Matter and Measurements

Definition and Classification of Matter

Matter is defined as anything that has mass and occupies space. Understanding the classification of matter is fundamental to chemistry.

• States of Matter: Matter exists in three primary states: solid, liquid, and gas.

• Pure Substances: Substances with a fixed composition. They can be further classified as:

  • Elements: Substances that cannot be broken down into simpler substances by chemical means. Examples include hydrogen (H) and oxygen (O).

  • Compounds: Substances composed of two or more elements chemically combined in fixed proportions. Examples: water (H2O), carbon dioxide (CO2).

Example: Table salt (NaCl) is a compound, while gold (Au) is an element.

The Periodic Table and Atomic Structure

The periodic table organizes all known elements by increasing atomic number, which is the number of protons in the nucleus of an atom.

• Atoms: The basic unit of an element, consisting of three subatomic particles:

  • Protons: Positively charged particles located in the nucleus.

  • Neutrons: Neutral particles also found in the nucleus.

  • Electrons: Negatively charged particles that orbit the nucleus.

Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Chemical Bonds

Chemical bonds are the forces that hold atoms together in compounds.

• Ionic Bonds: Formed when electrons are transferred from a metal to a nonmetal, resulting in the formation of oppositely charged ions.

• Covalent Bonds: Formed when two atoms share one or more pairs of electrons, typically between nonmetals.

Example: Sodium chloride (NaCl) forms via ionic bonding, while water (H2O) forms via covalent bonding.

SI Units and Measurements

The International System of Units (SI) provides standard units for scientific measurements:

• Meter (m): Unit of length

• Kilogram (kg): Unit of mass

• Second (s): Unit of time

• Kelvin (K): Unit of temperature

• Mole (mol): Unit for the amount of substance

Example: The mass of a sample may be measured in kilograms, and its temperature in kelvins.

Significant Figures

Significant figures indicate the precision of a measured quantity. The number of significant figures in a measurement includes all certain digits plus one uncertain digit.

• 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.

Example: 0.00450 has three significant figures.

Density

Density is a physical property defined as the mass of a substance divided by its volume.

• Formula:

• Where d is density, m is mass, and V is volume.

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