A&P I Chemistry - Chapter 2 Lecture Notes

Chemistry is fundamental to understanding physiological reactions in the body.
- The body is made up of numerous chemicals.
- Chemistry underlies all physiological processes, such as:
- Movement
- Digestion
- Pumping of the heart
- Functioning of the nervous system
Chemistry can be categorized into two subfields:
- Basic Chemistry
- Biochemistry

Energy is defined as the capacity to do work or to put matter into motion.
Energy exists in two primary forms:
- Kinetic Energy:
- Energy of movement (energy in action).
- Potential Energy:
- Stored energy (inactive) that can be transformed into kinetic energy.
The transformation of energy from potential to kinetic can result in action.

All matter is composed of elements, defined as substances that cannot be broken down into simpler substances by ordinary chemical methods.
Four key elements constitute about 96% of the human body:
- Carbon (C)
- Oxygen (O)
- Hydrogen (H)
- Nitrogen (N)
An additional 9 elements makeup approximately 3.9% of the body, while 11 elements constitute less than 0.01%.
The Periodic Table lists all known elements.

There are 90 naturally occurring elements, with 12 found in living organisms in substantial amounts.
The four elements that make up 96.3% of human body weight are C, H, O, and N.
Organic molecules primarily consist of these elements, often referred to by the acronym CHON.
Some trace elements, though minimal in quantity, are essential for physiological functions such as:
- Methane
- Acetone

All elements consist of atoms, which are the unique building blocks of each element.
- Atoms are the smallest particles of an element that retain the properties of that element.
- Understanding atomic structure is essential for grasping the nature of biological molecules.

Each element has a one or two-letter atomic symbol.
- Example: “O” for oxygen, “C” for carbon.
- Some symbols derive from Latin names: “Na” (from natrium) for sodium, and “K” (from kalium) for potassium.

There are two common models of atomic structure:
1. Planetary Model:
- Electrons orbit around the nucleus like planets around the sun.
1. Orbital Model:
- Electrons are found in an electron cloud surrounding the nucleus, with orbitals representing probable locations.

Elements are characterized by differing numbers of subatomic particles:
- Hydrogen: 1 proton, 0 neutrons, and 1 electron.
- Helium: 2 protons, 2 neutrons, and 2 electrons.
- Lithium: 3 protons, 4 neutrons, and 3 electrons.

Element Definition:
- Any substance that cannot be chemically broken down into simpler substances.
Atomic Number:
- The number of protons in the nucleus; unique for each element, denoted as a subscript to the left of the atomic symbol (e.g., 3Li).
Mass Number:
- The total number of protons and neutrons in the nucleus; written as a superscript to the left of the atomic symbol (e.g., 7Li).

The periodic table organizes elements according to their valence electrons; the outermost electrons determining chemical properties.
- Valence Electrons: Electrons in the outermost energy level.
- Inert (nonreactive) elements possess all eight electrons in their valence shell.
Octet Rule: Atoms strive for a complete outer energy level, typically eight electrons (with exceptions like H and He, which seek only 2).

Mass refers to the quantity of substance.
Weight refers to the gravitational force on the substance.
The atomic mass is the sum of protons and neutrons, with each having a mass of approximately 1 Dalton.

Isotopes are structural variations of the same element that share the same number of protons but differ in neutrons, leading to different mass numbers.
Atomic Weight: The average mass number of all isotopes of an element.
Radioactive Isotopes: Unstable isotopes that emit radiation as they decay; defined by their half-life, which is the time required for half of the atoms in a sample to decay.

Molecules: General term for 2 or more atoms bonded together (can be identical or different atoms).
Compounds: Specific type of molecule consisting of two or more different types of atoms bonded together (e.g., C6H12O6).
Homogeneous Molecules: Molecules composed exclusively of one type of atom (e.g., O2 or H2).

Chemical Bonds: Represent energy relationships between electrons of reacting atoms.
Chemical bonds are not physical structures but instead ensure stable associations among atoms.

Electrons: Subatomic particles that play a crucial role in chemical interactions.
- Electrons occupy regions around the nucleus called electron shells, which are synonymous with energy levels.
The outermost shell, known as the valence shell, holds the electrons that dictate chemical behavior and stability.
Electron shells can accommodate a designated number of electrons:
- Shell 1: Max of 2 electrons
- Shell 2: Max of 8 electrons
- Shell 3: Max of 18 electrons

Atoms seek to have 8 electrons in their valence shell (Octet Rule).
- Exceptions include smaller atoms (like H and He), which only desire 2 electrons.
The drive for stability led to the formation of chemical bonds as most atoms seek to complete their outer valence shell.

Chemically Inert Elements: Possess a complete valence shell, leading to stability and lack of reactivity (e.g., He and Ne).
Chemically Reactive Elements: Have an incomplete valence shell, readily engaging in chemical reactions (e.g., H, C, O, Na).

What subatomic particles determine the mass of an atom?
- Protons and Neutrons determine atomic mass.
What subatomic particles determine the charge of an atom?
- Protons and Electrons determine atomic charge.
What is the relationship of the octet rule and chemical stability?
- Achieving a full valence shell of eight electrons (or two for hydrogen and helium) leads to chemical stability.