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Atoms and Elements CHAPTER 2

Early day scientists - Greeks were the first to try and explain chemical changes. Believed that all matter consisted of four basic things. (fire, air, water and earth)

Democritus Greek, 460-370 B.C. Created the word atomus (atom) Believed everything was composed of atoms Proposed that the world is made up of empty space and atoms. He believed everything was composed of this and the atom was indivisible.

Alchemy - A pseudo science, purpose of the science was to attempt to make gold. Such elements as Hg, S, and Sb were discovered due to this science.

John Dalton (1766-1844) - English - first to prepare a table of relative atomic weights and the Law of multiple proportions. Dalton’s early day symbols

Law of multiple Proportions - when two elements form a series of compounds , the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. Ex: NO and NO2

Law of Multiple Proportions 2 Law of Multiple Proportions 9 2.1

Dalton's Atomic Theory - 1. Each element is made up of tiny particles called atoms. 2. The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways. 3. Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative numbers and types of atoms. 4. Chemical reactions involve reorganization of the atoms -- changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.

J.J. Thomson English, (1856 - 1953) In 1897 discovered the particle the electron. Discovered it by using a cathode ray.

What charge does an electron have? Negative

Cathode Ray Tube A stream of electrons is produced at the negative pole of an applied electric field. The electron was isolated using this device.

J.J. Thomson, measured mass/charge of e- (1906 Nobel Prize in Physics) 14 2.2

George J. Stoney Don’t take down Irish, 1826-1911 In 1891, he proposed the term 'electron' to describe the fundamental unit of electrical charge, and his contributions to research in this area laid the foundations for the eventual discovery of the particle by J.J. Thomson in 1897. Don’t take down

The modern view of the atom was developed by Ernest Rutherford of New Zealand (1871-1937).

(1908 Nobel Prize in Chemistry) particle velocity ~ 1.4 x 107 m/s (~5% speed of light) atoms positive charge is concentrated in the nucleus proton (p) has opposite (+) charge of electron mass of p is 1840 x mass of e- (1.67 x 10-24 g) 17 2.2

Ernest Rutherford Canterbury University in Christchurch, NZ Rutherford laboratory

Rutherford

Ernest Rutherford New Zealand, ( 1871 - 1937) Named the alpha and beta particles and the gamma ray. Named the proton and is known for the use of the foil method to detect the proton. Conducted the gold foil experiment , which led to the discovery of the nucleus

James Chadwick English, (1891-1974) Isolated the neutron in 1932.

ATOMS AND ELEMENTS

ATOM COMPOSITION The atom is mostly empty space protons and neutrons in the nucleus. the number of electrons is equal to the number of protons. electrons in space around the nucleus. extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.

Proton - comes from the Greek meaning " the primary one". Positive charged particle equal in magnitude to the electron's negative charge. Mass = 1.672623 x 10-24 g.

Atomic Number tells the number of protons. 13 Atomic number Al Atom symbol 26.981 Atomic weight

Neutron - neutrally charged particle which has the same mass as the proton. Mass = 1.674926 x 10 -24 g. To find the number of neutrons (Mass # - Atomic # = # neutron)

Electron - Negatively charged particle found orbiting the nucleus of the atom. An atom's activity is primarily determined by the electron. Occupies most of the atom's volume. In a neutral atom , # of electrons = # protons.

ATOMIC COMPOSITION Summary Protons + electrical charge mass = 1.672623 x 10-24 g relative mass = 1.007 atomic mass units (u) Electrons negative electrical charge relative mass = 0.0005 u Neutrons no electrical charge mass = 1.009 u

Antoine Lavoisier French, (1743 - 1794) First to truly explain the true nature of combustion. Used quantitative measurements in his experiments, which led to the Law of conservation of mass.

Antoine Lavoisier Lavoisier named phlogiston (oxygen). The word oxygen comes from the Greek meaning " to form an acid". Was beheaded during the French Revolution.

Law of conservation of mass - states that mass is neither created nor destroyed.

Joseph Proust French, (1754 - 1826) Came up with the principle known as the Law of definite proportions.

Law of Definite Proportions States that a compound always contains exactly the same proportions of elements by weight.

Benjamin Franklin American (1706 - 1790) Discovered two types of electric charge. He named them positive and negative. Experiments showed that like charges repel each other and unlike charges attract each other.

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Georg Baurer 1500’s - German Development of metallurgy

Paracelsus – 1500’s - Swiss Studied the medicinal application of minerals.

Robert Boyle English, (1627- 1691) First person to perform truly quantitative physical experiments.

Georg Stahl (1660-1734) German Believed a substance called phlogiston flowed out of burning materials.

Joseph Priestley (1733- 1804) English First to isolate “Phloiston”, oxygen, by heating mercuric oxide. First to observe graphite as an electrical conductor.

Priestley Observed a gas being given off during the fermentation of grains, (CO2), this gas could be dissolved in water to make a drink called seltzer.

Atomic Weight This tells us the mass of one atom of an element relative to one atom of another element. Tells the number of protons and neutrons in an atom. The average mass of an element. Standard = carbon

Question What is the atomic weight of Tin? 118.71

What is the atomic number of Antimony? 51

What is the atomic number of gold? 79

Joseph Guy- Lussac (1778-1850) French Performed experiments in which he measured the volume of gases if the temperature and pressure were held constant. 1808 - He was the co-discoverer of boron.

1804 - He and Jean-Baptiste Biot made a hot-air balloon ascent to a height of 6.4 kilometres in an early investigation of the Earth's atmosphere. He wanted to collect samples of the air at different heights to record differences in temperature and moisture.

Particles in a Mole Avogadro’s Number Amedeo Avogadro 1776-1856 6.02214199 x 1023 There is Avogadro’s number of particles in a mole of any substance.

Amadeo Avogadro Italian, (1776 - 1856) Avogadro's Hypothesis - states that at the same temperature and pressure, equal volumes of different gases contain the same number of particles.

Who discovered the electron? Thomson

Who discovered the proton? Rutherford

Jons Jakob Berzelius Swedish, (1779 -1848 ) Discovered elements Si, Ce, Th, Se. Came up with 50 accurate masses for elements known at the time. Invented a simple set of symbols for the elements.

Robert Millikan American, 1868-1953 Measured the charge of the electron thus enabling scientists to measure the mass of the electron to be 9.11 x 10-31 g.

Thomson’s charge/mass of e- = -1.76 x 108 C/g Measured mass of e- (1923 Nobel Prize in Physics) e- charge = -1.60 x 10-19 C Thomson’s charge/mass of e- = -1.76 x 108 C/g e- mass = 9.10 x 10-28 g 55 2.2

Henri Becquerel French (late 1800's) Did the very first studies with radioactive elements.

Radioactivity The emission of radiation, decay of nucleus to form a different nucleus.

Types of Radioactive Emissions

Types of Radioactive Emissions

I thought this was going to easy!!

Radioactive Particles Alpha – has a +2 charge, a charge twice that of the electron and with opposite sign. A piece of paper will deflect it.

Radioactive Particles Beta – High speed electron. A piece of aluminum foil will deflect it.

Radioactive Particles Gamma – High energy light. One foot of solid concrete will stop it.

Nucleus Center of atom containing the proton and neutron. Makes up most of the atom’s mass. Protons and neutrons are very tightly packed in the nucleus. Very dense.

Pierre and Marie Curie Poland-(1867-1934), France-(1859 - 1906) Worked to isolate polonium and radium from pitch blend. Marie is the only person to have won the Nobel Peace Prize in Science twice.

Michael Faraday English (1791- 1867) Showed that the same quantity of electric current caused different quantities of different metals to deposit, and postulated that those quantities were related to the relative masses of the atoms of those elements.

Hey Get your own meal!

Atomic Mass Unit (amu) - equals 1/12th of the mass of an atom of carbon with 6 protons and 6 neutrons. (To convert to grams use 1.661 x 10-24 g = 1 amu)

Problem : How many neutrons , electrons , and protons does the following element have and what is this element? 238 92 X (The top number tells the atomic mass and the bottom number the atomic number. P+ = 92 E- = 92 No = 238-92 = 146 The element is Uranium.

Problem: What is the mass number of a fluorine atom with ten neutrons? Such an atom has a mass of 18.9984 amu. What is the mass in grams? 9 p+ + 10 no = mass number 19. (18.9984) 18.9984 amu 1.661 x 10-24 g amu =3.156 x 10-23 g

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Isotopes - atoms with the same number of protons but different number of neutrons. Ex: 26 12 Mg would have 14 neutrons.

Find the number of neutrons. 10846 Pd Is this an isotope? Why or why not?

Isotopes Atoms of the same element (same Z) but different mass number (A). Boron-10 has 5 p and 5 n: 105B Boron-11 has 5 p and 6 n: 115B 10B 11B

11H 21H 31H Hydrogen Isotopes Hydrogen has _____ isotopes 1 proton and 0 neutrons, protium 11H 1 proton and 1 neutron, deuterium 21H 1 proton and 2 neutrons, tritium radioactive 31H

Isotope Composition Isotope Protons Neutrons Electrons Sulfur-32 Bromine-79

Isotopes & Their Uses 9943Tc Emits gamma rays Heart scans with radioactive technetium-99. 9943Tc Emits gamma rays

Masses of Isotopes determined with a mass spectrometer

10B 11B Isotopes Because of the existence of isotopes, the mass of a collection of atoms has an average value. Average mass = ATOMIC WEIGHT Boron is 19.9% 10B and 80.1% 11B. That is, 11B is 80.1 percent abundant on earth. For boron atomic weight = 0.199 (10.0 u) + 0.801 (11.0 u) = 10.8 u

Isotopes & Atomic Weight Because of the existence of isotopes, the mass of a collection of atoms has an average value. 6Li = 7.5% abundant and 7Li = 92.5% Atomic weight of Li = ______________ 28Si = 92.23%, 29Si = 4.67%, 30Si = 3.10% Atomic weight of Si = ______________

Problem: Silver has 2 isotopes , one with 60 neutrons and the other with 62 neutrons. What are the mass numbers and symbols of these isotopes? 107 47 Ag and 109 47 Ag

Problem Bromine has 2 naturally occurring isotopes, one with a mass of 78.918336 amu and a percent abundance of 50.69%. The other isotope, of mass 80.916289 amu has a percent abundance of 49.31 %. Calculate the atomic mass of bromine. (.5069 x 78.918336 amu) + (.4931 x 80.916289 amu) = 79.90 amu

Enrico Fermi Italian, 1901-1954 Successfully split an uranium atom in the first nuclear fission reaction

Niels Bohr Danish, (1885 - 1962) Compared the motion of electrons to the motion of the planets orbiting the sun. Electrons in motion enable them to overcome the attraction of the positive attraction of the nucleus.

Alkali Earth Metal Noble Gas Halogen Alkali Metal Period Group 85 2.4

Groups/Families in the Periodic Table 86

Groups Run vertical Elements are arranged with similar chemical and physical properties.

Regions of the Periodic Table

Element Abundance C O Al Si Fe http://www.webelements.com/

Group IA: Alkali Metals Li, Na, K, Rb, Cs Cutting sodium metal Reaction of potassium + H2O

Alkali Metals Group IA +1 Charge Very reactive Solids at room temperature

Group IIA: Alkaline Earth Metals Be, Mg, Ca, Sr, Ba, Ra Magnesium Magnesium oxide

Alkaline Earth Metals +2 Group IIA

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Group IIIA: B, Al, Ga, In, Tl Oxidation # +3 Cu Al Al resists corrosion (here in nitric acid). Gallium is one of the few metals that can be liquid at room temp. Oxidation # +3

Group 4A: C, Si, Ge, Sn, Pb Quartz, SiO2 Diamond

Group IVA Exceptions: Sn and Pb have +2 or +4 charge

Group VA: N, P, As, Sb, Bi White and red phosphorus Ammonia, NH3

Group VIA: O, S, Se, Te, Po Oxidation # -2 Elemental S has a ring structure. Sulfuric acid dripping from snot-tite in cave in Mexico Oxidation # -2

Group VIIA: Halogens F, Cl, Br, I, At -1 Charge Very reactive Gases at room temperature. Halogen means salt formers.

Halogens

Group VIIIA: Noble Gases He, Ne, Ar, Kr, Xe, Rn Charge 8 valence electrons Except He Only has 2

Colors of Transition Metal Compounds Nickel Cobalt Copper Zinc Iron

Group B Transition Elements Iron in air gives iron(III) oxide Lanthanides ( 1st row at bottom) and actinides (2nd row at bottom)

Transition Metals Charges vary Exceptions to learn: Zn +2 Cd +2 Ag +1

Periods in the Periodic Table

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Periods - run horizontal and period number tells the number of energy levels.

Metals - have such properties as shiny, conduct electricity, and heat, malleable and ductile. Tend to lose electrons and therefore carry a positive charge. Located left of the zig-zag line.

Ductile - metals can be drawn into wires.

Malleable - metals can be hammered into thin sheets.

Non - metals - Located right of zig - zag line. Tend to gain electrons and therefore tend to carry a negative charge.

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Metalloids - have properties of both metals and non - metals. Located along zig - zag line. B, Si, Ge, As, Sb, Te

Dmitri Mendeleev Russian, (1834 - 1907) Arranged the elements on the periodic table according to their properties and atomic weight. Others who suggested some form of periodic table were Chancourtois, Newland, and Meyer.

Periodic Table Dmitri Mendeleev developed the modern periodic table. Argued that element properties are periodic functions of their atomic weights. We now know that element properties are periodic functions of their ATOMIC NUMBERS.

H.G. Moseley English (1887 - 1915) Arranged the elements according to atomic #. Died in WWI

Hydrogen Shuttle main engines use H2 and O2

Allotropes - when an element can often exist in several different and very distinct forms. Ex: Carbon - graphite, coal and diamond.

Oxygen - most abundant element in the earth's crust.

Selenium - Se Studies have shown that areas having a soil content high in selenium tend to have lower cancer rates. Found in the heart muscle.

Silicon - Si - second most abundant element in the earth's crust. Most of the earth's rocks sand and soil are made up of SiO2. Silicon has helped make computer solid state circuitry.

Sulfur - S - ancient times called "brimstone“. Found in two states TX and LA.

Was he the brides side or the grooms?

Nitrogen - most abundant element in the earth's atmosphere.

Iron - found in hemoglobin helps in carrying O2.

Americium - used in smoke detectors in the U.S.

Bismuth - last element in Periodic Table that is not radioactive.

Phosphorus Phosphorus first isolated by Brandt from urine, 1669 exists as P4 in nature, white phosphorus.

Boron in Death Valley Death Valley has been a major source of borax ( a washing powder )and other boron-containing minerals. Borax was transported out of Death Valley, where it was mined by wagons pulled by teams of 20 mules.

Gems & Minerals Sapphire: Al2O3 with Fe3+ or Ti3+ impurity gives blue whereas V3+ gives violet. Ruby: Al2O3 with Cr3+ impurity

Distillation - is a widely used method for separating mixtures, mostly liquids, based on differences in their boiling points. A liquid is boiled, capturing and cooling the resultant hot vapors, and collecting the condensed vapors.

Simple Distillation: Apparatus Put in boiling stone!

Correct Thermometer Placement Thermometer must be below this level