Lecture 2: Significant Figures, Calculations, States of Matter, and Composition of Matter

Flashcards covering significant figures, calculations with measured numbers, states of matter, physical and chemical properties, extensive and intensive properties, definitions of elements, molecules, compounds, and mixtures, separation techniques, and fundamental laws of chemistry.

Significant Figures (S.F.)

Digits in a number that carry meaning contributing to its precision.

Any nonzero digit

Digits from 1 to 9, which are always significant.

Zeros between nonzero digits

Zeros located between two nonzero digits, which are always significant.

Leading zeros

Zeros to the left of the first nonzero digit, which are not significant (e.g., in 0.0023, the zeros are not significant).

Trailing zeros with a decimal

Zeros to the right of the last nonzero digit that are significant if a decimal is present (e.g., 1.200 has four significant figures).

Trailing zeros without a decimal

Zeros to the right of the last nonzero digit in a number without a decimal point, which may or may not be significant; scientific notation is used to avoid ambiguity.

Scientific Notation (for S.F.)

A method used to express significant figures unambiguously, especially for trailing zeros without a decimal.

Significant figures in addition and subtraction

The result cannot have more digits to the right of the decimal point than the number with the fewest digits after the decimal point among the original numbers.

Significant figures in multiplication and division

The number of significant figures in the final product or quotient is determined by the original number that has the smallest number of significant figures.

Exact numbers

Numbers considered to have an infinite number of significant figures and, therefore, do not limit the number of significant figures in a calculation result.

Rounding rule (<5)

If the first digit to be dropped is less than 5, round down (drop the digits without changing the preceding digit).

Rounding rule (≥5)

If the first digit to be dropped is 5 or greater, round up (add 1 to the preceding digit).

Multistep calculations (rounding)

Round only at the end of the calculation to reduce rounding errors, generally keeping at least one extra digit until the final step.

Accuracy

How close a measurement is to the true value.

Precision

How close a series of replicate measurements are to one another.

Solid

A state of matter with a fixed shape and volume; can be hard or soft, rigid or flexible.

Liquid

A state of matter with a varying shape that conforms to the container, but a fixed volume, and has an upper surface.

Gas

A state of matter with no fixed shape or volume and therefore no surface.

Physical Properties

Properties a substance shows by itself without interacting with another substance (e.g., color, melting point, boiling point, density).

Chemical Properties

Properties a substance shows as it interacts with, or transforms into, other substances (e.g., flammability, corrosiveness).

Extensive properties

Properties that are dependent on the amount of substance present (e.g., mass and volume).

Intensive properties

Properties that are independent of the amount of substance (e.g., density).

Element

The simplest type of substance with unique physical and chemical properties, consisting of only one type of atom, and cannot be broken down into simpler substances by physical or chemical means.

Molecule

A structure that consists of two or more atoms chemically bound together, behaving as an independent unit.

Compound

A substance composed of two or more elements that are chemically combined.

Mixture

A group of two or more elements and/or compounds that are physically intermingled.

Heterogeneous mixture

A mixture with one or more visible boundaries between its components, resulting in a non-uniform composition.

Homogeneous mixture

A mixture with no visible boundaries because its components are uniformly mixed at an atomic, ionic, or molecular level; also called a solution.

Solution

Another term for a homogeneous mixture.

Aqueous solutions

Solutions in which water is the solvent.

Filtration

A separation technique that separates components of a mixture based on differences in particle size, typically separating a precipitate from solution.

Crystallization

A separation technique based on differences in solubility of the components in a mixture.

Distillation

A separation technique based on differences in volatility (the tendency of a substance to become a gas).

Chromatography

A separation technique based on differences in solubility in a solvent versus a stationary phase.

Law of Mass Conservation

States that the total mass of substances present does not change during a chemical reaction.

Law of Definite (or Constant) Composition

States that no matter what its source, a particular compound is composed of the same elements in the same parts (fractions) by mass.