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Periodic Trends Project
среда 08 апреля admin 7
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Periodic Trends
Copy of 050 Periodic Table and Trends Copy of 030 Chemical Reactions and Balancing Copy of Mole Copy of 130 Moles Copy of Reactions and Equations Copy of Electricity Unit 1 Science Skills Copy of Forces and Newton's Laws Periodic Poster Project Worksheet Chapter 6 Periodic Table Periodic Table N Periodic Table Trends N2 Periodic Trends Lab.
We will be discussing 4 trends found in the periodic table. We will first define them.
1.Atomic radius (size) – ½ the distance from center to center of two like atoms.
2.Ionization energy – the amount of energy needed to remove an electron from a specific atom or ion in its ground state
a.A + energy à A+ + e-
b.The amount of energy absorbed is equal to the ionization energy. It is an ENDOTHERMIC process, therefore, the number will always be positive.
electron
electron
electron
3. Electronegativity – the ability of an atom to attract
high electronegativity value means a strong
Increases as you move down a family
Why??? As you move down any family, another principle energy level is added.
Decreases as you move from left to right within a period.
Why??? As the number of protons increase within the nucleus, the positive charge of the nucleus increases. As a result, the nucleus exerts a greater pull on all the electrons in the atom. Hence, pulling the electrons closer to the nucleus and decreasing the atomic size.
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2.Ionization energy
Decreases as you move down a family.
Why??? The electrons that are removed from atoms of each succeeding element in a group are in a higher energy level. Therefore, since they are farther from the nucleus they receive less pull and are easily removed.
Increases as you move from left to right within a period.
Why??? The nuclei of succeeding elements in a period exert more pull on their electrons because of the increase of positive charge. The stronger pull means more energy is required to remove an electron. The harder the hold, the harder it is to remove.
3. Reactivity down a group of nonmetals.
From the middle of the d block going outward, the
reactivity increases across a period . In other words,
across a period reactivity will decrease until the
increasing.
4. Electronegativity Going down a group, the electronegativity value
Going across a period, the electronegativity value
Electronegativity values are arbitrary scales of
Using Electronegativity Values in Bonding:
Subtracting the values of each element in a compound can indicate what type of bond exists between the elements.
As bond strength increases, the electronegativity value increases.
Polarity -- the formation of partially charged atoms in a molecule
If the difference in electronegativity is:
0 – 0.5 the bond is non-polar covalent
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0.5 – 1.6 the bond is polar covalent -- will dissolve
1.6 or higher the bond is ionic -- Ex: MgCl2 -- will
What is the e-neg value of Cs?
This is the smallest e-neg value there is. This means the atom has very little ability to gain an electron. Instead, the atom loses an electron to obtain a 1+ charge.
What is the e-neg value of F?
This is the highest value. It means the atom attracts electrons very strongly. It will gain one electron o form a 1- ion.
The difference is 3.3. Therefore, the bond is ionic. This is a very strong bond.
Example:PH3
The e-neg value for P is
The e-neg value for H is
Both have equal e-neg values and attracting abilities. Therefore, neither element can take electrons away from the other. Therefore, they share the electrons equally. This is called a non-polar covalent bond.
Example:H2O
E-neg value for H:
E-neg value for O:
Difference:
When the difference is 0.5 – 1.6, a polar covalent bond is formed. This means the sharing of the electrons is not equal and the bonding electrons are more strongly attracted by one of the atoms. The uneven sharing causes the more electronegative atom to have a partial negative charge. The other atom will have a partial positive charge.