Matter and Its Classification

Definition and States of Matter

Matter is defined as anything that has mass and occupies space. It exists in three primary states, each with distinct physical properties.

• Solid: Definite shape and volume; particles are closely packed and vibrate in place.

• Liquid: Definite volume but no definite shape; particles are less tightly packed and can move past one another.

• Gas: No definite shape or volume; particles are far apart and move freely.

Classification of Matter

Matter can be classified as pure substances or mixtures. Pure substances have a fixed composition, while mixtures contain two or more substances physically combined.

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

• Compound: A pure substance composed of two or more elements chemically combined. Examples: Water (H2O), Carbon dioxide (CO2).

Atomic Structure and the Periodic Table

Atoms and Subatomic Particles

Atoms are the basic units of matter, consisting of three main 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.

The Periodic Table

The periodic table organizes elements by their atomic number, which is the number of protons in the nucleus. It provides a systematic way to study the properties and relationships of elements.

• Atomic Number: Number of protons in an atom; determines the element's identity.

• Example: Carbon has an atomic number of 6, meaning it has 6 protons.

Chemical Bonds

Ionic and Covalent Bonds

Chemical bonds are forces that hold atoms together in compounds. The two main types are:

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

• 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 and Units in Chemistry

SI Units

The International System of Units (SI) is used for scientific measurements. The fundamental SI units relevant to chemistry are:

• 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 measurement. The number of significant digits reflects the certainty in the measured value.

• Rule: All nonzero digits are significant; zeros between nonzero digits are significant; leading zeros are not significant; trailing zeros in a decimal number are significant.

• Example: 0.00450 has three significant figures.

Density

Density is a physical property defined as mass per unit volume. It is used to characterize substances and can be calculated using the following formula:

• 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