1. The Periodic Table and Periodic Law

2. Development of the Modern Periodic Table

3.  Until the 1790s, only 23 different elements were known, such as silver, gold, carbon, oxygen, etc  These elements had been known for hundreds or thousands of years  The 1800s brought forth many changes to the scientific community, including an explosion in the number of elements known

4.  By 1870, there were about 70 known elements  With the increase in the number of elements, came an increased need to organize them  The man given the most credit for organizing the elements is Dmitri Mendeleev  He organized the elements in order of increasing mass, and when he did this, he noticed a pattern in the properties of the elements

5.  Mendeleev arranged his periodic table similar to a winning configuration of solitaire  Within rows, the elements were arranged by increasing mass  Within columns, elements were arranged by similar chemical properties  The usefulness of Mendeleev’s table was confirmed by the discovery of new elements that matched predicted properties according to their location on the periodic table

7.  Mendeleev’s table was a good step forward, but it was not completely correct  It soon became apparent, based on certain chemical properties, that some elements were not in the correct order  It was not until 1913 when Henry Moseley discovered that each element has a unique positive charge that this was corrected

8.  Mendeleev did not know about subatomic particles when he made his periodic table  The fact that each element has a unique charge, while the mass can vary because of isotopes caused the periodic table to be rearranged  The modern periodic table would then now be arranged by the atomic number

9.  The modern periodic table is arranged by atomic number  When the periodic table is arranged in this fashion, there is a periodic repetition of chemical properties from row to row. This is called periodic law

10.  The rows on the periodic table are called periods  The columns on the periodic table are called groups or families  Groups can be numbered in two separate methods – groups can be designated with a number and a letter, or just numbered 1-18

11.  The A groups (IA-VIIIA) are called representative elements because they represent a wide variety of chemical and physical properties  The B groups (IB-VIIIB) are the transition elements. They transition from very metallic to less metallic

13.  Starting below boron, draw imagine a staircase down to the bottom of the periodic table  Elements below and to the left of this staircase, but not touching (aluminum is the exception) are metals  Metals are generally shiny, solid at room temperature, good conductors of heat and electricity, malleable, and ductile  The far left group (IA) is called the alkali metals  The next group (IIA) is called the alkaline earth metals

14.  Alkali metals and alkaline earth metals tend to be chemically active  The alkali metals are more reactive than alkaline earth metals  Within the group of alkali and alkaline earth metals, reactivity increases as we go down the group

15.  The B elements (transition elements) are divided into two groups: the transition metals and the inner transition metals  The inner transition metals are the two rows located below the main body of the periodic table  Inner transition metals (specifically the lanthanide series) are used as phosphors, substances that emit light when struck by electrons

17.  To the right and above (but not touching) the staircase are the nonmetals  Nonmetals are generally gases at room temperature, brittle, dull, poor conductors of heat and electricity, and nonductile  The group VIIA nonmetals are called the halogens – from the Greek halos meaning salt and genesis meaning formation  The halogens are extremely reactive and react readily with metals. Within the halogen group, fluorine is the most reactive and reactivity decreases as we move down the group  Group VIIIA are called the noble gases, which are extremely UNreactive

18.  The elements that border the staircase are the metalloids (only element touching the staircase that is not a metalloid is aluminum)  Metalloids have properties that can be similar to both metals and nonmetals, depending on temperature, other compounds present, etc.  Silicon is a good example. In a computer, silicon is used to conduct electricity in circuit boards. In baking, silicon is used to make heat resistant oven mitts

19. Classification of the Elements

20.  What is a valence electron?  Atoms in the same group have the same number of valence electrons  Because elements in the same group have the same number of valence electrons, they have similar chemical properties  Within a period, the number of valence electrons increases from left to right  The number of valence electrons in representative elements can be found on the periodic table. The number paired with the A heading indicates the number of valence electrons

21.  Remember electron configurations? Write the electron configuration for iron

23.  The electron dot diagram explains why we start a new row after each noble gas  Their outer electron level gets full, so anything added after needs to be added to a new energy level  The rows on the periodic table indicate what energy level those electrons are occupying

24.  The periodic table is divided into blocks, the s-, p-, d-, and f-block  These blocks are the same as the s, p, d, and f energy sublevels we talked about earlier

26. Periodic Trends

27.  Technically defined, atomic radius is the area where there is a 90% probability of finding electrons  Essentially, it is the size of the atom  Atomic radius increases from top to bottom within a group. Why?  Within a period, atomic radius decreases. Why?  It decreases because we are adding protons and electrons, but staying on the same energy level. This increases effective nuclear charge which pulls the electrons in tighter, making the atom smaller

28.  Atoms can gain or lose electrons  When they do this they form an ion, which is an atom that has a net positive or negative charge  When an atom loses electrons, it forms a positive charge and the radius decreases from its neutral atom  When an atom gains electrons, it forms a negative charge and the radius increases from its neutral atom  Within a period ionic radius of positive ions decreases, then increases as it changes from positive to negative ions, then decreases again  Within a group, ionic radius increases

29.  Ionization energy – the energy required to remove an electron from an atom  Ionization energy increases from left to right across a row. Why?  Ionization energy decreases from top to bottom. Why?  Atoms can have second or third ionization energies as well

30.  Electronegativity is the desire for electrons  Electronegativity increases from left to right across a period  Electronegativity decreases from top to bottom  The noble gases have very minimal electronegativity  The most electronegative element is fluorine, while the least is francium