Introduction to Chemistry and Atomic Structure: Study Notes for General Biology

Introduction to Chemistry

Matter: Definition and Properties

Matter is anything that has mass and occupies volume. All physical substances in the universe are forms of matter, and understanding its properties is fundamental to chemistry and biology.

• Mass: The amount of material in a substance.

• Volume: The space that a substance occupies.

Types of Pure Substances

Pure substances are materials with a uniform and definite composition. They are classified into elements and compounds.

Type	Definition	Key Properties
Elements	Substances made of only one kind of atom.	Pure forms Smallest unit: atom Unique chemical and physical properties Building blocks for all substances
Compounds	Substances composed of two or more different elements chemically combined in fixed ratios.	Combinations of different elements Elements in fixed ratios Distinct properties from their elemental components Formed and broken by chemical reactions

Atomic Structure

Components of the Atom

An atom consists of a central nucleus surrounded by an electron cloud. The arrangement and properties of these components determine the chemical behavior of elements.

• Nucleus:

  • Contains protons and neutrons

  • Extremely dense

• Electron Cloud:

  • Contains electrons

  • Mostly empty space

Subatomic Particles

Atoms are made up of three main subatomic particles, each with distinct properties.

Particle	Charge	Relative Mass
Proton	+1	1 unit of mass
Neutron	0	1 unit of mass
Electron	-1	Negligible mass

Atomic Number

The atomic number (Z) of an element is the number of protons in the nucleus of an atom. It determines the identity of the element.

• Symbol: $Z$

• Example: Carbon has $Z = 6$

Additional info:

• The number of electrons in a neutral atom equals the number of protons.

• Atoms of the same element can have different numbers of neutrons; these are called isotopes.