Unit 4 - Periodic Trends

The Periodic Law

• The periodic law: When elements are arranged in order of increasing atomic number, there is a repetition of their physical and chemical properties.
• The properties of the elements within a period change as you move across a period from left to right.
• The pattern of properties within a period repeats as you move from one period to the next.

Searching For an Organizing Principle

Chlorine, bromine, and iodine have very similar chemical properties.

• In 1869, Dimitri Mendeleev arranged all of the known elements in order of increasing atomic mass and chemical properties of the atoms. He found a pattern that exists and is repeated, or is periodic, in all the elements.
• http://www.youtube.com/watch?v=fPnwBITSmgU

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Henry Moseley’s modern periodic table is arranged in order of increasing atomic number and would look like this if we didn’t move the rare earth elements to below

• The pattern exists because there is a pattern in the valence electrons.
• The pattern is…

Atoms in the 1st column have 1 valance e^-

“ 2nd “ 2 valance e^-

“ 3rd “ 3 valance e^-

• Valence e^- are in the outer orbit
• They are responsible for the atoms chemical & physical properties
• Atoms are most stable when their outer orbit is either completely full or empty.

• The valence e^- are responsible for the elements chemical and physical properties
• Ex)

Li 1s²2s¹

Na 1s²2s²2p⁶3s¹

K 1s²2s²2p⁶3s²3p⁶4s¹

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Notice that there is only 1 e^- in the outermost orbital

(They all have one valence e^-)

Thus, all elements in a column have similar prop.

Isoelectronic

-Elements/ions that have the same electron configuration (Same number of electrons)

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Ex. O^-2 is isoelectronic with Ne

(Both have 10 e^-1)

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-Usually, isoelectronic atoms will have a full octet, meaning they will have the same number of electrons as a Noble Gas

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Practice

1. What is a -3 ion that is isoelectronic with Neon?
2. What is a +2 ion that is isoelectronic with Argon?
3. What has a -1 charge and is isoelectronic with Al⁺³?
4. What has a +1 charge and is isoelectronic with Se^-2?
5. What has a +2 charge and is isoelectronic with K⁺¹?

Practice

• What is a -3 ion that is isoelectronic with Neon? N^-3 (Must have the charge!)
• What is a +2 ion that is isoelectronic with Argon? Ca⁺² (Must have the charge!)
• What has a -1 charge and is isoelectronic with Al⁺³?
• What has a +1 charge and is isoelectronic with Se^-2?
• What has a +2 charge and is isoelectronic with K⁺¹?

Practice

• What is a -3 ion that is isoelectronic with Neon? N^-3 (Must have the charge!)
• What is a +2 ion that is isoelectronic with Argon? Ca⁺² (Must have the charge!)
• What has a -1 charge and is isoelectronic with Al⁺³? F^-1 (Must have the charge!)
• What has a +1 charge and is isoelectronic with Se^-2? Rb⁺¹ (Must have the charge!)
• What has a +2 charge and is isoelectronic with K⁺¹? Ca⁺² (Must have the charge!)

“Secret Agent” Activity

Major Regions of the Periodic Table

TOP

Non-Metals

Non-metals

• Right of the “zig-zag” line
• Non-metals are…
• Usually gas at room temp.
• Brittle
• Dull
• Poor conductors
• Typically gain e^-1
• All of these properties result from more

tightly held valence electrons in nonmetals

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P

Metals

Metals

• Left of “zig-zag” line
• Metals are…
• Shiny luster
• Malleable
• Ductile
• Good conductors

of Heat & Electricity

• Lose their e^-
• All of these properties result from

loosely held valence electrons in metals

P

Metalloids

• Touch the zig-zag line
• Solids at room temperature
• Sometimes they act like metals, sometimes they act like non-metals - it depends on the conditions such as temp and pressure
• Semi-conductors of electricity

Silicon

Important Families of the Periodic Table

Alkali Metals

• The most reactive metals
• Never found alone, always in a compound
• Like to form + ions b/c they tend to lose 1 e^- to become stable
• http://www.youtube.com/watch?v=m55kgyApYrY

Alkaline Earth Metals

• Reactive, usually produce a base
• Always found in a compound
• Like to lose 2 e^-

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Transition Metals

• Properties of metals
• Not very reactive

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Transition Elements�The “Group B” elements are displayed in the main body of the periodic table. They have electrons in d sublevels and are all classified as metals.��Inner Transition Metals are found within the Transition Metals and contain electrons in f sublevels

Boron Family

• Likes to lose 3 e^-

Carbon Family

• Will lose or gain 4 e^-

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Nitrogen Family

• Gains 3 e^-

Oxygen Family

• Gains 2 e^-

Halogens

• Gains 1 e^-
• Very reactive, used for killing microorganisms
• Whenever a metal and a halogen combine, they form a “salt”

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Noble Gases

• Very unreactive
• Their outer orbit is full

Today’s Schedule

-Warm Up/ On your own: Review Families of the Periodic Table

-30 min

1. Finish “Coulombic Attraction”
2. Finish ChemQuest Packet

-20 min

1. Start discussing trends

Periodic Trends

Periodic Trends

Warm Up

1. Which of the following elements has a smaller atomic radius?
1. Calcium or Potassium
2. Nitrogen or Phosphorus
3. Aluminum or Silicon
4. Nitrogen or Oxygen

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2) What would happen to the radius of Lithium when it becomes and ion? Why?

3) Would a smaller atom or a larger atom be more likely to lose an electron? Why?

How is radius determined?

Trends on the periodic table:

• Atomic radius - size of the atom
• Ionization energy - energy required to steal/remove/take away an e^-
• Electronegativity - tendency for the atom to attract (or, gain) e^-

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Summary of Periodic Trends

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2. Ionic Radius:

↓ Increases

→ Decreases until

you reach “-”

ions where there

is an ↑ then they

↓ again

3. Ionization energy:

↓ Decreases

→ Increases

4. Electronegativity:

↓ Decreases

→ Increases

1. Atomic Radius:

↓ Increases

→ Decreases

Atomic radius

atomic radius

increases

smallest

atom

largest

atom

Which is larger?

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1. N or P 2. Al or Si 3. Na or Cs 4. N or O

atomic radius

increases

Ions

• Positive and negative ions form when electrons are transferred between atoms.

Ions

• Positive and negative ions form when electrons are transferred between atoms.

Ionic radius:

• cations: smaller than their parent atoms
• anions: larger than their parent atoms
• follows same pattern as atomic radius

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Which is larger?

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S or S^2– K⁺¹ or K

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Na⁺¹ or Mg²⁺ Mg²⁺ or Ca²⁺

Trends in Ionization Energy

• The energy required to remove an electron from an atom is called ionization energy.
• The energy required to remove the first electron from an atom is called the first ionization energy.
• The energy required to remove an electron from an ion with a 1+ charge is called the second ionization energy.

Ionization energy:

I.E.

increases

highest

I.E.

lowest

I.E.

Which has the higher ionization energy?

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B or C Zn or Ga Na or K

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K or Ca Mg or Al B or Al

I.E.

increases

Trends in Electronegativity

• Trends in Electronegativity
• Electronegativity is the ability of an atom to attract electrons when the atom is in a compound.
• In general, electronegativity values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period.

Electronegativity:

Electro. increases

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highest

electro.

lowest

electro.

Which has the higher electronegativity?

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B or C Zn or Ga Na or K

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O or F P or N F or Cl

Electro. increases

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Trends in Electronegativity

• Representative Elements in Groups 1A through 7A

6.3

Which element would you expect to have the largest radius? Why?

Which element would you expect to have the lowest ionization energy? Why?

(Be the easiest to remove an electron from)

Which element would you expect to have the largest electronegativity? Why?

(Most likely to gain an electron)