Atoms and Elements

The internal structure of the human body is organized into six hierarchical levels. Students must know all six levels of organization for the course: - Chemical Level: This is the most basic level, involving atoms and molecules. Examples include phosphorus atoms and phospholipid molecules. - Cellular Level: Molecules combine to form cells, the basic functional units of life. An example given is the squamous epithelial cell, which possesses features like a cell membrane. - Tissue Level: Groups of similar cells that work together to perform a specific function. An example is stratified squamous epithelium. - Organ Level: Multiple tissue types combine to form a structure with a specific function. The example provided is the esophagus. - Organ System Level: Groups of organs that work together to meet a major physiological need. The example provided is the digestive system. - Organism Level: The highest level of organization, representing the human being as a whole.

Atoms: Defined as the "building blocks" of chemistry.
Elements of the Human Body: Elements are categorized by their abundance within the body: - Major Elements ( $96\%$ ): These constitute the bulk of the body's mass. - Mineral Elements ( $< 4\%$ ): These occur in smaller amounts but are essential for physiological function. - Trace Elements ( $0.01\%$ ): These appear in extremely minute quantities.
Periodic Table Information: - Atomic Number: Represents the number of protons in an atom. This number determines the specific type of chemical element. - Atomic Mass: Represents the sum of the number of protons and the number of neutrons in the nucleus. - Atomic Symbol: A one or two-letter abbreviation for an element. If a symbol consists of two letters, the first must be capitalized and the second must be lower-case.
Note on Rare Earth Elements: According to the provided periodic table, rare earth elements are not found in the human body.

Subatomic Particles: - Protons ( $p^+$ ): Possess a positive electrical charge and are found in the nucleus. - Neutrons ( $n^0$ ): Possess no electrical charge (neutral) and are found in the nucleus. - Electrons ( $e^-$ ): Possess a negative electrical charge and spin around the nucleus in specific energy levels or shells.
Atomic Composition Rules: - The number of protons and electrons in a neutral atom is usually the same. - The number of neutrons is often different from the number of protons.
Models of Atomic Structure: - Planetary Model: Electrons are depicted in fixed orbits (rings) at precise distances from the nucleus, similar to planets orbiting the sun. This model is shown using Helium as an example. - Electron Cloud Model: Electrons are shown in various locations they might occupy at different distances from the nucleus over time. This model is shown using Carbon as an example.

Electrons are arranged in energy levels (shells) surrounding the nucleus: - $1^{st}$ Energy Level: Can hold a maximum of $2$ electrons. - $2^{nd}$ and $3^{rd}$ Energy Levels: Can each hold up to a maximum of $8$ electrons.
Examples of Basic Atomic Structures: - Hydrogen ( $H$ ): Includes $1$ proton, $0$ neutrons, and $1$ electron ( $1p^+$ , $0n^0$ , $1e^-$ ). - Helium ( $He$ ): Includes $2$ protons, $2$ neutrons, and $2$ electrons ( $2p^+$ , $2n^0$ , $2e^-$ ). - Lithium ( $Li$ ): Includes $3$ protons, $4$ neutrons, and $3$ electrons ( $3p^+$ , $4n^0$ , $3e^-$ ).

To determine the number of particles in an element based on its periodic table entry (e.g., $\text{Mass Number (A)}$ over $\text{Atomic Number (Z)}$ next to the symbol): - Number of Protons ( $p$ ): Equal to the Atomic Number. - Number of Electrons ( $e$ ): In a neutral atom, equal to the number of protons. - Number of Neutrons ( $n$ ): Calculated by subtracting the Atomic Number from the Atomic Mass ( $\text{Mass} - \text{Protons} = n$ ).

Follow these five steps to draw an atom (e.g., Sulfur-34, $\text{}^{34}_{16}S$ ): 1. Determine the number of each type of particle ( $p$ , $n$ , $e$ ). 2. Draw the nucleus and insert the specific number of protons and neutrons. 3. Draw the $1^{st}$ energy level and insert the maximum of $2$ electrons. 4. Draw the $2^{nd}$ energy level and insert the maximum of $8$ electrons. 5. Continue drawing energy levels until all electrons are used.

Valence Electrons: The number of electrons present in the atom's outermost energy level.
Vacancies: The number of empty spots remaining in the outer energy level. This is calculated by subtracting the number of valence electrons from the maximum capacity of that specific level.
Example: Potassium ( $\text{}^{39}_{19}K$ ) - Total electrons: $19$ - $1^{st}$ shell: $2$ electrons - $2^{nd}$ shell: $8$ electrons - $3^{rd}$ shell: $8$ electrons - Remaining electrons for outermost shell: $19 - 2 - 8 - 8 = 1$ - Valence Electrons: $1$ - Vacancies: Since the $4^{th}$ level's limit is not specified here, but following the octet rule for calculations provided: $8 - 1 = 7$ vacancies.

Oxygen-16 ( $\text{}^{16}_{8}O$ ): - $p = 8$ , $n = 8$ , $e = 8$
Phosphorus-31 ( $\text{}^{31}_{15}P$ ): - $p = 15$ , $n = 16$ , $e = 15$
Chlorine-35 ( $\text{}^{35}_{17}Cl$ ): - $p = 17$ , $n = 18$ , $e = 17$
Sulfur-33 ( $\text{}^{33}_{16}S$ ) [Homework]: - $p = 16$ , $e = 16$ , $n = 17$
Calcium-40 ( $\text{}^{40}_{20}Ca$ ) [Homework]: - $p = 20$ , $e = 20$ , $n = 20$

Carbon-12 ( $\text{}^{12}_{6}C$ ): - Nucleus: $6p$ , $6n$ . Electrons: $2$ in first shell, $4$ in second shell.
Sodium-23 ( $\text{}^{23}_{11}Na$ ): - Nucleus: $11p$ , $12n$ . Electrons: $2$ in first shell, $8$ in second shell, $1$ in third shell.
Sulfur-33 ( $\text{}^{33}_{16}S$ ) [Homework]: - Nucleus: $16p$ , $17n$ . Electrons: $2$ in first shell, $8$ in second shell, $6$ in third shell.
Calcium-40 ( $\text{}^{40}_{20}Ca$ ) [Homework]: - Nucleus: $20p$ , $20n$ . Electrons: $2$ in first shell, $8$ in second shell, $8$ in third shell, $2$ in fourth shell.

Helium ( $\text{}^{4}_{2}He$ ): - Valence Electrons: $2$ - Vacancies: $0$
Magnesium ( $\text{}^{24}_{12}Mg$ ): - Valence Electrons: $2$ - Vacancies: $6$
Phosphorus ( $\text{}^{31}_{15}P$ ): - Valence Electrons: $5$ - Vacancies: $3$