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, in contrast, consist of two or more substances physically combined and can be separated by physical means. (Additional info: Mixtures can be homogeneous or heterogeneous.)

Atomic Structure and the Periodic Table

Structure of the Atom

Atoms are the fundamental units of matter, composed of three primary 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.

The nucleus contains most of the atom's mass, while electrons occupy most of its volume.

The Periodic Table

The periodic table organizes 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.

• Mass number (A): Total number of protons and neutrons.

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. Example: Sodium chloride (NaCl).

• Covalent Bonds: Formed when two atoms share one or more pairs of electrons, typically between nonmetals. Example: Water (H2O).

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 indicate the precision of a measured quantity. The number of significant figures in a measurement includes all certain digits plus the first uncertain digit.

• When multiplying or dividing, the result should have as many significant figures as the measurement with the fewest significant figures.

• When adding or subtracting, the result should have as many decimal places as the measurement with the fewest decimal places.

Density

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

• Formula:

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

• Common units: g/cm3 or kg/m3.

Example: Calculating Density

• If a sample has a mass of 10.0 g and a volume of 2.0 cm3, its density is: