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 physical states:

• Solid: Has a definite shape and volume; particles are closely packed in a fixed arrangement.

• Liquid: Has a definite volume but takes the shape of its container; particles are close but can move past one another.

• Gas: Has neither a definite shape nor volume; particles are far apart and move freely.

Pure Substances and Mixtures

Pure substances have a fixed composition and distinct properties. They can be classified as:

• Elements: Substances that cannot be broken down into simpler substances by chemical means. Examples: Oxygen (O2), Gold (Au).

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

Mixtures (not detailed in the original notes) are physical combinations of two or more substances and can be separated by physical means.

Atomic Structure and the Periodic Table

Structure of the Atom

Atoms are the basic units of matter and consist of three fundamental subatomic particles:

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles (no charge) also located in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus in electron clouds or shells.

The Periodic Table

The periodic table organizes elements by increasing atomic number (number of protons). It groups elements with similar chemical properties into columns called groups or families.

• Atomic Number: The number of protons in an atom, unique to each element.

• Example: Hydrogen has atomic number 1; carbon has atomic number 6.

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 two atoms (usually nonmetals) share one or more 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 the standard for scientific measurements. Key SI base units include:

• 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 (sig figs) indicate the precision of a measured quantity. The number of significant figures in a measurement includes all certain digits plus one uncertain (estimated) digit.

• Example: 2.35 g has three significant figures.

Density

Density is a physical property defined as mass per unit volume. It is calculated using the formula:

• 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 .