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, each with distinct properties.

• 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 definite shape nor volume; particles are far apart and move freely.

Example: Ice (solid), water (liquid), and steam (gas) are all forms of H2O in different states.

Pure Substances and Mixtures

Pure substances have a fixed composition and distinct properties. They can be classified as elements or compounds.

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

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

Additional info: Mixtures, unlike pure substances, consist of two or more substances physically combined and can be separated by physical means.

Atomic Structure and the Periodic Table

Structure of the Atom

Atoms are the basic units of matter, composed of three fundamental 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 in electron clouds.

Additional info: The number of protons defines the atomic number and the identity of the element.

The Periodic Table

The periodic table organizes elements by increasing atomic number (number of protons). Elements in the same group (column) have similar chemical properties.

• Rows: Called periods; indicate energy levels.

• Columns: Called groups or families; elements share similar valence electron configurations.

Chemical Bonds

Ionic and Covalent Bonds

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

• Ionic Bonds: Formed by the transfer of electrons from a metal to a nonmetal, resulting in oppositely charged ions that attract each other.

• Covalent Bonds: Formed when two nonmetal atoms 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): Length

• Kilogram (kg): Mass

• Second (s): Time

• Kelvin (K): Temperature

• Mole (mol): Amount of substance

Significant Figures

Significant figures reflect the precision of a measured quantity. The number of significant figures in a value indicates the certainty of the measurement.

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant; trailing zeros are significant only if there is a decimal point.

Example: 0.00450 has three significant figures.

Density

Density is a physical property defined as mass per unit volume. It is useful for identifying substances and predicting whether an object will float or sink in a fluid.

• 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 .