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.

Classification of Matter

Matter can be classified based on its composition:

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

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

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

Example: Table salt (NaCl) is a compound, while iron (Fe) is an element.

Atomic Structure and the Periodic Table

Structure of the Atom

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

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 (column) have similar chemical properties.

• Atomic Number: The number of protons in an atom, unique to each element.

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

• Periods: Horizontal rows; properties change progressively across a period.

Chemical Bonding

Ionic and Covalent Bonds

Atoms combine to form compounds through chemical bonds, which involve the transfer or sharing of electrons.

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

Example: Sodium chloride (NaCl) forms via ionic bonding, while water (H2O) forms via covalent bonding.

Measurement in Chemistry

SI Units

The International System of Units (SI) is the standard for scientific measurements. Key SI base units include:

• Meter (m): Unit of length

• Kilogram (kg): Unit of mass

• Second (s): Unit of time

• Kelvin (K): Unit of temperature

• Mole (mol): Unit for amount of substance

Significant Figures

Significant figures indicate the precision of a measured quantity. The number of significant figures reflects the certainty in a 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 .