1. The Periodic Table and Periodic Trends
CH 6
The Periodic Table and Periodic Trends

2. Organizing the Elements
Mendeleev arranged the elements in his periodic table in order of increasing atomic mass
1869

3. The Periodic Law
When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties

4. Periods and Groups Periods – rows on a periodic table
Groups – columns on a periodic table

6. The Periodic Table Displays symbols and names of the elements
Information about the structure of the atom
Average atomic mass
Atomic number

7. Metals Good conductors of electricity and heat Luster Ductile
Malleable

8. Nonmetals Poor conductors of heat and electricity Brittle
Varies in states (solids, liquids, gases)

9. Metalloids Along the stair-step
Properties similar to those of metals and nonmetals
Conduct heat and electricity somewhat

11. Important Regions Alkali metals – Group 1A
Alkaline earth metal – Group 2A
Halogens – Group 7A
Noble gases – Group 8A
Transition metals
Inner Transition metals
Lanthanides
Actinides

13. Electron Configurations in Groups
Elements can be sorted into noble gases, representative elements, transition metals, inner transition metals based on their electron configurations
Every element ends in the same last term in the electron configuration

14. Representative Elements
Groups 1,2,13,14,15,16,17
Called representative elements because they display a wide range of physical and chemical properties

15. Transition Elements
In atoms of a transition metal, the highest occupied s sublevel and a nearby d sublevel contain electrons.
These elements are characterized by the presence of electrons in the d orbitals
Inner transition elements contain unfilled f orbitals

16. Periodic Trends
Atomic radius – ½ the distance between the nuclei of two atoms of the same element when the atoms are joined
Extremely small – measured in picometers
Atomic size (radius) increases from top to bottom within a group and decreases from left to right across a period.

17. Periodic Trends Atomic radius – WHY???
Group trends – as the atomic number increases within a group, the charge on the nucleus increases and the number of occupied energy levels increases.
The increase in positive charge draws the electrons closer to the nucleus
The increase in the number of occupied orbitals shields the electrons in the highest occupied energy level from the attraction of the protons in the nucleus.

18. Periodic Trends Atomic Size – WHY????
Periodic trends – each element has one more proton and one more electron that then preceding element.
Across a period, the electrons are added to the same principal energy level. The shielding effect is constant for all the elements in a period
The increasing nuclear charge pulls the electrons in the highest occupied energy level closer to the nucleus and the atomic size decreases

20. Ions
Positive and negative ions form when electrons are transferred between atoms\
Metals form cations – they lose electrons to form a positive charge
Nonmetals form anions – they gain electrons to form a negative charge

22. Periodic Trends
Ionization Energy – the energy required to remove an electron from an atom
Measured in the gaseous state
The energy required to remove the first electron – first ionization energy
The energy required to remove the second electron – second ionization energy
The energy required to remove the third electron – third ionization energy

23. Periodic Trends Ionization Energy
Can help you predict what ions will form
The first ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period

25. Periodic Trends Ionization Energy – WHY????
Atomic size increases as the atomic number increases within a group. As the size of the atom increases, nuclear charge has a smaller effect on the electrons in the highest occupied energy level. So less energy is required to remove an electron

26. Periodic Trends Ionization Energy – WHY????
The nuclear charge increases across the period, but the shielding effect remains constant. So there is an increase in the attraction of the nucleus for an electron. Thus, it takes more energy to remove an electron from an atom

30. Periodic Trends Ionic Size
Cations are always smaller than the atoms from which they form
Anions are always larger than the atoms from which they form

34. Periodic Trends
Electronegativity – the ability of an atom of an element to attract electrons when the atom is in a compound

35. Periodic Trends
Electronegativity – decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period
Metals have low values
Nonmetals have higher values
Fluorine – highest with value of 4

36. Summary of Trends