Atomic Mass Because the masses of atoms are so small, the units of grams is much too large to be used conveniently. Therefore, the Atomic Mass Unit (amu) is used. The amu is defined by assigning a mass of exactly 12 to and atom of the carbon 12 isotope: 1 amu = 1.660 538 73 x 10-24 g We will revisit this shortly
ATOMIC COMPOSITION • Protons • + electrical charge • mass = 1.67262158 x 10-24 g • relative mass = 1.0073 (amu) • Electrons • negative electrical charge • mass = 9.10938188 x 10-28 g • relative mass = 0.0005486 amu • Neutrons • no electrical charge • mass = 1.67492716 x 10-24 g • mass = 1.0087 amu
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.
Atomic symbols Nuclear symbol - describes the number of particles in the nucleus of an atom. Atomic # (Z) number of protons in the nucleus Mass # (A) total number of protons and neutrons in the nucleus
Example: How many protons, neutrons and electrons are in the following atom? Hyphen notation
11B 10B Isotopes • Atoms of the same element (same Z) but different mass number (A). • Boron-10 (10B) has 5 p and 5 n • Boron-11 (11B) has 5 p and 6 n Bone scans with radioactive technetium-99.
Atomic Mass Remember, the amu is defined by assigning a mass of exactly 12 to and atom of the carbon 12 isotope. Therefore, 1amu = 1/12 the mass of a Carbon-12 isotope, or 1/12 the mass of 6 neutrons and 6 protons (electrons are negligible)
Periodic Table • Dmitri Mendeleev developed the modern periodic table. He argued that element properties are periodic functions of their atomic masses. • We now know that element properties are periodic functions of their ATOMIC NUMBERS. • Groups vs. Periods
Hydrogen Shuttle main engines use H2 and O2 The Hindenburg crash, May 1939.
Group 1A: Alkali Metals Reaction of potassium + H2O Cutting sodium metal
Group 2A: Alkaline Earth Metals Magnesium Magnesium oxide
Group 3A: B, Al, Ga, In, Tl Aluminum Boron halides BF3 & BI3
Group 4A: C, Si, Ge, Sn, Pb Quartz, SiO2 Diamond
Group 5A: N, P, As, Sb, Bi White and red phosphorus Ammonia, NH3
Group 6A: O, S, Se, Te, Po Sulfuric acid dripping from snot-tite in cave in Mexico Sulfur from a volcano
XeOF4 Group 8A: He, Ne, Ar, Kr, Xe, Rn • Lighter than air balloons • “Neon” signs
Transition Elements Lanthanides and actinides Iron in air gives iron(III) oxide
Colors of Transition Metal Compounds Nickel Cobalt Copper Zinc Iron