Matter and Its Classification

Definition and States of Matter

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

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

• Solids: Have definite shape and volume; particles are closely packed.

• Liquids: Have definite volume but take the shape of their container; particles are less tightly packed than in solids.

• Gases: Have neither definite shape nor volume; particles are far apart and move freely.

Pure Substances and Mixtures

Chemistry distinguishes between pure substances and mixtures based on composition and properties.

• Pure Substance: Has a fixed composition and distinct properties.

• Element: A pure substance that cannot be broken down by chemical means. Examples: hydrogen (H), oxygen (O).

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

Atomic Structure and the Periodic Table

Atoms and Subatomic Particles

Atoms are the basic units of matter, 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.

The Periodic Table

The periodic table organizes elements by their atomic number, which is the number of protons in the nucleus.

• Atomic Number: Determines the identity of an element.

• Organization: Elements are arranged in rows (periods) and columns (groups) based on similar properties.

Chemical Bonds

Ionic and Covalent 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, typically between nonmetals.

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

Measurement in Chemistry

SI Units

The International System of Units (SI) is used 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 amount of substance

Significant Figures

Significant figures indicate the precision of a measured value.

• Definition: All the digits in a measurement that are known, plus one estimated digit.

• Application: Used in calculations to reflect the accuracy of measurements.

Density

Density is a physical property that relates mass and volume.

• Formula:

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

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