Half-life problems:
(a) hg-197 has a half-life of 64 hours. if you have 164g of hg-197 today, how much will you have in 448 hours?

(b) 263 minutes ago we had 5.12g of i-134 and now we only have 0.16g. how long is the half-life of i-134?

(c) c-14 has a half-life of 5730 years. if animal remains are found to have 1/16 of the amount of c-14 found in animals living today, how old are the remains?

(d) an average smoke detector for domestic use contains about 0.29 micrograms of
am-241 which has a half-life of 432 years. how long would it take to decay to 0.0725 micrograms? (3 pts)

A) answer 1.281 grams

B) 52.60 days

C) 23250 years  

D)  864 years  

Explanation:

A) Solution

Ending Amount = Beginning Amount / 2(time / half-life)

Ending Amount = 164 / 2(⁴⁴⁸/⁶⁴)

Ending Amount = 164 / 2⁷

Ending Amount = 164 / 128

Ending Amount = 1.281 grams

B) solution

Half life = (time * log 2) / log (beginning amount / ending amount)

Half life = (263 * .30103) / log (5.12 / 0.16)

Half life = 79.17 / log (32)

Half life = 79.17 / 1.505

Half life =  52.60 days

C) Solution

As we have half-life =5730  

1/16 =  6.2 percent  

Remains =    23250 years  

D) solution

elapsed time = half life * log (beginning amount / ending amount) / log 2

elapsed time = 432 * (log (0.29 / 0.0725) / .30103)

elapsed time = 432 * (0.602 / .30103)

elapsed time=  432 (2)

= 864 years  

14,16 18 reacts with group

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.