This section covers atomic structure, the arrangement of electrons, and the differences between elements, compounds, and mixtures. Separation techniques for mixtures are also covered.
Atoms: protons (+1, mass 1) and neutrons (0, mass 1) in nucleus; electrons (-1, negligible mass) orbit in shells. Proton number (Z): identifies the element. Nucleon number (A): protons + neutrons. Isotopes: atoms of the same element with different numbers of neutrons (same Z, different A). Relative atomic mass: weighted average mass considering isotope abundances.
Electrons fill shells: 1st shell = 2, 2nd = 8, 3rd = 8 (for first 20 elements). Configuration determines chemical properties. Group number = electrons in outer shell. Period = number of occupied shells. Noble gases have full outer shells (stable). Electron configuration examples: Na = 2,8,1; Cl = 2,8,7; Ar = 2,8,8.
Element: one type of atom. Compound: two or more elements chemically bonded. Mixture: substances not chemically combined. Separation techniques: filtration (insoluble solid from liquid), evaporation (dissolved solid from solution), simple distillation (solvent from solution), fractional distillation (liquids with different boiling points), chromatography (components of a mixture based on solubility).
Chemical reactions involve electrons (forming bonds, losing/gaining electrons). Isotopes have the same number of protons and electrons, so they form the same bonds and react identically. The different number of neutrons changes the mass but does not affect the electron configuration or chemical behaviour. However, isotopes differ in physical properties like density and radioactive stability.
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