2. Discovering a Pattern
In 1869, Russian chemist Dmitri Mendeleev arranged the elements in order of increasing atomic mass.

3. His Periodic table showed that
Elements with similar properties occurred in a repeating pattern
There were gaps in its pattern
He could predict the properties of the missing elements
By 1886, all of the gaps had been filled and Mendeleev’s predictions were right.

4. Changing the Arrangement
A few elements’ properties did not fit in the pattern of Mendeleev’s table.
1914: British scientist Henry Moseley found the atomic number of atoms.
Elements arranged by atomic number fit the pattern in Mendeleev’s table.

5. Elements are arranged:
Vertically into Groups
Horizontally Into Periods

6. Why?

7. Each group has distinct properties
The periodic Table is divided into several groups based on the properties of different atoms.

8. If you looked at one atom of every element in a group you would see…

9. Each atom has the same number of electrons in it’s outermost shell.
An example…

10. The group 2 atoms all have 2 electrons in their outer shells
Be (Beryllium)
Atom
Mg (Magnesium) Atom

11. Valence electrons
Definition: the number of electrons in the outer shell of an element
Electrons held most loosely
an outer shell is considered complete when it contains 8 electrons
Each element has specific number from 1 to 8
effects the way an atom bonds
Period ends when valence = 8
determines many properties of the element
elements within a group usually have similar properties.

12. One way to represent atoms and molecules is to use electron-dot diagrams. An electron-dot diagram shows only the valence electrons in an atom.

13. If you looked at an atom from each element in a period
you would see…

14. Each atom has the same number of electron holding shells.
An example…

15. The period 4 atoms each have 4 electron containing shells
4th Shell
K (Potassium)
Atom
Kr (Krypton)
Atom
Fe (Iron) Atom

16. The Periodic Table and Classes of Elements
Elements are classified as metals, nonmetals, and metalloids based on number of electrons in outer shell
The zigzag line on the periodic table can help you recognize which elements belong in which category.

17. Metals found to the left of the zigzag line
have few electrons in their outer energy level.
shiny, ductile, malleable, and are good conductors of electric current and thermal energy.

18. Metalloids border the zigzag line
have about half of a complete set of electrons in their outer energy level.
Metalloids have some properties of metals and some properties of nonmetals.
Metalloids are also called semiconductors.

19. Nonmetals to the right of the zigzag line
have an almost complete set of electrons in their outer energy level.
not shiny, ductile, or malleable, and poor conductors of electric current and thermal energy.

21. Group 1: Alkali Metals Alkali metals properties: metals
1 electron in the outer level
very reactive
softness, color of silver, shininess, low density
So reactive that only found combined with other elements

22. Group 2: Alkaline-Earth Metals
Alkaline-earth metals properties:
metals
2 electrons in the outer level
very reactive, but less reactive than alkali metals
color of silver, higher densities than alkali metals
Silvery-White Metals
Fairly reactive
Many are found in rocks in the earth’s crust

23. Group 3–12: Transition Metals
Properties of Transition Metals vary widely but include:
metals
1 or 2 electrons in the outer level
less reactive than alkaline-earth metals
shininess, good conductors of electricity & heat and , malleable
Don’t give up their electrons as easily as Group 1 & 2

24. Group 3–12: Transition Metals, continued
Lanthanides and Actinides Some transition metals from Periods 6 and 7 appear in two rows at the bottom of the periodic table. Elements in the first row are called lanthanides and elements in the second row are called actinides.
Actinides are radioactive
Lanthanides: shiny, reactive metals (some are used to make steel)

25. Group 13: Boron Group Group 13 properties:
one metalloid and five metals
3 electrons in the outer level
reactive
solids at room temperature
Al is the most common element in this group

26. Group 14: Carbon Group Group 14 properties:
one nonmetal, two metalloids, and two metals
4 electrons in the outer level
reactivity varies among the elements
solids at room temperature
Form a variety of compounds such as proteins, fats and carbohydrates

27. Group 15: Nitrogen Group Group 15 properties:
two nonmetals, two metalloids, and two metals
5 electrons in the outer level
reactivity varies among the elements
solids at room temperature (except for nitrogen, which is a gas)

28. Group 16: Oxygen Group Group 16 properties:
group contains three nonmetals, one metalloids, and one metal
6 electrons in the outer level
reactive
solids at room temperature (except for oxygen, which is a gas)
Contains an elements that is crucial for substances to burn

29. Chapter 12 Group 17: Halogens
Section 2 Grouping the Elements
Group 17: Halogens
Halogens are the elements in Group 17. Group 17 properties:
group contains nonmetals
7 electrons in the outer level
very reactive non metals
poor conductors of electric current, never in uncombined form in nature

30. Halogens
Most are Poisonous
Fairly reactive

31. Chlorine Gas was used as a chemical weapon during World War I.
It was used by the Nazis in World War II.

32. Group 18: Noble Gases
Noble gases are the elements in Group 18. Group 18 properties:
group contains nonmetals
8 electrons in the outer level (except helium, which has 2)
unreactive
colorless, odorless gases at room temperature

33. Jellyfish lamps made with noble gases artist- Eric Ehlenberger

34. Colors Noble Gases produce in lamp tubes:
Ne (Neon): orange-red
Hg (Mercury): light blue
Ar (Argon): pale lavender
He (Helium): pale peach
Kr (Krypton): pale silver
Xe (Xenon): pale, deep blue

35. Hydrogen
The properties of hydrogen do not match the properties of any single group, so hydrogen is set apart.
a nonmetal
1 electron in the outer level
reactive
colorless, odorless gas at room temperature, low density