1. Variation Across a Period Valence Electrons
5-2 & 5-3
Periodic Law
How is the current periodic table organized?
Periods
Groups
Atomic Mass
Atomic Mass Unit
Isotopes of Chlorine
Weighted Averages
Classes of Elements
Metals, Nonmetals, Metalloids
Variation Across a Period
Valence Electrons
Why are these important and how are they represented in the periodic table?
For the following, Be specific on properties they share!!!
The Alkali Metals
The Alkaline Earth Metals
The Boron Family
The Carbon Family
The Nitrogen Family
The Oxygen Family
The Halogens
The Noble Gasses

2. Variation Across a Period Valence Electrons
5-2 & 5-3
Periodic Law
How is the current periodic table organized?
Periods
Groups
Atomic Mass
Atomic Mass Unit
Why are the Isotopes of Chlorine
Weighted Averages
Classes of Elements
Metals, Nonmetals, Metalloids
Variation Across a Period
Valence Electrons
Why are these important and how are they represented in the periodic table?
For the following, Be specific on properties they share!!!
The Alkali Metals
The Alkaline Earth Metals
The Boron Family
The Carbon Family
The Nitrogen Family
The Oxygen Family
The Halogens
The Noble Gasses

3. Variation Across a Period Valence Electrons
5-2 & 5-3
Periodic Law
How is the current periodic table organized?
Periods
Groups
Atomic Mass
Atomic Mass Unit
Why are the Isotopes of Chlorine
Weighted Averages
Classes of Elements
Metals, Nonmetals, Metalloids
Variation Across a Period
Valence Electrons
Why are these important and how are they represented in the periodic table?
For the following, Be specific on properties they share!!!
The Alkali Metals
The Alkaline Earth Metals
The Boron Family
The Carbon Family
The Nitrogen Family
The Oxygen Family
The Halogens
The Noble Gasses

4. Variation Across a Period Valence Electrons
5-2 & 5-3
Periodic Law
How is the current periodic table organized?
Periods
Groups
Atomic Mass
Atomic Mass Unit
Why are the Isotopes of Chlorine
Weighted Averages
Classes of Elements
Metals, Nonmetals, Metalloids
Variation Across a Period
Valence Electrons
Why are these important and how are they represented in the periodic table?
For the following, Be specific on properties they share!!!
The Alkali Metals
The Alkaline Earth Metals
The Boron Family
The Carbon Family
The Nitrogen Family
The Oxygen Family
The Halogens
The Noble Gasses

5. Variation Across a Period Valence Electrons
5-2 & 5-3
Periodic Law
How is the current periodic table organized?
Periods
Groups
Atomic Mass
Atomic Mass Unit
Why are the Isotopes of Chlorine
Weighted Averages
Classes of Elements
Metals, Nonmetals, Metalloids
Variation Across a Period
Valence Electrons
Why are these important and how are they represented in the periodic table?
For the following, Be specific on properties they share!!!
The Alkali Metals
The Alkaline Earth Metals
The Boron Family
The Carbon Family
The Nitrogen Family
The Oxygen Family
The Halogens
The Noble Gasses

6. Variation Across a Period Valence Electrons
5-2 & 5-3
Periodic Law
How is the current periodic table organized?
Periods
Groups
Atomic Mass
Atomic Mass Unit
Why are the Isotopes of Chlorine
Weighted Averages
Classes of Elements
Metals, Nonmetals, Metalloids
Variation Across a Period
Valence Electrons
Why are these important and how are they represented in the periodic table?
For the following, Be specific on properties they share!!!
The Alkali Metals
The Alkaline Earth Metals
The Boron Family
The Carbon Family
The Nitrogen Family
The Oxygen Family
The Halogens
The Noble Gasses

7. The eight-note interval between any two notes on a keyboard with the same name is an octave. The sounds of musical notes that are separated by an octave are related, but they are not identical. In a similar way, elements in the same column of the modern periodic table are related but not identical.

8. The Modern Periodic Table
The Periodic Law- The pattern of repeating properties
In the modern periodic table, elements are arranged by increasing atomic number (number of protons).

9. The Periodic Law
The modern periodic table is based on atomic number, or number of protons.

10. Periods- each row in the table of elements.
Hydrogen, the first element in Period 1, has one electron in its first energy level.
Lithium, the first element in Period 2, has one electron in its second energy level.
Sodium, the first element in Period 3, has one electron in its third energy level.
This pattern applies to all the elements in the first column on the table.

11. Groups- each column in the periodic table.
The elements in a group have similar electron configurations, so members of a group in the periodic table have similar chemical properties.

12. The Periodic Law
Periodic Table of the Elements

13. Atomic Mass- a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes.
Atomic Mass Units- (amu) is defined as one twelfth the mass of a carbon-12 atom.
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.

14. Atomic Mass
There are four pieces of information for each element.

15. There are four pieces of information for each element.
Atomic Mass
There are four pieces of information for each element.
Atomic number

16. There are four pieces of information for each element.
Atomic Mass
There are four pieces of information for each element.
Atomic number
Element symbol

17. 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

18. 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

19. 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.
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.

20. Atomic mass is a weighted average due to the isotopes that occur more often in nature.
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

21. The periodic table presents three different ways to classify elements.
State: solid—black symbol, liquid—purple symbol, or gas—red symbol
Occurrence in nature: elements that do not occur naturally—white symbol.
General properties: metal—blue background, nonmetal—yellow background, or metalloid—green background

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

23. Classes of Elements
A When magnesium reacts with oxygen, a dull layer forms on its surface. The layer can be removed to reveal magnesium’s shiny surface. B Many telescope mirrors are coated with aluminum to produce a surface that reflects light extremely well.

24. Transition metals- 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.

25. Classes of Elements
A compound of oxygen and the transition element erbium is used to tint the pink glass lenses.

26. Nonmetals- 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.

27. Classes of Elements
Fluorine is the most reactive nonmetal. The gases in Group 18 are the least reactive elements in the table. Some toothpastes use a compound of the nonmetal fluorine and the metal sodium to help prevent tooth decay.

28. Metalloids- elements with properties that fall between those of metals and nonmetals
Metalloid elements are located on the periodic table between metals and nonmetals.
Most useful property is their varying ability to conduct electricity
Semiconductors- are substances that can conduct electricity under some conditions but not under other conditions
Silicon (Si) and germanium (Ge) are good insulators at low temperatures and good conductors at high temperatures.

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

30. Sodium reacts violently with water.
Magnesium will not react with water unless the water is hot.
Aluminum does not react with water, but it does react with oxygen.
Silicon is generally unreactive.
Phosphorus and sulfur do not react with water, but they do react with oxygen.
Chlorine is highly reactive.
Argon hardly reacts at all.

31. 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

32. 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

33. 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

34. 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

35. 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.

36. 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

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

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