Chemical Periodicity

Chemical Periodicity

• 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

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 Periodic Law

•The periodic law: When elements are arranged in order of increasing atomic number, there is a periodic 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.

IsoelectronicIons with the same electronic configuration as a noble gas

are said to be isoelectronic with a noble gas.

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

• The pattern is…Atoms in the 1st column have 1 valance e-

“ 2nd “ 2 valance e-

“ 3rd “ 3 valance e-

• Valance 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.

• Periodic - repeats according to a pattern– Patterns on the p chart are caused by patterns

in the e- configurations

s11stHighest orbital# of e-Group

s22nd

p13rd

p24th

p35th

p46th

p57th

p68th

The atoms in the 8th column have full energy levels (noble gasses)

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

• Ex)Li 1s22s1

Na 1s22s22p63s1

K 1s22s22p63s23p64s1

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.

Major Regions of the Periodic Table

What’s on the periodic table?

MetalsAlkali Metals

Alkaline Earth MetalsTransition Metals

Non-metals(To the right of the “zig-zag” line)

*polyatomic nonmetal*noble gases

*halogens

MetaloidsTouch the “zig-zag” line

Metals• Left of “zig-zag” line• Metals are…

– Shiny luster– Malleable – Ductile– Good conductors

• Heat & Electricity– Lose their e-

– All of these properties result from loosely held valence electrons in metals

P

Metals

Non-metals• Right of the “zig-zag” line• Non-metals are…

– Usually gas at room temp.– Brittle– Dull– Poor conductors– Gain e-

– Typically gain e-1

– All of these properties result from more tightly held valence electrons in nonmetals

TOP

Non-Metals

Metalloids• Touch the 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

P

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-

Transition Metals• Properties of metals• Not very reactive

Transition ElementsThe “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-

Nitrogen Family·Gains 3 e-

Oxygen Family·Gains 2 e-

Halogens• Gains 1 e-

• Very reactive, used for killing germs• Whenever a metal and a halogen

combine, they form a “salt”

Noble Gases• Very unreactive• Their outer orbit is full

Periodic TrendsPeriodic Trends

Trends on the periodic table:• Atomic radius - size of the atom• Ionization energy - energy required to

steal an e-

• Electronegativity - tendency for the atom to attract e- when chemically combined with another atom

Summary of Periodic Trends

2. Ionic Radius: Cation: Radius Decreases Anion:

Radius Increases

3. Ionization energy: ↓ Decreases → Increases

4. Electronegativity: ↓ Decreases → Increases

• Atomic Radius: ↓ Increases→ Decreases

Atomic radiusatomic radius

decreases

smallestatom

largestatom

Which is larger?

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

atomic radius

increases

How is radius determined?

Why can’t we just measure the radius of one atom?

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

Which is larger?

S or S2– K+1 or K

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

highestI.E.

lowestI.E.

Which has the higher ionization energy?

B or C Zn or Ga Na or K

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 of an

element 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

highestelectro.

lowestelectro.

Which has the higher electronegativity?

B or C Zn or Ga Na or K

O or F P or N F or Cl

Electro. increases

Trends in Electronegativity• Representative Elements in Groups 1A through 7A

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