Chemistry Basics for Pre-Medical Students

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Pre-Med Chemistry Basics

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Chemistry Overview

Chemistry is the science that studies matter. You’ll learn about matter’s properties, changes to matter, and what kinds of energy changes occur when those changes happen. As a pre-medical student you’ll be taking 8 credits of chemistry. That’s 2 semesters worth. In addition, you’ll be taking 8 credits of organic chemistry, a topic which be covered in another lectures. 

The Nature of Matter

All chemistry classes tend to begin by introducing you to the lingo.  What is matter? What is Energy? What are fundamental particles? All of this you’ll cover first which will help you really understand the other topics. We’re going to begin with some basic definitions – things you should know. Then go into some study strategies. 

Chemistry: The science that studies matter – its properties, the changes it undergoes, and the energy changes that accompany those processes.
Organic Chemistry: The study of Carbon and how it combines with hydrogen, nitrogen, and sulfur.
Inorganic Chemistry: Study of compounds not covered in Organic Chemistry.
Analytical Chemistry: The branch of chemistry concerned with the detection or identification of substances in a sample (qualitative analysis) or with the amount of each substance present (quantitative analysis).
Physical Chemistry: Applies the mathematical theories and methods of physics to the properties of matter and to the study of chemical processes and their accompanying energy changes.
Biochemistry: The study of the chemistry of processes in living organisms.
Matter: Anything that has mass and occupies space.
Mass: A measure of the quantity of matter in a sample of any material.
Energy: The capacity to do work or to transfer heat.
Kinetic Energy: The energy of motion. Easily transferred between objects. Capacity for doing work directly.
Potential Energy: The energy an object possesses because of position, composition, or condition.

Atom: The smallest particle of an element that maintains its chemical identify through all chemical and physical changes is called an atom.
Fundamental Particles: Electrons, Protons, and Neutrons. All matter is comprised of this.
Atomic Number (Z): The number of protons in the nucleus.
Molecule: The smallest particle of an element of an element or compound that can have a stable independent existence. Can be a single stable atom or a definite number of atoms.
Element: Contains a single type of atom. Cannot be decomposed into simpler substances by chemical changes. 

Solid (s): Rigid with definite shape & volume. Volume does not vary much with changes in temperature and pressure. A state of matter.
Liquid (l): Takes the shape of its container. Definite volume. Volume does not vary much with changes in temperature and pressure. A state of matter.
Gas (g): No definite shape or volume. Highly compressible with pressure. Expands indefinitely upon heating. 

Properties: Chemical and Physical.
Chemical Properties: Exhibited by matter as it undergoes changes in composition.
Physical Properties: Observed in the absence of any change in composition. Examples are color, density, hardness, melting point, boiling point, electrical, and thermal conductivity.

Chemical Change: (1) One or more substances are used up (at least partially). (2) One or more new substances are formed. AND (3) Energy is absorbed or released.  All three must occur.
Physical Change: A change that occurs with no change in chemical composition.
Mixture: A combination of two or more pure substances in which each substance retains its own composition and properties.
Heterogeneous: Type of Mixture. Contents have recognizably different properties.
Homogeneous: Type of mixture that’s also called a ‘solution’. Has uniform properties throughout.
Substance: Cannot be broken down or purified by physical means. Can be changed in identity and properties by chemical methods. Under identical conditions, properties do not vary.
Compound: A substance that can be decomposed by chemical means into simplier substances, always in the same ratio by mass.
Element: A substance that cannot be decomposed into simpler substances by chemical changes.
Law of Definite Proportions / Law of Constant Composition: Different samples of any pure compound contain the same elements in the same proportions by mass.
Symbols: Used to represent elements.

 

Fundamental Units of Measurement

7 Fundamental Units of Measurement: Time (second), Length (meter), Mass (kg), Electric Current(amp), Temperature(K),Luminous Intensity (candela), Amount of Substance (mole).
Mass: The measure of a quantity of matter that a body contains.
Weight: The measure of the gravitational attraction on a body exerted by the center of the ___ (earth)
Kilogram: Basic mass unit of the SI system.
Volume: In SI the basic unit is the cubic meter. In metric it is the liter.
Dimensional Analysis / Factor-Label Method / Unit Factor Method: “Multiplying by a ratio that = one”
Unit Factors: May be constructed from any two terms that describe the same / equivalent amounts. Does not affect significant figures because they are exact! 
Temperature: Measures the intensity of heat in a body.
Heat: A form of energy that always flows spontaneously from a hotter body to a colder body.
Joule: 1kg x (m2 / s2) Basic unit of energy and work. 
Exothermic Process: Evolution of heat that occurs simultaneously with a physical or chemical reaction. 
Endothermic Process: Absorption of heat that occurs simultaneously with a physical or chemical reaction.
Heat Capacity: The amount of heat required to raise a body’s temp by 1oC

Formulas and Laws

Ok, so that was a bit of an information dump above. You have to get done some of the key terms though in order to know what’s going on in chemistry. Now, let’s look at some important formulas, laws, and strategies that will help you both in the class and on the MCAT. I recommend committing all of the following to memory!


Density: Mass per unit of volume. Or d = m / v
Kelvin:
 The SI measurement for temperature. (K = TC + 273)
Tc to Tf Calculation: 1.8 x Tc + 32 =Tf <– C to F <– Celsius to Fahrenheit (Memorize in one direction!)
Kinetic Energy Calculation: .5(m)(v2)
calorie: 4.184J. In foods 1 Calorie = 1000 calories.
Specific Heat: The amount of heat required to raise the temperature of 1g of the substance by 1o Celsius.

Also memorize these three laws

Law of Conservation of Matter:
 Matter cannot be created or destroyed during a physical change or during a chemical reaction. 
Law of Conservation of Energy: Energy cannot be created or destroyed during a physical change or a chemical reaction. It can only be converted from one form to another.
Law of Conservation of Matter and Energy: The combined amount of energy and matter available in the universe is fixed.

 

 

Key Strategies for Early Chemistry Content

This early content really is important, but it doesn’t get too detailed yet. Here’s my tips for studying it.

  1. Be able to clearly articulate the difference between the different states of matter. 
  2. Memorize the order of first 18 elements on the periodic table. This will help you later.
  3. Memorize ALL of the formulas. You’ll need them on exams and the MCAT.
  4. If your class lets you bring a formula ‘cheat sheet’ to exams, use it, but don’t rely on it.
    1. The MCAT will not let you bring in cheat sheets. 
    2. Do enough homework and studying before the exam that you don’t even need your cheat sheet.
  5. Do your chemistry homework at least 3 times before the exam. 
    1. Once for credit
    2. Again for review
    3. A third time to make sure it’s memorized!

 

Units and Conversions

I found two great videos on these HIGH YIELD topics for chemistry. Watch them and read my advice on those very tricky topic. In fact, I’d say sig figs and unit conversions are solely responsible for many a pre-med’s demise. Here’s my tips on how to master the content.

  • Memorize the common metric units. You should be able to convert from kilograms to milligrams without even thinking. This is very important for exams.
  • Watch these videos and as she explains how to do the work, do it yourself – on paper.
  • Once you think you understand it, try to do some homework problems. You can do class homework AND  find some extra work online. Notice I said AND
  • Go Slow. Even when you have it down pat. Go slow. Double check every conversion.
  • Never, ever, neglect significant figures. If you don’t have the right number of sig figs on your answer… it’s wrong.  Confused about sig figs – re-watch the video.

Reactions, Ions, & Redox

I’d tell you this part was easy, but then I’d be lion! Alright, I’ll save the humor and tell you to just remember one phrase for later in this section “LEO GER”.

(L)oss
(E)lectrons
(O)xygenation

(G)ain
(E)lectrons
(R)eduction

So part of chemistry is all balancing equations. When you have a chemical reaction you may be altering compounds and forming new molecules, but your never violating the first law or third law of thermodynamics. We reviewed the three laws before.

The first says: “Matter cannot be created or destroyed during a physical change or chemical reaction”

The third says: “The combined amount of energy and matter available in the universe is fixed.”

Or in other words everything needs to be balanced! Balanced how? You are now asking, confused and a little annoyed.

Chemistry is like a math equation. You have a right side an equal sign and a left side. And just like math, if you take something away on the right (an element) you need to make sure the same element appears properly on the left. Let’s look at a very simple example.

H2O <–> OH- + H+

Still confused? Go watch Taylor DeWitt, the Bob Ross of chemistry, as he calmly explains how to balance equations much better and more effectively then we can. Just know that you absolutely need to know how to do this dead cold. You will see this many times on your exams. 

Let’s talk about that LEO GER:

This lets you know if a reaction is an oxidation / reduction reaction aka a REDOX reaction. These are actually pretty cool reactions. However, learning REDOX reactions is another topic that murders pre-meds on chem exams. It’s probably because it’s complex and confusing to learn at first and often people procrastinate because it’s hard. Our advice, practice. practice. practice. Use resources like this article by Lumen Learning and get tutoring when you are first coming up to this chapter!

Don’t Try This at Home! 

REDOX reactions can be used for stuff like electroplating! Which is pretty darn cool in this writer’s opinion!

Water, Solutions, and States

"Water, water everywhere and not a drop to drink!"

Samuel Taylor Coleridge

The Crash Course Series is one of the best ways to be introduced to pretty advanced science courses. Make sure you don’t rely on it entirely for your studying though! As detailed as these videos are, you still need to do your homework, labs, and read your textbook.

So we’ve reached the part about water – and a lot of other stuff. Water is a big topic and a topic you’ll see again as a pre-medical student. It comes up over and over again in biochemistry, biology, several medical topics. It’s also an amazing topic. It’s big enough that it deserves it’s own section. Instead we combined it with a bunch of other stuff! Here ya go!

Hydrophilic: Water loving.
Hydrophobic: Water hating.
Emulsifiers: Allows hydrophobic colloids to exist in polar solvents. 
Micelles: ‘tails’ with a polar end and a nonpolar end.
Surfactant: Soaps and detergents. 
“Hard” Water: Contains Fe, Ca, or Mg all of which displace Na
Detergents: Contain sulfonate or sulfate instead of carboxylate groups.
Eutrophication: A high concentration of phosphorous which causes vegetation growth.

 

Now, let’s define different states of matter and what holds them together. Pay special attention to the concent of hydrogen bonding. Many of water’s novel properties come from these weak transient hydrogen bonds .

Condensed Phases: Liquids and Solids. Particles close together and which interact strongly. Created by intramolecular forces.
Intermolecular Attractions / Forces: Those between molecules or ions.
Intramolecular Attractions / Forces: Forces within a single atom or molecule.
Miscible: When liquids diffuse into other liquids, mix and produce a homogenous solution.
Hydrogen Bonding: Causes the attractive forces between water molecules. A type of dipole – dipole intramolecular force. Hydrogen Bonding is stronger than other dipole-dipole bonds.
Ionic Compounds: Close together, usually very high melting points. Higher magnitude charges, usually higher melting point.
Dipole: Positive and negative ends with charges.
Polar Molecules: Permanent Dipoles. Setup so that it always has a partial positive and negative ends.
Non-Polar Molecules: No dipole moment. Usually non-polar due to symmetry. Example CCl4.
Dipole-Dipole Interactions: An intramolecular force created by the interaction of different polar ends of polar covalent molecules. Effective only over short distances and weaker than ionic forces. Less important as temperature decreases. Makes compounds more volatile than ionic bonds.
Hydrogen Bonds: A strong dipole-dipole interaction. Occurs amongst polar covalent molecules containing H bonded to one of the three small, highly electronegative elements. The hydrogen serves as the permanent positive part of a permanent dipole.

Physical Properties of Matter

Now let’s look at physical properties of matter. These are important, but we’re not going to spend a great deal of time on them. Just a few that tend to be important to chemistry or medicine. 

Physical Properties (Boiling Point, Melting Point, Viscosity, Surface Tension) are all governed by the strength of the intermolecular forces sticking molecules together.
Viscosity: The resistance to flow of a liquid. Honey = High Viscosity. Gasoline = Low Viscosity.
Surface Tension: A measure of inward forces that must be overcome to expand the surface area of a liquid. Causes drops of a liquid to form a sphere, due to a desire to minimize surface area via IMFA.
Cohesive Forces: The forces holding a liquid together.
Adhesive Forces: The force of attraction between a liquid and another surface. Think side of a beaker.
Meniscus: Concave = Adhesive > Cohesive. Convex = Adhesive < Cohesive.
Capillary Action: If adhesive forces > cohesive forces, then the liquid creeps up the sides of the tube until a balanced is reached between the weight of the liquid and the cohesive forces. Roots of a plant.
Evaporation / Vaporization: Process by which molecules on the surface of a liquid break away and go into a gas phase. Requires some min. kinetic energy greater than where it is at a stable liquid phase.
Cooling by Evaporation: The particles with the most kinetic energy ‘heat’ leave the liquid, thereby removing heat and cooling the remaining liquid. (The type of cooling often recommended for mild heat exertion!)
LeChatelier’s Principle: A system at, or changing towards, equilibrium tends responds in a way that tends to relieve or undo any “stress” placed upon it. (This is important for medicine and for life!)

To keep this readable, I cut a lot of different things out of this Basic Chemistry review, including many different forces. You’ll need to be aware of and memorize more of them for a chemistry class! We’re going to just look at a few more concepts before moving on. 

Boiling Point: The temperature at which the vapor pressure of the liquid equals the external pressure.
Distillation: Method by which a mixture of liquids, with significantly different boiling points, can be separated into its components through boiling.
Specific Heat: The amount of heat that must be to the stated mass of a liquid to raise its temperature by one degree Celsius.
Heat of Condensation: The amount of heat that must be removed from steam to convert it to water without changing its temperature.
Melting Point (Freezing Point): The temperature at which its solid and liquid phases coexist in equilibrium.

Solutions, Solvents, & Solutes. yay.

 

Solution: A homogeneous mixture, at the molecular level, of two or more substances. 
Solvent: The medium in which solutes are dissolved. 
Solutes: Usually dissolve to give ions or molecules in solution.
Powdered tea is the solute. Water is the solvent. Iced Tea is the solution.
(Not totally accurate, but bear with me)


*Key Concept Warning!!*
Many Ionic solids dissolve by endothermic process.
 Adding heat quickens the dissolving because it places stress on the system in such a manner that is relieved by dissolving faster!
Some solids and many liquids and gases dissolve by exothermic process: In these cases the solubility decreases as temperatures decrease.

~~ Osmotic Pressure: This is an important concept for a lot of medicine. ~~

Semipermeable Membrane: A membrane that allows water to pass through it.
Osmotic Pressure: The pressure required to stop osmosis.
Colloids (Colloidal Dispersion): Represent an intermediate kind of mixture in which the solute particles, or dispersed phase, are suspended in the solvent phase, or dispersing medium.

Two Final Concepts to Remember

Chemical Processes Naturally Favor:

  • A decrease in the energy of a system it’s an Exothermic Process and results in…
  • An increase in the disorder (more chaos!!) of a system. (Aka Entropy)

So when your parents ask you why your room isn’t clean, just let them know that BreakThru Mentoring, LLC says it’s due to the natural entropy of the universe. Then, before we get an angry email, clean your room. 

Acids and Bases

As we said before, the Crash Course Series is one of the best around for learning biology, chemistry, physics, and so on. Make sure you subscribe to their channel! 

Acids and bases in movies are a bit scarier in movies then they are in real life. Don’t get me wrong, they are extremely dangerous and can seriously blind, scar, or injure you if spilled. But when I took chemistry class I was expecting to need to wear full body suits when handling the sulfuric acid. Turns out gloves, and some general caution is all you need to be ok. 

  • Know your pH Scale
    • Know examples on the pH Scale
    • Water has a pH of 7 (can be changed by adding stuff to it.)
    • Formula: pH = -log[H+]
      • You’ll need a calculator that can do log! Know how to do this before your exam!
  • If the pH is less than 7 the solution is considered to be acidic. If the pH is above 7 the solution is considered to be basic, or alkaline.
  • What makes something acidic or alkaline?
    • The more H+ ions = the more acidic.
    • The more OH- ions = the more basic.
  • Are there different definitions on acids and bases?
    • Yes! The names of the important ones are
      • Bronsted-Lowry Definition
        • Acids are proton donors (H+ Donors)
        • Bases are proton acceptors.
      • Arrhenius Definition
        • Any compound that increases the H+ ion concentration is an acid.
      • Lewis Theory (Important in organic chemistry!)
        • A Lewis Acid is an electron pair acceptor.
        • A Lewis Base is an electron pair donor.
        • You gotta remember this one for organic chem! The highest of high yield!
    • Is the difference important?
      • Yes! For your tests at least! Be sure to tell based on a given formula which definition is being referenced.
  • Conjugate Acids and Bases
    • Every acid has a conjugate base.
    • Think of it like a fighter jet.
      • When the jet leaves its base, it’s like an acid leaving it’s conjugate based. 
      • Ex. H2SO4 <-> H+ + HSO4-
        • The acid is the H+ and the conjugate base is the HSO4-
      • Practice will make identified acids and conjugate bases easier.
  • Strong & Weak Acids and Bases
    • A strong acid or base dissociates completely in an aqueous solution.
    • Or in other words…
      • A strong acid like HBr will go right to H+ + Br-
      • The gases make up the strongest acids. 
    • Strong Acids are always paired with weak bases. 
  • Want to read more? Check out this free chemistry chapter on acids and bases!

Gases

A very solid video on the gas laws. For a pre-med in chemistry half the battle is learning the laws, half the battle is learning the formulas, and half the battle is knowing when to apply them. We pride ourselves on our math skills here at BreakThru.

 

I’m going to introduce just a few key concepts, some formulas, + an important Theory. That’ll wrap up our Basic Chemistry Review!

Barometer: a simple device for measuring atmospheric pressure.
Boyle’s Law: PV = k, or P1V1 = P2V2
Absolute Zero: -273.15 Kelvin
Charles Law: V/T = k, As temp goes up, volume goes up.
Standard Temperature and Pressure (STP): 0 0C (273K) and 1 atm (760 torr)
Combined Gas Law  Equation: PV / T = PV / T
Avogadro’s Law
: At the same temp and pressure, equal volumes of all gases contain (very nearly) the same number of molecules. (1 mole of gas per 22.414 liters.)
Ideal Gas: A gas that exactly obeys the gas laws.
Ideal Gas Law / Equation: PV = nRT, where n = number of moles and R = 0.0821 * L * atm / mol * K
Partial Pressure: The pressure that each gas exerts in a mixture.
Gas Velocity: V = sqrt (3RT / MW)
Effusion: The escape of a gas through a tiny hole. Lighter gas molecules effuse faster than heavier ones.
Diffusion: The movement of a gas into a space, or the mixing of one gas with another.
Non-Ideal Gas Behavior: Most significant at high pressures and/or low temperatures.
Van Der Waals Equation: P,V,T,n are the measured values. a = attraction coefficient, and b = ‘bigness’ coefficient.
Dispersion Forces: Result from short-lived electrical dipoles produced by the attraction of one atom’s nucleus for another atom’s electrons. Exists in all molecules, but especially important for nonpolar molecules which would never liquidize otherwise.

Kinetic-Molecular Theory: 4 Basic assumptions about ideal gases.

  1. Gas molecules are discrete, very small, and very far apart (relative to their own sizes).
  2. The gas molecules move in continuous, random, straight-line motion with varying velocities. 
  3. The collisions between gas molecules and with the walls of the container are elastic, no net energy is lost or gained.
  4. At any given instant the only a small fraction of molecules are involved in collisions. When not colliding they travel in straight motions with constant velocities.

And that’s Basic Chemistry! Good work!

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