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 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 are 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. Additional info: Mixtures can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).

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 (no charge) also located in the nucleus.

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

The nucleus is the dense central core of the atom, containing protons and neutrons, while electrons move in regions of space around the nucleus.

The Periodic Table

The periodic table is a systematic arrangement of elements in order of increasing atomic number (number of protons). It helps predict element properties and chemical behavior.

• Groups: Vertical columns with similar chemical properties.

• Periods: Horizontal rows indicating energy levels.

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 atoms (usually nonmetals) share one or more pairs of electrons.

Example: Sodium chloride (NaCl) forms via ionic bonding between sodium (Na, a metal) and chlorine (Cl, a nonmetal). Water (H2O) forms via covalent bonding between hydrogen and oxygen atoms.

Measurements 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 reflects the certainty in a measurement, and rules exist for determining which digits are significant.

• 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.

Density

Density is a physical property defined as mass per unit volume. It is useful for identifying substances and solving problems 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 .