Chemistry 110 UNIT 1

Describe scientific method

Describe scientific method

Apply the COAST approach to problem solving

• Collect and Organize

  • Identify key concepts and skills required to solve a problem; assemble the information needed.

• Analyze

  • Evaluate information and relationships or connections; sometimes units will help identify steps needed to solve the problem.

• Solve

  • Perform calculations, check units, etc.

• Think About It

  • Is the answer reasonable? Are the units correct?

Distinguish between the classes of matter between the physical and chemical properties of pure substances

Physical Properties:

• Intensive property:

  • independent of amount of substance

  • Example: color, melting point, density

• Extensive property:

  • dependent with quantity of substance present

  • Example: volume, mass

Chemical Property:

• property of substance only observed by reacting it with another substance

• Example: H2 and O2 reacting to create compound water

States of Matter

Pure substance or mixture

Law of conservation

states that energy cannot be created nor destroyed, but it can be converted from one form to another

Prefixes

Tera = 12

Giga = 9

Mega = 6

Kilo = 3

Hecto = 2

Deka = 1

Deci = -1

Centi = -2

Mili = -3

Micro = -6

Nano = -9

Pica = -12

Convert C to K

K = C + 273.15

Sig Figs

34.023 = 5

0.068 = 2

0.0680 = 3

*zeros at the end of the number with a decimal point are significant

110 = 2

110. = 3

1.234 x 10^-5 = 4

1.234 x 10^5 = 4

1.2340 x 10^5 = 5

Precision in Calculation

1. When adding or subtracting

   1. of decimal places in the answer = # decimal places in the number with the fewest places

   2. least precise determines the answer

2. When multiplying or dividing

   1. of sig figs in means = # sig figs in number with the fewest sig figs

3. Precision is based on experimental values

Quantum theory

Energy = hv

• energy = proton energy

• h = plancks contant 6.626 X 10 -34 J

• v = frequncy

Quantized States

• Quantized states: Discrete energy levels (e.g., steps)

• Unquantized states: smooth transition between levels (e.g., ramp)

Black Body Radiation

Objects heated > emits radiation

Key Idea: Wavelength distribution of the radiation depends on temperature

• Planck introduced concept that energy is released or absorbed in discrete “chunks”

• Quantization of energy required for theory to match

E = hv

E= energy

V = frequency

h= Planck’s constant

• the key overall point is energy is emitted or absorbed in chunks and that is related to temperature

Line Spectrum

Dark lines = Bright lines

• Emitted light (bright line) at the same “energy” as absorbed light (dark line)

• SO… there must be certain characteristic energy states in a gas that are reversible (can take in or give off energy)

Atomic Emission Spectra

• bright line emission spectra are unique for different elements and therefore a key way to identify unknown elements

  • more complex the elements the more lines

The Photoelectric Effect

Key Idea: When a photon hits a metal surface it ejects an electron

*einstein

Experimental Observations:

1. No electrons are ejected unless the light exceeds a threshold frequency ( if not enough or below freq then no ejection of electrons)

2. The kinetic energy of the electrons increases linearly with the frequency of the light

3. But the kinetic energy of the electrons is independent of the light intensity

4. Even at a low light intensity, electrons are ejected immediately

Experimental Results: If you triple the number of photons then it triples the electrons

-higher freq of light increases then velcity increaese

Photoelectric Effect Overall

• Observation

Electons are emitted by metal only if light has frequnwcy greater than certain minimum value, no mater how intese the light

• When electons are emitted, the number emitted is proportional to tlight intenisty