Periodic Table Trends Flashcards
You’d be surprised how many MCAT questions simply require an understanding of the periodic table. But this can be tougher than it looks, and closely related topics like electron affinity, electronegativity, and ionization energy are easy to confuse. Use these cards to master periodic trends and ace these questions whenever you see them.
Where are the alkali metals located on the periodic table?
the first column
(Group IA)
What is the valence shell configuration of all alkali metals, and to which oxidation state do they ionize?
s1
Alkali metals are relatively electropositive, so they will lose 1 valence electron and form a +1 oxidation state.
Where are the alkaline earth metals located on the periodic table?
the second column
(Group IIA)
What is the valence shell configuration of all alkaline earth metals, and to which oxidation state do they ionize?
s2
They are relatively electropositive, so they will lose 2 valence electrons and form a +2 oxidation state.
Where are the halogens located on the periodic table?
the fifth column of the p block
(Group VIIA)
What is the valence shell configuration of all halogens? What oxidation state do they ionize to?
s2p5
They are quite electronegative, so they will accept one additional valence electron to take on a -1 oxidation state.
Where are the noble gases located on the periodic table?
the sixth column of the p block
(Group VIIIA)
What is the valence shell configuration of all noble gases, and to which oxidation state do they ionize?
s2p6
Trick question! Since they already have a completely filled octet, noble gases do not ionize, and they typically exist in the 0 oxidation state as free particles.
Exceptions are Kr and Xe, since they are below the 3rd row, can exceed their octet and make coordinate covalently bonded compounds such as XeF6.
What is the oxygen group, and where is it located on the periodic table?
It is the group (column) below oxygen.
It includes elements such as S and Se that are chemically similar to oxygen. Elements generally share similar properties with the other elements in their group.
Where are the transition metals located on the periodic table?
the entire d block
Why do transition metals have high conductivity?
Due to their unfilled d subshells
d electrons, by their nature, are loosely bound to the atom. As such, elements with partially-filled d subshells can be thought of as nuclei floating in a sea of unattached electrons, prime conditions for electrical conductivity.
What are the representative elements, and where are they located on the periodic table?
They are the most common elements in the solar system and the universe.
They are found in the s block and the p block of the Periodic Table.
By standard nomenclature, these are groups IA, IIA, IIIA, IVA, VA, VIA, VIIA, and VIIIA.
What is the valence subshell for the elements in the first two columns of the periodic table?
s
Group IA has an s1 valence configuration, while IIA is s2.
Note that helium also has a valence s subshell, but is typically listed on the farthest column with the noble gases, as it is chemically more similar to them than the alkaline earth metals.
What is the valence subshell for the elements in the last six columns of the periodic table?
p
For example, Group IIIA has an s2p1 valence configuration, while VIIIA is s2p6.
Note that although helium is typically listed on the farthest column with the noble gases in VIIIA, it actually has a valence s subshell.
Describe the properties of metals in terms of their:
- position in the periodic table
- electronegativity
- preferred oxidation state
Metals are generally:
- found in the lower-left areas of the periodic table.
- low in electronegativity, losing electron density when bonded to nonmetals.
- found in positive oxidation states when in compounds.
What are the main physical properties of metals?
Metals generally are/have:
- good conductors of heat and electricity.
- malleable, ductile, lustrous, and dense solids at room temp.
- fairly high melting and boiling points.
Describe the properties of nonmetals in terms of:
- position in the periodic table
- electronegativity
- preferred oxidation state
Nonmetals are generally:
- found in the upper-right areas of the periodic table.
- high in electronegativity, gaining electron density when bonded to metals.
- found in negative oxidation states when in compounds.
What are the main physical properties of nonmetals?
Nonmetals are/have:
- poor conductors of heat and electricity.
- dull and brittle if they form solids at room temperature.
- significantly lower melting and boiling points than metals (carbon is the primary exception).
How many valence electrons does oxygen, element 8, have?
6
Oxygen is the 6th element in its row. Its valence shell configuration is 2s22p4, for a total of 6 valence electrons.
How many valence electrons does iron, element 26, have?
8
Iron is the 8th element in its row. Its valence shell configuration is 4s23d6, for a total of 8 valence electrons.
Define:
first ionization energy
It is the energy required to remove one valence electron from an atom in the gas phase.
The generic ionization energy equation is:
X(g) ⇒ X+(g) + e-
Describe the general trend of ionization energy across a row of the periodic table.
It increases from left to right across a row of the periodic table.
Other notes about ionization energy:
- Atoms with fully-filled subshell will have high ionization energies.
- Atoms with half-filled subshells will have higher ionization energies than their neighbors.
- The alkali and alkaline earth metals have very low ionization energies.
Which has a higher first ionization energy, Cl or Br?
Cl
Remember that ionization energy decreases going down a column. Br is below Cl in the halogen column.
Describe the general trend of ionization energy heading down a column of the periodic table.
Ionization energy decreases heading down a column of the periodic table.
The further down a column an element lies, the easier to remove. These atoms have higher n values for their valence electrons. Higher n electrons sit further from the atomic nucleus, and are therefore less strongly bound to the nucleus.
Which has a higher first ionization energy, Si or P?
P
Remember that ionization energy increases from left-to-right across a column. P is to the right of Si in period 3.
What is an atom’s second ionization energy?
It is the energy required to remove a subsequent (second) valence electron from a singly-charged ion in the gas phase.
The generic second ionization energy equation is:
X+(g) ⇒ X2+(g) + e-
What are the relative magnitudes of any atom’s first and second ionization energies?
The second ionization energy is always larger in magnitude than the first ionization energy for every atom.
The removal of the first electron reduces the electron-electron repulsion energy of the molecule, allowing the positive nucleus to attract the remaining electrons more strongly and increasing the energy needed to remove subsequent electrons.
How does atomic radius vary as atomic shell increases down a column of the periodic table?
Atomic radius increases down a column of the periodic table.
Each increasing shell can be thought of as another “layer” of electrons, outside the previous layer, increasing the atom’s size. Below. the highlighted elements represent one column of the Periodic Table.
Which has a larger radius, Cl or Br?
Br
Remember that atomic radius increases going down a column, and Br is below Cl in the halogens column. The valence electrons from Br are in the n=4 shell, those from Cl are in the n=3 shell.
How does atomic radius vary as atomic number increases across a row of the Periodic Table?
It decreases across a row from left to right on the periodic table.
This can be explained by effective nuclear charge. As Zeff increases, the nucleus binds the electrons more tightly, pulling them in closer. Below, the highlighted elements represent one full row of the Periodic Table.
Which has a larger radius, Si or P?
Si
Remember that atomic radius decreases from left to right across a column, and P is to the right of Si in the third period.
Define:
electron affinity
It is the energy released when one valence electron is added to an atom in the gas phase.
The generic electron affinity equation is:
X(g) + e- ⇒ X-(g)
Describe the general trend of electron affinity across a row of the periodic table.
Electron affinity increases from left to right across a row.
The smaller an atom is, the closer a newly-added valence electron gets to the positively-charged nucleus, and the more energy released when that electron is added.
Describe the general trend of electron affinity down a column of the periodic table.
Electron affinity decreases down a column.
The further down a column an element lies, the higher the value of n for its valence electrons. Higher-n electrons sit further from the atomic nucleus, and so are less bound to the nucleus and release less energy when added.
Define:
electronegativity
It describes that atom’s tendency to attract electron density towards itself through a chemical bond.
Note that electronegativity only applies to atoms in a bond. There is no such concept as the electronegativity of a bare atomic species, although certain elements are said to be “more electronegative” due to their behavior when bonded.
Describe the general trend of electronegativity across a row of the periodic table.
Electronegativity increases from left to right across a row.
The smaller an atom is, the closer the electrons in its bonds get to the positively-charged nucleus, and the more strongly the electrons are attracted to the nucleus.
Describe the general trend of electronegativity heading down a column of the periodic table.
Electronegativity decreases heading down a column of the periodic table.
The further down a column an element lies, the larger its radius. This puts more space between the positively-charged nucleus and the electrons in any bonds it makes, reducing the attraction between the nucleus and the electrons.
Which element has the highest electronegativity?
Fluorine
Electronegativity increases toward the top right of the periodic table. Fluorine, which is the rightmost and uppermost element that isn’t a noble gas, has the greatest tendency to be electronegative.
On the Pauling scale, the most commonly-used scale for determining electronegativity values, fluorine has the highest value possible: 4.0.
What class of elements have the highest values of electronegativity?
Nonmetals
Fluorine is the element with the highest electronegativity, and as a general rule, the closer an element is to fluorine, the higher its electronegativity.
Some other notes about electronegativity:
- The halogens are the most electronegative group.
- Noble gases capable of making bonds (Xe and Kr) are relatively electronegative.
- Metals, particularly the alkali and alkali earth metals, are generally electropositive (very low electronegativity).
Which has a higher electronegativity, Cl or Br?
Cl
Remember that electronegativity decreases going down a column, and Br is below Cl in the halogens column.
Which has a higher electronegativity, Si or P?
P
Remember that electronegativity increases from left to right across a column, and P is to the right of Si in period 3.
