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MCAT GENERAL CHEMISTRY > Periodic Trends > Flashcards

Flashcards in Periodic Trends Deck (17):

What are two major factors that affect periodic trends on the periodic table?

1) Effective Nuclear Charge increases from left to right

2) Valence shell increases as you descend down the periodic table, increasing the distance between the valence electrons and the nucleus


What is true about atomic size (radius of the atom is defined as the distance from the center of the nucleus to the exterior of the valence electron cloud) across the periodic table (from left to right and from top to bottom?

Decreases from left to right and from bottom to top (as you ascend the periodic table) 


Why does atomic radius decrease from left to right and as you ascend up the periodic table?

1) Because eff nuclear charge increases (and when eff nuclear charge increases, the valence e- are closer to the nucleus because there is a greater attraction -- b/c of the greater amount of protons in the nucleus -- protons pull valence e- in closer)

2) As you ascend up the period table, there are less number of shells, thus the radius decreases


Atomic radius decreases as atomic number _________.



Helium has a larger radius than Hydrogen. This does not follow the atomic radius trend of the rest of the periodic table. Why is this?

electrons in n=1 repel one another more so than n=2, because they have the smallest interelectronic distance. The repulsion forces the e- away from each, increasing the atomic radius.


The smaller the atomic radius, the _______ the bond it forms when sharing e- with another atom. Shorter bonds create ______ bonds.

1) Shorter

2) Stronger


Energy required to remove the outer-most electron from the valence shell. What happens if this is a large number?

1) Ionization energy 

2) The harder it is the remove valence e- (usually indicates a higher eff nuclear charge and smaller atomic radius)


As ionization energy increases, atomic number _________.

Increases (thus ionization energy increases from left to right and from bottom to top of periodic table)


(although this is a general trend, there are exceptions)


What can ionization energy be used to predict?

Oxidation potential (lower ionization energy, higher the oxidation potential because that is when it is easiest to lose an e-)


Tendency of an element to gain an electron.


(can either be negative or positive -- meaning that gaining an electron can either be exothermic or endothermic)

(Also, a more negative electron affinity number corresponds to a greater affinity, because negative values refers to energy released upon a gain of an electron)


Electron affinity increases as atomic number __________.

increases (however, no trend for e- affinity is known for transitional metals) -- also note that for elements 20-31, the electron affinity is erratic because the d-shell stability is changing)


In general, elements release more energy when going from left to right bottom to top on periodic table.


There is a sudden increase in e- affinity from elements Be to B, Mg, Al, and Ca to Ga. Why is this?

these elements want to gain electron to have a more stable (lower energy) electron configuration  -- i.e. Filling shells


Ability of an atom to attract towards itself the electrons WITHIN A CHEMICAL BOND.

Electronegativity (dipole moment is important)


Also increases from left to right and bottom to top of periodic table


When electronegativity between two atoms are close the bond is _____. When it is greater than a difference of two, the bond is ______.

1) Covalent

2) Ionic


Group 1 of periodic table. Strong reducing agents that easily oxidize to +1 cation. Reactivity increases as you move down the column because it is easier to lose an e- from a shell that is further out. Soluble in water.

alkali metals


Group 2 on periodic table. Strong reducing agents that are easily oxidized to 2+ cations. Reactivity increases as you descend down the column. Cation is not as soluble in water as group 1 because of smaller radius and 2+.

Alkaline earth metals


What do alkaline earth metals usually produce when they react with water (except Be). What do they form when they react with oxygen gas?

1) metal hydroxide and hydrogen gas

2) oxides (MO)