Chemistry Midterm Review Terms

Scientific Method

* A logical method of problem solving.

Steps of the Scientific Method

* Making **observations** that lead to a **question.**
* Forming a **hypothesis** to answer the **question.**
* Testing the **hypothesis** by **experiments.**
* Making a **conclusion** based on the results of the experiment.

Observing

* Use of the senses and devices in the lab to obtain information.

Conclusion

* A statement based on observations and prior knowledge.

Quantitive Observations

* Includes numbers and units.

Qualitative Observations

* Does not include numbers and units.

Hypothesis

* An educted guess

What does a good hypothesis include?

* Explains the observation
* Can be tested
* Can predict an outcome.

What is an experiment?

* It is designed to test a hypothesis
* Involves variables.
* Is performed under controlled conditions.

What are variables?

* They are factors that can be changed.

What is the control?

* It is a variable that is held constant.

What is in a good experiment?

* Only two variables are allowed to change.
* The manipulated (independent) variable is changed by the scientist.
* The responding (dependent) variable changes as a result of the experiment.
* All other variables are controlled because they are held constant.

What is the difference between an observation and a conclusion?

* An observation is a physical fact.
* A conclusion is almost a prediction.

What is the International System?

* A measuring system used in science, AKA metric system.

What is length?

* Distance between two points.
* Base unit - meter (m)
* Instrument - meter stick or metric ruler.

What is mass?

* Amount of matter in a substance.
* Base unit - gram (g)
* Intrument - balance

What is volume?

* Amount of space an object occupies.
* Base unit - liter (L)
* Instrument - metric ruler or graduated cylinder.

What is time?

* Interval between two occurences.
* Base unit - seconds (S)
* Instrument - stopwatch

What is temperature?

* Average kinetic energy
* Base unit - celsius (C) or Kelvin (K)
* Instrument - thermometer

Measuring example

* Width of textbook = 21 mm.
* A measurement includes both a number and a unit.

What are significant figures?

* Measured numbers plus one estimated number.

Rectangular Volume Formula

\- V = L x W x H

Irregular Volume of a Solid

* Water Displacement

Sig. Fig. Rule 1

* All non-zero digits are significant (1,2,3,4,5,6,7,8,9, etc.)

Sig. Fig. Rule 2

* Final Zeros to the right of the decimal point are significant.

Sig. Fig. Rule 3

* Zeros between two significant digits are significant.

Sig. Fig. Rule 4

* Zeros used for spacing the decimal point are not significant.

Sig. Fig. Rule 5

* For numbers in scientific notation, all of the digits before the “x10” are significant.

What does your scientific notation formula look like?

M x 10^N

What does the M value have to be?

* Greater than or equal to 1 or less than or equal to 10.

What are metric prefixes?

* One larger thing equals many smaller things.

What are the steps to convert units?

* Question mark format
* Cancel units
* Insert fact
* Do the math.

What are physical properties?

* They can be observed without chemically changing matter.

What are chemical properties?

* They describe how a substance interacts with other substances.

What are some examples of physical properties?

* Malleability
* Density
* Color
* Texture
* Solubility
* Mass

What are some examples of chemical properties?

* Reactivity
* Combustibility
* Flammability
* Acidity
* Ability to rust

What are solids?

* Definite Shape
* Definite Volume
* Particles are packed together

What are liquids?

* Indefinite shape
* Definite volume
* Particles have room to move

What are gases?

* Indefinite Shape
* Indefinite Volume
* Particles far apart

What is a physical change?

* No change in identity of substance.

What is a chemical change?

* One or more new substances produced.

Phase changes are what?

* PHYSICAL CHANGES

What is freezing point?

* Liquid to soild (0 degrees Celsius)

What is melting point?

* Solid to liquid (0 degrees Celsius)

What is boiling point?

* Liquid to gas (100 degrees Celsius)

What is condensation point?

* Gas to liquid (100 degrees Celsius)

What is sublimation point?

* Solid to gas (-78.5 degrees Celsius)

What are some examples of physical changes?

* Tearing
* Crushing
* Phase changes

What are some examples of chemical changes?

* Combustion
* Acid Rain

What is the Law of Conservation of Mass?

* Mass cannot be created or destroyed.

What is an element?

* Pure Substance
* One kind of atom.
* Represented by one or two letter symbol
* Ex: helium (He)

What is a compound?

* Two or more elements chemically combined.
* Represented by chemical formula.
* Ex: Water (H2O)
* H20 decomposes into hydrogen gas and oxygen gas.
* Combines in same proportions.
* Created and separated only be chemical reactions.

What is a mixture?

* Two or more substances physically combined.
* Do not combine in same proportions.

What is a heterogeneous mixture?

* Not uniform.

What is a homogeneous mixture?

* (Solution) Uniform
* Pure substances.

What is an alloy?

* Solution of two or more metals.

What physical properties allow the components of a mixture to be separated?

* Magnetism
* Density

What is a centrifuge?

* An instrument that uses density to separate mixtures when tiny solid particles are dissolved in a liquid.

What is filtration?

* Used to separate liquids and solids?

How do you separate solutions?

* Evaporation
* Distillation

What is chromatography?

* Method of separating mixtures by using a moving solvent on filter paper.

What is density?

* Mass per unit of volume.

What is the formula to find density?

* Density = mass/volume.

What are the common units for density?

* g/mL
* g/cm^3

What is a model?

* A familiar idea used to explain unfamiliar facts observed in nature.

What is a theory?

* An explanation of observable facts and phenomena.

What must theories have in order to remain valid?

* Explain all known facts.
* Enable scientists to make correct predictions.

Who is Democritus?

* Proposed the existence of an atom.
* Word comes from the greek word “atomis” which means not to cut or “indivisible”

Who is Aristotle?

* Rejected the idea of the atom.
* Said matter could be cut continually.

What was Dalton’s theory?

* Atoms are building blocks of matter.
* Atoms are indivisible.
* Atoms of the same element are identical.
* Atoms of different elements are different.
* Atoms unite in small, whole number rations to form compounds.

Who is J.J. Thomson?

* Credited with discovery of electron: a blow to Dalton’s indivisible atom.
* Proposed the plum pudding model of the atom: negatively charged electrons embedded in a ball of positive charge.

What is the Law of Multiple Proportions?

* Whenever the same two elements for more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small numbers.

Who is Rutherford and what is his Gold-Foil experiment?

* Aimed alpha particles at gold foil.
* Most passed through.
* A few particles were deflected.
* Some particles even bounced back.

What are the conclusions of Rutherford’s experiment?

* Most of the atom is empty space.
* Dense positively charged core.

What are nucleons?

* Particles in the nucleus of the atom.
* Protons
* Neutrons

What is the atomic number?

* Number of protons in the nucleus of an atom.

What is a neutral atom?

* The number of protons equals the number of electrons.

What is an isotope?

* Atoms of an element that have different numbers of neutrons.

What is mass number?

* The total number of protons and neutrons in an atom.

What is atomic mass?

* The average of the masses of all the element’s isotopes.
* Unit is amu which is 1/12th the mass of a carbon-12 atom. One amu is nearly, but not exactly, equal to one proton/one neutron.

What equals the atomic number?

* The number of protons.

What equals the atomic number?

* The number of electrons.

What equals the mass number?

* The number of neutrons.

What are nucleons?

* Are particles occupying the nucleus.
* Consist of positively charged protons and neutral neutrons.
* Have almost 2000 times the mass of electrons.
* Are made up of quarks and leptons.

What happens when strong forces act on nucleons?

* Forces of attraction between nucleons.
* Are independent of the charge of the nucleon.
* Are short range (exist only between closest neighbors)

What happens when electrical force acts on nucleons?

* Force of repulsion between positively charged protons.
* Are long range.

When are nuclei unstable?

* Large Nuclei (Z > 82)
* Electrical forces of protons are greater than strong forces of neutrons.


* Wrong neutron: proton unstable

What is radioactive isotope?

* Has an unstable nucleus.
* Spontaneously emits a particle and decays into another element.

What is transmutation?

* Changing into another element through radioactive decay.

What is half-life?

* The time it takes for half the mass of a radioactive sample to decay.
* Ranges from a fraction of a second to billions of years.
* Is not affected by external conditions.

What is nuclear fusion?

* The combination of two nuclei into one with release of energy.

What are Bohr’s Energy Levels?

* Electrons in certain energy levels
* Low energy levels: Closer to nucleus
* High energy levels: farther from nucleus
* Ground state: electron in lowest energy possible.

What is an excited atom?

* Atom has absorbed energy
* Excited state is UNSTABLE
* Atom soon emits same amount of energy absorbed
* Energy seen as visible light

What is wavelength?

* Distance between corresponding points on adjacent waves.

What is frequency (f)?

* The number of waves passing a given point in a given time.

What is the formula to find speed of a wavelength?

* Speed = wavelength x frequency

What are quantum numbers?

* N, L, M, S
* Used to describe an electron in an atom.

What is the *n* quantum number?

* principle quantum electron
* represents main energy level of electron.

What is the *l* quantum number?

* The 2nd quantum number
* describes the orbital shape within an energy level
* number of orbital shapes possible in energy level = n

What are orbital shapes?

* Designate s, p, d, f
* Level 1 - s
* Level 2 - s, p
* Level 3 - s, p, d
* Level 4 - s, p, d, f