Atoms and Molecules

• An atom is the smallest unit of matter retaining the properties of its element.
• A molecule is a structure containing multiple atoms bonded together.
• Atoms are indivisible, whereas molecules can be broken down.

Atoms

• Atoms are the smallest units of matter that still retain the properties of their element.
• Atoms consist of:
  • Neutrons: Neutral subatomic particles in the nucleus.
  • Protons: Positively charged subatomic particles in the nucleus.
  • Electrons: Negatively charged subatomic particles orbiting the nucleus.
• The nucleus is the atom's center, made of protons and neutrons, and generally remains unchanged during chemical reactions (except nuclear reactions).
• The Atomic number equals the number of protons, defining the element.
• Atomic mass is the weighted average of isotopes.
• Mass number is the sum of protons and neutrons.
• Electrons participate in chemical reactions, changing the atom's charge.
• An ion is an atom with a different number of electrons compared to protons.
  • Anions are negative ions formed by gaining electrons.
  • Cations are positive ions formed by losing electrons.

Molecules

• A molecule is two or more atoms bonded together.
• Atoms are the building blocks of molecules.
• Atoms attach by donating or sharing electrons, creating a molecule.
• Molecules creation happens via chemical reactions involving electron donation or sharing.
• Water consists of one oxygen and two hydrogen atoms.

Examples of Atoms and Molecules

• Examples of atoms: Oxygen, hydrogen, nitrogen, copper, sulfur.
• Examples of molecules: Carbon dioxide, molecular oxygen, water, ammonia, glucose.

Difference Between Atoms and Molecules

• Atoms are the smallest unit of matter; molecules are made of multiple atoms.
• Atoms make up molecules.

Molecules and Compounds

• A compound is a molecule made of two or more different elements.
• All molecules are not compounds.
• Molecular oxygen (O₂) is a molecule, not a compound, as it consists of two oxygen atoms.
• Carbon dioxide (CO₂) is both a molecule and a compound, as it contains carbon and oxygen atoms.

Types of Bonds

• Molecules and compounds form when two or more atoms bond.
  • Ionic bonds.
  • Covalent bonds.
• Bonds can form molecules and compounds and break down to release individual atoms during a chemical reaction.
• Chemical reactions occur naturally or are catalyzed by enzymes.

Ionic Bonds

• Ionic bonds form when atoms have different electronegativity (affinity for electrons).
• The less electronegative atom gives an electron to the more electronegative atom.
• The atom accepting the electron becomes an anion, and the atom donating becomes a cation.
• Charges hold the atoms together in an ionic bond.

Covalent Bonds

• Covalent bonds form when atoms share electrons due to relatively equal electronegativity.
• Covalent bonds typically form between nonmetals like carbon, oxygen, and hydrogen.

Ionic Bonds vs. Covalent Bonds

• Covalent bonds involve electron sharing.
  • Electronegativity of atoms is relatively equal.
  • Example: Carbon dioxide.
• Ionic bonds involve electron donation.
  • Electronegativity of atoms is different.
  • Example: Sodium chloride.

Mixtures

• A mixture is a physical blend of atoms, compounds, or molecules not bonded together.
• Each component in a mixture retains its chemical properties.
• Mixtures differ from compounds and molecules where atoms are bonded and have new properties.
• Air is a mixture of molecular oxygen, molecular nitrogen, and other gases, each with its properties.
• Mixtures can be separated into components, distinguishing them from compounds and molecules.
• Salt water is a mixture where sodium chloride and water mix.
• Salt separates from water by boiling, retaining their original properties.