1. The Periodic Table and Periodic Law
Chemistry Chapter 6
The Periodic Table and Periodic Law

2. 6.1 Development of the Modern Periodic Table
Objectives:
1. Explain how elements are organized in a periodic table
2. Identify key features of the periodic table

3. How the Elements are Organized + Early & Modern
Chemists used the properties of elements to sort them into groups
Dimitri Mendeleev was the first to arrange the elements in the periodic table in order of increasing mass
In the modern periodic table, elements are arranged in order of increasing atomic number

4. The pattern of properties within a period repeats as you move from one period to the next
Elements that have similar properties end up in the same column in the table
PERIODIC LAW: when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties
Q: How many periods are there in a periodic table?
A: 7

5. Key Features: 3 Broad Classes
Groups with letter A are called representative elements
Table has three categories: metals, non-metals, and metalloids
Metals to the left, non-metals to the right, and metalloids along the stair step
Metalloids are also called semiconductors

6. Metals have:
High conductivity
High luster (when clean)
Are ductile-drawn into wires
Are malleable
Non-metals:
Poor conductors
nonlustrous

7. Metalloids (border the stairstep) generally have some properties of metals and some properties of nonmetals
Here’s a preview of the table:
1A metal elements known as alkali metals
2A metal elements known as alkaline earth metals
7A nonmetal elements known as halogens (halogens means “salt formers”
0 nonmetal elements known as noble gases (also called group 8A)

8. On the flat of part of the table between groups 3 – 12 lie the group B elements
These are the transition elements which are divided into transition metals and inner transition metals
The inner transition metals are further divided into the lanthanide series and actinide series
The inner transition metals are sometimes called the rare earth metals

9. 6.2 Classification of the Elements
Objectives:
1. Explain why elements in the same group have similar properties
2. Identify the four blocks of the periodic table based on their electron configuration

10. Classifying by Electron Configuration
Elements can be sorted in noble gases, representative elements, transition metals or inner transition metals based on their electron configurations
Electrons exist in “shells” (similar to orbits) around the nucleus

11. The first shell can hold up to 2 electrons
The second shell can hold up to 8 electrons & the third up to 18 e- (count the number of elements across the period)
If the shells are full, the atom is especially stable
All elements in Group 8A, also called the 0 elements, have full outer shells
These are the noble gases and they are inert & nonreactive with other elements because of their full shells
The elements in the 8A group have a charge of 0

12. Elements on the table are neutral, but the groups have tendencies
All elements in group 1A, the alkali metals, readily lose one electron to complete their outer shell
If they lose that one electron, the 1A element will carry a charge of 1+
Group 2A, the alkaline earth metals, readily loses 2 electrons
Group 2A will carry a charge of 2+
Group 3A will carry a charge of 3+ if it loses 3 electrons

13. Group 4A has 2 possible charges: 4+ or 4- because it can either lose or gain 4 electrons to complete its outer shell
Group 5A also has 2 possible charges: 5+ or 3-
Group 6A carries a 2- charge because it gains 2 electrons to complete its outer shell
7A (the halogens) has a 1- charge
8A (the nobles) has a 0 charge because its outer shell is already full
The representative elements are located in the elevated part of the table and are group A

14. The transition metals, on the flat part of the table, are the B elements
Two main groups: transition metals and inner transition metals
Inner transition metals also known as the rare-earth elements
Many elements in the transition group can have variable charges

15. There are some general, more common charges these elements have
Most elements in this group have a charge of 2+ except for the groups beginning with chromium (Cr, 6B) and copper (Cu, 1B)
Elements in the Cr and Cu groups generally have a 1+ charge
80% of elements are metals, almost all solid at room temperature

16. Metals are located downstairs to the left on the table
Metalloids are located on either side of the stairs
Nonmetals are about 20% of the elements & are located upstairs to the right with the exception of hydrogen
General rules:
1. positive elements react with negative elements
2. elements with full outer shells do not react

17. The Four Blocks The four blocks are called s, p, d and f
This explains the odd shape of the periodic table
Each block represents an atom’s energy sublevel being filled with valence electrons
S level holds up to 2 e- (one orbital)
P level holds up to 6 e- (three orbitals)
D level holds up to 10 e- (five orbitals)
F level can hold up to 14 e- (seven orbitals)

18. 6.3 Periodic Trends
Objectives:
1. Compare period and group trends of several properties
2. Relate period and group trends in atomic radii to electron configuration

19. Trend in Atomic Size
Size is expressed as atomic radius
Definition: atomic radius is one half the distance between the nuclei of two atoms of the same element when the atoms are joined
In general, atomic size increases from top to bottom within a group and decreases from left to right across a period

20. Trend in Ions
Definition: an ion is an atom or group of atoms that has a positive or negative charge due to loss or gain of an electron
An atom is electrically neutral due to equal numbers of electrons and protons
Electrically neutral atoms are different from stable atoms
Stable atoms have full outer electron shells
Atoms strive to have the stable configuration of the nobles

21. Positive and negative ions form when electrons are transferred between atoms
The transfer occurs in way that the charge will add up to zero
Definition: a cation is an ion with a positive charge
Definition: an anion is an ion with a negative charge
Ionic radius from left to right across the period for positive ions gradually decreases
Beginning about group 5A or 6A the size of the much larger anions gradually decreases

22. Ionization Energy, Size & Trends
Definition: the energy required to remove an electron from an atom is the ionization energy
This energy is measured when the atom is in a gaseous state
Definition: the energy required to remove the first electron is the first ionization energy

23. First ionization energies tend to decrease from top to bottom within a group and increase from left to right across a period
SIZEWISE: Cations are always smaller than the atoms from which they formed (because they lost one or more electrons)
SIZEWISE: Anions are always larger than the atoms from which they form (because they gained one or more electrons)

24. Trend in Electronegativity
Definition: electronegativity is the ability of an atom of an element to attract electrons when the atom is in a compound
In general, nobles don’t attract electrons or form many compounds
Electronegativity is small to zero for nobles
The most electronegative element is fluorine

25. Electronegativity generally decreases as you move down a group and increases from left to right across a period
For representative elements, the values tend to increase from left to right across a period
The trends that exist among these properties can be explained by variations in atomic structure