Chemistry Notes: States of Matter, Changes, Properties, and Significant Figures

Solids (States of Matter)

Particles are held very close together, creating a rigid structure that maintains its shape.

Mixtures

Combinations of substances that can be separated by physical means.

Physical Change

An alteration in the appearance of a substance, but not in its chemical composition.

Chemical Change

A change involving a transformation in the substance

s identity, leading to new substances.

Extensive Properties

Properties that depend on the amount of substance present (e.g., mass, volume, length).

Intensive Properties

Properties that do not depend on the amount of substance present (e.g., melting point, density, temperature, color).

Density (\rho)

An intensive property defined as mass per unit volume, calculated as \rho = \frac{m}{V}.

Significant Figures

Digits in a measurement that reflect its precision, preventing the implication of unwarranted accuracy.

Significant Figures Rule: Nonzero Digits

All nonzero digits (1-9) are always significant.

Significant Figures Rule: Zeros between Nonzero Digits

Zeros located between nonzero digits are always significant (e.g., 0.505 has 3 sig figs).

Significant Figures Rule: Leading Zeros

Zeros to the left of the first nonzero digit are not significant (e.g., 0.0023 has 2 sig figs).

Significant Figures Rule: Trailing Zeros after a Decimal Point

Zeros to the right of the last nonzero digit in a number with a decimal point are significant (e.g., 12.3400 has 6 sig figs).

Significant Figures Rule: Trailing Zeros in a Whole Number (Ambiguous)

Trailing zeros in a whole number without a decimal point are ambiguous; scientific notation should be used to clarify their significance (e.g., 1.50\times 10^3 for 3 sig figs).

Addition and Subtraction Rule for Significant Figures

The result must be reported with the same number of decimal places as the measurement with the fewest decimal places among the terms.

Multiplication and Division Rule for Significant Figures

The result must have the same number of significant figures as the measurement with the fewest significant figures among the inputs.

Solid

A state of matter where particles are held very close together, are rigid, and maintain a fixed shape.

Mixture

Combinations of substances that can be separated by physical means.

Physical Change

A change that alters the appearance of a substance but not its chemical composition.

Chemical Change

A change that involves a change in the substance
’s identity and composition.

Extensive Property

A property that depends on the amount of substance present (e.g., mass, volume, length).

Intensive Property

A property that does not depend on the amount of substance present (e.g., melting point, density, temperature, color).

Density (\rho)

An intensive property defined as mass per unit volume: \rho = \frac{m}{V}.

Significant Figures

Digits in a measurement that contribute to its precision, reflecting the reliability of the measurement.

Nonzero Digits

Always significant figures in a number (e.g., 1-9).

Zeros Between Nonzero Digits

Always significant figures (e.g., in 0.505, the '0' is significant).

Leading Zeros

Zeros to the left of the first nonzero digit; are not significant (e.g., in 0.0023, the '0's are not significant).

Trailing Zeros After a Decimal Point

Are significant figures (e.g., in 12.3400, the '00' are significant).

Trailing Zeros Without a Decimal Point

Are ambiguous; scientific notation should be used for clarity to indicate significance (e.g., 1500 vs. 1.50 \times 10^3).

Addition/Subtraction with Sig Figs Rule

The result should have the same number of decimal places as the measurement with the fewest decimal places.

Multiplication/Division with Sig Figs Rule

The result should have the same number of significant figures as the measurement with the fewest significant figures among the inputs.