1. how many pairs of electrons are shared in a molecule of o 2 ? 2. how many electrons are shared in...
TRANSCRIPT
1. How many pairs of electrons are shared in a molecule of O2?
2. How many electrons are shared in a molecule of N2?
3. Which formula represents an ionic compound? (1) KCl (2) N2O (3) CCl4 (4) CO2
4. Which formula represents covalent compound? (1) CaCl2 (2) CrCl3 (3) NH3 (4) KBr
5. How many carbon atoms are in the following molecule: C6H12O6
6. How many oxygen atoms are in the following molecule: Ca(NO3)2
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Half-Life of a Radioisotope
The time for the radiation level to fall (decay) to one-half its initial value
decay curve
8 mg 4 mg2 mg 1 mg
initial
1 half-life
23
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Examples of Half-Life
Isotope Half lifeC-15 2.4 secRa-224 3.6 daysRa-223 12 daysI-125 60 daysC-14 5700 yearsU-235 710 000 000 years
1. How long is a half-life for carbon-14?_____________
2. If only 25% of the carbon-14 remains, how old is the material containing the carbon-14?________
3. If a sample originally had 120 atoms of carbon-14, how many atoms will remain after 16,110 years? _______
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Learning Check NR3
The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 26 hours?
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Solution NR3
t1/2 = 13 hrs
26 hours = 2 x t1/2
Amount initial = 64mg
Amount remaining = 64 mg x ½ x ½
= 16 mg
• After 42 days a 2.0 g sample of phosphorus-32 contains only 0.25 g of the isotope. What is the half-life of phosphorus-32?
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Nuclear Fission
large nuclei break upNuclei bombarded with neutrons
235U + 1n 139Ba + 94Kr + 3 1n + 92 0 56 36 0
Energy
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Nuclear Fusion
Fusion small nuclei combine
2H + 3H 4He + 1n + 1 1 2 0
Occurs in the sun and other stars
Energy
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Learning Check NR4
Indicate if each of the following are(1) Fission (2) fusion
A. Nucleus splits B. Large amounts of energy releasedC. Small nuclei form larger nucleiD. Hydrogen nuclei react
Energy
ORGANIC CHEMISTRY
Carbom: capable of forming stable, extended chains of atoms through single, double, or triple bonds with
itself
Hydrocarbons- contain hydrogen and carbon
Carbon- 4 bondsHydrogen- 1 bond
Mnemonic for First Four Prefixes
First four prefixes• Meth-• Eth-• Prop-• But-
Monkeys
Eat
Peeled
Bananas
Functional Groups
• Specific arrangement of atoms in an organic compound that largely determines the chemical and physical properties of the organic compound
• Organic compounds classified according to their functional groups
• Examples on Page 799
• Which element is capable of forming stable, extended chains of atoms through single, double, or triple bonds with itself?
• A. CarbonB. OxygenC. NitrogenD. Phosphorus
• The chemical and physical properties of an organic compound are largely determined by the presence of a(n)?
• A. IsomerB. AllotropeC. Functional group D. Skeletal structure
•