High School Chemistry : Identifying Periodic Trends

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

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Example Question #321 : High School Chemistry

Which of the following elements has the highest electronegativity?

Possible Answers:

Fluorine

Oxygen

Sulfur

Neon

Chlorine

Correct answer:

Fluorine

Explanation:

Electronegativity increases as the we move up and to the right of the periodic table. Noble gases are stable by themselves and have very low electronegativities. Fluorine is the most electronegative, because it is the most upper right element that is not a noble gas.

Example Question #21 : The Periodic Table

Why do atomic radii tend to shrink going from the left side to the right side of the periodic table?

Possible Answers:

Because there are more electrons, which are attracted to each other and thus "pull-in" towards the center

Because the nucleus gets more compact with additional neutrons

Because there are less electrons, so the atom takes up less space

Because the neutrons are negatively charged, and thus attract the electrons, which are positive

There are more protons, and thus stronger attraction between the electron cloud and the nucleus

Correct answer:

There are more protons, and thus stronger attraction between the electron cloud and the nucleus

Explanation:

Electrons have a negative charge. Protons have a positive charge. Through Coulombic interactions, they are attracted to each other. Increasing the charge increases the attraction between them, and thus increases their pull on each other. Also, going from left to right of the periodic table does not indicate any additional energy shells, so each added electron is the same distance from the nucleus, as opposed to going from the top to the bottom of the periodic table, where new energy levels are added and subsequent elements have electrons that are further from the nucleus, thus greatly increasing the atomic radius.

Example Question #21 : Identifying Periodic Trends

Which of the following usually decreases across a period from left to right?

Possible Answers:

Atomic weight

Electronegativity

Number of electron shells

Number of neutrons

Atomic radius

Correct answer:

Atomic radius

Explanation:

The atomic radius of atoms will decrease across a period from left to right. Atomic radius is defined by two factors. The amount of electron shells in the atom, and the attraction between the protons in the nucleus and the electrons. Going across the period atoms will have more protons and electrons. This increases the amount of attraction between them and creates a higher nuclear charge. Since the attraction is stronger, the distance between the electrons and protons will be shorter. This means that that the atomic radius is smaller. 

Example Question #323 : High School Chemistry

Across a period from left to right, what kind of trend does electronegativity follow? 

Possible Answers:

It decreases, then increases

It increases

It decreases

It stays constant

It increases, then decreases

Correct answer:

It increases

Explanation:

Electronegativity is the likelihood of an element to attract electrons and from bonds. Generally speaking all atoms follow the octet rule. They want to have eight electrons in the outer electron shell. Across a period there are more electrons in the outer shell. The elements are closer to achieving the octet rule, and thus they are more reactive. 

Example Question #324 : High School Chemistry

Generally speaking, what kind of trend does first ionization energy follow across a period from left to right? 

Possible Answers:

It increases, then decreases

It remains constant

It increases

It decreases, then increases

It decreases

Correct answer:

It increases

Explanation:

First ionization energy is the amount of energy required to remove an electron from an atom. Elements on the left side of the periodic table have less electrons in their outer shell. This means they will achieve the octet rule more easily by giving away their electrons, and are more likely to do so. Elements on the right side of the periodic table have more electrons in their outer shell, and will have an easier time achieving the octet rule by gaining electrons.

Example Question #22 : Identifying Periodic Trends

From sulfur to potassium, what trend does the atomic radius of the elements follow?

Possible Answers:

It stays constant

It increases

It decreases, and then increases

It decreases

It increases, and then decreases

Correct answer:

It decreases, and then increases

Explanation:

The atomic radius from sulfur to argon decreases. The amount of protons and electrons increases from sulfur to argon. With more protons and electrons the attraction is stronger. This draws the nucleus and outer electron closer together, and the atomic radius is smaller. Potassium however puts the latest electron into a new electron shell. Even though potassium has one more electron and one more proton than argon, the extra electron shell will increase the atomic radius. 

Example Question #326 : High School Chemistry

Which of the ground state atoms from the listed elements has five electrons in the outer electron shell?

Possible Answers:

Sodium

Fluorine

Sulfur

Phosphorus

Carbon

Correct answer:

Phosphorus

Explanation:

The amount of electrons in the outer shell is easily determined by which group an element is in. Elements in group 15 have 5 electrons in the outer shell. P is the only listed element in group 15.

Example Question #327 : High School Chemistry

Which of these elements has the greatest ionization energy?

Possible Answers:

Rubidium

Sodium

Potassium

Lithium

Correct answer:

Lithium

Explanation:

Lithium has the greatest ionization energy because it is the smallest of the options available. The smaller an element/atom is, the closer to the nucleus of the atom the valence electrons are. The closer valence electrons are to the center of an atom, the harder it us to take one away, because it's strongly attracted to the protons in the center of an atom. The trend for ionization energy is as follows: ionization energy increases from left to right within a row and from bottom to top within a group on the periodic table.

Example Question #23 : Identifying Periodic Trends

Which of these elements has the greatest ionization energy?

Possible Answers:

Lithium

Sodium

Rubidium

Potassium

Correct answer:

Lithium

Explanation:

Lithium has the greatest ionization energy because it is the smallest of the options available. The smaller an element/atom is, the closer to the nucleus of the atom the valence electrons are. The closer valence electrons are to the center of an atom, the harder it us to take one away, because it's strongly attracted to the protons in the center of an atom. The trend for ionization energy is as follows: ionization energy increases from left to right within a row and from bottom to top within a group on the periodic table.

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