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five easy question from chemistry class please help me ASAP

Submitted by Anonymous on 26 October 2004 - 4:39am.

1. what are the period number and group number of the
element that has atomic number 15?

2. which elements w/an atomic number greater then 40
can be expected to have chemical properties similar to
those of the element bromine (Br)?

3. t or f? it always takes energy to remove an
electron from a neutral atom.

4. of the atoms Na, Mg, and K, which should be the
most difficult to ionize?

5. what is the mass in grams of a billion billion (10
to the 18th) atoms of 24 to the Mg? The atomic mass of
24 Mg is 23.9850 amu.

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Submitted by Anonymous on 27 October 2004 - 2:05pm.

1. 15 is Phosphorus, Period 3, group 5 (Mendeleyev's style), group 15 (IUPAC style)

2. Iodine, Astatine (all are halogens as bromine does)

3. False. Removing the electron from Hydrogen and put it to Oxygen forming water releases energy.

4. Magnesium, because you have to take 2 electron away from it while Na and K only 1

5. 1 atomic mass unit = 1.660538 ? 10^(-27) kilograms (copied from google)
Then your magnesium should weight
=23.9850 ? 10^(18) ? 1.660538 ? 10^(-27) kilograms
=23.9850 ? 10^(-9) ? 1.660538 ? 10^3 grams
=23.9850 ? 10^(-6) ? 1.660538 grams
=3.98280 ? 10^(-5) grams

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Submitted by Anonymous on 27 October 2004 - 5:41pm.

Deryck wrote:
3. False. Removing the electron from Hydrogen and put it to Oxygen forming water releases energy.

What you say here isn't incorrect, but if the question just means the removal of an electron from a neutral atom, then the answer is true. All ionisation energies are positive == it always takes energy.

Deryck wrote:
4. Magnesium, because you have to take 2 electron away from it while Na and K only 1

You're right there, although I suspect we are only asked to look at the first ionisation energies. In which case Mg has a greater attraction to a more positively charged nucleus (cf. Na) and is closer (cf. both Na and K), hence it is more difficult to remove even one electron.

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Submitted by Anonymous on 11 November 2004 - 10:45pm.

allan_chemist wrote:
Deryck wrote:
3. False. Removing the electron from Hydrogen and put it to Oxygen forming water releases energy.

What you say here isn't incorrect, but if the question just means the removal of an electron from a neutral atom, then the answer is true. All ionisation energies are positive == it always takes energy.

I agree with Allan.

About second question, halogens are group of elements with most common properties, so you can just watch in the PT (periodic table) which one's atomic number is bigger than 40 :wink:

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