THE PERIODIC TABLE
A. DEVELOPMENT OF THE PERIODIC TABLE
1. Mendeleev –


2. Moseley
–

Periodic Law –
B. ARRANGEMENT OF THE PERIODIC TABLE
period –

group (or family) –


Group A Elements (Representative Elements) –


Group B Elements (Transition Metals) –


Name
C. CLASSIFICATION OF ELEMENTS
1. Metals –
S block:
All are soft, silvery metals
Harder, denser than group 1A
All have configuration ns1 (form +1 ions)
All have configuration ns2 (form +2 ions)
All are extremely reactive
Less reactive than group 2A
Not found free in nature
Not found free in nature
Combine vigorously with nonmetals
Combine easily with nonmetals
D block:
Harder, denser than group 1 or 2A metals
Good conductors of electricity
All have ns2 configuration in their highest energy level (will often form +2 ions)
Have more than one ionic charge if electrons in shell beneath the outermost also bond *
Some groups are non-reactive and found free in nature (ex: Gold)
Ex: Fe # 26
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d6
Ex: Cu # 29
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d9
1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10
F block:
1st row: Lanthanide series –


Shiny metals
Most are reactive
2nd row: Actinide series –


Ex: Ce # 58
All are unstable and radioactive
Most have very short half lives
2
8
18
20
8
2
Am # 95
2
8
18
32
25
8
2
2. Semi Metals –

Located on either side of the “stairs” between metals and nonmetals in the p block
(Aluminum and Boron generally acts as metals and form +3 ions)
3. Nonmetals –

Located in upper right corner of the p block in groups 5A, 6A and 7A in the

Gain 3, 2, or 1 electrons respectively to achieve stable octet

Halogens –
-- All have configuration ns2 np5 ; all gain 1 electron to form –1 ions
-- React with hydrogen to form strong acids
4. Noble Gases – Last column on the right in the p block and Helium

D. PERIODIC TRENDS
1. Atomic Size –
(also called atomic radii)
The size of an atom depends on the # of energy levels
and # of protons (nuclear charge)

Across a Period: the size of an atom decreases b/c
increasing numbers of protons pull
electrons within the same energy
level in closer to the nucleus

Down a Group:
the size of an atom increases due
to the addition of energy levels
which are farther from the nucleus
2. Metallic vs Nonmetallic Character
Metallic Character –

Across a Period: metallic character decreases b/c the smaller the atom, the stronger the
the pull from the nucleus, the harder to lose electrons

Down a Group:
metallic character increases b/c the larger the atom, the less pull
from the nucleus, the easier to lose electrons
Nonmetallic Character –

Across a Period: nonmetallic character increases b/c the smaller the atom, the greater the
pull from the nucleus, the easier to gain electrons
(also approaching nonmetals that want to gain electrons)

Down a Group:
nonmetallic character decreases b/c the larger the atom, the less pull
from the nucleus, the harder to gain electrons
3. Shielding Effect –

Across a Period: shielding effect is unchanged because all the atoms in a period are on
the same energy level so there is no additional shielding

Down a Group:
shielding effect increases due to additional energy levels between the
nucleus and the outer shell electrons
4. Speed of Reaction –
A. Speed of Reaction of Metals –

Across a Period: Metals become less reactive because the atoms are smaller (hold
electrons tighter), they need to lose more electrons to achieve a
stable octet, and toward the left are the nonmetals that want to gain e-

Down a Group:
Metals become more reactive because atomic size increases
(larger atoms’ outer electrons are farther from the pull of the nucleus)
and electrons can be lost more easily.
B. Speed of Reaction of NonMetals –

Across a Period: Nonmetals become more reactive because as atomic size decreases,
and protons are added within the same energy level, the pull of the
nucleus is greater so it is easier to gain electrons. Also, the further to
the left, the fewer electrons must be gained to achieve a stable octet.

Down a Group:
Nonmetals become less reactive because as atomic size increases
there is less pull from the nucleus so it is more difficult to gain electrons.
5. Ionization Energy –
1st ionization energy – energy required to remove the first electron from an atom
2nd ionization energy – energy required to remove the second electron from an atom
3rd ionization energy – energy required to remove the third electron from an atom
4th ionization energy – energy required to remove the fourth electron from an atom
2
8
1
Na
2
8
2
Mg
2
8
3
Al
1s2
2s2
2p6
1st IE
2nd IE
3rd IE
4th IE
119
1090
1652
2281
176
347
1848
2519
138
434
656
2767
3s1
1s2 2s2 2p6 3s2
1s2 2s2 2p6 3s2 3px1
For Group A Metals – as electrons are removed one by one from an atom, there is a
steady rise in the ionization energy until the structure of a noble
gas is achieved. Then there is a dramatic rise when the stable
octet is disturbed.

Across a Period: 1st ioniz. energy increases because it takes more energy to remove
an electron from a smaller atom (outer e- closer to pull of nucleus)

Down a Group:
1st ioniz. energy decreases because it takes less energy to remove
an electron from a larger atom (outer e- farther from pull of nucleus)
For Group B (Transition ) Metals – in the d block of periods 5, 6, & 7 there is a sharp
drop in ionization energy between the last transition element and
where the next energy level’s p sublevel begins because the p
sublevel is farther from the nucleus
Metals have low ionization energies because
Nonmetals have high ionization energies because
6. Electron Affinity –
If energy is released when an atom gains an electron,
Nonmetals have high electron affinities because
to achieve the electron configuration of a noble gas.
If energy is absorbed when an atom gains an electron,
Metals have low electron affinities because
to achieve the electron configuration of a noble gas.

Across a Period: electron affinity increases because atomic size decreases, nuclear
charge increases and it is favorable for nonmetals to gain electrons

Down a Group:
electron affinity decreases because atomic size increases and there
is less pull form the nucleus so it is more difficult to gain an electron
Halogens (Group 7A) have the highest electron affinities because they only need to
gain one electron to achieve a stable octet.
7. Ionic Size –
Metals lose electrons to form positive ions that are smaller than their respective atoms
because
K
atom
K+1
ion
.
Nonmetals gain electrons to form negative ions that are larger than their respective
atoms because
F
atom
F-1
ion
1
2
3
4
5
6
7
gain
3e-
gain
2e-
gain
1e-
o
lose
1e-
lose
2e-
lose
3e-
lose
4e-

Across a Period: there is a gradual decrease in the size of positive ions as more
electrons are lost and then at group 5 begin the large negative ions
that gradually decrease in size as fewer electrons are gained

Down a Group:
the size of both positive and negative ions increases because of the
increasing number of energy levels
8. Electronegativity –
Electronegativity values help predict the type of bonding between atoms in a compound.
Metals
Nonmetals

Across a Period: electronegativity increases because smaller atoms have a greater
pull on electrons

Down a Group:
electronegativity decreases because larger atoms have less of a
pull on electrons