The Periodic Table 6.3 Periodic Trends

Atomic Size Atoms are very small so we can’t measure their size directly. When atoms of the same element are joined together, molecules are formed. The atomic radius can be determined by taking half of the distance between two atoms. Measured in picometers (1 trillion pm in a m)

Atomic Size In general, atomic size increases top to bottom within a group and right to left across a period.

Ions Ion: atom with a positive/negative charge. Happens when ELECTRONS are transferred between atoms. Positive charge = CATION (less electrons) Negative charge = ANION (more electrons)

Ions Continued METALS usually lose electrons NONMETALS usually gain electrons

(First) Ionization Energy Energy required to remove an (first) electron (move to higher energy level) Increases bottom to top in a group and left to right in a period (opposite of atomic size).

Ionic Size Cations (+) are SMALLER than their initial atom. Anions (-) are LARGER than their initial atom. Same trend as size

Electronegativity The ability of an atom to attract electrons in a compound. Increase bottom to top in a group and left to right in a period.

Electronegativity Continued LEAST electronegative = cesium (tends to LOSE electrons in reactions) MOST electronegative = fluorine (tends to GAIN electrons in reactions)

SUMMARY! (pg. 178) NOTE: Electron affinity = Electronegativity