Matter, Measurement, and Problem Solving

SI Units and Prefixes

The International System of Units (SI) is the standard for scientific measurements. SI units use prefixes to indicate multiples or fractions of base units.

• Base Units: meter (m) for length, kilogram (kg) for mass, second (s) for time, kelvin (K) for temperature, mole (mol) for amount of substance, ampere (A) for electric current, candela (cd) for luminous intensity.

• Common Prefixes:

  • kilo- (k):

  • centi- (c):

  • milli- (m):

  • micro- (\mu):

  • nano- (n):

• Example: 1 kilometer (km) = meters (m)

Significant Figures

Significant figures (sig figs) reflect the precision of a measured or calculated quantity.

• Rules:

  • All nonzero digits are significant.

  • Zeros between nonzero digits are significant.

  • Leading zeros are not significant.

  • Trailing zeros are significant only if there is a decimal point.

• Addition/Subtraction: The result should have the same number of decimal places as the measurement with the fewest decimal places.

• Multiplication/Division: The result should have the same number of significant figures as the measurement with the fewest significant figures.

• Example: (rounded to 2 sig figs)

Temperature Conversions

Temperature can be measured in Celsius (°C), Kelvin (K), or Fahrenheit (°F). Conversions are as follows:

• Example: Convert 25°C to K:

Density Calculations

Density is the ratio of mass to volume and is a physical property of matter.

• Formula:

• Common units: g/cm3 or kg/m3

• Example: If a sample has a mass of 10.0 g and a volume of 2.0 cm3, its density is

Definitions: Accuracy, Precision, States of Matter, Mixtures, Solutions

• Accuracy: How close a measurement is to the true or accepted value.

• Precision: How close repeated measurements are to each other.

• States of Matter:

  • Solid: Definite shape and volume.

  • Liquid: Definite volume, takes shape of container.

  • Gas: No definite shape or volume; expands to fill container.

• Mixture: A combination of two or more substances that are not chemically bonded.

• Solution: A homogeneous mixture of two or more substances.

Scientific Method Steps

The scientific method is a systematic approach to research and discovery.

• 1. Make observations

• 2. Formulate a hypothesis

• 3. Conduct experiments

• 4. Analyze data

• 5. Draw conclusions

• 6. Communicate results

Physical and Chemical Changes

• Physical Change: Alters the form or appearance of matter but does not change its composition (e.g., melting, boiling).

• Chemical Change: Alters the composition of matter, resulting in new substances (e.g., rusting, burning).

• Example: Ice melting is a physical change; iron rusting is a chemical change.

Atoms and Elements

Average Atomic Mass, Moles, Molar Mass, and Mass Percent

These concepts are fundamental for quantifying elements and compounds in chemistry.

• Average Atomic Mass: The weighted average of the masses of all naturally occurring isotopes of an element.

  • Formula:

• Number of Moles:

• Molar Mass: The mass of one mole of a substance, in g/mol.

• Mass Percent:

• Example: Calculate the number of moles in 18 g of water ():

  • Molar mass of =

  • Moles =

Protons, Neutrons, and Electrons

Atoms are composed of protons, neutrons, and electrons.

• Protons: Positively charged particles in the nucleus; atomic number equals the number of protons.

• Neutrons: Neutral particles in the nucleus; number = mass number - atomic number.

• Electrons: Negatively charged particles outside the nucleus; in a neutral atom, the number of electrons = the number of protons.

• Example: Carbon-14 has 6 protons, 8 neutrons, and 6 electrons.

Isotopes

• Isotope: Atoms of the same element with different numbers of neutrons (and thus different mass numbers).

• Example: and are isotopes of carbon.

Definitions: Atom, Molecule, Cation, Anion, Ion

• Atom: The smallest unit of an element that retains its chemical properties.

• Molecule: Two or more atoms bonded together.

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.

• Cation: A positively charged ion (loss of electrons).

• Anion: A negatively charged ion (gain of electrons).

• Example: Na+ is a cation; Cl- is an anion.