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

2

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

3

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? _______

5

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?

6

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?

8

Nuclear Fission

large nuclei break upNuclei bombarded with neutrons

235U + 1n 139Ba + 94Kr + 3 1n + 92 0 56 36 0

Energy

9

Fission

10

Nuclear Fusion

Fusion small nuclei combine

2H + 3H 4He + 1n + 1 1 2 0

Occurs in the sun and other stars

Energy

11

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

Alkane

• Hydrocarbon with only single bonds • Compound names end in –ane

• CH4 simplest hydrocarbon

Mnemonic for First Four Prefixes

First four prefixes• Meth-• Eth-• Prop-• But-

Monkeys

Eat

Peeled

Bananas

?Decade

Decimal

Decathalon

Other Prefixes

• Pent-

• Oct-

• Dec-

• Hex-, Hept-, Non-

CH4

Methane

C2H6

Ethane

C3H8

• Propane

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

•

• A hydrocarbon with the formula C8H18 is called?

• A. Octene B. Octane C. Octyne D. Propane

• Chromium-48 has a short half-life of 21.6 h. How long will it take 360.00 g of chromium-48 to decay to 11.25 g