radioactive body, differing from uranium and thorium and the simple bodies actually known. I thought that if this were indeed the case, I might hope to extract this substance from the ore by the ordinary methods of chemical analysis.” [Curie 1961 (1903), p. 16].

In her own wordsIf we assume that radium contains a supply of energy which it gives out little by little, we are led to believe that this body does not remain unchanged, as it appears to, but that it undergoes an extremely slow change. Several reasons speak in favor of this view. First, the emission of heat, which makes it seem probable that a chemical reaction is taking place in the radium. But this is no ordinary chemical reaction, affecting the combination of atoms in the molecule. No chemical reaction can explain the emission of heat due to radium. Furthermore, radioactivity is a property of the atom of radium; if, then, it is due to a transformation, this transformation must take place in the atom itself. Consequently, from this point of view, the atom of radium would be in a process of evolution, and we should be forced to abandon the theory of the invariability of atoms, which is the foundation of modern chemistry [M. Curie 1904].

Ernest RutherfordAug. 30, 1871 New Zealand – Oct. 19, 1937

In Simpler terms…

So what just happened?It was almost as incredible as if you fired a 15-inch

shell at a piece of tissue paper, and it came back to hit you

"On consideration, I realized that this scattering backwards must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive center carrying a charge."

WTH?

So what’s an atom look like?

The Planetary Model

Robert A. MillikanMarch 22, 1868, U.S.A. – Dec. 19 1953

• Established the charge of an electron and

• Determined the atomic structure of electricity

So What’d He Do?

Well, what’s that thingy?

www.physchem.co.za

So, what’d it look like inside?

www.nikhef.nl

So, what changed?

A Nagging Concern

Rutherford’s Model

Positive Protons and Oppositely Charged ElectronsWhat should happen?Collapse!

Skipping Ahead• I’m skipping a lot of scientists and a lot of

story• We have a nucleus and it contains Protons and

Neutrons• Electrons are on the outside in set patterns

Nucleus Masses• Protons have masses of 1.67262e-27kg• Neutrons have masses of 1.67493e-27kg• OK, talking about that mass is obnoxious. So

chemists came up with another scheme. They took an atom of Carbon, which has 6 neutrons and 6 protons, and they said 1/12 of that mass is now 1 amu.

• Protons by themselves have a mass of 1.0073 amu. Neutrons have a mass of 1.0087 amu.

Electrons• Protons are over 1800 times larger than

electrons. So, chemists say electrons have no mass.

• This is not exactly true, it’s more like they have negligible mass.

Charge• Protons have a charge of +1• Electrons have a charge of -1• Neutrons have no charge at all.• Oppositely charged particles attract.• Similarly charged particles repel.• If an atom has an equal number of protons

and electrons the atom has no charge. For every extra proton it has +1 charge. For every extra electron it has -1 charge.

Periodic TableHydrogen is the element1 is the atomic number1.0079 is the atomic mass

Elements• The number of protons is called the atomic

number.• If two elements have the same atomic number

they are the same element. If two elements have different atomic numbers they are different.

The TableGroups/families are up and downRows/periods are left to right

The Table

Group 1. Alkali MetalsGroup 2. Alkaline Earth MetalsGroup 3-12 Transition MetalsGroup 17. HalogensGroup 18. Noble Gases

H, C, N, O, P, S, Se are organic elements57-71 lanthanides89-103 actinidesB, Si, Ge, As, Sb, Te, Po are metaloids

Metals• Shiny• Reflect• Malleable (bendable)• Ductile (can be drawn into strips)• Conduct electricity• LOSE ELECTRONS

Non-Metals• Dull• Brittle• Don’t conduct• GAIN ELECTRONS(think graphite)

Metalloids• Mixed Properties• Semiconductors• Some dull, some shiny• Etc.

Get Ready• Monday – 1/3 review, 1/3 New Material, 1/3

test review• TEST WEDNESDAY!!!