Introduction to Chemical Foundations in Biology

This study guide covers the foundational chemical concepts essential for understanding cell biology. It introduces the nature of matter, atomic structure, the periodic table, electron shells, and the types of chemical bonds that form the basis of biological molecules.

What is Matter?

Matter is anything that takes up space and has mass. All living and non-living things are composed of matter, which is made up of elements.

• Element: A pure substance that cannot be broken down into simpler substances by chemical means. Each element is made up of one type of atom.

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

• Major Elements in Biology: Most biological matter is composed of four main elements: carbon (C), oxygen (O), nitrogen (N), and hydrogen (H).

• Other Elements: Elements such as sulfur, calcium, potassium, sodium, and phosphorus are also important in smaller amounts.

Atomic Structure

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle that orbits the nucleus in electron shells.

• Atomic Number: The number of protons in an atom, which defines the element.

• Mass Number: The sum of protons and neutrons in the nucleus.

• Isotopes: Atoms of the same element with different numbers of neutrons.

The Periodic Table

The periodic table organizes elements by increasing atomic number and groups elements with similar chemical properties together.

• Groups: Vertical columns; elements in the same group have similar properties.

• Periods: Horizontal rows; elements in the same period have the same number of electron shells.

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

Electron Shells and Orbitals

Electrons occupy energy levels called shells, which are divided into orbitals. The arrangement of electrons determines how atoms interact and bond.

• Electron Shell: A set of orbitals with similar energy levels. The first shell holds up to 2 electrons, the second up to 8, and so on.

• Valence Shell: The outermost electron shell, which determines chemical reactivity.

• Orbital: A region of space where an electron is likely to be found. s orbitals are spherical; p orbitals are shaped like dumbbells.

Example: Neon (Ne) has two electrons in its first shell and eight in its second shell, making it chemically inert.

Three-Dimensional Electron Distribution

Electron orbitals have three-dimensional shapes, which influence how atoms bond and interact. The geometry of these orbitals is crucial for the structure and function of biological molecules.

• sp3 Hybridization: In carbon, the mixing of s and p orbitals forms four equivalent sp3 orbitals, allowing for tetrahedral geometry in molecules like methane (CH4).

• Electron Geometry: Determines the shape of molecules and the angles between bonds.

Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules. The main types of bonds in biology are covalent, ionic, and hydrogen bonds.

• Covalent Bond: The sharing of one or more pairs of valence electrons between atoms. Covalent bonds are strong and form the backbone of biological molecules.

• Ionic Bond: The transfer of electrons from one atom to another, resulting in oppositely charged ions that attract each other.

• Hydrogen Bond: A weak attraction between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom.

Example: In water (H2O), the oxygen atom forms covalent bonds with two hydrogen atoms, and hydrogen bonds form between water molecules.

Table: Comparison of Chemical Bonds

Conservation of Matter in Chemical Reactions

In chemical reactions, matter is neither created nor destroyed. Atoms are rearranged to form new substances, but the total number of atoms remains the same.

• Law of Conservation of Mass:

• Forward and Backward Reactions: Many reactions are reversible, and the direction depends on the conditions.

Summary

• All living things are made of matter, which is composed of elements and atoms.

• Atoms consist of protons, neutrons, and electrons arranged in shells and orbitals.

• The periodic table organizes elements by atomic number and properties.

• Chemical bonds (covalent, ionic, hydrogen) form the basis of biological molecules.

• The conservation of matter applies to all chemical reactions in biology.