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 are extremely small and occupy the space around the nucleus.Electrons are extremely small and occupy the space around the nucleus. The atom is mostly empty space

Scientists Chadwich Becquerel Rutherford Millikan Thomsom Curie Bohr

The modern view of was developed by Ernest Rutherford Ernest Rutherford the “Nuclear Atom” the “Nuclear Atom”

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. 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 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.

Mass Number, A Mass Number (A) = # p + # nMass Number (A) = # p + # n 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 For a boron atomFor a boron atom A = 5 p + 5 n = = 10 amu = 10 amu

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

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 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. Today: element properties are periodic functions of theirToday: element properties are periodic functions of their ATOMIC NUMBERS.

Periodic Table History Henry Mosley- Henry Mosley- -Grouped elements in order of atomic number -credited with modern periodic table Came up with Period Law- -physical and chemical properties of elements are a periodic function of their atomic numbers

Modern Periodic Table Glen Seaborg- Glen Seaborg- -Grouped elements according to their electron configurations -credited with periodic table as it looks today

Modern Periodic Table Groups (families)  Groups (families)  a vertical column  of elements. determined by # of valence electrons

Modern Periodic Table Periods (  ) Periods (  ) horizontal row horizontal row of elements. -determined by the electron’s energy level.

METALS METALLOIDS NONMETALS NOBLE GASES

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

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

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

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

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

Group 8A: NOBLE GASES 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

Periods Groups/ Families 1A 2A 8A 3A 4A 5A 6A 7A “B” or Transition Metals Alkali Alkaline Earth Halogens Noble Gases Rare Lanthanides Earth Actinides