Notes on Distance Scales, Purity, and Building Blocks of Matter

Matter is studied at different distance scales; what matter is made of depends on the distance scale considered.
Distance scales in chemistry are measured in the meter (m); scientific notation is used for very large or very small distances.
Examples:
- Gold nugget: about the middle scale ~1 mm = 10^{-3} m.
- At the atom level: ~100 pm = 10^{-10} m.
Image/camera analogy: the scale of an image corresponds to the real distance of the matter shown; scales vary across images and experiments.
Practical note: scales span from macroscopic to atomic to subatomic levels.

Matter’s organization depends on the distance scale;
Pure vs impurities: a mostly pure sample is a mixture with one main type of matter plus small amounts of other types (impurities).
Gold nuggets can be heterogeneous on some scales and homogeneous on others.
Impurities and the degree of purity are important in chemistry and are studied/measured.

Homogeneous: looks the same throughout (homo = Latin for "same").
Heterogeneous: contains different parts in different regions (hetero = Latin for "different").
In STM images, substitutions of non-gold atoms can occur, showing heterogeneity on some scales.

All matter is composed of a limited set of building blocks called elements.
There are a little over 100 kinds of atoms (elements).
Elements are the basic building blocks of matter (e.g., gold, carbon, hydrogen, oxygen).
The periodic table organizes elements and is a powerful model for understanding and predicting properties.
The goal of the course is to use the periodic table to understand, analyze, and control matter.

Global agreement on symbols for elements (e.g., Au for gold, C for carbon).
Formulas indicate composition and bonding (e.g., H2O is not OH2).
IUPAC sets rules for naming chemicals and counting atoms to ensure consistent communication.

Atoms are tiny, have mass and occupy space; different atoms have different masses and sizes.
Atoms are often represented as color spheres (e.g., hydrogen as white, oxygen as red).
A molecule is two or more atoms bound together and moving as a unit.
Example: Water is H2O (two hydrogen atoms for every one oxygen atom).
A single glass of water (8 oz) contains about $7.9 \times 10^{24}$ molecules, each moving independently in the liquid.