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

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

• Gas: No definite shape or 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

Matter can be classified as either pure substances or mixtures:

• Pure Substance: Has a fixed composition and distinct properties. Examples include elements and compounds.

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

• Compound: Consists of two or more elements chemically combined in fixed proportions. Example: Water (H2O), Carbon Dioxide (CO2).

Additional info: Mixtures, unlike pure substances, can be separated by physical means and do not have fixed compositions.

Atomic Structure and the Periodic Table

Structure of the Atom

Atoms are the basic units of matter and are 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 or shells.

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

The Periodic Table

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

• Atomic Number (Z): Number of protons in the nucleus of an atom.

• Groups: Vertical columns; elements share similar valence electron configurations.

• Periods: Horizontal rows; elements have the same number of electron shells.

Chemical Bonding

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): Length

• Kilogram (kg): Mass

• Second (s): Time

• Kelvin (K): Temperature

• Mole (mol): 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 digit.

• Rules: 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 for calculations involving mass and volume.

• 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 .