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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