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 the study of chemistry.

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

• Solids: Have a definite shape and volume.

• Liquids: Have a definite volume but take the shape of their container.

• Gases: Have neither definite shape nor volume; they expand to fill their container.

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.

• Compound: A pure substance composed of two or more elements chemically combined, such as water (H2O) or 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 according to their atomic number, which is the number of protons in the nucleus.

• Atomic Number: Defines 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.

• 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 the amount of substance

Significant Figures

Significant figures indicate the precision of a measured value.

• Definition: The digits in a measurement that are known with certainty plus one digit that is estimated.

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

Density

Density is a physical property that relates mass and volume.

• Formula:

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

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