College Chemistry : Atoms and Elements

Study concepts, example questions & explanations for College Chemistry

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Example Questions

Example Question #11 : Atoms And Elements

When a   atom undergoes bombardment with an  particle,  neutrons, and an isotope of phosphorus are produced. What is the mass number of phosphorus?

Possible Answers:

Correct answer:

Explanation:

In order to begin determination of the mass number of phosphorus, we must first write out the equation and then solve for the mass number of phosphorus.

We know there is  present and it is bombarded by an  particle. An alpha particle is equivalent to . Next by reading the results  of the bombardment we can see that    , which are our reactants, produce  neutrons and an isotope of phosphorus. A neutron is an uncharged particle that has a "Z" value is equal to , and its atomic mass number is equal to . This gives us   since there are two neutrons. Next, we must look at the periodic table to find the atomic number of Phosphorus, which is . Since we must calculate its mass number, for now we mark it as unknown '', so for phosphorus we have . This means our products are 

Now let's write out the reaction that occurs and all of its reactants and products, so we can solve for X:

 

Now we can solve for the unknown mass number of phosphorus by adding up the mass numbers on each side of the equation and solving for the unknown.

On the reactants side we have  (from Al)  (from the alpha particle), and we set that equal to the products sum of mass numbers which are  (from the neutrons) .

This leaves us: 

Therefore the mass number of phosphorus is . This answer can be checked by plugging it into the bombardment equation and seeing if a true result is obtained.

Example Question #7 : Radioactive Decay

 undergoes electron capture to produce which of the following?

Possible Answers:

Correct answer:

Explanation:

In an electron capture, an electron is absorbed meaning the atomic number of the product is reduced by 1. Therefore we can write out our radioactive decay equation as:

   

Where  is the element name of the product

is the mass number of the product

and  is the atomic number of the product.

Since the mass number doesn't change at all . Since we are capturing an electron the atomic number is reduced by , therefore it becomes . Element  is , therefore   is the right answer.

Example Question #8 : Radioactive Decay

 undergoes 2  decays to produce which of the following?

Possible Answers:

Correct answer:

Explanation:

In  decay a  nucleus is emitted, and 2  decays can be written as  so knowing this we can now write out the decay equation.

Where  is the element name of the product.

 is the atomic number of the product.

and  is the mass number of the product.

We can quickly determine the atomic number/element name by making an equation with an unknown with all the atomic numbers. This would be:

therefore the atomic number is  and the element polonium.

We can do the same for mass numbers to get the equation:

, so the final answer is .

Example Question #9 : Radioactive Decay

What is the daughter nuclide after  undergoes alpha decay?

Possible Answers:

Correct answer:

Explanation:

Recall what an alpha particle is: .

Now, write the equation for the alpha decay of polonium-214. The polonium will be emitting an alpha particle.

Make sure that the masses and the atomic numbers on both sides of the equation will add up.

Example Question #11 : Atoms And Elements

Possible Answers:

Correct answer:

Explanation:

This is a question regarding radioactive decay, specifically alpha decay. An alpha particle has the same identity as the nucleus of a  atom, or . To solve this problem, we must perform simple addition and subtraction.

, and . So, the two new numbers become  and , eliminating one of the answer choices. Next, we must remember that the bottom number, in this case , signifies atomic number. Atomic number defines the identity of the element. So, we must find the element with the atomic number , which is .

Example Question #11 : Atoms And Elements

Which of the following elements has the most metallic character: ?

Possible Answers:

Correct answer:

Explanation:

The metallic character of elements increases as you move down a group. All of the listed elements are in Group 5. Since  is the furthest down, it must have the most metallic character.

Example Question #2 : Periodic Trends

Which of the following elements has the largest atomic radius: ?

Possible Answers:

Correct answer:

Explanation:

When looking at a periodic table, you should notice that all of these elements are in the same period. Recall that atomic radii decrease as you move right on a period. Thus, this is the order of the elements by decreasing radius:

, or gallium, has the largest radius because it is the furthest left on the periodic table.

Example Question #3 : Periodic Trends

The set of elements with the highest first ionization energies are known as which of the following? 

 

Possible Answers:

Alkaline earth metals

Alkali metals

Halogens

Metalloids

Noble gases

Correct answer:

Noble gases

Explanation:

The noble gases possess a full octet of electrons. They have the largest first ionization energies because of their tendency to keep all of their valence electrons. Halogens have the highest electron affinity; therefore, they have high—but not the highest—ionization energies. The alkali and alkaline earth metals have low electron affinities and low ionization energies. Last, the metalloids possess ionization energies that are neither high nor low.

Example Question #4 : Periodic Trends

Rank the following in order of increasing metallic character: 

Possible Answers:

Correct answer:

Explanation:

The correct answer is 

 has the most nonmetallic characteristics while  has the most metallic characteristics. According to periodic trends, metallic character decreases from left to right across a period and increases top to bottom. Therefore,  will show less metallic character than .  

Example Question #5 : Periodic Trends

Which of these atoms is the smallest?

Possible Answers:

Magnesium

Strontium

Barium

Beryllium

Calcium

Correct answer:

Beryllium

Explanation:

The atomic radii is the size of an atom when it is not bonded to any other atoms. The periodic table can be used to estimate the size of the atomic radii of atoms. As you move down the periodic table the atomic radii increase, but as you move from left to right on the periodic table, the size of the atomic radii decrease. 

Beryllium, magnesium, calcium, strontium, and barium are all in the same group on the periodic table, so the smallest element is the element closest to the top of the periodic table since the atoms become larger as you go down the periodic table. Therefore, the smallest atom of this group is beryllium. 

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