CHM-130 Week 2 Interactive Study Guide

Atomic Structure Concept On Exam

The 3 Subatomic Particles

Particle	Charge	Location	How to Find It
Protons (p+)	Positive (+)	Nucleus	= Atomic number (bottom number)
Neutrons (n0)	Neutral (0)	Nucleus	= Mass number - Atomic number
Electrons (e-)	Negative (-)	Electron cloud	= Protons (in a neutral atom)

Remember: PEN

Protons = Positive, Electrons = nEgative, Neutrons = Neutral

Neutrons = Mass Number - Atomic Number

The mass number is the top number (or the number after the hyphen, like Neon-21)

Example: Neon-21

1

Neon's atomic number = 10 (look it up on the periodic table). This means 10 protons.

2

Mass number = 21 (it says "Neon-21")

3

Neutrons = 21 - 10 = 11 neutrons

4

Neutral atom: electrons = protons = 10 electrons

Neon-21: 10 protons and 11 neutrons

Exam Trick: "Atomic Number is the ID"

The atomic number NEVER changes for an element — it defines what the element IS. If you change the protons, you change the element entirely. The mass number CAN change (that's what isotopes are).

Atomic Size Trends

On the periodic table:

Going DOWN a group: Atomic size INCREASES (more electron shells)
Going LEFT across a period: Atomic size INCREASES (fewer protons pulling electrons in)

Memory Trick

"Big atoms live in the Bottom-Left corner"

Cesium (Cs) — bottom-left of the main group — is the largest naturally occurring atom.

Periodic Table Fact (True/False on Exam)

The periodic table shows the average mass for all isotopes of an element, NOT the mass of one individual atom. This is TRUE and it's a common exam question.

Molecular Weight & Molar Mass Formula On Exam

What is it?

Molar mass = the weight of ONE mole of a substance, measured in g/mol. You find it by adding up the atomic masses of every atom in the formula from the periodic table.

Memory Trick

"Molar Mass = Mall Shopping"

You go through the formula and "shop" for each element's atomic mass on the periodic table, then add up your total at checkout.

How to Calculate Molar Mass

1

Write out the chemical formula and identify each element and how many atoms of it there are.

2

Look up each element's atomic mass on the periodic table (the decimal number under the symbol).

3

Multiply each element's atomic mass by the number of atoms of that element.

4

Add them all up. That's your molar mass in g/mol.

Example: Carbon Monoxide (CO)

1

CO has: 1 Carbon (C) + 1 Oxygen (O)

2

C = 12.01 g/mol and O = 16.00 g/mol

3

12.01 + 16.00 = 28.01 g/mol

Exam Example: Magnesium Chloride (MgCl2)

1

MgCl2 has: 1 Mg + 2 Cl

2

Mg = 24.305 g/mol, Cl = 35.453 g/mol

3

24.305 + 2(35.453) = 24.305 + 70.906 = 95.211 g/mol

Molar mass of MgCl2 = 95.211 g/mol

Converting Between Moles and Grams

grams = moles x molar mass

Rearranged: moles = grams / molar mass

Mnemonic: "GMM" Triangle

G = M x MM (Grams = Moles x Molar Mass)

Think of it like a pyramid: G on top, M and MM on the bottom. Cover what you want to find — what's left is your formula.

Exam Example: 0.70 mol of H2O2

1

Molar mass of H2O2: 2(1.008) + 2(16.00) = 2.016 + 32.00 = 34.016 g/mol

2

grams = 0.70 mol x 34.016 g/mol = 23.8 g

0.70 mol H2O2 = ~23.8 g

The Mole Concept Concept On Exam

What is a Mole?

A mole is just a counting word — like "dozen" means 12, a mole means 6.02 x 1023 of something.

Think of it this way

1 dozen eggs = 12 eggs | 1 mole of atoms = 6.02 x 1023 atoms

Same idea, just a WAY bigger number.

Subscripts Tell You Mole Ratios

In a chemical formula, the subscript tells you how many moles of each element are in 1 mole of the compound.

The "Multiply the Subscript" Trick

Moles of element = moles of compound x subscript. That's it!

C12H22O11 (sucrose): 3 mol sucrose → 3 x 22 = 66 mol H
C6H12O6 (fructose): 2 mol fructose → 2 x 12 = 24 mol H
CH4 (methane): 4 mol CH4 → 4 x 4 = 16 mol H

Exam Alert: Two-Step Molecule-to-Mole Problems

If they give you molecules and ask for moles of an element, do it in two steps:
Step 1: Convert molecules to moles (divide by 6.02 x 1023)
Step 2: Multiply by the subscript

Example: 2.4 x 1024 molecules of CH4 → how many moles of CH4?
2.4 x 1024 / 6.02 x 1023 = ~4.0 mol CH4

Avogadro's Number Concept On Exam

1 mole = 6.02 x 1023 particles (atoms, molecules, etc.)

moles = number of molecules / 6.02 x 1023

molecules = moles x 6.02 x 1023

How to Remember 6.02 x 1023

"6:02 on October 23rd" — Mole Day!

Chemists celebrate Mole Day on 10/23 at 6:02.

Which way do I go?

Molecules → Moles: DIVIDE by 6.02 x 1023 (shrinking the number)
Moles → Molecules: MULTIPLY by 6.02 x 1023 (growing the number)

"Big to small = divide. Small to big = multiply."

Reactants vs. Products Reactions On Exam

REACTANTS → PRODUCTS

Left side = what goes IN | Right side = what comes OUT

Memory Trick

"You READ left to right — Reactants are what you READ first"

Reactants = left side (starting materials). Products = right side (what's produced by the reaction).

Exam Example

In: C6H12O6 + 6O2 → 6CO2 + 6H2O

Reactants: C6H12O6 and O2 (left side)
Products: CO2 and H2O (right side)

Exam question pattern

"What are the substances produced by a chemical change on the right side?" → Products. Always.

Balancing Chemical Equations Reactions On Exam

Why Balance?

Atoms can't appear or vanish. Whatever goes in must come out — just rearranged. Same number of each atom on both sides.

Balancing Order

"Balance Metals first, then Nonmetals, save H and O for last"

NEVER change subscripts!

Subscripts change what the molecule IS. Coefficients (numbers in front) change how MANY. Only adjust coefficients.

Example: Zn + HCl → H2 + ZnCl2

1

Count: Left: Zn=1, H=1, Cl=1 | Right: H=2, Zn=1, Cl=2. Not balanced!

2

Fix: Put 2 in front of HCl. Left: Zn=1, H=2, Cl=2

3

Check: Zn: 1=1, H: 2=2, Cl: 2=2. Balanced!

1 Zn + 2 HCl → 1 H2 + 1 ZnCl2

Exam Example: S2 + O2 → SO2

1

Count: Left: S=2, O=2 | Right: S=1, O=2. S is off!

2

Fix S: Put 2 in front of SO2. Right: S=2, O=4. Now O is off!

3

Fix O: Put 2 in front of O2. Left: S=2, O=4. Check: S 2=2, O 4=4.

1 S2 + 2 O2 → 2 SO2 (Coefficients: 1, 2, 2)

Oxidation & Reduction Reactions On Exam

The #1 Mnemonic in Chemistry

"OIL RIG"

Oxidation Is Loss (of electrons) | Reduction Is Gain (of electrons)

Oxidation	Reduction
LOSES electrons	GAINS electrons
Charge becomes more positive	Charge becomes more negative
Oxidation number increases	Oxidation number decreases

Also: "LEO the lion says GER"

Lose Electrons = Oxidation | Gain Electrons = Reduction

Exam wording alert

The exam asks: "Reduction is characterized by:" → Answer: Gain of an electron. Don't overthink it — OIL RIG.

Reaction Types Reactions On Exam

Remember All 5 Types

"Some Dudes Can't Sing Duets"

Synthesis, Decomposition, Combustion, Single Replacement, Double Replacement

+

Synthesis (Combination)

A + B → AB

Two things combine into one. "Coming together."

÷

Decomposition

AB → A + B

One breaks into pieces. "Breaking up."

↔

Single Replacement

A + BC → AC + B

One element steals another's partner.

⇔

Double Replacement

AB + CD → AD + CB

Two compounds swap partners.

How to Tell Them Apart on the Exam

Count the reactants and products:
• 2 reactants → 1 product = Synthesis/Combination (things joining)
• 1 reactant → 2+ products = Decomposition (things splitting)
• Element + Compound → Different Element + Different Compound = Single Replacement
• Compound + Compound → Compound + Compound = Double Replacement

Exam Quick Reference

Reaction	Type	Why
SO2 + H2O → H2SO3	Combination	2 things → 1 thing
2HI → I2 + H2	Decomposition	1 thing → 2 things
CuO + H2 → Cu + H2O	Single Replacement	Element + compound swap
HBr + KOH → H2O + KBr	Double Replacement	2 compounds swap partners

Endothermic vs. Exothermic Concept On Exam

Memory Trick

"EXO = EXIT = energy exits" | "ENDO = ENTER = energy enters"

Exothermic	Endothermic
Energy is released	Energy is absorbed
Surroundings get warmer	Surroundings get cooler
Fire, combustion, respiration	Ice packs, evaporation, melting

Exam Patterns (2 questions on midterm!)

• "Heat is produced during respiration" → Exothermic (heat = released energy)
• "A glass of water turns cold when something is added" → Endothermic (it's absorbing heat FROM the water)
• "Lighting a match" / "Burning paper" → Exothermic (fire = energy released)
• "Hot pad for back pain" → Exothermic (it releases heat)

The Tricky One

"Endothermic cools the surroundings" sounds backwards but it makes sense: the reaction is ABSORBING heat from its surroundings, so the surroundings lose heat and feel cold.

Conversions Using Chemical Equations Formula On Exam

The Big Idea

The coefficients in a balanced equation give you the mole ratio. This ratio is your conversion factor.

3CH4 → C3H8 + 2H2

3 mol CH4 : 1 mol C3H8 : 2 mol H2

The Stoichiometry Road Map

Grams A → Moles A → Moles B → Grams B

Convert to moles first. Use the ratio. Convert out if needed. If you start with moles, skip the first step!

Exam Pattern 1: Moles → Moles

0.75 mol C3H8 produced → how many mol H2?

1

Ratio: 1 mol C3H8 : 2 mol H2

2

0.75 x (2/1) = 1.5 mol H2

1.5 mol H2

Exam Pattern 2: Moles → Grams

3 mol CH4 → how many grams of C3H8?

1

Ratio: 3 mol CH4 → 1 mol C3H8. So 3 mol CH4 = 1 mol C3H8

2

Molar mass of C3H8: 3(12.01) + 8(1.008) = 44.09 g/mol

3

1 mol x 44.09 = 44.09 g

44.097 grams of C3H8

States of Matter Concept On Exam

Property	Solid (s)	Liquid (l)	Gas (g)
Shape	Definite/Fixed	Takes container	Fills container
Volume	Definite/Fixed	Definite/Fixed	Expands to fill
Density	HIGH	Medium-High	Low
Particles	Vibrate in place	Slide past each other	Move freely
Compressible?	No	No	Yes

Exam Shortcuts

"Definite shape?" = Solid | "High density?" = Solid | "Compressible?" = Gas

Gas Laws Gas Laws On Exam

Ideal Gas Law

PV = nRT

P = pressure (atm) | V = volume (L) | n = moles | R = 0.0821 | T = Kelvin

Remember PV = nRT

"Pivnert" — say it out loud a few times!

ALWAYS Convert to Kelvin First!

TK = TC + 273. If they give you Celsius, convert BEFORE plugging in. Forgetting this = wrong answer every time.

Rearranged for What You Need

P

P = nRT / V

V

V = nRT / P

n

n = PV / RT

T

T = PV / nR

Exam Example: 2.67 mol, 5.00 L, 25.0°C

1

Convert T: 25.0 + 273 = 298 K

2

P = nRT / V = (2.67)(0.0821)(298) / 5.00

3

P = 65.33 / 5.00 = 13.1 atm

P = 13.1 atm

Pressure Conversions

1 atm = 760 mmHg = 760 torr

To convert mmHg to atm: divide by 760

Exam Example

Blood pressure of 100 mmHg → atm?
100 / 760 = 0.132 atm. Just divide by 760 every time.

Dalton's Law of Partial Pressures

PTotal = PA + PB + ...

Total = sum of each gas's pressure. To find one, subtract the others.

Think of it like...

"Dalton's Law = Everyone pays their share"

Each gas contributes its "share" of the total pressure. Add all shares = total. Missing one? Subtract.

Exam Pattern

PT = 0.900 atm, PNeon = 0.799 atm → PArgon = 0.900 - 0.799 = 0.101 atm
It's always just subtraction. That's it.

Study Guide Questions — Worked Out

Click each button to reveal the full solution. Try it yourself first!

1

Blanca needs 0.50 mol of CO. How many grams?

1

Molar mass of CO: 12.01 + 16.00 = 28.01 g/mol

2

grams = 0.50 x 28.01 = 14.005 g

14.01 grams of CO

2

3 mol of sucrose (C12H22O11). How many moles of hydrogen?

1

Subscript on H = 22. So 1 mol sucrose has 22 mol H.

2

3 x 22 = 66 mol H

66 moles of hydrogen

3

1.8 x 1024 molecules of CO2. How many moles?

1

moles = 1.8 x 1024 / 6.02 x 1023

2

= 1.8/6.02 x 10(24-23) = 0.299 x 10 = ~2.99 mol

~3.0 moles of CO2

4

Balance: Zn + HCl → H2 + ZnCl2

Put a 2 in front of HCl. Now: Zn=1/1, H=2/2, Cl=2/2.

1 Zn + 2 HCl → 1 H2 + 1 ZnCl2

5

Oxidation = ? Reduction = ?

OIL RIG: Oxidation Is Loss of electrons. Reduction Is Gain of electrons.

Oxidation = loss of electrons | Reduction = gain of electrons

6

Which is a double replacement reaction?

A) CuO + H2 → Cu + H2O = Single Replacement
B) HBr + KOH → H2O + KBr = Double Replacement (two compounds swap)
C) NH3 + HCl → NH4Cl = Synthesis
D) CaCO3 → CaO + CO2 = Decomposition

Answer: B

7-8

Energy released = ___? Cools surroundings = ___?

EXO = EXIT. ENDO = ENTER.

Q7: Exothermic | Q8: Endothermic

9

0.5 mol C3H8 produced → mol of H2? (3CH4→C3H8+2H2)

Ratio: 1 C3H8 : 2 H2. So 0.5 x 2 = 1.0

1.0 mol H2

10

3 mol CH4 → grams of C3H8?

Ratio: 3 CH4 = 1 C3H8. Molar mass C3H8 = 44.09. So 1 x 44.09 = 44.09g

44.09 grams C3H8

11

High density = which state of matter?

Solid

12

2 mol gas, 4.00 L, 25.0°C. Find pressure.

1

T = 25 + 273 = 298 K

2

P = nRT/V = (2)(0.0821)(298)/4.00 = 48.93/4.00 = 12.2 atm

P = 12.2 atm

13

PT=0.900 atm, PHe=0.500 atm. Find PO2.

PO2 = 0.900 - 0.500 = 0.400

PO2 = 0.400 atm

Midterm-Style Practice Quiz Exam Prep

These are modeled after actual midterm questions. Pick your answer — instant feedback!

E1

Based on the information given, choose the best answer for Neon-21.

Wait — none of these are right! That's the point. Neon-21 has 10 protons and 11 neutrons. Option A says that, but the exam answer was marked as A. Let's check: Ne atomic # = 10, so 10 protons. 21-10 = 11 neutrons. A is correct!

E2

Determine the molecular weight of Magnesium Chloride (MgCl2) in grams.

E3

A student needs 0.70 moles of Hydrogen Peroxide (H2O2). Calculate how many grams are needed.

E4

A student has 2 mol of fructose (C6H12O6). How many moles of hydrogen are in their sample?

E5

A sample of methane (CH4) contains 2.4 x 1024 molecules. How many moles of CH4?

E6

Reduction is characterized by:

E7

Which of the following is a combination (synthesis) reaction?

E8

Heat is produced during respiration. What type of reaction best describes this energy release?

E9

Which of these is an example of an endothermic reaction?

E10

What are the substances produced on the right side of a chemical equation?

E11

Balance: S2 + O2 → SO2. What should the coefficients be?

E12

In C6H12O6 + 6O2 → 6CO2 + 6H2O, is O2 a reactant?

E13

3CH4 → C3H8 + 2H2. If 0.75 mol C3H8 is produced, how many mol H2?

E14

3CH4 → C3H8 + 2H2. How many grams of C3H8 from 3 mol CH4?

E15

Definite shape is a characteristic of which state of matter?

E16

A client's blood pressure is 100 mmHg. Express in atm.

E17

2.67 mol gas in 5.00 L tank at 25.0°C. What is the pressure?

E18

Neon + Argon: PT = 0.900 atm, PNe = 0.799 atm. Find PAr.

Quick Reference Cheat Sheet

Key Formulas

What	Formula
Grams from moles	g = mol x molar mass
Moles from grams	mol = g / molar mass
Moles from molecules	mol = molecules / 6.02 x 1023
Neutrons	mass number - atomic number
Ideal Gas Law	PV = nRT (R = 0.0821, T in K)
Celsius to Kelvin	K = °C + 273
mmHg to atm	atm = mmHg / 760
Dalton's Law	PT = PA + PB + ...

All Mnemonics at a Glance

Topic	Mnemonic
Subatomic Particles	PEN (Protons=Positive, Electrons=Negative, Neutrons=Neutral)
Oxidation / Reduction	OIL RIG or LEO says GER
Reaction Types	Some Dudes Can't Sing Duets
Exo vs. Endo	EXO = EXIT \| ENDO = ENTER
Avogadro's Number	6:02 on October 23rd
Ideal Gas Law	"Pivnert"
Molar Mass	GMM Triangle (G = M x MM)
Stoichiometry	Grams A → Moles A → Moles B → Grams B
Reactants vs Products	READ left = Reactants first
Atomic Size	Big atoms = Bottom-Left