A TOMS AND E LEMENTS

Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

ATOMIC COMPOSITION ProtonsProtons –+ electrical charge –mass = x g –relative mass = atomic mass units (amu) ElectronsElectrons – negative electrical charge –relative mass = amu NeutronsNeutrons – no electrical charge –mass = amu

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

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

Ernest Rutherford Canterbury University in Christchurch, NZ Rutherford laboratory

The modern view of the atom was developed by Ernest Rutherford ( ). Screen 2.9

Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al Atomic number Atom symbol Atomic weight

Atomic Weight This tells us the mass of one atom of an element relative to one atom of another element.This tells us the mass of one atom of an element relative to one atom of another element. OR — the mass of 1000 atoms of one relative to 1000 atoms of another.OR — the mass of 1000 atoms of one relative to 1000 atoms of another. For example, an O atom is approximately 16 times heavier than an H atom.For example, an O atom is approximately 16 times heavier than an H atom. Define one element as the standard against which all others are measuredDefine one element as the standard against which all others are measured Standard = carbonStandard = carbon

Mass Number, A C atom with 6 protons and 6 neutrons is the mass standardC atom with 6 protons and 6 neutrons is the mass standard = 12 atomic mass units= 12 atomic mass units Mass Number (A) = # protons + # neutronsMass Number (A) = # protons + # neutrons A boron atom can have A = 5 p + 5 n = 10 amuA boron atom can have A = 5 p + 5 n = 10 amu

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

Isotopes & Their Uses Bone scans with radioactive technetium-99.

Isotopes & Their Uses The tritium content of ground water is used to discover the source of the water, for example, in municipal water or the source of the steam from a volcano.

Masses of Isotopes determined with a mass spectrometer

Isotopes Because of the existence of isotopes, the mass of a collection of atoms has an average value.Because of the existence of isotopes, the mass of a collection of atoms has an average value. Average mass = ATOMIC WEIGHTAverage mass = ATOMIC WEIGHT Boron is 20% 10 B and 80% 11 B. That is, 11 B is 80 percent abundant on earth.Boron is 20% 10 B and 80% 11 B. That is, 11 B is 80 percent abundant on earth. For boron atomic weightFor boron atomic weight = 0.20 (10 amu) (11 amu) = 10.8 amu = 0.20 (10 amu) (11 amu) = 10.8 amu 10 B 11 B

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

Counting Atoms Mg burns in air (O 2 ) to produce white magnesium oxide, MgO. How can we figure out how much oxide is produced from a given mass of Mg?

Counting Atoms Chemistry is a quantitative science—we need a “counting unit.” 1 mole is the amount of substance that contains as many particles (atoms, molecules) as there are in 12.0 g of 12 C. MOLE

Particles in a Mole x Avogadro’s Number There is Avogadro’s number of particles in a mole of any substance. Amedeo Avogadro

Molar Mass 1 mol of 12 C = g of C = x atoms of C g of 12 C is its MOLAR MASS Taking into account all of the isotopes of C, the molar mass of C is g/mol

One-mole Amounts

PROBLEM: What amount of Mg is represented by g? How many atoms? Mg has a molar mass of g/mol. = 4.95 x atoms Mg How many atoms in this piece of Mg?

Periodic Table Dmitri Mendeleev developed the modern periodic table. Argued that element properties are periodic functions of their atomic weights.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.We now know that element properties are periodic functions of their ATOMIC NUMBERS. See CD-ROM, Screen 2.16.See CD-ROM, Screen 2.16.

Periods in the Periodic Table

Groups in the Periodic Table

Regions of the Periodic Table

Element Abundance Fe C Al O Si

HydrogenHydrogen Shuttle main engines use H 2 and O 2 The Hindenburg crash, May 1939.

Group 1A: Alkali Metals Cutting sodium metal Reaction of potassium + H 2 O

Magnesium Magnesium oxide Group 2A: Alkaline Earth Metals

Calcium Carbonate—Limestone The Appian Way, Italy Champagne cave carved into chalk in France

Group 3A: B, Al, Ga, In, Tl Aluminum Boron halides BF 3 & BI 3

Gems & Minerals Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet.Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet. Ruby: Al 2 O 3 with Cr 3+ impurityRuby: Al 2 O 3 with Cr 3+ impurity

Group 4A: C, Si, Ge, Sn, Pb Quartz, SiO 2 Diamond

Group 5A: N, P, As, Sb, Bi White and red phosphorus Ammonia, NH 3

Phosphorus Phosphorus first isolated by Brandt from urine, 1669

Group 6A: O, S, Se, Te, Po Sulfuric acid dripping from snot-tite in cave in Mexico Sulfur from a volcano

Group 7A: F, Cl, Br, I, At

Group 8A: He, Ne, Ar, Kr, Xe, Rn Lighter than air balloons “Neon” signs XeOF 4

Transition Elements Lanthanides and actinides Iron in air gives iron(III) oxide

Colors of Transition Metal Compounds Iron Cobalt Nickel CopperZinc