Chemistry: States of Matter and Atoms

State of Matter

• Matter is composed of substance
• Substance is made of Compound
• Compound is made of Molecules
• Molecules are made of elements
• Elements are made of Atoms
• A bond is a smaller unit of an atom
• A group of atoms which are not combined with bonds are called elements
• A group of molecules is called a compound
• Hydrogen exists as H₂ (molecule)
• A group of molecules called a compound

Atoms

• Atoms are the smallest unit of an element
• An atom consists of protons (p), neutrons (n), and electrons (e)
• Protons and neutrons are found in the nucleus (center of the atom).
• Electrons orbit the nucleus.
• Protons have a positive charge, neutrons have no charge and electrons have a negative charge.
• Atoms have equal numbers of protons and electrons, making them electrically neutral in their natural state.
• Atomic number is the number of protons in the atom's nucleus
• Atomic mass (or weight) is the total number of protons and neutrons in the nucleus
• Examples: Hydrogen (H), Sodium (Na)

Molecules

• Molecules are formed when two or more atoms are bonded together
• Molecules can be made up of the same type of atom or different types
• Molecules are held together by chemical bonds
• Ex: H₂ (hydrogen molecule)

Compounds

• Compounds are formed when two or more different types of atoms combine chemically
• Compounds are formed from molecules
• In a compound, the ratios of atoms are fixed

Ions

• Atoms can gain or lose electrons, becoming electrically charged particles
• Positively charged ions are called cations
• Negatively charged ions are called anions
• Gaining or losing electrons alters the charge of an atom without changing the number of protons or neutrons