CHAPTER 6: THE PERIODIC TABLE
Problems: 5-13, 17-18, 26-36, 41-44, 47-49, 59-70, 73 (a,c,d), 74 (c,d), 75-79, 80(a,b,d)
6.1
CLASSIFICATION OF THE ELEMENTS
Dimitri Mendeleev organized elements in tables so that elements with similar
properties were in the same column or row.
– He found that elements display recurring properties if they are arranged
according to increasing atomic mass
⇒ Periodic Table originally arranged with elements in order of increasing
atomic mass.
6.2
THE PERIODIC LAW CONCEPT
Henry G.J. Moseley’s high-energy X-ray radiation experiments on atomic nuclei
→ Repeating properties of elements more clearly reflected by the
arrangement of elements according to increasing atomic number
→ Periodic Table’s arrangement today
Trends for increasing atomic mass are identical with those for increasing
atomic number, except for Ni & Co, Ar & K, Te & I.
Neils Bohr’s introduction of electron energy levels
→ Periodic Table’s shape
– Indicates filling of electron orbitals and element’s electron configuration
6.3
GROUPS AND PERIODS OF ELEMENTS
A vertical column is called a group or family.
– Elements belonging to the same group exhibit similar properties.
A horizontal row is called a period or series.
Representative (Main-group or A Group) Elements
Those elements in groups IA to VIIIA
Group IA:
alkali metals
Group IIA:
alkaline earth metals
Group VIIA: halogens
Group VIIIA: noble gases (because they are gases that never react)
CHM 130: Chapter 6
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Transition Metals
Group B elements (in middle of the Periodic Table)
– More difficult to predict the behavior and properties of transition metals
Inner Transition Elements (beneath the main body of Periodic Table)
– lanthanide series: Ce-Lu, also called rare earth metals since these elements
make up less than 0.005% of the earth's crust
– actinide series: Th-Lr, also called transuranium elements, generally all man
made and exist for only very short periods of time before decaying to other
elements
Example: Give the element symbol that matches each description below:
a. The noble gas in the third period: ______
b. The halogen in the fourth period: ______
6.4
PERIODIC TRENDS
Atomic Size: distance from nucleus to outermost electrons
– Increases down a group: More p+, n, and e– ⇒ bigger radius
– Decreases from left to right along a period:
– Effective nuclear charge: # of protons – # of outermost electrons
– Number of p+ and e– increases, but electrons going into same orbitals.
– The higher the effective nuclear charge ⇒ smaller radius because
nucleus pulling in electrons
Trend from top to bottom ⇒ like a snowman
Trend from left to right ⇒ like a snowman
that fell to the right
Metallic Character:
– Decreases from left to right along a period:
Metals concentrated on left-hand side of P.T., nonmetals on right-hand side
— Increases down a group: Looking at groups IVA and VA, go from
nonmetals (C & N) to semimetals (Si & As) to metals (Sn & Bi)
→ Same snowman trends as for atomic radius!
CHM 130: Chapter 6
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6.5 PROPERTIES OF ELEMENTS
When designing the Periodic Table, Mendeleev placed elements with similar
properties in the same group.
→
One can predict the properties and behavior of elements belonging
to the same group.
Predicting properties of elements in the same group
Ex. 1: Sodium reacts violently with water. Which element below is also likely to
react violently water water?
K
Mg
Al
Si
P
Li
Cl
Ar
Ex. 2: Nitrogen reacts with hydrogen to form NH3.
Give the formula for the compound that
forms when phosphorus reacts with hydrogen. _______________
6.7 VALENCE ELECTRONS
core electrons: innermost electrons belonging to filled electron shells
An electron shell is filled when all orbitals in the row are filled.
– 2 e – in 1s orbital → 1st shell filled
– 2 e – in 2s orbital and 6 e – in 2p orbitals → 2nd shell filled
– 2 e – in 3s orbital and 6 e – in 3p orbitals → 3rd shell filled
– 2 e – in 4s orbital, 10 e – in 3d orbitals, 6 e – in 4p orbitals → 4th shell filled
valence electrons: electrons in the outermost shell
– Atoms want filled electron shells to be most stable, so they combine with
other atoms with unfilled shells (gaining or losing e –s) to be more stable.
→ Valence electrons lead to chemical bonds and reactions between atoms
For Main Group (A) elements, Group # → # of valence electrons
– Elements in Group IA: each have 1 valence electron
– Elements in Group IIA: each have 2 valence electrons
– Elements in Group IIIA: each have 3 valence electrons
– Elements in Group IVA: each have 4 valence electrons
– Elements in Group VA: each have 5 valence electrons
– Elements in Group VIA: each have 6 valence electrons
– Elements in Group VIIA: each have 7 valence electrons
– Elements in Group VIIIA: each have 8 valence electrons
CHM 130: Chapter 6
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Example: Indicate the number of valence electrons for each of the following:
Mg: ____
Br: ____
Rb: ____
Se: ____
N:
Al:
Si:
Xe: ____
____
____
____
6.8 ELECTRON DOT FORMULAS
– Shows the atom of an element with
1. Element symbol representing the nucleus and core electrons
2. Dots representing the valence e–
Rules for writing Electron Dot Formulas (EDF)
1. Write down the element symbol
2. Determine the number of valence electrons using the group number
3. Assume the atom has four sides, and distribute electrons with one electron
per side before pairing electrons.
Write the electron dot formula for each of the following:
boron:
phosphorus:
silicon:
oxygen:
fluorine:
sodium:
calcium:
argon:
nitrogen:
CHM 130: Chapter 6
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6.9 IONIZATION ENERGY:
– Amount of energy necessary to remove an electron from a neutral
to make it a charged ion.
atom
Ionization energy TRENDS
– Decreases down a group:
Bigger the atom, the further away electrons are from protons in nucleus
→ electrons held less tightly and are more easily removed
– Increases from left to right along a period:
– Elements with fewer (1–3) valence electrons can more easily give up
electrons to gain noble gas configuration (stability)
– Elements with more (4–7) valence electrons can more easily gain
electrons to gain noble gas configuration (stability)
Trend from top to bottom
→ like an upside-down snowman
Trend from left to right
→ like a upside-down snowman that
fell to the right
6.10 IONIC CHARGES
Representative elements generally form ions—i.e., gain or lose electrons—to
achieve a noble gas electron configuration, so they can be stable.
Example: Indicate the number of protons and electrons for the following:
loses 1 electron
"""""""#
Na+
Na
gains 2 electrons
"""""""
"#
S
CHM 130: Chapter 6
S2–
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Metals lose electrons from their valence shell
→ positively charged ions = cations
Nonmetals gain electrons, adding electrons to their valence shell
→ negatively charged ions = anions
Charges shown as superscripts
Group IA elements → +1 charge: Li+ ("+" = "+1")
Group IIA elements → +2 charge: Mg+2
Group IIIA elements → +3 charge: Al+3
Group VA elements → –3 charge: N-3
Group VIA elements → –2 charge: O -2
Group VIIA elements → –1 charge: F– ("–" = "–1")
Note: Charges on ions can be shown with the sign before or after the
number—e.g. magnesium ion can be shown as Mg+2 or Mg2+.
Example: Give the formula for the ion formed by each of the following:
chlorine: _______
calcium: _______
phosphorus: _______
sodium: _______
oxygen: _______
aluminum:
_______
Representative elements form ions and get a noble gas electron configuration
→ Ions from representative metals are usually isoelectronic with—i.e. have
the same number of electrons as—one of the noble gases!
ELECTRON CONFIGURATION OF IONS
For IONS, one must account for the loss or gain of electrons:
# electrons = atomic # – (charge = change in # of valence electrons)
Or you can simply use the Periodic Table,
– Move to the left for electrons lost
– Move to the right for electrons gained
– Figure out with which element (usually a noble gas) it is isoelectronic, then
give the electron configuration for that element.
Note: Some ions are not isoelectronic with a noble gas (e.g. Sn or Pb).
CHM 130: Chapter 6
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Example 1: Fill in the blanks for the following ions:
Ion
Isoelectronic with
Electron Configuration
(using core notation)
Na+
P3Ti+4
Ba2+
Al3+
Br-
Example 2: Circle all the ions below that are isoelectronic with argon:
Al+3
Ti+4
CHM 130: Chapter 6
P3-
K+
Cl-
Ca +2
S-2
Na+
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