1. Chapter 5
The Periodic Table

2. Organizing the Elements
Mendeleev’s original periodic table was arranged by atomic mass. A periodic table is an arrangement of elements in columns, based on a set of properties that repeat from row to row.

3. Mendeleev’s Periodic Table

4. Mendeleev’s Periodic Table
Mendeleev named missing elements after elements in the same group. He gave the name eka-aluminum to the missing element one space below aluminum in the table. Mendeleev predicted that eka- aluminum would
be a soft metal,
have a low melting point, and
have a density of 5.9 g/cm3.

5. Mendeleev’s Periodic Table
In 1875, a French chemist discovered a new element. He named the element gallium (Ga) in honor of France. (The Latin name for France is Gallia.) Gallium
is a soft metal,
has a melting point of 29.7°C, and
has a density of 5.91 g/cm3.

6. Assessment Questions
In Mendeleev’s periodic table, elements with similar properties were grouped
in the same row.
in the same column.
in diagonal lines that run from top left to the bottom right.
in pairs of two.

7. Assessment Questions
In Mendeleev’s periodic table, elements with similar properties were grouped
in the same row.
in the same column.
in diagonal lines that run from top left to the bottom right.
in pairs of two. ANS: B

8. Assessment Questions
For which element did Mendeleev correctly predict the properties even before it had been discovered?
gallium
hydrogen
bromine
aluminum

9. Assessment Questions
For which element did Mendeleev correctly predict the properties even before it had been discovered?
gallium
hydrogen
bromine
aluminum
ANS: A

10. The Periodic Law
The modern periodic table is arranged by atomic number. A period is a row in the periodic table. A group is a column in the periodic table.

11. The Periodic Law

12. Classes of Elements
Elements are classified as metals, nonmetals, and metalloids. Metals are elements that are good conductors of electric current and heat. Nonmetals are elements that are poor conductors of heat and electric current. Metalloids are elements with properties that fall between those of metals and nonmetals.

13. Atomic Mass Atomic Mass Units
The mass of an atom in grams is extremely small. In order to have a convenient way to compare the masses of atoms, scientists chose one isotope to serve as a standard.
Scientists assigned 12 atomic mass units to the carbon-12 atom, which has 6 protons and 6 neutrons.
An atomic mass unit (amu) is defined as one twelfth the mass of a carbon-12 atom.

14. There are four pieces of information for each element.
Atomic Mass
There are four pieces of information for each element.
Atomic number
Element symbol
Element name
Atomic mass

15. Atomic Mass Isotopes of Chlorine
In nature, most elements exist as a mixture of two or more isotopes. The element chlorine has an atomic mass of amu. Where does the number come from?
There are two natural isotopes of chlorine, chlorine- 35 and chlorine-37.
An atom of chlorine-35 has 17 protons and 18 neutrons.
An atom of chlorine-37 has 17 protons and 20 neutrons.

16. Atomic Mass Weighted Averages
This table shows the atomic masses for the two naturally occurring chlorine isotopes. The value of the atomic mass for chlorine is a weighted average. If you add the atomic masses of the isotopes and divide by 2, you get , not

17. Classes of Elements Metals
The majority of the elements on the periodic table are classified as metals. Metals are elements that are good conductors of electric current and heat.
Except for mercury, metals are solids at room temperature.
Most metals are malleable.
Many metals are ductile; that is, they can be drawn into thin wires.

18. Classes of Elements
The metals in groups 3 through 12 are called transition metals. Transition metals are elements that form a bridge between the elements on the left and right sides of the table.
Transition elements, such as copper and silver, were among the first elements discovered.
One property of many transition metals is their ability to form compounds with distinctive colors.

19. Nonmetals generally have properties opposite to those of metals.
Classes of Elements
Nonmetals
Nonmetals generally have properties opposite to those of metals.
Nonmetals are elements that are poor conductors of heat and electric current.
Nonmetals have low boiling points–many nonmetals are gases at room temperature.
Nonmetals that are solids at room temperature tend to be brittle. If they are hit with a hammer, they shatter or crumble.

20. Classes of Elements Metalloids
Metalloid elements are located on the periodic table between metals and nonmetals.
Metalloids are elements with properties that fall between those of metals and nonmetals.
For example, a metalloid’s ability to conduct electric current varies with temperature. Silicon (Si) and germanium (Ge) are good insulators at low temperatures and good conductors at high temperatures.

21. Variations Across a Period
Across a period from left to right, the elements become less metallic and more nonmetallic in their properties.

22. Variations Across a Period
From left to right across Period 3, there are three metals (Na, Mg, and Al), one metalloid (Si), and four nonmetals (P, S, Cl, and Ar).

23. What determines the atomic mass of an element?
Assessment Questions
What determines the atomic mass of an element?
the natural distribution of isotopes and the atomic numbers of those isotopes
the natural distribution of isotopes and the masses of those isotopes
the mass of the isotope of the element that has the most neutrons
the average number of protons in the element’s nucleus

24. What determines the atomic mass of an element?
Assessment Questions
What determines the atomic mass of an element?
the natural distribution of isotopes and the atomic numbers of those isotopes
the natural distribution of isotopes and the masses of those isotopes
the mass of the isotope of the element that has the most neutrons
the average number of protons in the element’s nucleus ANS: B

25. Which of the following is not characteristic of metals?
Assessment Questions
Which of the following is not characteristic of metals?
ductile
good electrical conductor
typically solid at room temperature
brittle

26. Which of the following is not characteristic of metals?
Assessment Questions
Which of the following is not characteristic of metals?
ductile
good electrical conductor
typically solid at room temperature
brittle
ANS: D

27. Assessment Questions
Within a period of the periodic table, how do the properties of the elements vary?
Metallic characteristics increase from left to right.
Metallic characteristics decrease from left to right.
Reactivity increases from left to right.
Reactivity decreases from left to right.

28. Assessment Questions
Within a period of the periodic table, how do the properties of the elements vary?
Metallic characteristics increase from left to right.
Metallic characteristics decrease from left to right.
Reactivity increases from left to right.
Reactivity decreases from left to right. ANS: B

29. Assessment Questions
In the modern periodic table, elements are arranged in order of increasing atomic mass. True False

30. Assessment Questions
In the modern periodic table, elements are arranged in order of increasing atomic mass. True False
ANS: F, atomic number

31. Valence Electrons Why do elements in a group have similar properties?
Elements in the same group have similar properties because they have the same number of valence electrons.
A valence electron is an electron that is in the highest occupied energy level of an atom.

32. Valence Electrons
The number of valence electrons is equal to the group number for groups 1A – 8A in the periodic table.
Elements in the same group have similar properties because they have the same number of valence electrons.
The properties are not identical because the valence electrons are in different energy levels.

33. The Groups The elements in Group 1A are called alkali metals.
All have 1 valence electron
Extremely reactive
Found only in compounds
Stored in oil or argon gas to keep from reacting with water in air.
The reactivity for Group 1A elements increases from top to bottom.

34. The Groups The elements of Group 2A are called alkaline earth metals
All have 2 valence electrons
Harder than Group 1A metals
Less reactive than Group 1A metals
Higher melting points than Group 1A metals
The reactivity for Group 2A elements also increases from top to bottom.

35. The Groups Group 3A elements are called the boron family.
All elements have 3 valence electrons
Boron is a metalloids, aluminum, gallium, indium, and thallium are metals.

36. The Groups Group 4A elements are called the carbon family.
All elements have 4 valence electrons
Carbon is a nonmetal, silicon and germanium are metalloids, and tin and lead are metals.
Carbon is found in most compounds in your body, except water

37. The Groups Group 5A elements are called the nitrogen family.
All elements have 5 valence electrons
Nitrogen and phosphorus are nonmetals, arsenic and antimony are metalloids, and bismuth is a metal

38. The Groups Group 6A elements are called the oxygen family.
All elements have 6 valence electrons
Oxygen, sulfur, and selenium are nonmetals, tellurium and polonium are metalloids

39. The Groups Group 7A elements are called the halogens.
Each element has 7 valence electrons
Fluorine and Chlorine are gases, Bromine is a liquid, and Iodine is a solid
They are all nonmetals, except astatine is a metalloid
React most easily with metals (Group 1A especially)
The reactivity for Group 7A decreases from top to bottom. Fluorine is the most reactive halogen.

40. The Groups Group 8A elements are called the noble gases.
Helium has 2 valence electrons
Each of the other noble gases has 8 valence electrons
When electric current passes through noble gases, they emit different colors.
The noble gases are colorless, odorless, and extremely unreactive.

41. Assessment Questions
Why do elements in a group have similar chemical properties?
They have the same number of valence electrons
They have the same ratio of protons to neutrons.
Their atomic masses are multiples of the least massive element of the group.
They have the same number of total electrons.
Answer: A

42. Assessment Questions
True or False: In general, the metallic characteristics of A group elements within a period decreases from left to right.
Answer: True