Elements and Compounds

Definitions and Examples

Understanding the basic building blocks of matter is essential in biology, as all living organisms are composed of chemical elements and compounds.

• Element: A pure substance that cannot be broken down into other substances by chemical means. Each element is defined by its number of protons. Example: Oxygen (O)

• Compound: A substance formed when two or more elements are chemically bonded together in fixed proportions. Example: Water (H2O)

Elements Essential to Life

Major and Trace Elements

Living organisms are primarily composed of a small number of elements, with a few making up the vast majority of body mass.

• Four Major Elements: The four elements that make up approximately 96% of the human body are:

  • Oxygen (O)

  • Carbon (C)

  • Hydrogen (H)

  • Nitrogen (N)

• Other Essential Elements: Elements such as calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium (Na), chlorine (Cl), and magnesium (Mg) are also present and essential for various biological functions.

• Trace Elements: Elements required by an organism in minute quantities. Example: Iron (Fe) is necessary for oxygen transport in blood.

Atomic Structure

Atoms and Subatomic Particles

An atom is the smallest unit of an element that retains its chemical properties. Atoms are composed of subatomic particles:

• Protons: Positively charged particles found in the nucleus.

• Neutrons: Neutral particles found in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus.

Example: A helium atom consists of 2 protons, 2 neutrons, and 2 electrons.

Isotopes and Radioactivity

Radioactive Isotopes and Their Uses

Isotopes are atoms of the same element with different numbers of neutrons. Some isotopes are unstable and radioactive, emitting radiation as they decay.

• Radioactive Isotope: An isotope with an unstable nucleus that decays over time, releasing radiation.

• Applications:

  • Medical imaging and diagnosis (e.g., PET scans)

  • Cancer treatment (radiotherapy)

  • Biological research (tracing biochemical pathways)

Electron Configuration

Electron Distribution in Atoms

Electrons are arranged in shells around the nucleus. The distribution of electrons determines the chemical properties of an atom.

• Atomic Number: Number of protons in the nucleus.

• Mass Number: Total number of protons and neutrons.

• Valence Electrons: Electrons in the outermost shell, important for chemical bonding.

Example: Sodium (Na) has atomic number 11 (11 protons), mass number 23 (11 protons + 12 neutrons), and 1 valence electron.

Chemical Bonds

Types of Chemical Bonds

Atoms combine to form molecules through chemical bonds. The main types of bonds are:

Electronegativity and Bond Polarity

Bond Types and Molecular Polarity

Electronegativity is the ability of an atom to attract electrons in a covalent bond. Differences in electronegativity lead to bond polarity:

• Nonpolar Covalent Bond: Electrons are shared equally between atoms (e.g., O2).

• Polar Covalent Bond: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

In water, oxygen is more electronegative than hydrogen, making water a polar molecule with partial negative (O) and partial positive (H) regions.

Special Properties of Water

Bonding in Water and Biological Implications

• Bonds in Water: The atoms of hydrogen and oxygen in a water molecule are connected by polar covalent bonds. Water molecules are held together by hydrogen bonds.

• Gecko Adhesion: Geckos can climb walls due to van der Waals interactions between the tiny hairs on their feet and the surface.

Chemical Reactions

Reactants, Products, and Photosynthesis

Chemical reactions involve the breaking and forming of bonds, transforming reactants into products.

• Reactant: A substance that undergoes change during a chemical reaction.

• Product: A substance formed as a result of a chemical reaction.

• Example (Photosynthesis):

The general equation for photosynthesis is:

Here, carbon dioxide and water are reactants; glucose and oxygen are products.

Summary Table: Subatomic Particles

Additional info: These notes expand on the worksheet questions by providing definitions, examples, and context for each concept, ensuring a comprehensive understanding suitable for exam preparation in General Biology.