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 S1

• 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 S2

• 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

MgCl2

Groups 3-12 transition metals

• Highest energy level ends with S2

but d-orbitals are being filled

• Tend to lose the S2 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 S2P1

• Lose the three S2P1 e-, forming +3 cations

• Both metalloids and metals in this group

Groups 14

• Electron configuration ends with S2P2

• Don’t tend to form ions

• Non metals, metalloids and metals in this group

Groups 15

• Electron configuration ends with S2P3

• Tend to gain 3 e-, forming -3 anions

• Non metals, metalloids and metals in this group

Groups 16

• Electron configuration ends with S2P4

• 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 S2P5

• 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 S2P6

• 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.