Atoms, Elements, and Chemical Bonds: Foundations for Anatomy & Physiology

Atoms and Atomic Structure

Definition and Components of the Atom

The atom is the smallest unit of matter that cannot be broken down further by chemical means. Understanding atomic structure is fundamental to grasping chemical processes in the human body.

• Nucleus:

  • Contains protons (positively charged) and neutrons (neutral).

  • Responsible for most of the atom's mass.

• Electron Cloud:

  • Contains electrons (negatively charged).

  • Electrons have almost no mass compared to protons and neutrons.

Subatomic Particle	Mass (kg)	Charge	Mass	Charge
Electron (e-)	9.11 × 10-31	-1	0	-1
Proton (p+)	1.67 × 10-27	+1	1	+1
Neutron (n0)	1.67 × 10-27	0	1	0

The Periodic Table

Organization and Groups

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

• Period: Horizontal rows; tells the number of electron shells.

• Group: Vertical columns; main group numbers (1-8) indicate the number of valence electrons.

• Metals, Metalloids, Nonmetals:

  • Metals: Good conductors, malleable, found on the left and center.

  • Nonmetals: Poor conductors, found on the right.

  • Metalloids: Properties intermediate between metals and nonmetals.

Type	Location on Table	Properties
Metals	Left/Center	Conductive, malleable
Nonmetals	Right	Poor conductors
Metalloids	Stair-step line	Intermediate properties

Atomic Number, Mass Number, and Isotopes

Key Definitions

• Atomic Number: Number of protons in an atom.

• Mass Number: Number of protons plus neutrons.

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

• Atomic Mass: Weighted average of all isotopes.

Example: Carbon isotopes:

• $^{12}C$: 6 protons, 6 neutrons

• $^{13}C$: 6 protons, 7 neutrons

• $^{14}C$: 6 protons, 8 neutrons

Mole Concept

Definition and Application

The mole is a unit for counting atoms and molecules. One mole contains $6.022 \times 10^{23}$ units (Avogadro's number).

• Formula: $\text{Number of particles} = \text{moles} \times 6.022 \times 10^{23}$

• Used to relate atomic/molecular quantities to measurable amounts.

Major Elements in the Human Body

Essential Elements and Their Functions

Seven major elements are vital for life, with trace elements also playing important roles.

• CHNOPS: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur

• Other important ions: Ca2+, K+, Na+, Cl-, Mg2+

Element	Biological Role
Calcium (Ca)	Structural component of bones, muscle contraction, nerve signaling
Potassium (K)	Major intracellular ion, nerve impulse transmission
Sodium (Na)	Major extracellular ion, fluid balance, nerve impulses
Magnesium (Mg)	Enzyme cofactor, muscle and nerve function
Iron (Fe)	Oxygen transport (hemoglobin)
Trace elements	Required in small amounts for enzyme function

Chemical Bonds

Ionic Bonds

Ionic bonds are formed by the electrostatic force of attraction between oppositely charged ions, created by the transfer of electrons.

• Cation: Positive ion (e.g., Na+)

• Anion: Negative ion (e.g., Cl-)

• Example: $\text{NaCl} \rightarrow \text{Na}^+ + \text{Cl}^-$

Covalent Bonds

Covalent bonds involve the sharing of electrons between atoms.

• Equal sharing: Nonpolar (hydrophobic)

• Unequal sharing: Polar (hydrophilic), e.g., H2O

Hydrogen Bonds

Hydrogen bonds are weak electrostatic attractions between polar molecules, especially when hydrogen is bonded to nitrogen, oxygen, or fluorine.

• Important for the structure of water and biological macromolecules.

Water: Properties and Importance

Physical and Chemical Properties

Water is essential for life and makes up about two-thirds of body weight.

• High boiling point

• Low vapor pressure

• High temperature of vaporization

• Hydrogen bonding keeps molecules "stuck together"

Example: Water's high heat capacity helps regulate body temperature.

Solutions and pH

Definitions

• Solvent: Substance that dissolves another

• Solute: Substance being dissolved

• Solution: Solvent containing the solute

Acids and Bases

• Acid: Gives off H+ in water (e.g., HCl)

• Base: Gives off OH- in water (e.g., NaOH)

• Strong acids/bases: Complete dissociation in water

• Weak acids/bases: Incomplete dissociation

pH Scale

The pH scale measures the concentration of hydrogen ions in solution.

• Formula: $\text{pH} = -\log [\text{H}^+]$

• pH 7 is neutral; lower values are acidic, higher values are basic.

[H+]	pH
1.0 × 10-1	1
1.0 × 10-2	2
1.0 × 10-3	3
1.0 × 10-4	4
1.0 × 10-5	5
1.0 × 10-6	6
1.0 × 10-7	7
1.0 × 10-8	8
1.0 × 10-9	9
1.0 × 10-10	10
1.0 × 10-11	11
1.0 × 10-12	12
1.0 × 10-13	13
1.0 × 10-14	14

Buffers

Buffers minimize changes in pH by combining a weak acid and its corresponding weak base.

• Example: $\text{H}_2\text{O} + \text{CO}_2 \leftrightarrow \text{H}_2\text{CO}_3$ (carbonic acid) $\leftrightarrow \text{HCO}_3^-$ (bicarbonate) $+$ H+

• Buffers play a crucial role in maintaining homeostasis.

Summary Table: Principal Elements in the Human Body

Element	Biological Significance
Calcium (Ca)	Important for blood clotting, muscle contraction, nerve function
Potassium (K)	Major intracellular ion, nerve impulse transmission
Sodium (Na)	Major extracellular ion, fluid balance, nerve impulses
Magnesium (Mg)	Enzyme cofactor, muscle and nerve function
Iron (Fe)	Essential for oxygen transport, part of hemoglobin
Trace elements	Required in small amounts for enzyme function and other processes

Additional info: Some context and explanations have been expanded for clarity and completeness, including definitions, examples, and formulas relevant to Anatomy & Physiology students.