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Periodic Table
Chemistry Regents June 2005 - Question 04 Print E-mail
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Correct Answer:  (4) increasing in atomic number

Why:

The Periodic Table is an arrangement of chemical elements into a tabular form that groups similar elements together and helps demonstrate patterns in the chemical and physical properties of not only known elements but also elements yet to be discovered.

The Table is also organized from lowest atomic number (top Left) to highest (bottom right).  The atomic number of an element represents how many protons the element contains. Remember unless the element is charged the number of protons equals the number of electrons.

The Periodic Table is organized mainly with two trends, Groups and Periods.  Groups are the vertical (up and down) lines of the table and Periods are the horizontal (left and right) lines of the table.  The Period trends represent the maximum number of electrons that can be accommodated in the elements largest electron shell.  For example Row 1 can have two electrons, Row 2: 8 electrons  Row 3: 8 electrons  Row 4:18 electrons Row 5: 18 electrons  The Groups are organized into elements that  exhibit similar physical and chemical properties, and who have the same number of electrons in their outer most shell.

In Summary the Periodic table is organized from lowest atomic number to highest, and is arranged in periods and groups.  Horizontal periods represent the capability of having more electrons in the largest shell and Vertical groups represent having the same number of electrons only in the outer shell making the elements behave similarly.

Answering this question:

You may immediately eliminate choices 1 and 2 because you know that the Periodic table goes from smallest to biggest starting in the Upper Left.  Therefore you know there are no decreasing trends on the periodic table.

When considering choices 3 and 4 you must remember that the period represents the maximum number of electrons possible whereas a group represents only the number of electrons in the outer shell.  Because the elements are neutral you can conclude that having a bigger maximum number of electrons must also mean a larger number of protons, and therefore the atomic number must be increasing.  Remember the Atomic Mass is the Protons and the Neutrons and would only be applicable in this situation if asked what the trend in a group was from top to bottom.
 
Chemistry Regents June 2005 - Question 05 Print E-mail
chemjune05q05
Correct Answer: (3) Cd, Sb, and I

 

Why:

The periodic table is organized in trends of periods and groups so that it is often possible to tell the physical and chemical characteristics of an element at a glance.  This is much easier than memorizing all of the elements and it allows us to make predictions for elements that haven't even been discovered yet.

With the exception of Hydrogen (H) the periodic table has all its various metals to the left and middle.  There is a stair-stepping line of elements beginning with B(Atomic Number 5) going down to Si(14) then to Ge(32) and As(33), further down to Sb(51) and Te(52) ending at Po(84).  All of these compromise the Metalloids.  Everything to the Right of the metalloids are non-metals, including the very last group (vertical line) which are the noble gases.  Using the periodic table it is then easy to determine that answer (3) has one of each a metal, metalloid, and a nonmetal.

Answering this question:

The easiest method of answering this question is to memorize the metalloid "line" and know that to the left are metals and to the right are nonmetals.  However even if you aren't sure where the distinguishing lines are it is still possible to use the periodic table and answer this correctly just by knowing that the table separates elements based on its properties.

Looking at (1) you'll see that Zn, Ga, and Ge are right next to each other in a line.  This should make you concerned that they may not have the different physical properties called for in the question.  Looking at (2) again you'll see that they're grouped right together in a vertical line and probably will not span three different types of physical properties.  Looking at (4) gives you another group right together and spanning very little of the periodic table.  The only answer that spreads itself out at all is (3) and would lead you to the correct answer.

 
Chemistry Regents June 2005 - Question 21 Print E-mail
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Correct Answer (1) Carbon

Why:

Carbon is a naturally abundant nonmetallic element that occurs in many inorganic and in all organic compounds.  It is capable of bonding to itself to form an enormous variety of chemical and biological molecules.

The periodic table organizes elements by chemical and physical properties into groups (vertical lines) and periods (horizontal lines).  The tall groups (not the transition metals in the middle) in the periodic table show us how many valence electrons are in the element, and will therefore help us know how it bonds with itself or other elements.   Beginning with Hydrogen that is group 1 and has one valence electron, group two begins with Be and has two valence electrons, group 3 has B and has three valence electrons, C begins group 4,  N begins group 5, O begins group 6, F begins group 7 and He begins group 8.

Nitrogen has five valence electrons, and we're analyzing its ability to self bond into long chains or rings as the question specified.  We also know that elements make every attempt to fill their valence shell with 8 electrons.  With a little analysis we'll quickly see that the best way to combine two N atoms is into a triple bond. And in fact most naturally occurring Nitrogen gas is actually N2 .

Oxygen has six valence electrons and when self bonding the most stable structure is a double bond between two Oxygen atoms leaving no room for additional oxygen.  Fluorine has seven valence electrons and only needs one more to complete its shell.  To self bond it combines a single bond with one other F and then has no additional room any other atom. Lastly, Carbon has  four valence electrons.  You can see that self bonding a Carbon with another Carbon in a single or even in an tripple or double bonds leaves electrons available to bond to another C and long chains and rings are possible.

Answering this question:

The simplest way to answer this question is to use some general knowledge of chemistry and the world around us and realize that carbon is in every organic substance as well as many non organics such as diamonds, plastic, and graphite.  If you have trouble remembering that then the best way to answer this question is just as explained above use the periodic table and see which answer will self bond the best.  Carbon becomes the best option and is the correct answer.
 
Chemistry Regents June 2005 - Question 34 Print E-mail
chemjune05q34
Correct answer: (4) Ar

 

The atom is said to have no charge at all.  Keeping this in mind, the number of positively-charged protons should be equal to the number of negatively-charged electron.

The number of protons can be obtained from the Periodic Table of Elements wherein the atomic number can be found.  This atomic number located in the upper left-hand corner for each boxed element is equals to the number of protons.

There are instances wherein an atom either gains or loses an electron, thus, making it an ion.  In cases like this, the element does not change, rather, the net charge does.  This change in net charge is denoted either by a superscript ‘+' or ‘-‘ after the symbol.  When an electron is removed, the atom will become positively charged and the resulting ion will bear a superscript ‘+'  On the other hand, when an electron is added, the resulting ion is negative which will be indicated by a superscript ‘-‘

Answering the question:

S2- is the negative ion of Sulfur.  Its atomic number is 16; it is then equivalent to the number of protons and the number of electrons.  It is to be noted that the superscript of ‘2-‘ indicates that 2 electrons are added to it.  Thus, the number of electrons of S2- is 16 + 2 or 18 electrons.

O2- is the negative ion of Oxygen.  Its atomic number is 8.  The symbol indicates that it gains 2 electrons, thus, the total number of electrons is 10.  Option no. 1 is eliminated.

Option no. 2 is eliminated because Si has an atomic number of 14 which is equivalent to the number of electrons.  We are looking for an atom with 18 electrons.

Option no. 3 is also eliminated having an atomic number of 34 plus a gain of 2 electrons.  Se2- has a total number of 36 electrons.

Option no. 4, Ar, has an atomic number of 18.  Thus, it is also the number of electrons.  This option is the correct symbol which represents the same number of electrons as S2-.

 
Chemistry Regents June 2005 - Question 35 Print E-mail
chemjune05q35

Correct answer: (3) 166 pm

The Periodic Table is the tabular representation of chemical elements arranged by rows and in columns.  The specific arrangement shows their recurring trends in the properties of the elements.

 

The periodic table is divided into periods and groups.  A period is seen in the table as the elements that are arranged in rows, while a group is seen as those arranged in columns.

Answering the question:

Atomic radius refers to the distance which is equivalent to half the total distance from center to center of two adjacent atoms.

 

Following the trends in the periodic table, atomic radius is said to be increasing from top to bottom of a group.

 

Therefore, if we are to follow the above elements Xx, Yy and Zz showing the correct trend for the atomic radius, increasing values should be evident.  In order to satisfy this rule, option nos. 1, 2 and 4 are easily eliminated.  Option no. 3 is the answer to suit the expected increasing trend for the property of the atomic radius.

 
Chemistry Regents June 2005 - Question 53 Print E-mail
chemjune05q53

Correct Answer:

Germanium and silicon are chemically similar for a number of reasons. Firstly they are both members of the group 14 elements in the periodic table. Group 14 is an unusual group which contains carbon, silicon, germanium, tin and lead. Group 14 elements range from non-metals in the case of carbon to metalloids in the case of silicon and germanium to metals in the case of tin and lead.

Looking at group 14, silicon and germanium are both semiconductors, have similar physical appearances and the same number of available electrons in their valence orbital. In terms of atomic size, both these elements are similar with silicon having an atomic radius of 0.117nm and germanium having a radius of 0.122nm. This causes both elements to behave in a similar manner.

 
Chemistry Regents June 2005 - Question 61 Print E-mail
chemjune05q61

Correct Answer:

Element

Number of Protons

Number of Neutrons

Mass Number

Nuclide

C

6

6

12

C-12

N

7

9

16

N-16

Ne

10

9

19

Ne-19

S

16

16

32

S-32

Answering the Questions:

This question is based on the above chart. In order to fill in the table, look for the point on the chart representing neon (Ne). The number of protons has already been entered in the table, by following the chart along the y-axis we can determine the number of neutrons, which is 9. The mass number of an atom is the sum of the number of protons and neutrons. In the case of Ne the number of protons is 10 and the number if neutrons is 9 giving a mass number of 19.

A nuclide is the nucleus of an atoms characterized by its constitution (number of protons and number of neutrons).

 
Chemistry Regents June 2005 - Question 62 Print E-mail
chemjune05q62

Correct Answer:

S-32 is a stable nuclide primarily as a result of two things. One, it has an equal number of protons and neutrons, two it has an atomic number less than 83 and three it has an even number of protons and an even number of neutrons. Nuclides are atoms of different elements and are considered stable when they do not decay, that is they do not break down to form other elements or are radioactive.

There are a number of factors which contribute to this stability. Protons are positively charged subatomic particles found in the nucleus. However, unlike electrons protons are found very closely packed together. As can be expected packing like charges together causes strong forces of repulsion and hence instability. The neutrons are thought to be the binding force keeping the nucleus together. When there are small number of protons and an equal number of neutrons nuclides are usually stable (1:1 ratio). As the atomic number of nuclides increases over 20, more neutrons are needed to keep the nucleus stable (up to 1:1.5 ratio).

Nuclides with a mass number above 83 are all unstable, and it is believed that the repulsive forces are simple too strong for the neutrons to compensate.

The above explanation places S-32 in the category of a stable nuclide. It has an atomic number less than 20. It has an even number of protons (16) and an even number of neutrons (16). S-32 also has a 1:1 ratio of neutrons to protons. All these factors contribute to the stability of the S-32 nuclide.

 
Chemistry Regents June 2005 - Question 63 Print E-mail
chemjune05q63

Correct Answer: 1.286

Answering the Question:

The neutron to proton ratio is calculated by determining the number of neutrons present for each proton. The ratio is calculated by dividing the number of neutrons by the number of protons (number of neutrons/number of protons). If you calculate the neutron to proton ratio and there is an equal number of protons and neutrons the ratio is 1. For fewer neutrons than protons it is less than 1 and for more neutrons than protons it is greater than 1. If you get a result outside of this then it is an indication that you probably have an error in the calculation.

 


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