Chemistry: Matter and Chemical Bonds

Matter, Atoms, and Elements

• Matter is anything that has mass and takes up space.
• All matter is made of atoms.
• An element is a substance consisting of only one kind of atom (e.g., hydrogen, carbon, oxygen).
• Atoms have a nucleus containing protons (positive charge) and neutrons (neutral charge).
• Electrons (negative charge) orbit the nucleus.
• Atomic number is the number of protons in an atom, defining the element.
• Isotopes are atoms of the same element with different numbers of neutrons (e.g., Carbon-12 vs. Carbon-14).

Chemical Bonds

• Covalent bonds: Atoms share electrons (strong bond).
• Polar covalent bonds: Electrons are shared unequally (e.g., water).
• Nonpolar covalent bonds: Electrons are shared equally.
• Ionic bonds: One atom takes an electron from another, creating ions (charged atoms).
• Cations are positively charged ions.
• Anions are negatively charged ions.
• Hydrogen bonds: Weak bonds between a hydrogen atom and an electronegative atom (e.g., N, O, F).
• Van der Waals interactions: Very weak attractions between oppositely charged atoms.

Water and Its Properties

• Water is a polar molecule.
• Polarity is due to unequal sharing of electrons between oxygen and hydrogen.
• Hydrogen bonding: Water molecules form hydrogen bonds, which give water unique properties:
  • Cohesion (water molecules stick to each other)
  • Adhesion (water molecules stick to other substances)
  • High specific heat (water resists temperature changes)
  • High heat of vaporization (a lot of energy is needed to turn water into vapor)
  • Universal solvent (water dissolves many substances)

Acids, Bases, and pH

• Acids release H+ ions in water, lowering pH (more acidic).
• Bases release OH- ions in water, raising pH (more basic).
• pH scale measures the concentration of H+ ions in a solution.
• pH 7 is neutral (pure water).
• pH < 7 is acidic.
• pH > 7 is basic.
• Buffers help maintain stable pH levels in living organisms (e.g., blood pH is maintained between 7.35 and 7.45).

Chemical Reactions

• Chemical reactions involve breaking and forming bonds.
• Reactants turn into products.
• Activation energy is needed to start a reaction.
• Hydrolysis breaks down complex molecules into simpler ones using water.
• Condensation combines simpler molecules into complex ones, releasing water.