Notes on Atoms, Elements, and the Periodic Table (Pages 1–5)

Chemical Symbol Origin

Elements are referenced by chemical symbols derived from their names in English, Latin, or Greek, e.g., Oxygen (O) from English, Gold (Au) from Latin "aurum".

Major elements in animal body

Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N) constitute approximately 96% of body mass.

Oxygen (O) in Body

Atomic number Z = 8, makes up ext{65.0%} of body mass, necessary for cellular respiration and a component of water.

Carbon (C) in Body

Atomic number Z = 6, makes up 18.5% of body mass, a primary component of organic molecules.

Atom

The smallest unit of an element that retains the element’s properties.

Proton

A positively charged subatomic particle with a mass of approximately 1 atomic mass unit (amu), located in the nucleus.

Neutron

An electrically neutral subatomic particle with a mass of approximately 1 amu, located in the nucleus.

Electron

A negatively charged subatomic particle with very small mass, orbiting the nucleus in regions called electron clouds.

Atomic Number (Z)

The number of protons in an atom’s nucleus, which defines the element.

Mass Number (A)

The total number of protons and neutrons in an atom's nucleus, calculated as A = Z + N\_n.

Neutral Atom

An atom where the number of protons equals the number of electrons (Z = E), resulting in no net electrical charge.

Ion

An atom that has lost or gained electrons, resulting in a net electrical charge (q = Z - E).

Isotope

Atoms of the same element (same number of protons) but with a different number of neutrons.

Carbon-14 Dating

A method using the radioactive decay of carbon-14 (half-life t\_{1/2} = \frac{\ln 2}{\lambda}) to estimate the age of fossils and geological samples.

Electron Shells

Regions around the nucleus where electrons occupy specific energy levels, with the first shell (closest) having the lowest energy electrons.

Planetary Model of Atom

A simplified model depicting electrons orbiting the nucleus like planets around the sun, primarily for basic understanding.

Orbital Model of Atom

A three-dimensional electron cloud representation showing the most probable locations of electrons around the nucleus, reflecting probability distributions.