The arrangement of electrons in an atom helps determine the properties and behavior of that atom

Electrons live in something called energy levels.

Only so many electrons can be in any energy level.

The electrons in the outer most energy level of any element are called valence electrons.

Find out which period (row) your element is in.

•Elements in the 1st period have one energy level.•Elements in the 2nd period have two energy levels, and so on.

1

2

3

4

5

6

7

The electron shells surrounding the nucleus each hold a particular number of electrons.

Shells are named with letters:

1 = K shell = 2 electrons2 = L shell = 8 electrons3 = M shell = 8 electrons4 = N shell = 18 electrons5-7 = O, P, Q = up to 32 electrons

Remember: The outer shell of an atom (no matter what letter) can only hold 8 electrons!

An octet is 8 valence electrons is associated with the stability of the noble gases (does not occur with He; He is stable with 2 valence electrons)

Valence ElectronsHe 2Ne 8 Ar 8

Kr 8In order to achieve an octet,

elements will form ions.

Metals form cations

by losing their valence electrons resemble the nearest noble gas have fewer electrons than protons

Group 1 metals ion 1+

Group 2 metals ion 2+

Group 3 metals ion 3+

Sodium achieves an octet by losing its one valence electron.

Nonmetals form anions

gain electrons have more electrons than protons

form negatively charged ions with 3–, 2–, or 1– charges

Chlorine achieves an octet by adding an electron to its valence electrons.

Ionization EnergyIonization Energy

Energy needed to remove one of atom’s electrons from its outermost shell

Atoms with high ionization energies hold onto their electrons very tightly.

Atoms with low ionization energies are more likely to lose one or more of their outermost electron.

Hydrogen Helium

The value for helium is higher than hydrogen because there are now two protons in the nucleus. The charge is greater so the pull on the outer electrons is stronger.

1310 kJ/mol 2370 kJ/mol

Ionization EnergyIonization Energy

Hydrogen Helium

Lithium

•FURTHER AWAYFURTHER AWAY from the nucleus = less attraction for an electron

519 kJ/mol1310 kJ/mol 2370 kJ/mol

Ionization EnergyIonization Energy

Lithium atoms have 3 protons so you would expect the pull on electrons to be greater. However, the Ionization Energy of lithium is lower than that of helium because…

Value decreases down the Group the outer electrons are easier to remove because of the greater distance from the nucleus

519 kJ/mol

Li

494 kJ/mol418 kJ/mol

Na K

Ionization EnergyIonization Energy

Electronegativity is a chemical property that describes the tendency of an atom to attract electrons towards itself.

An atom's electronegativity is affected by its atomic number. Higher atomic number elements tend to be less electronegative because of the distance from their nucleus to their valence electrons.

ELECTRONEGATIVITYELECTRONEGATIVITY

Pauling’s electronegativity scale

Fluorine is the most electronegative element

It has an electronegativity value of 4.0

ELECTRONEGATIVITYELECTRONEGATIVITY