Chemistry Chapter: Matter and Atoms

Matter and Elements

• Matter is anything that occupies space and has mass.
• Elements are substances that cannot be broken down into simpler substances.
• Compounds are formed when two or more elements combine in a fixed ratio.
• Trace elements are essential for various biological functions, such as iron for red blood cells and iodine for hormone regulation.

Atoms

• Atoms are the smallest unit of an element that retains its chemical properties.
• Atoms are made up of subatomic particles: protons, neutrons, and electrons.
• Protons carry a positive charge, neutrons have no charge, and electrons carry a negative charge.
• Protons and neutrons reside in the atomic nucleus, while electrons orbit the nucleus.

Atomic Number and Mass Number

• The atomic number of an element is the number of protons in its nucleus.
• The mass number of an element is the total number of protons and neutrons in its nucleus.
• Atomic mass is approximately equal to the mass number.

Isotopes

• Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
• Radioactive isotopes are unstable and decay over time, releasing energy as radiation.

Radioactive Isotopes

• Radioactive isotopes are used in medical diagnosis and treatment.
• They can be used to track metabolic processes, detect cancer cells, and deliver radiation therapy.
• Radiation can be harmful to healthy cells, causing side effects and potentially increasing cancer risk.

Chemical Bonds

• Chemical bonds form between atoms due to interactions between their electrons.
• Covalent bonds involve the sharing of electrons between two nonmetals:
  • Polar covalent bonds: electrons are shared unequally.
  • Nonpolar covalent bonds: electrons are shared equally.
• Ionic bonds form when electrons are transferred from a metal to a nonmetal.
• Hydrogen bonds are weak interactions between a hydrogen atom and a highly electronegative atom like oxygen or nitrogen.

Properties of Water

• Water is a polar molecule due to the uneven distribution of electrons in its covalent bonds.
• Water's polarity allows it to form hydrogen bonds with other water molecules and other polar substances.
• Water has several important properties that support life:
  • High boiling point: due to strong hydrogen bonds.
  • High heat capacity: water can absorb a lot of heat without significant temperature changes.
  • Universal solvent: water's polarity allows it to dissolve many substances.
  • High surface tension: water molecules at the surface are strongly attracted to each other.
  • Cohesive and adhesive properties: water molecules stick to each other (cohesion) and to other polar surfaces (adhesion).

Biological Macromolecules

• Carbon is the basis of all organic compounds, including biological macromolecules.
• Carbohydrates serve as fuel and structural components for living organisms.
• Monosaccharides are simple sugars that act as monomers—building blocks for larger carbohydrates.
• Polysaccharides are polymers made up of many monosaccharide units:
  • Starch: energy storage in plants.
  • Glycogen: energy storage in animals.
  • Cellulose: structural component of plant cell walls.