A few of us here at MedLife Mastery are big Avatar: The Last Airbender fans, so it stings a little to admit there are more than four elements! The count is 118, and IUPAC has named and confirmed every one of them.
Sadly, we still can’t bend any of them. We can walk you through the periodic table on the MCAT, though, from what you get on test day to the four trends and the groups that show up in questions. Let’s get started!
Do You Get a Periodic Table on the MCAT?
Yes! The AAMC says you’ll have access to the periodic table while you answer questions in the Chem/Phys and Bio/Biochem sections. You can’t bring notes or reference sheets into the testing room, so you’ll work from this table.
The AAMC also posts its periodic table as a free PDF. Keep it open while you do practice questions, so finding an element feels automatic by test day!
So skip memorizing element names and numbers. Put that time into the trends below, since those are what the questions ask you to reason with 🙂
Periodic Table on the MCAT: What You Need to Know
General chemistry makes up about 30% of the Chem/Phys section and 5% of Bio/Biochem, by the AAMC’s estimates. Periodic table MCAT questions can show up inside a passage or as stand-alone (discrete) questions.
Before you start, brush up on atomic structure and electron configuration, especially how electrons fill shells and subshells. Every trend on this page comes back to where the outermost electrons sit! These are the four things to learn.
- How the table is organized into periods, groups and element types
- Valence electrons and effective nuclear charge (Zeff)
- The four periodic trends (atomic radius, ionization energy, electron affinity and electronegativity)
- The main chemical groups and how each one reacts
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Electronegativity, atomic radius, ionization energy and effective nuclear charge, which way each one runs, and why. Five pages.
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Periodic Table Basics: Periods, Groups and Element Types
The periodic table orders the elements by atomic number, the number of protons. Periods are the rows, read left to right, and groups are the columns, read top to bottom. Groups are also called families.
With each step to the right in a period, the atom gains one proton and one electron. With each step down a group, it gains a new shell, as the principal quantum number (n) goes up by one.
Elements in the same group share the same valence electron configuration, so they react in similar ways. That’s why one column can tell you so much about an element!
Metals, nonmetals and metalloids
Metals behave a lot alike as a group. Nonmetals vary more from one element to the next.
Electrical conductivity runs high on the left and in the middle, where the metals are. Moving right across a period, elements turn into metalloids, which conduct partway, and then nonmetals, which are poor conductors. Graphite, a form of carbon, is the classic exception.
Our basics of the periodic table notes cover the element types in more depth, with more examples!
Valence Electrons and Effective Nuclear Charge (Zeff)
Valence electrons are the electrons in an atom’s outermost shell. They’re the ones that react and form bonds, so they decide how an element behaves.
Effective nuclear charge (Zeff) is the net positive pull the nucleus has on those valence electrons. The inner (core) electrons sit between the nucleus and the valence shell and block part of that pull. That blocking is called electron shielding.
On the MCAT, a quick estimate is enough! Subtract the core electrons (S) from the protons (Z). Lithium has 3 protons and 2 core electrons, so its valence electron feels a Zeff of about +1.
Across a period, Zeff increases
As you move right, each element adds a proton and a valence electron, and the core stays the same. Z goes up while S holds steady, so Zeff rises, from +1 for lithium to +2 for beryllium.
Down a group, Zeff stays about the same
As you move down, each element adds a full shell of core electrons along with its new protons. The extra shielding cancels the extra charge, so sodium’s Zeff is about +1, the same as lithium’s.
Sodium’s valence electron sits in the n = 3 shell, farther from the nucleus, so the nucleus holds it more loosely.
How hard the nucleus pulls (Zeff) and how far out the valence shell sits (n). Work out those two and you can rebuild any periodic trend on test day!
Our valence electrons and effective nuclear charge notes have more practice problems if you’d like them!
Periodic Table Trends on the MCAT
Two arrows cover all four trends! Ionization energy, electron affinity and electronegativity climb toward fluorine at the top right, and atomic radius grows toward cesium at the bottom left.
Atomic radius
Atomic radius is half the distance between the nuclei of two touching atoms of the same element. It shrinks from left to right, because a rising Zeff pulls the same shell in tighter.
It grows down a group, because each new shell puts the valence electrons farther out.
Ionization energy
Ionization energy is the energy needed to remove an electron from a gaseous atom, so it’s always endothermic. It rises from left to right as Zeff grips the valence electrons harder. It falls down a group as those electrons sit farther from the nucleus.
Group 1 metals give up their one valence electron easily, so they have the lowest ionization energy in each period. The noble gases have some of the highest.
After the first electron, each one costs more energy, since it comes off an ion that’s already positive. The jump is huge once the atom has a noble gas configuration, so sodium’s second ionization energy dwarfs its first.
Electron affinity
Electron affinity is the energy released when a gaseous atom gains an electron. It increases from left to right and decreases down a group, following Zeff and distance the same way ionization energy does.
Halogens have the highest values, since one more electron completes their octet!
Electronegativity
Electronegativity measures how strongly an atom pulls on the electrons it shares in a covalent bond. It increases from left to right and decreases down a group. Fluorine is the most electronegative element, at about 4.0 on the Pauling scale.
Electron affinity and electronegativity are easy to mix up, and it’s a common slip! Electron affinity is about a lone, neutral atom gaining an electron. Electronegativity is about an atom tugging on electrons in a bond.
All three sit in period 3, so the plain trend says Al > Mg > Na. Check for the exception first! Aluminum’s outermost electron is a lone 3p electron, higher in energy than magnesium’s 3s pair, so it comes off more easily.
So the order is Mg > Al > Na. Nice work if you caught it!
Our main trends of the periodic table notes go deeper on each one!
(Optional) If you’d like to practice trend questions in full passages with a top scorer beside you, our 6-Week Live MCAT Accelerator runs 12 live strategy classes taught by a 520+ scorer.
Specific Chemical Groups on the MCAT
Since chemical groups are columns, the easiest way to learn them is by their valence electrons. That count tells you whether an element tends to lose electrons or gain them!
Alkali and alkaline earth metals (groups 1 and 2)
On the far left, these metals have low ionization energies, electron affinities and electronegativities. Losing one or two electrons gives them a noble gas configuration, so they form cations easily.
As cations, they bond ionically with anions. Together, groups 1 and 2 are called the active metals.
Chalcogens and halogens (groups 16 and 17)
On the right side, oxygen, sulfur and the halogens have high ionization energies, electron affinities and electronegativities. With six or seven valence electrons, gaining electrons is the quick route to an octet!
Halogens react readily with the alkali and alkaline earth metals, and the electron transfer forms ionic compounds like NaCl. Our bonding and chemical reactions guide covers ionic and covalent bonds.
Noble gases (group 18)
Noble gases already have a full valence shell, eight electrons for all of them except helium, which has two. Gaining or losing an electron would break that stable setup, so they’re nearly unreactive. They’re also called the inert gases!
Transition metals (groups 3 to 12)
Transition metals are the d-block elements, since their highest-energy electrons fill a d subshell. Like other metals, they have low ionization energies, electron affinities and electronegativities.
They can lose different numbers of electrons from their s and d orbitals, so many have several oxidation states. Iron shows up as Fe2+ or Fe3+, and copper as Cu+ or Cu2+.
They’re less reactive than the alkali metals as a group, and gold and platinum barely react at all!
Our Specific Chemical Groups notes go group by group in more detail, if you’d like more!
To see how top scorers handle these questions under time pressure, our Chem/Phys & Bio/Biochem Mastery Course has 100+ strategy lessons from 130+ scorers, including 70+ AAMC passage walkthroughs.
Important Definitions and Key Terms
Periodic Table MCAT FAQs
Is the periodic table given on the MCAT?
Yes! The AAMC gives you access to a periodic table during the Chem/Phys and Bio/Biochem sections. It isn’t available during CARS or Psych/Soc, which don’t test chemistry.
Do you have to memorize the periodic table for the MCAT?
No. You’ll have the table on test day, so you don’t need element names, atomic numbers or masses memorized. Learn the four trends, the group names and where the metalloid staircase runs instead!
What does the MCAT periodic table look like?
It’s a standard periodic table. The AAMC links its version from its section overview pages as a free PDF, so you can practice with it before test day.
Which periodic trends should I know for the MCAT?
Atomic radius, ionization energy, electron affinity and electronegativity, plus Zeff, which explains all four. Atomic radius increases down and to the left, and the other three increase up and to the right!
Are orbitals on the MCAT?
Yes, as part of electron configuration. Expect the order orbitals fill in (the Aufbau principle), Hund’s rule and the quantum numbers. Our atomic structure guide walks through them!
What is electron affinity on the MCAT?
It’s the energy released when a neutral, gaseous atom gains an electron. Electronegativity is similar, but it describes an atom pulling on shared electrons in a covalent bond, while electron affinity describes a lone atom.
Final Thoughts on the Periodic Table for the MCAT
You get the table itself on test day, so the periodic table is one of the friendlier MCAT topics! Learn the two arrows, tie each trend back to Zeff and distance, and these questions start to feel predictable.
If you’d like help building that habit, our 6-Week Live MCAT Accelerator pairs live strategy classes with seven 1:1 sessions with a 515+ scorer.
If the cohort dates don’t line up with your test, 1:1 MCAT tutoring with a 515+ scorer works at your own pace, and if Chem/Phys is your weakest section, we’ll match you with a 130+ C/P scorer.
You’ve got this, and we’re rooting for you :)
Additional Reading Links: Study Notes for Periodic Table on the MCAT
Additional Reading: General Chemistry MCAT Topics:
- Atomic Structure on the MCAT
- Acids and Bases on the MCAT
- Bonding and Chemical Reactions on the MCAT
- Chemical Kinetics on the MCAT
- Electrochemistry on the MCAT
- Equilibrium on the MCAT
- Solutions on the MCAT
- Stoichiometry on the MCAT
- The Gas Phase on the MCAT
- Thermochemistry on the MCAT
- Redox Reactions General Chemistry MCAT
Supplemental Resources
Want to go deeper on this topic? Here's where to read, watch and practice it next.
Read
- Kaplan MCAT General Chemistry Review 2026-2027, Chapter 2
- The Princeton Review MCAT General Chemistry Review, sections 4.7 through 4.8
Watch
- “The periodic table” (Khan Academy)
- “Electron affinity: period trend” (Khan Academy)
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