Atomic Structure, Isotopes, and Periodic Trends: Study Notes

Atomic Structure and Isotopes

Representations of Atomic Nuclei

Atomic nuclei are composed of protons (red spheres) and neutrons (gray spheres). The number of protons determines the element, while the number of neutrons determines the isotope.

• Proton (p+): Positively charged particle in the nucleus. The number of protons is the atomic number (Z).

• Neutron (n0): Neutral particle in the nucleus. The sum of protons and neutrons is the mass number (A).

Each nucleus (A–E) can be described by its atomic symbol: Element-A or AZElement, where:

• A = mass number = protons + neutrons

• Z = atomic number = number of protons

Isotopes are atoms of the same element (same Z) with different numbers of neutrons (different A).

Example: Determining Atomic Symbols and Isotopes

Suppose the nuclei are as follows (based on the image):

Nucleus	Protons	Neutrons	Atomic Symbol
A	6	6	$^{12}_{6}\text{C}$
B	6	7	$^{13}_{6}\text{C}$
C	6	8	$^{14}_{6}\text{C}$
D	7	7	$^{14}_{7}\text{N}$
E	6	6	$^{12}_{6}\text{C}$

Additional info: The actual proton and neutron counts are inferred based on typical textbook examples and the visual representation of red and gray spheres.

• Isotopes: Nuclei with the same number of protons but different numbers of neutrons. In this example, A, B, C, and E are isotopes of carbon.

Classification of Elements: Metals, Nonmetals, and Metalloids

Element Types Based on Atomic Structure

Elements can be classified as metals, nonmetals, or metalloids based on their position in the periodic table and their properties.

• Metals: Good conductors of heat and electricity, malleable, ductile, and typically solid at room temperature.

• Nonmetals: Poor conductors, can be gases, liquids, or brittle solids.

• Metalloids: Have properties intermediate between metals and nonmetals.

Nucleus	Element	Classification
A	Carbon (C)	Nonmetal
B	Carbon (C)	Nonmetal
C	Carbon (C)	Nonmetal
D	Nitrogen (N)	Nonmetal
E	Carbon (C)	Nonmetal

Additional info: All nuclei shown represent nonmetals, as both carbon and nitrogen are classified as nonmetals.

Periodic Trends: Atomic Size of Alkali Metals

Comparing Atomic Radii of Li, Na, K, and Rb

The alkali metals (Group 1: Li, Na, K, Rb) show a trend of increasing atomic radius as you move down the group in the periodic table.

• Atomic radius increases from top to bottom within a group due to the addition of electron shells.

• Order of increasing atomic radius: Li < Na < K < Rb

Sphere	Element	Relative Size
D	Li	Smallest
A	Na	Small
C	K	Large
B	Rb	Largest

Example: The largest sphere (B) represents rubidium (Rb), while the smallest (D) represents lithium (Li).

Additional info: The matching of spheres to elements is inferred from the known periodic trend in atomic size for alkali metals.