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. Chlorine, bromine, and iodine have very similar chemical properties. The numbers shown are the average atomic masses for these elements. *

Isoelectronic Ions with the same electronic configuration as a noble gas are said to be isoelectronic with a noble gas.

Valance e- are in the outer orbit 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 s 1 1st Highest orbital # of e- Group s 2 2nd p 1 3rd p 2 4th p 3 5th p 4 6th p 5 7th p 6 8th The atoms in the 8th column have full energy levels (noble gasses)

Thus, all elements in a column have similar prop. 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? Metals Alkali Metals Alkaline Earth Metals Transition Metals Non-metals (To the right of the “zig-zag” line) *polyatomic nonmetal *noble gases *halogens Metaloids Touch 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 Carbon Family Nitrogen Family Oxygen 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 Trends Periodic 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

Atomic Radius: ↓ Increases → Decreases Ionization energy: ↓ Decreases Summary of Periodic Trends Atomic Radius: ↓ Increases → Decreases Ionization energy: ↓ Decreases → Increases Electronegativity: ↓ Decreases → Increases 2. Ionic Radius: Cation: Radius Decreases Anion: Radius Increases

Atomic radius atomic radius decreases smallest atom atomic radius increases largest atom Which is larger? 1. N or P 2. Al or Si 3. Na or Cs 4. N or O

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. When a sodium atom loses an electron, it becomes a positively charged ion. When a chlorine atom gains an electron, it becomes a negatively charged ion. Interpreting Diagrams What happens to the protons and neutrons during these changes? *

Ions Positive and negative ions form when electrons are transferred between atoms. When a sodium atom loses an electron, it becomes a positively charged ion. When a chlorine atom gains an electron, it becomes a negatively charged ion. Interpreting Diagrams What happens to the protons and neutrons during these changes? *

Ionic radius: Which is larger? S or S2– K+1 or K 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: B or C Zn or Ga Na or K K or Ca Mg or Al B or Al I.E. increases highest I.E. I.E. increases lowest I.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

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: B or C Zn or Ga Na or K O or F P or N F or Cl Electro. increases highest electro. Electro. increases lowest electro. Which has the higher electronegativity? B or C Zn or Ga Na or K O or F P or N F or Cl

Trends in Electronegativity 6.3 Trends in Electronegativity Representative Elements in Groups 1A through 7A *