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 in chemistry.

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

• Pure Substance: A pure substance has a fixed composition and distinct properties.

• Element: An element is a pure substance that cannot be broken down into simpler substances by chemical means.

• Compound: A compound consists of two or more elements chemically combined in fixed proportions. Examples: Water (H2O), Carbon Dioxide (CO2).

The Periodic Table and Atomic Structure

The periodic table is a systematic arrangement of elements based on their atomic number, which is the number of protons in the nucleus.

• Atomic Structure: Atoms are composed of three fundamental 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.

Chemical Bonds

Chemical bonds are forces that hold atoms together in compounds.

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

• Covalent Bonds: Formed when atoms share pairs of electrons.

• Example: Sodium chloride (NaCl) is an ionic compound; water (H2O) is a covalent compound.

Measurement and SI Units

Measurements in chemistry are expressed using the International System of Units (SI).

• SI Units:

  • Meter (m): Unit of length

  • Kilogram (kg): Unit of mass

  • Second (s): Unit of time

  • Kelvin (K): Unit of temperature

  • Mole (mol): Unit for amount of substance

Precision and Significant Figures

Significant figures indicate the precision of a measured quantity. The number of significant digits reflects the certainty in measurement.

• Example: 2.50 g has three significant figures.

Density

Density is a physical property defined as mass per unit volume.

• Formula:

• Where: d = density, m = mass, V = volume

• Example: If a sample has a mass of 10 g and a volume of 2 cm3, its density is