Ch. 1 Atomic Structure and Chemical Properties: Foundations of General Biology

Atomic Structure and Chemical Properties

What Determines the Properties of a Compound?

The properties of a chemical compound are determined by the types of atoms present and how these atoms are bonded together. The arrangement and interactions of atoms influence the compound's behavior and characteristics.

• Atoms and Bonding: The specific atoms involved and the nature of their chemical bonds define the compound's properties.

• Protons: The number of protons in an atom determines its identity as a particular element.

• Electron Distribution: The arrangement of electrons, especially in the outer shell, determines an atom's ability to form chemical bonds.

• Properties: Attributes or behaviors of a compound, such as reactivity, solubility, and physical state.

• Example: Water (H2O) is composed of hydrogen and oxygen atoms bonded in a specific way, giving it unique properties like high surface tension and polarity.

Elements, Compounds, and Molecules

Understanding the basic units of matter is essential in biology. Elements, compounds, and molecules are foundational concepts.

• Element: A substance that cannot be broken down into simpler substances by chemical means.

• Compound: A substance formed from two or more different types of atoms bonded together.

• Molecule: Two or more atoms bonded together; all compounds are molecules, but not all molecules are compounds (e.g., O2).

• Essential Elements: Elements required in large amounts for life (e.g., C, O, H, N make up 96% of living matter).

• Trace Elements: Elements required in very small amounts (less than 0.01%), but still vital for biological processes.

Type	Definition	Examples
Essential Elements	Needed in large amounts	C, O, H, N
Trace Elements	Needed in minute amounts	Fe, I, Zn

Atomic Structure: Subatomic Particles

Atoms are composed of smaller particles called subatomic particles, which determine their chemical properties and behavior.

• Proton (+): Located in the nucleus; determines the element's identity.

• Neutron (0): Located in the nucleus; affects isotopic form but not chemical identity.

• Electron (-): Located outside the nucleus in electron shells; involved in chemical bonding.

• Subatomic Particles: Much smaller than the atom itself.

Particle	Charge	Location	Role
Proton	+1	Nucleus	Identity of element
Neutron	0	Nucleus	Isotope formation
Electron	-1	Electron shell	Chemical bonding

Atomic Number and Atomic Mass

Each element is defined by its atomic number and atomic mass, which are fundamental for understanding chemical reactions and isotopes.

• Atomic Number (Z): Number of protons in the nucleus; unique for each element.

• Atomic Mass: Sum of protons and neutrons in the nucleus; measured in daltons.

• Electrons: So small that their mass does not significantly contribute to the atomic mass.

• Example: Carbon has an atomic number of 6 and an atomic mass of approximately 12.01.

Formula:

$\text{Atomic Mass} = \text{Number of Protons} + \text{Number of Neutrons}$

Isotopes and Radioactivity

Isotopes are variants of elements with different numbers of neutrons. Some isotopes are radioactive and decay spontaneously, emitting particles and energy.

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

• Example: Carbon-14 has 6 protons and 8 neutrons (6 + 8 = 14), but is still carbon.

• Radioactive Isotopes: Unstable isotopes that decay, releasing energy and particles.

• Not all isotopes are radioactive.

Isotope	Protons	Neutrons	Radioactive?
Carbon-12	6	6	No
Carbon-14	6	8	Yes

Application: Radioactive isotopes are used in medicine (e.g., tracers) and in dating fossils (radiometric dating).

Additional info: These foundational concepts are essential for understanding chemical reactions, molecular biology, and the behavior of biological molecules.