Download Periodic Trends

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Periodic Trends
Many properties of the elements tend to change in a predictable way, known as trends. Trends among
elements in the periodic table include their sizes and their abilities to lose or attract electrons.
Atomic Size
Definition:
Atomic size is related the atomic radius of an element, which is defined as half the distance between
adjacent nuclei of two atoms of that element.
The Trend:
Going across the periodic table, atomic radius tends to get smaller.
This is because there is an increase of positive charge (more
protons), also known as nuclear charge, which has a greater
attraction to the valence electrons (which are increasing as
well). This pulls the valence electrons closer to the nucleus.
Going down the periodic table, atomic radius tends get bigger
within a group. Even though the number of protons is
increasing, new energy levels are added as you move down
which move the valence electrons further away. Also, the
additional orbitals between the nucleus and the outer electrons
are occupied, these electrons shield the out electrons from the
nucleus.
1. Summarize in your own words what is atomic size and the trends going across and down the
periodic table. Be sure to explain WHY these trends take place. Use an analogy if needed.
Ionic Radius
Definition:
The radius of an atom when it has gained or lost one or
more electrons (become and ion). If an atom becomes a
cation (positive ion, loses electrons), then it will become
smaller because there is a smaller attraction to the positive
nucleus AND (this is the big one) it loses an energy level.
If an atom becomes an anion (negative ion, gains electrons),
then it will become larger because there is an increase in the
repulsion of electrons which will push them further away
from each other.
The Trend:
Going across the periodic table the ionic radius decreases
with a big jump in size when the atoms start to form anions
rather than cations.
Going down the periodic table the ionic radius increases.
2. Summarize in your own words what is ionic size and the trends going across and down the
periodic table. Be sure to explain WHY these trends take place. Use an analogy if needed.
Ionization Energy
Definition:
The energy required to remove an (one) electron from an
atom. Another way to look at it is how strongly the
atom’s nucleus hold onto its valence electrons. The more
valence electrons it has, the hard it is for the atom to give
one up. This is the first ionization energy.
There are trends when looking at removing more than one
electron. These are second (2 electrons), third (3
electrons), and so on ionization energies. These will
increase slightly until that atom has reached its octet rule,
or in other words have the electron configuration of a noble gas. See Table 7.2 for examples.
The Trend:
For the first ionization energy, going across the
periodic table the ionization energy will generally
increase. This is because the nuclear charge increases,
pulling the valance electrons tighter to the nucleus.
Going down the periodic table the ionization decreases
because the electrons are further from the nucleus and
there is more shielding which makes it so less energy is
required to remove an electron.
3. Summarize in your own words what is ionization energy and the trends going across and
down the periodic table. Be sure to explain WHY these trends take place. Use an analogy if
needed.
Electronegativity:
Definition:
Electronegativity is the relative ability of an atom to attract electrons in a chemical bond. This helps
determine if a bond is nonpolar, polar, or ionic. The atom with the higher electronegativity more strongly
attracts the bond’s electrons.
The Trend:
Going across the periodic table electronegativity increases as the nuclear charge increases. Noble gasses
do not have electronegativity values because they do not form chemical compounds.
Going down the periodic table electronegativity decreases because there is more shielding from the
nucleus.
4. Summarize in your own words what is electronegativity and the trends going across and
down the periodic table. Be sure to explain WHY these trends take place. Use an analogy if
needed.
5. On the periodic table below, draw arrows to indicate the general trends for atomic size, ionization
energy, and electronegativity both across and down the periodic table. Be sure to label each arrow
(you should have 6 total).
6. Which element has the largest atomic size?
_________________________________
7. Which element has the largest ionic radius?
_________________________________
8. Which element has the highest ionization energy?
_________________________________
9. Which element has the largest electronegativity?
_________________________________
10. Rank the following elements by increasing atomic radius: carbon, aluminum, oxygen, potassium.
11. Rank the following elements by increasing electronegativity: sulfur, oxygen, neon, aluminum.
12. Why does fluorine have a higher ionization energy than iodine?
13. Why do elements in the same family generally have similar properties?
14. What trend in atomic radius occurs down a group on the periodic table? What causes this trend?
15. What trend in ionization energy occurs across a period on the periodic table? What causes this
trend?
16. What ionization (1st, 2nd, 3rd, etc) does the jump in ionization energy occur for each group?
a. Alkali metals
e. Nitrogen Family
b. Alkali Earth Metals
f. Oxygen Family
c. Boron Family
g. Halogens
d. Carbon Family
h. Nobel Gases
17. Circle the atom in each pair that has the largest atomic radius.
a. Al or B
b. Na or Al
c. S or O
d. O or F
e. Br or Cl
f. Mg or Ca
18. Circle the atom in each pair that has the greater ionization energy.
a. Li or Be
b. Ca or Ba
c. Na or K
d. P or Ar
e. Cl or Si
f. Li or K
19. Circle the atom in each pair that has the greater electronegativity.
a. Ca or Ga
b. Br or As
c. Li or O
d. Ba or Sr
e. Cl or S
f. O or S