MCAT Physical : Periodic Table Groupings

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

Example Question #41 : Atoms, Elements, And The Periodic Table

A mystery element is found in nature. It is very conductive and is able to be hammered into a thin layer without breaking. Based on these properties, where would you least expect to find this element on the periodic table?

Possible Answers:

The middle of the table

The lanthanide period

This element could be found anywhere on the periodic table

The left side of the table

The right side of the table

Correct answer:

The right side of the table

Explanation:

First off, it is important to know that the ability to be hammered into a sheet and conduct electricity are characterisitcs typically reserved for metals. With this in mind, we can check the periodic table, and see where on the table metals reside. Metallic character generally decreases as you go from left to right on the table, which results in nonmetals being found on the right side of the table. As a result, we would not expect to find this element and its metallic characteristics on the right side.

Example Question #12 : Periodic Table Groupings

What class of element is krypton?

Possible Answers:

Metalloid

Halide

Lanthanide

Noble gas

Correct answer:

Noble gas

Explanation:

The non-metals in group 8 are called noble gases because they tend to resist reactions with other atoms. Noble gases are the only elements to have valence octets in their ground states ().

Halides are the gases in group 7, which are most stable as negative ions to reflect the octet configurations of the noble gases. Lanthanides are the elements in period 6 that have an incomplete f shell. The metalloids are arranged along the diagonal between boron and polonium and divide the periodic table between the metals (to the left) and nonmetals (to the right).

Example Question #13 : Periodic Table Groupings

An unknown element has been shown to be unreactive. It has a low boiling point and an extremely high ionization energy. Which group does the element most likely belong to?

Possible Answers:

Halogens

Alkali metals

Alkaline earth metals

Noble gases

Correct answer:

Noble gases

Explanation:

The properties described fit well with the noble gases. Alkali and alkaline earth elements are solid at room temperature, meaning that they have a high boiling point. Halogens can be gaseous at room temperature, but are very reactive. Noble gases have low boiling points and rarely act in spontaneous reactions. Their properties are due to their full valence shell, which is the source of their stability. Changes to their electron configuration (such as removing an electron) require large amounts of energy.

Example Question #11 : Periodic Table Groupings

Which of the following groups has the highest number of valence electrons?

Possible Answers:

Alkaline earth metals

Noble gases

Halogens

Alkali metals

Correct answer:

Noble gases

Explanation:

The amount of valence electrons increases as you go from left to right on the periodic table. The lowest number of valence electrons is found in the alkali metals (group 1), which have only one valence electron per atom. The largest amount is found in the noble gases (group 18), which have a total of eight valence electrons. Noble gases have a complete octet; therefore, they are inert molecules that do not readily participate in chemical reactions.

Alkaline earth metals have two valence electrons, and halogens have seven.

Example Question #11 : Periodic Table Groupings

A noble gas has __________ number of  orbitals and __________ number of empty  orbitals compared to the halogen element in the same period.

Possible Answers:

a greater . . . a greater

an equal . . . a greater

an equal . . . an equal

a smaller . . . a greater

Correct answer:

an equal . . . an equal

Explanation:

The question asks us to compare halogens and noble gases in the same row of the periodic table. To solve this question, let’s use fluorine and neon as examples.

Fluorine has an electron configuration of  and neon has an electron configuration of . The electron configurations reveal that both fluorine and neon only contain  orbitals in the second shell (). Recall that a shell can contain three  orbitals; therefore, fluorine and neon contain a total of three  orbitals, and all of them are found in the second shell. Although they have a different number of electrons in their  orbitals, fluorine and neon have the same number of  orbitals.

Fluorine has five electrons in its  orbitals and neon has six. Fluorine will have two  orbitals with two electrons and one  orbital with one electron. Neon will have two electrons in each of its three  orbitals. There are no empty  orbitals in fluorine and neon; therefore, they will have the same number of empty  orbitals (zero). 

Note that you will get the same answer if you compare another halogen and noble gas from the same row (for example: chlorine and argon, or bromine and krypton).

Example Question #16 : Periodic Table Groupings

Which group on the periodic table has the first completely filled p subshell?

Possible Answers:

Group 16

Group 17

Group 14

Group 2

Correct answer:

Group 16

Explanation:

Valence orbitals are filled with one electron at a time until all orbitals of the same energy levels have one electron. Valence orbitals will then begin to be completely filled. The p orbital has three subshells, so three electrons will be in each p orbital before any one becomes completely filled.

Oxygen has the electron configuration . This means that oxygen will have two completely full s orbitals and four electrons distributed between the three p orbitals. These four electrons will first fill each orbital with a single electron, then add the fourth electrons to on p orbital to form a lone pair. The result is three lone pairs (2 s orbitals and 1 p orbital) and two unbonded electrons. This configuration is shared by all elements in the oxygen group, group 16.

Example Question #17 : Periodic Table Groupings

All of the following elements have the same number of valence electrons except __________.

Possible Answers:

Ca

Sr

Be

Rb

Mg

Correct answer:

Rb

Explanation:

Beryllium (Be), magnesium (Mg), calcium (Ca), and strontium (Sr) are all alkaline earth metals with two valence electrons.

Rubidium (Rb) is an alkali metal and has only one valence electron.

Example Question #1 : Elements And The Periodic Table

What class of element is zinc?

Possible Answers:

Alkali metal

Non-metal

Transition metal

Metalloid

Correct answer:

Transition metal

Explanation:

In general, the metals fall on the left side of the periodic table and are separated from the non-metals by the metalloids. Transition metals fall in the d block of the periodic table, in groups (columns) 3-12. Examples of metals, non-metals, transition metals, and metalloids are calcium, oxygen, zinc, and arsenic, respectively.

Alkali metals are a special class of metal only found in group 1 of the periodic table.

Example Question #11 : Periodic Table Groupings

Which of the following is likely to have multiple oxidation states?

Possible Answers:

Oxygen

Silicon

Ytterbium

Sodium

Neon

Correct answer:

Ytterbium

Explanation:

Transition elements have multiple oxidation states because of the d-orbitals they possess. This allows them to lose or gain electrons in a variety of ways, often leading to the standard characteristics of metals, such as electrical conductivity. Lanthanides and actinides are less commonly tested, but also have the ability to form multiple oxidation states due to their large and variable orbitals. Ytterbium is one of the lanthanides, and has Yb(II) and Yb(III) oxidation states.

Example Question #20 : Periodic Table Groupings

The multiple oxidation states of transition metals are due to which of the following properties?

Possible Answers:

The instability of the p orbitals

The weak attraction between the nucleus and its core electrons

The large number of valence electrons

The presence of incomplete d orbitals

Correct answer:

The presence of incomplete d orbitals

Explanation:

The transition metals are defined in the region of the periodic table in which atoms are being added to the d subshell. As a result, the transition metals have unfilled or incomplete orbitals within the d shell. Since each orbital is filled with one electron before orbitals start to become completely filled, there are increasing numbers of unpaired d shell orbitals. This allows transition metals to give up variable numbers of electrons, while maintaining stability, as electrons move between d orbitals.

A common example is iron, which is stable in both the and electron configurations.

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