1. Chapter 12
Section 1 Arranging the Elements
Bellwork
Think of all the ways a deck of cards could be laid out so that the cards form some sort of identifiable pattern.

2. Chapter 12 Discovering a Pattern
Section 1 Arranging the Elements
Discovering a Pattern
In 1869, Russian chemist Dmitri Mendeleev arranged the elements in order of increasing atomic mass.
Periodic Properties of the Elements When the elements are arranged in order of increasing atomic mass, those that had similar properties occurred in a repeating pattern.
These repeating patterns are periodic, meaning that they happen at regular intervals.

3. Chapter 12
Section 1 Arranging the Elements
Predicting Properties of Missing Elements Mendeleev’s arrangement had gaps in its pattern. Mendeleev predicted that elements yet to be found would fill these gaps. He also predicted 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
Chapter 12
Section 1 Arranging the Elements
Changing the Arrangement
A few elements’ properties did not fit in the pattern of Mendeleev’s table.
In 1914, British scientist Henry Moseley found the number of protons—the atomic number—in an atom.
When the elements were arranged by atomic number, they fit the pattern in Mendeleev’s table.

5. Chapter 12
Section 1 Arranging the Elements

6. The Periodic Table and Classes of Elements
Chapter 12
Section 1 Arranging the Elements
The Periodic Table and Classes of Elements
Elements are classified as metals, nonmetals, and metalloids, according to their properties.
The number of electrons in the outer energy level of an atom is one characteristic that helps determine which category an element belongs in.
The zigzag line on the periodic table can help you recognize which elements belong in which category.

7. Chapter 12
Section 1 Arranging the Elements
Metals are found to the left of the zigzag line. Atoms of most metals have few electrons in their outer energy level.
Most metals are shiny, ductile, malleable, and are good conductors of electric current and thermal energy.

8. Chapter 12
Section 1 Arranging the Elements
Nonmetals are found to the right of the zigzag line. Atoms of most nonmetals have an almost complete set of electrons in their outer energy level.
Nonmetals are not shiny, ductile, or malleable, and are poor conductors of electric current and thermal energy.

9. Chapter 12
Section 1 Arranging the Elements
Metalloids are the elements that border the zigzag line. Atoms of metalloids 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.

10. Decoding the Periodic Table
Chapter 12
Section 1 Arranging the Elements
Decoding the Periodic Table
Each Element is Identified by a Chemical Symbol Each square on the periodic table includes an element’s name, chemical symbol, atomic number, and atomic mass.
For most elements, the chemical symbol has one or two letters. The newest elements have temporary three-letter symbols.

11. Chapter 12
Section 1 Arranging the Elements
Rows Are Called Periods Each horizontal row of elements is called a period. The chemical and physical properties of elements in a row follow a repeating pattern as you move across the period.
Columns Are Called Groups Each vertical column of elements is called a group. Elements in the same group often have similar chemical and physical properties.

12. Chapter 12
Section 2 Grouping the Elements
Bellwork
How do you know that a bird is a bird, that a kangaroo is a kangaroo, and that a shark is a shark? What characteristics of each animal help you to tell the animals apart? How can such an analysis of characteristics be applied to elements?

13. Chapter 12 Group 1: Alkali Metals
Section 2 Grouping the Elements
Group 1: Alkali Metals
Alkali metals are elements in Group 1 of the periodic table. Alkali metal properties:
group contains metals
1 electron in the outer level
very reactive
softness, color of silver, shininess, low density

14. Group 2: Alkaline-Earth Metals
Chapter 12
Section 2 Grouping the Elements
Group 2: Alkaline-Earth Metals
Alkaline-earth metals are elements in Group 2. Alkaline-earth metal properties:
group contains metals
2 electrons in the outer level
very reactive, but less reactive than alkali metals
color of silver, higher densities than alkali metals

15. Group 3–12: Transition Metals
Chapter 12
Section 2 Grouping the Elements
Group 3–12: Transition Metals
Transition metals are in Groups 3–12. Some of the transition metals are shown below.

16. Chapter 12 Properties of Transition Metals vary widely but include:
Section 2 Grouping the Elements
Properties of Transition Metals vary widely but include:
groups contains metals
1 or 2 electrons in the outer level
less reactive than alkaline-earth metals
shininess, good conductors of electric current and thermal energy

17. Chapter 12
Section 2 Grouping the Elements
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.

18. Chapter 12 Group 13: Boron Group
Section 2 Grouping the Elements
Group 13: Boron Group
Aluminum is the most common element from Group 13. Group 13 properties:
group contains one metalloid and five metals
3 electrons in the outer level
reactive
solids at room temperature

19. Chapter 12 Group 14: Carbon Group Group 14 properties:
Section 2 Grouping the Elements
Group 14: Carbon Group
Group 14 properties:
group contains one nonmetal, two metalloids, and two metals
4 electrons in the outer level
reactivity varies among the elements
solids at room temperature

20. Chapter 12 Group 15: Nitrogen Group Group 15 properties:
Section 2 Grouping the Elements
Group 15: Nitrogen Group
Group 15 properties:
group contains 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)

21. Chapter 12 Group 16: Oxygen Group Group 16 properties:
Section 2 Grouping the Elements
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)

22. 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
poor conductors of electric current, never in uncombined form in nature

23. Chapter 12 Group 18: Noble Gases
Section 2 Grouping the Elements
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

24. Chapter 12
Section 2 Grouping the Elements
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