Ch 2– Atoms,Molecules & Ions – part 2

# Ch 2– Atoms,Molecules & Ions – part 2

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## Ch 2– Atoms,Molecules & Ions – part 2

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1. Ch 2–Atoms,Molecules & Ions – part 2

2. 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

3. 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

4. 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.

5. 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

6. Example: How many protons, neutrons and electrons are in the following atom? Hyphen notation

7. 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.

8. Masses of Isotopesdetermined with a mass spectrometer

9. 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)

10. 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

11. Regions of the Periodic Table

12. Hydrogen Shuttle main engines use H2 and O2 The Hindenburg crash, May 1939.

13. Group 1A: Alkali Metals Reaction of potassium + H2O Cutting sodium metal

14. Group 2A: Alkaline Earth Metals Magnesium Magnesium oxide

15. Group 3A: B, Al, Ga, In, Tl Aluminum Boron halides BF3 & BI3

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

17. Group 5A: N, P, As, Sb, Bi White and red phosphorus Ammonia, NH3

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

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

20. XeOF4 Group 8A: He, Ne, Ar, Kr, Xe, Rn • Lighter than air balloons • “Neon” signs

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

22. Colors of Transition Metal Compounds Nickel Cobalt Copper Zinc Iron