Atoms and the Periodic Table

Study Notes

Matter is anything that occupies space and has mass.
Extensive properties depend on the amount of matter, e.g., mass and volume.
Intensive properties are quantity-independent and depend on the type of matter, e.g., density and color.

Mixtures consist of two or more substances.
Homogeneous mixtures have evenly distributed components, difficult to distinguish visually.
Heterogeneous mixtures have unevenly distributed components, easily distinguished by the eye.

Pure substances can be either elements or compounds.
Elements consist of identical atoms, while compounds are made of two or more different elements in a fixed ratio.

Dobereiner’s Triad (1817): Similar elements grouped in threes; average atomic weight of the second equals the average of the first and third.
Newlands’ Law of Octaves (1866): Elements arranged by increasing atomic mass, with the properties of the eighth element repeating those of the first.
Mendeleev’s Table (1869): Elements’ atomic weights relate to periodic variations in properties; predicted Gallium's existence.
Henry Moseley (1894): Discovered that atomic charge (atomic number) is distinct from atomic mass.

Metals give electrons, nonmetals accept electrons, and metalloids possess characteristics of both categories.

Physical properties do not change the substance's composition; examples include hardness and malleability.

Atomic Radius: Distance between the nucleus and valence shell; increases down the group.
Electron Affinity: Energy released when an atom gains an electron; higher affinity the closer to fluorine.
Ionization Energy: Energy required to remove an electron; increases as the atom approaches fluorine.
Electronegativity: Atom's ability to attract electrons; higher values indicate proximity to fluorine.