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3 years ago

What should I do for science fair

Chemistry

2 answers:

Natasha2012 [34]3 years ago

8 0

Don't do a volcano at the same time you want to be creative and I personally feel that a volcano is too cliché.

Strike441 [17]3 years ago

5 0

You could Build a Gumdrop Geodesic Dome !

Geodesic domes are approximately sphere-like structures made up of interconnected triangles. A famous geodesic dome is Spaceship Earth at EPCOT in Walt Disney World, Florida, but geodesic domes are also commonly found as climbing domes at playgrounds. In this science activity, you will get to build a simple geodesic dome using gumdrops and toothpicks. Once it is built, you may be surprised by how strong it is! Get ready to do some tasty engineering!

Materials:
 Gumdrops (11). Alternatively, jelly beans or other semi-firm, chewy candies may be used. Toothpicks (25)
--
Instructions:

1.Attach five toothpicks together using the gumdrops to form a flat pentagon (five-pointed) shape. You should have a gumdrop at each point and a toothpick along each edge.
2.Poke two more toothpicks into each gumdrop, arranging the new toothpicks so that they are pointing up.
3.Take five new gumdrops and attach them to the top of the new toothpicks, putting two toothpicks into each gumdrop, to form triangles. (The pentagon should form the base of the triangle, and the new gumdrops should form the top point.) You should end up with five triangles this way.
4.Attach a toothpick between the top points of the triangles you just made, connecting the triangles together. This uses five toothpicks, and will create another pentagon shape, this time at the top of the dome.
5.Take five more toothpicks and poke one into each of the five gumdrops that make up the top pentagon. Arrange the new toothpicks so that they are pointing up. Then poke all five toothpicks into a gumdrop in the middle, and at the top, of the dome. Your geodesic dome is complete!
6.Gently press down on the top of your geodesic dome. If it does not break, try carefully pressing down on it a little more.

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3 years ago

explain why the first ionization energy of krypton is greater than the first ionization energy of bromine

4vir4ik [10]

Answer:

The atomic radius of krypton is similar to that of bromine. However, the effective nuclear charge of krypton is greater than that of bromine.

Explanation:

Ionizing an atom require moving an electron from the electron cloud of the atom to a point infinitely far away from the atom. The first ionization energy of this atom is the energy change in this process.

The electron and the nucleus are oppositely-charged. There is an electrostatic force between the two. Removing the electron requires overcoming this attraction. The size of the energy input depends on the electrostatic potential energy of the electron (the gravitational potential energy is much smaller than the electrostatic potential energy.) The separation between the electron and the nucleus is much larger than their radii. Both objects can be considered as point charges. Coulomb's Law gives the electrostatic potential energy of the two point charge that are close to each other.

$\displaystyle \text{Electrostatic Potential Energy} = -\frac{k\cdot (q_1\cdot q_2)}{r}$ ,

where

$k$ is Coulomb's constant,
$q_1$ and $q_2$ are the two charges, and
$r$ is the separation between the two charges.

Krypton and bromine are right next to each other in the same period. Their atomic radii will be similar to each other. The separation $r$ between the outermost electron and the nucleus will also be similar for the two elements.

The first charge $q_1$ can be the electron. However, data show that for elements after helium, the second charge $q_2$ is smaller than the sum of charges on all protons in the nucleus. It turns out that the inner shell electrons (all of which are also negative) repel electrons in the outermost valence shell. The effective nuclear charge $Z_\text{eff}$ of a neutral atom is approximately the same as the number of protons minus the number of non-valence electrons. That number will be slightly larger for krypton than for bromine. As a result, the electrostatic potential energy on a 4p (the outermost orbital for both Kr and Br) electron of krypton will be more negative than that on a 4p electron in bromine. Removing that electron will take more energy in Kr than in Br. The first ionization energy of Kr is hence greater than that of Br.

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