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: Has a definite shape and volume; particles are closely packed and vibrate in place.

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

• Gas: Has neither definite shape nor 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 and can be further divided into elements and compounds.

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

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

Example: Water (H2O) is a compound because it consists of hydrogen and oxygen atoms chemically bonded.

Atomic Structure and the Periodic Table

Organization of Elements

The periodic table arranges elements by their atomic number, which is the number of protons in the nucleus of an atom. This organization reveals periodic trends in properties.

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

• Periodic Table: A chart that organizes elements by increasing atomic number and groups elements with similar chemical properties.

Structure of the Atom

Atoms are 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 in electron shells.

Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Chemical Bonding

Ionic and Covalent Bonds

Chemical bonds are forces that hold atoms together in compounds. The two main types are ionic and covalent bonds.

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

• Covalent Bond: Formed when two atoms share one or more pairs of electrons, typically between nonmetals.

Example: Sodium chloride (NaCl) is formed by an ionic bond between sodium (Na) and chlorine (Cl). Water (H2O) is formed by covalent bonds between hydrogen and oxygen.

Measurements 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 the amount of substance

Significant Figures

Significant figures indicate the precision of a measured value. The number of significant digits reflects the certainty in a measurement.

• Rule: 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 used to characterize substances and can be calculated using the following formula:

• Formula:

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

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