5.2 The Modern Periodic Table 5-2 & 5-3 Periodic Law –How is the current periodic table organized? –Periods –Groups Atomic Mass –Atomic Mass Unit –Isotopes

5.2 The Modern Periodic Table

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





• Atomic Mass– Atomic Mass Unit– Why are the Isotopes of

Chlorine– Weighted Averages



















































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.


II. The Modern Periodic TableA. The Periodic Law- The pattern of repeating properties

1. In the modern periodic table, elements are arranged by increasing atomic number (number of protons).


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

The Periodic Law


2. Periods- each row in the table of elements.

a. Hydrogen, the first element in Period 1, has one electron in its first energy level.

b. Lithium, the first element in Period 2, has one electron in its second energy level.

c. Sodium, the first element in Period 3, has one electron in its third energy level.

d. This pattern applies to all the elements in the first column on the table.


3. Groups- each column in the periodic table.

a. The elements in a group have similar electron configurations, so members of a group in the periodic table have similar chemical properties.


The Periodic LawPeriodic Table of the Elements


B. Atomic Mass- a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes.

1. Atomic Mass Units- (amu) is defined as one twelfth the mass of a carbon-12 atom.a. In order to have a convenient way to compare the

masses of atoms, scientists chose one isotope to serve as a standard. 1) Scientists assigned 12 atomic mass units to the

carbon-12 atom, which has 6 protons and 6 neutrons.


There are four pieces of information for each element.

Atomic Mass



Atomic Mass

Atomic number



Atomic Mass

Atomic number

Element symbol



Atomic Mass

Atomic number

Element symbol

Element name



Atomic Mass

Atomic number

Element symbol

Element name

Atomic mass


2. Isotopes of Chlorine

a. In nature, most elements exist as a mixture of two or more isotopes.

b. The element chlorine has an atomic mass of 35.453 amu.

1) There are two natural isotopes of chlorine, chlorine-35 and chlorine-37.

2) An atom of chlorine-35 has 17 protons and 18 neutrons.

3) An atom of chlorine-37 has 17 protons and 20 neutrons.


3. 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 35.967, not 35.453.


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


1. Metals- elements that are good conductors of electric current and heat.

a. The majority of the elements on the periodic table are classified as metals.

b. Except for mercury, metals are solids at room temperature.

c. Most metals are malleable (can be hammered into thin sheets.)

d. Many metals are ductile (can be drawn into thin wires.)

C. 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.

Classes of Elements


e. Transition metals- elements that form a bridge between the elements on the left and right sides of the table.

1) Transition elements, such as copper and silver, were among the first elements discovered.

2) One property of many transition metals is their ability to form compounds with distinctive colors.


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

Classes of Elements


2. Nonmetals- elements that are poor conductors of heat and electric current.

a. Nonmetals have low boiling points–many nonmetals are gases at room temperature.

b. Nonmetals that are solids at room temperature tend to be brittle. If they are hit with a hammer, they shatter or crumble.


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.

Classes of Elements


3. Metalloids- elements with properties that fall between those of metals and nonmetals

a. Metalloid elements are located on the periodic table between metals and nonmetals.

b. Most useful property is their varying ability to conduct electricity

1) Semiconductors- are substances that can conduct electricity under some conditions but not under other conditions

a) Silicon (Si) and germanium (Ge) are good insulators at low temperatures and good conductors at high temperatures.


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

D. 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).


• 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.


Assessment Questions

1. What determines the atomic mass of an element? a. the natural distribution of isotopes and the atomic

numbers of those isotopes

b. the natural distribution of isotopes and the masses of those isotopes

c. the mass of the isotope of the element that has the most neutrons

d. the average number of protons in the element’s nucleus



1. What determines the atomic mass of an element? a. the natural distribution of isotopes and the atomic

numbers of those isotopes

b. the natural distribution of isotopes and the masses of those isotopes

c. the mass of the isotope of the element that has the most neutrons

d. the average number of protons in the element’s nucleus

ANS: B



2. Which of the following is not characteristic of metals? a. ductileb. good electrical conductorc. typically solid at room temperatured. brittle



2. Which of the following is not characteristic of metals? a. ductileb. good electrical conductorc. typically solid at room temperatured. brittle

ANS: D



3. Within a period of the periodic table, how do the properties of the elements vary? a. Metallic characteristics increase from left to right.

b. Metallic characteristics decrease from left to right.

c. Reactivity increases from left to right.

d. Reactivity decreases from left to right.



3. Within a period of the periodic table, how do the properties of the elements vary? a. Metallic characteristics increase from left to right.

b. Metallic characteristics decrease from left to right.

c. Reactivity increases from left to right.

d. Reactivity decreases from left to right.

ANS: B



1. In the modern periodic table, elements are arranged in order of increasing atomic mass.

TrueFalse



1. In the modern periodic table, elements are arranged in order of increasing atomic mass.

TrueFalse

ANS: F, atomic number

Documents

5.2 The Modern Periodic Table 5-2 & 5-3 Periodic Law –How is the current periodic table organized? –Periods –Groups Atomic Mass –Atomic Mass Unit –Isotopes