4.8 Chemistry Basics
Key Takeaways
- Protons (+) and neutrons (0) sit in the nucleus; electrons (-) occupy shells; atomic number = protons, mass number = protons + neutrons
- Ionic bonds transfer electrons (metal + nonmetal); covalent bonds share electrons (nonmetal + nonmetal)
- The pH scale is logarithmic: each unit is a 10-fold change in H+ concentration; below 7 is acidic, 7 neutral, above 7 basic, blood ~7.4
- Reaction types: synthesis, decomposition, single replacement, double replacement, and combustion; mass is conserved when balancing
- Molarity (mol/L) measures concentration; exothermic reactions release energy, endothermic reactions absorb it
Why Chemistry Is on a Nursing Exam
The ATI TEAS 7 tests fundamental chemistry because medications, body fluids, and lab values are all chemistry in action. You will need to read atomic structure, predict bond types, recognize reaction patterns, balance simple equations, and interpret the pH scale — the same scale nurses use to read arterial blood gases.
Atomic Structure
| Particle | Charge | Location | Mass |
|---|---|---|---|
| Proton | Positive (+) | Nucleus | ~1 amu |
| Neutron | Neutral (0) | Nucleus | ~1 amu |
| Electron | Negative (–) | Electron shells | ~0 amu |
Three numbers define an atom:
- Atomic number = number of protons — this identifies the element.
- Mass number = protons + neutrons.
- Atomic mass = weighted average of an element's isotopes (atoms with different neutron counts).
Reading the Periodic Table
| Group | Members | Key Property |
|---|---|---|
| Alkali metals | Li, Na, K | Very reactive, 1 valence electron |
| Alkaline earth metals | Mg, Ca | Reactive, 2 valence electrons |
| Halogens | F, Cl, Br, I | Very reactive nonmetals, 7 valence electrons |
| Noble gases | He, Ne, Ar | Unreactive, full outer shell |
- Periods are the horizontal rows (each row adds an electron shell).
- Groups are the vertical columns (members share chemical properties because they have the same number of valence electrons, the outermost electrons that drive bonding).
Chemical Bonding
| Bond | What Happens | Forms Between | Example |
|---|---|---|---|
| Ionic | Electrons transfer | Metal + nonmetal | NaCl (table salt) |
| Covalent | Electrons shared | Nonmetal + nonmetal | H2O (water) |
| Hydrogen | Weak attraction | H to O, N, or F | Between water molecules |
A quick test for any bonding question: transfer = ionic, share = covalent. Atoms bond to reach a full outer shell (the octet rule, eight valence electrons).
The Five Reaction Types
| Type | Pattern | Example |
|---|---|---|
| Synthesis | A + B to AB | 2H2 + O2 to 2H2O |
| Decomposition | AB to A + B | 2H2O to 2H2 + O2 |
| Single replacement | A + BC to AC + B | Zn + 2HCl to ZnCl2 + H2 |
| Double replacement | AB + CD to AD + CB | AgNO3 + NaCl to AgCl + NaNO3 |
| Combustion | Fuel + O2 to CO2 + H2O | CH4 + 2O2 to CO2 + 2H2O |
Balancing by Conservation of Mass
The law of conservation of mass says atoms are never created or destroyed in a reaction, so the same number of each atom must appear on both sides. You balance by adjusting coefficients (the big numbers in front), never the subscripts.
Worked Example: Balance H2 + O2 to H2O.
- Unbalanced count: left has 2 H and 2 O; right has 2 H and only 1 O.
- Place a coefficient of 2 on water: H2 + O2 to 2H2O. Now the right has 4 H and 2 O.
- Balance hydrogen by placing 2 in front of H2: 2H2 + O2 to 2H2O.
- Final check: 4 H and 2 O on each side. Balanced.
States of Matter
| State | Shape | Volume | Particle Motion |
|---|---|---|---|
| Solid | Fixed | Fixed | Vibrate in place |
| Liquid | Takes container | Fixed | Slide past each other |
| Gas | Takes container | Expands to fill | Move fast and freely |
Adding energy drives changes of state: melting (solid to liquid), vaporization (liquid to gas); removing energy drives freezing and condensation.
Acids, Bases, and the pH Scale
| Property | Acids | Bases |
|---|---|---|
| pH | Below 7 | Above 7 |
| H+ ions | Donate H+ | Accept H+ |
| Taste / feel | Sour | Bitter, slippery |
| Examples | HCl, vinegar, citrus | NaOH, ammonia, soap |
The pH scale runs 0–14 and is logarithmic: each one-unit change equals a ten-fold change in hydrogen-ion concentration. So pH 3 has ten times more H+ than pH 4 and is ten times more acidic. Pure water is neutral at 7, and human blood is tightly held near 7.4.
Solutions and Concentration
A solution is a solute dissolved in a solvent (water is the universal solvent). Concentration is most often given as molarity (M) — moles of solute per liter of solution. Diluting a solution with more solvent lowers its molarity. Reactions that release energy are exothermic (give off heat); those that absorb energy are endothermic.
pH Worked Example: A solution measures pH 5; a second measures pH 2. How much more acidic is the second? Each pH unit is one factor of ten, and the gap is 5 − 2 = 3 units, so the pH 2 solution is 10 x 10 x 10 = 1,000 times more acidic than the pH 5 solution.
What type of bond forms when electrons are transferred from a metal to a nonmetal?
A solution has a pH of 3. How does its acidity compare to a solution with a pH of 5?
Which reaction type follows the pattern AB + CD to AD + CB?
The number of protons in an atom is called its atomic ___ and determines which element the atom is.
Type your answer below
Order these solutions from most acidic to most basic by pH.
Arrange the items in the correct order