protons set identity
⚗️HESI A2 STUDY GUIDE
HESI A2 Chemistry Study Guide
Review atoms, periodic patterns, bonding, reactions, moles, solutions, acids, bases, and common calculations.
8 key ideas8 flashcards5 practice questions
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Count particles, charge, moles, and liters before calculating.
atoms and charge stay equal
moles divided by liters
Key ideas to know
Start with the relationships between ideas. Then close the notes and explain each one from memory.
- 01
Atomic number equals the number of protons in an atom's nucleus.
- 02
Isotopes of one element share proton count but differ in neutron count.
- 03
Ionic bonding involves attraction between oppositely charged ions; covalent bonding shares electron pairs.
- 04
A balanced chemical equation keeps each element's atom count equal on both sides.
- 05
One mole represents 6.022 × 10²³ specified particles.
- 06
Molarity equals moles of solute divided by liters of solution.
- 07
Acids donate hydrogen ions under the Brønsted-Lowry model, while bases accept them.
- 08
The pH scale is logarithmic, so a one-unit difference represents a tenfold difference in hydrogen-ion concentration.
PART OF THE HESI A2 GUIDE
See every set in this course and follow a focused review order.
Open the full HESI A2 guide →Two ideas worth correcting now
NOT QUITE
→Electrons determine an element's atomic number
USE THIS INSTEAD
Protons determine atomic number.
NOT QUITE
→A pH difference is linear
USE THIS INSTEAD
Each pH unit represents a tenfold concentration ratio.
Flashcards
Answer before opening each card. The effort to retrieve is part of the learning.
1What does atomic number count?Show answer ＋
Protons.
2How do isotopes differ?Show answer ＋
They have different neutron counts.
3What happens in an ionic bond?Show answer ＋
Oppositely charged ions attract.
4What happens in a covalent bond?Show answer ＋
Atoms share electron pairs.
5What must be conserved in a balanced equation?Show answer ＋
The count of each element's atoms and total charge.
6What is one mole?Show answer ＋
6.022 × 10²³ specified particles.
7How is molarity calculated?Show answer ＋
Moles of solute divided by liters of solution.
8What does a one-unit pH difference represent?Show answer ＋
A tenfold hydrogen-ion concentration difference.
Explain it in your own words
Use the answer as a check after you have written or spoken your response.
01An atom has 8 protons and 10 electrons. What is its net charge?
Two negative, because it has two more electrons than protons.
02How many moles are in 0.5 L of a 2.0 M solution?
Moles equal molarity times liters: 2.0 × 0.5 = 1.0 mol.
03Why may coefficients be altered when balancing but subscripts may not?
Coefficients alter particle counts; subscripts alter the chemical identity.
04How do acids and bases form a conjugate pair?
They differ by one transferred proton.
05Why is pH 3 not twice as acidic as pH 6?
The logarithmic scale gives a 1,000-fold difference in hydrogen-ion concentration.
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