Properties of Elements

Atomic Radius A measure of the size on an atom. What determines an atom’s size? Remember, the nucleus is very very small and compact. It is the electrons that determine how big the atom is.

Atomic Radius It is hard to measure where the moving e- are at any moment, so they can not be easily used to measure size. DEFINITION: Half the distance between the nuclei of two adjacent atoms in a crystal ½ distance

Ionization Energy DEFINITION: The amount of energy it takes to remove the outermost e- from a neutral atom in the gas phase X + Ionization energy X + + e- Neutral atom Cation electron

Electronegativity DEFINITION: A measure of the attraction an atom has for electrons when it is bonded to another atom. Scale is from 0.7 (low, Cs) to 4.0 (high, F)

Trends in Atomic Radius Across a period: radius decreases because there are more protons in each successive atom’s nucleus, pulling harder on the e- and making the atom smaller Down a group: radius increases because the atoms have more energy levels farther from the nucleus, making the atom bigger

Trends in Ionization Energy Across a period: I.E. increases because there are more protons in each successive atom’s nucleus, pulling harder on the e- and making it harder to remove the e- Down a group: I.E. decreases because the atoms have more energy levels farther from the nucleus, so the outer e- are less attracted to the nucleus and are therefore easier to remove. Also, inner e- “shield” the outer e- from the pull of the nucleus.

Trends in Electronegativity Across a period: Electronegativity increases because there are more protons in each successive atom’s nucleus, pulling harder on the e- Down a group: Electronegativity decreases because the atoms have more energy levels farther from the nucleus, so the nucleus has less positive pull on the e-. Also, inner e- “shield” the outer e- from the pull of the nucleus

Ionic Radius If an atom GAINS e-, it gets bigger in size So….negative ions (anions) are bigger than their neutral atom

Ionic Radius If an atom LOSES e-, it gets smaller in size So… positive ions (cations) are smaller than their neutral atom

Group 1 alkali metals Electron configuration ends with S 1 Lose this outermost e- easily (low Ionization energy and electronegativity) forming +1 cations VERY reactive! Francium is MOST reactive Not found uncombined in nature Form stable compounds with non metals like NaCl

Group 2 alkaline earth metals Electron configuration ends with S 2 Lose these 2 outermost e- easily (low Ionization energy and electronegativity) but not as easily as Group 1 metals losing only 1 e- Form +2 cations Reactive! (but not as much as Group 1) Not found uncombined in nature Form stable compounds with non metals like MgCl 2

Groups 3-12 transition metals Highest energy level ends with S 2 but d-orbitals are being filled Tend to lose the S 2 e- easily, forming +2 cations, but many can also form +1 or +3 (multiple oxidation states) Less reactive than Groups 1 or 2 Form colorful ions and compounds

Groups 13 Electron configuration ends with S 2 P 1 Lose the three S 2 P 1 e-, forming +3 cations Both metalloids and metals in this group

Groups 14 Electron configuration ends with S 2 P 2 Don’t tend to form ions Non metals, metalloids and metals in this group

Groups 15 Electron configuration ends with S 2 P 3 Tend to gain 3 e-, forming -3 anions Non metals, metalloids and metals in this group

Groups 16 Electron configuration ends with S 2 P 4 Tend to gain 3 e-, forming -2 anions Non metals, and metalloids in this group Reactive! Tend to form stable compounds with metals like MgO

Groups 17 Halogens Electron configuration ends with S 2 P 5 Tend to gain one e-, forming -1 anions. Very high electronegativity and ionization energy. (F is highest electronegativity with 4.0) Non metals only in this group Only group to have all three phases of matter at room temperature (s, l, g) VERY Reactive! Not found uncombined in nature. Tend to form stable compounds with metals like NaCl. Most reactive is F.

Groups 18 Noble gases Electron configuration ends with S 2 P 6 Energy level is full Do not lose or gain e-. Do not form ions. UNreactive! Not found combined with other elements in nature. Do not form compounds.