chem 101: exam 1 (unfinished)

Matter

Anything with mass and volume/occupies space

Examples of matter

Water, oxygen, a rock, etc.

Examples of non-matter

Light, sound, heat, etc.

Physical property

Observed without changing the substances identity

Examples of physical property

Color, density, melting point, boiling point

Chemical property

Describes how a substance can form new substances

Chemical property examples

Flammability, rusting, reacting with acid, etc.

Physical change

No new substance forms

Physical change

Ice → water; water → steam; cutting paper

Chemical change

A new substance forms

Chemical change examples

Iron rusts; wood burns; acid + base reacts

Endothermic

Energy enters the system

Endothermic examples

Melting, vaporization, sublimation

Memory trick: endo= energy enters

Exothermic

Energy leaves the system

Exothermic examples

Freezing, condensation, deposition

Memory trick: exo = energy exits

Phase changes

(Change) (What happens)

Melting Solid → liquid

Freezing Liquid → solid

Vaporization Liquid → gas

Condensation Gas → liquid

Sublimation Solid → gas

Deposition Gas → solid

Phase changes examples

Dry ice(s) → CO_ gas = sublimation

When asked “physical vs chemical?”

Ask whether chemical identity/composition changed:

• if no → physical

• Is yes → chemical

When asked “physical vs chemical?” example

Boiling H2O = physical change

burning H2= chemical change

Density

D= mass (M)/volume (V)

Other rearrangements:

M= Density (D) x Volume (V); V = Mass (M)/Density (D)

Kelvin ←> Celsius

K = C + 273.15

OR

C = K - 273.15

Celsius ←> Fahrenheit

F = (C x 9/5) + 32

OR

C = (F - 32) x 5/9

Metric prefixes

Prefix Symbol Meaning

Kilo K 10³

Centi C 10^-2

Milli m 10^-3

Micro μ 10^-6

Nano n 10^-9

Example: Convert 2500 mL to L

2500mL x 1L/1000mL →mL cancels → 2.5L

Nonzero digits

All nonzero digits count

Nonzero digits example

45.6 = 3 sig figs

Captive zeros

Zeros between nonzero numbers count

Captive zero example

1002 = 4 sig figs

Leading zeros

Zeros before the first nonzero digits do NOT count

Leading zeros example

0.0045 = 2 Sig figs

Trailing zeros after a decimal

They DO count

Trailing zeros after a decimal example

2.500 = 4 Sig figs

Multiplication/division sig figs

Your answer has the same number of sig figs as the measurement with the fewest sig figs

Multiplication/division sig figs example

2.5 × 3.42 = 8.55

• 2.5 has 2 sig figs

Therefore:

8.6 (final answer)

Additional/subtraction sig figs

Use decimal places, NOT total sig figs

Addition/subtraction sig figs EXAMPLE

12.11 + 3.2 =15.31 15.31

• 3.2 has only 1 decimal place

Therefore:

15.3 (final answer)

Accuracy

How close a measurement is to the accepted/true value

Accuracy EXAMPLE

True value = 10.0

Measurement = 10.1

→ relatively accurate

Precision

How close repeated measurements are to each other

Precision EXAMPLE

9.81

9.82

9.81

These measurements are precise bc they’re clustered together

Atomic number

The # of protons. This identifies the element

Atomic number EXAMPLE

Oxygen has this type of number of 8

Therefore: 8 protons

Mass number

this is protons + neutrons

Finding neutrons

This is the mass number - protons

Finding neutrons EXAMPLE

Carbon-14

• mass number: 14

• Protons: 6

14-6=8 → 8 neutrons

Neutral atom

A neutral atom has protons = electrons

Neutral atom EXAMPLE

Sodium has 11 protons

Neutral sodium therefore has: 11 electrons

Cation

A positive ion is formed b losing electrons

Cation EXAMPLE

Na → Na^+ + e^-

• Na^+ has 11 protons and 10 electrons

Anion

A negative ion. It’s formed by gaining electrons

Anion EXAMPLE

Cl + e^- → Cl^-

• Cl^- has 17 protons and 18 electrons

Isotopes

The same element with the same # of protons but different # of neutrons

Isotopes EXAMPLE

Carbon - 12

• 6 protons And 6 neutrons

Carbon - 13

• 6 protons and 7 neutrons

Carbon - 14

• 6 protons and 8 neutrons

They’re are carbon because they all have 6 protons

Isotope notation

Looks like this: 14/6 C

• the top number = mass number

• The bottom number = atomic number = protons

So for this, there are 6 protons and 14-6=8 neutrons.

Finding electrons in ions

If its a positive charge then SUBTRACT electrons

Finding electrons in ions EXAMPLE

Mg²^+

• Mg has 12 protons, so: 12 - 2 =10

• Final answer: Mg²^+ = 10e^-

Negative charge

If theres a negative charge, you ADD electrons

Negative charge EXAMPLE

F^-

• F has 9 protons, so: 9 + 1 =10

• Final answer: F^- = 10e^-

Average atomic mass

Formula: AAM = E (zig-zig E) (isotope mass x fractional abundance)

*Multiply each isotopes mass by its decimal abundance, then add the results*

Average atomic mass EXAMPLE

Isotope A: 10 amu, 75%

Isotope B: 11 amu, 25%

Convert the percentages, then:

(10)(0.75) + (11)(0.25) → 7.50 + 2.75 → 10.25 amu (final answer)

When given an isotope notation, use this order…

1. Bottom number = protons

2. Top number - bottom number = neutrons

3. Look at charge to determine electrons

Isotope notation EXAMPLE

23/11 Na^+

• protons: 11

• Neutrons: 23-11=12

• Electrons: 11-1=10

Final answer: 11, protons, 12 neutrons and 10 electrons

Element

A pure substance containing one type of atom

Element EXAMPLE

• Fe

• O2

• Na

Compound

A substance containing different elements that are chemically bonded

Compound EXAMPLE

• H2O

• CO2

• NaCl

Empirical formula

The simplest whole-number ratio of atoms

Empirical formula EXAMPLES

1. C6H12O6

divide everything by 6: CH2O (final answer)

So:

• molecular formula: C6H12O

• Empirical formula: CH2O

Molecular formula

Shows the actual number of atoms in a molecule

Molecular formula EXAMPLE

C6H12O6 (thats it lol)

Ionic compounds

They’re usually metal + nonmetal

Ionic compounds EXAMPLE

• NaCI

• MgO

• CaCl2

Molecular/covalent compounds

Usually nonmetal + nonmetal

Molecular/covalent compounds EXAMPLE

• CO2

• N2O5

• SF6

Common ion charges

Group Common charge

1 +1

2 +2

13 +3

15 -3

16 -2

17 -1

18. 0

Writing ionic formulas

The total charge must be equal to zero

Writing ionic formulas EXAMPLE

AI³^+ and O²^-

We need:

2 Al = +6

3 O= -6

Therefore: Al2O3 (b/c (+6) + (-6) = 0

Naming transition-metal compounds

Transition metals can have multiple charges, so use a Roman numeral

Naming transition-metal compounds EXAMPLE

FeCl3

• each C = -1

Three Cl: -3

Therefore Fe must be +3

Name: iron(iii)chloride (final answer)

Molecular prefixes

Number Prefix

1 Mono

2 Di

3 Tri

4 Tetra

5 Penta

6 Hexa

7 Hepta

8 Octa

9 Nona

10. Deca

Molecular prefixes EXAMPLE

N2O5

• 2 nitrogen = dinitrogen

• 5 oxygen = pentoxide

Therefore: dinitrogen pentoxide (final answer)

Counting atoms

Be careful with parentheses

Counting atoms EXAMPLE

Al2(SO4)3

Al: 2

S: 1 × 3 = 3

O: 4 × 3 =12

Therefore: AI = 2 , S = 3 , O = 12

Avogadro’s number

1 mol = 6.022 × 10²³ particles

think: a mole is just a giant counting unit

Molar mass

Mass of one mole of a substance

Unit: g/mol

Molar mass EXAMPLE

H2O → 2 (1.008) + 16.00 → 18.02g/mol

Formula mass

The sum of atomic masses in a formula

Often expressed in: amu

Formula mass EXAMPLE

H2O

2(1.008) + 16.00 = 18.02

The mole map

Grams <> molar mass <> moles <> 6.022 × 10²³ <> particles

Grams → moles

Moles = grams/molar mass

Grams → moles EXAMPLE

36.0 g H2O:

36.0g/18.02g/mol = 2.00mol

Moles → grams

Grams = moles x molar mass

Moles → grams EXAMPLE

2.00 mol H2O: 2.00mol x 18.02g/mol = 36.0g

Moles → particles

Particles = moles x 6.022 × 10²³

Moles → particles EXAMPLE

0.500 mol: 0.500 (6.022 × 10²³) → 3.011 × 10²³ particles (final answer)

Particles → moles

Moles = particles / 6.022 × 10²³

Particles → moles EXAMPLE

1.2044 × 10^(24)

Particles: 1.2044 × 10^(24) / 6.022 × 10^(23)

Final answer: 2.00 mol

Wavelength

Wavelength: distance between wave peaks

Symbol: triangle looking thingy lol

Long wavelength: waves spread further apart

Short wavelength: waves packed closer together

Frequency

Frequency: # of waves passing a point per second

Symbol: v

Unit: Hz = s^-1

Wave equation

C = (triangle shape thingy)(v)

Speed of light: c = 3.00 × 10^8 m/s

So: v = c/ triangle symbol thingy