Chemical Foundations: Basic Chemistry for Cells

Chemical Foundations

Elements and Atoms

Understanding the chemical basis of life begins with the study of elements and atoms, which are the fundamental building blocks of matter.

• Element: A pure substance consisting of only one kind of atom. Elements cannot be broken down into simpler substances by ordinary chemical means.

• Most Common Elements in Living Organisms: Oxygen (O), Hydrogen (H), Carbon (C), Nitrogen (N), Phosphorus (P), and Sulfur (S).

• Atom: The smallest unit of an element that retains the properties of that element.

• Subatomic Particles:

  • Proton: Positively charged particle found in the nucleus.

  • Neutron: Neutral particle (no charge) found in the nucleus.

  • Electron: Negatively charged particle found in electron shells surrounding the nucleus.

Atomic Number and Mass Number

Atoms are identified by their atomic number and mass number, which relate to the number of protons, neutrons, and electrons they contain.

• Atomic Number (Z): The number of protons in the nucleus of an atom. It defines the element.

  • Example: Hydrogen has 1 proton (Z = 1), Carbon has 6 protons (Z = 6).

  • If you change the number of protons, you change the element.

• Mass Number (A): The sum of the number of protons and neutrons in the nucleus.

  • Electrons have negligible mass and are usually ignored in mass calculations.

  • Each proton and neutron has a mass of approximately 1 atomic mass unit (amu).

  • Example: Sodium (Na) has an atomic number of 11 and a mass number of approximately 23.

• Atomic Mass: The weighted average mass of all the isotopes of an element, often not a whole number due to the presence of isotopes.

Isotopes

Isotopes are atoms of the same element that have different numbers of neutrons, and therefore different mass numbers.

• Definition: Atoms with the same number of protons but different numbers of neutrons.

• Example:

  • Carbon-12: 6 protons, 6 neutrons

  • Carbon-14: 6 protons, 8 neutrons

• Hydrogen Isotopes:

  • Protium (¹H): 1 proton, 0 neutrons

  • Deuterium (²H): 1 proton, 1 neutron

  • Tritium (³H): 1 proton, 2 neutrons

Atomic Structure

The arrangement of subatomic particles within an atom determines its chemical properties and reactivity.

• Nucleus: Contains protons and neutrons.

• Electron Shells: Electrons are arranged in shells (energy levels) around the nucleus.

• Example: Magnesium (Mg) has atomic number 12 and mass number 24.

  • Protons: 12

  • Neutrons: 12 (24 - 12)

  • Electrons: 12 (in a neutral atom)

Chemical Bookkeeping

Chemical Formulas and Counting Atoms

Chemical formulas use element symbols and subscripts to represent the composition of molecules and compounds.

• Subscript: Indicates the number of atoms of each element in a molecule.

• Example: Glucose: $C_6H_{12}O_6$

  • 6 carbons, 12 hydrogens, 6 oxygens

• Practice: Name and count the atoms in the following compounds:

  • Calcium dihydrogen phosphate: $Ca(H_2PO_4)_2$

    • Ca: 1

    • H: 4

    • P: 2

    • O: 8

  • Cellulose: $2C_6H_7O_2(OH)_3$

    • C: 12

    • H: 20

    • O: 10

    Additional info: The actual structure of cellulose is more complex, but this formula is a simplified representation for counting atoms.

Common Elements in Biology

It is important to recognize the symbols for elements commonly found in biological systems.

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

• Nitrogen (N)

• Phosphorus (P)

• Sulfur (S)

• Iron (Fe)

• Chlorine (Cl)

• Sodium (Na)

• Magnesium (Mg)

• Potassium (K)

• Iodine (I)

• Calcium (Ca)