how elements are organized

mendeleevs periodic table of the elements

Mendeleev was a teacher as well as a chemist. He was writing a chemistry textbook and needed a way to organize the elements so it would be easier for students to learn about them. He made a set of cards of the elements, similar to a deck of playing cards, with one element per card. On the card, he wrote the elements name, atomic mass, and known properties. He arranged and rearranged the cards in many different ways, looking for a pattern. He finally found it when he placed the elements in order by atomic mass.

a repeating pattern

You can see how Mendeleev organized the elements in Figure 6.2. From left to right across each row, elements are arranged by increasing atomic mass. Mendeleev discovered that if he placed eight elements in each row and then continued on to the next row, the columns of the table would contain elements with similar properties. He called the columns groups. They are sometimes called families, because elements within a group are similar but not identical to one another, like people in a family. Mendeleevs table of the elements is called a periodic table because of its repeating pattern. Anything that keeps repeating is referred to as periodic. Other examples of things that are periodic include the monthly phases of the moon and the daily cycle of night and day. The term period refers to the interval between repetitions. In a periodic table, the periods are the rows of the table. In Mendeleevs table, each period contains eight elements, and then the pattern repeats in the next row.

textbook_image

predicting missing elements

Did you notice the blanks in Mendeleevs table (Figure 6.2)? They are spaces that Mendeleev left for elements that had not yet been discovered when he created his table. He predicted that these missing elements would eventually be discovered. Based on their position in the table, he could even predict their properties. For example, he predicted a missing element in row 5 of his group 3. He said it would have an atomic mass of about 68 and be a soft metal like other group 3 elements. Scientists searched for the missing element. They found it a few years later and named it gallium. Scientists searched for the other missing elements. Eventually, all of them were found. An important measure of a good model is its ability to make accurate predictions. This makes it a useful model. Clearly, Mendeleevs periodic table was a useful model. It helped scientists discover new elements and make sense of those that were already known.

basis of the modern periodic table

In the modern periodic table, elements are organized by atomic number. The atomic number is the number of protons in an atom of an element. This number is unique for each element, so it seems like an obvious way to organize the elements. (Mendeleev used atomic mass instead of atomic number because protons had not yet been discovered when he made his table.) In the modern table, atomic number increases from left to right across each period. It also increases from top to bottom within each group. How is this like Mendeleevs table?

the modern periodic table of the elements

A periodic table is still used today to classify the elements. Figure 6.3 shows the modern periodic table. You can see an interactive version at this URL: .

periods

Rows of the modern table are called periods, as they are in Mendeleevs table. From left to right across a period, each element has one more proton than the element before it. In each period, elements change from metals on the left side of the table, to metalloids, and then to nonmetals on the right. Figure 6.4 shows this for period 4. Some periods in the modern periodic table are longer than others. For example, period 1 contains only two elements. Periods 6 and 7, in contrast, are so long that some of their elements are placed below the main part of the table. They are the elements starting with lanthanum (La) in period 6 and actinium (Ac) in period 7. Some elements in period 7 have not yet been named. They are represented by temporary symbols, such as Uub. Many of these elements have only recently been shown to exist. Elements 114 and 116 were added to the table in 2011. Four more elements (113, 115, 117, and 118) were approved for addition in December 2015 and will be named at some later date.

textbook_image

reading the table

Besides atomic number, the periodic table includes each elements chemical symbol and class. Some tables include other information as well. The chemical symbol consists of one or two letters that come from the chemicals name in English or another language. The first letter is always written in upper case. The second letter, if there is one, is always written in lower case. For example, the symbol for lead is Pb. It comes from the Latin word plumbum, which means "lead." Find lead in Figure 6.3. What is its atomic number? You can access videos about lead and other elements in the modern periodic table at this URL: . The classes of elements are metals, metalloids, and nonmetals. They are color-coded in the table. Blue stands for metals, orange for metalloids, and green for nonmetals. You can read about each of these three classes of elements later in the chapter, in the lesson "Classes of Elements."

groups

Columns of the modern table are called groups, as they are in Mendeleevs table. However, the modern table has many more groups 18 to be exact. Elements in the same group have similar properties. For example, all elements in group 18 are colorless, odorless gases. You can read about the different groups of elements in this chapters lesson on "Groups of Elements."

instructional diagrams

description_image

Pictured below is a diagram of the periodic table. The periodic table is used today to classify elements. The elements in a periodic table are organized by the atomic number. The number of protons in an atom is what the atomic number represents on the chart. Rows on the periodic table are called periods. The columns in the periodic table are called groups. The modern periodic table have 18 groups. The elements are arranged in the periodic table by the atomic number from left to right from the lowest atomic numbers to highest.

description_image

This image shows the Periodic table. It is a table of the chemical elements arranged in order of atomic number, usually in rows, so that elements with similar atomic structure (and hence similar chemical properties) appear in vertical columns. This ordering shows periodic trends, such as elements with similar behaviour in the same column. It also shows four rectangular blocks with some approximately similar chemical properties. In general, within one row (period) the elements are metals on the left, and non-metals on the right. The rows of the table are called periods; the columns are called groups. The periodic table provides a useful framework for analyzing chemical behaviour, and is widely used in chemistry and other sciences.

description_image

The following image shows the Periodic Table of Elements. This is a list of known atoms. In the table, the elements are placed in the order of their atomic numbers starting with the lowest number. The atomic number of an element is the same as the number of protons in that particular atom. In the periodic table the elements are arranged into periods and groups. A row of elements across the table is called a period. Each period has a number: from 1 to 7. Period 1 has only 2 elements in it: hydrogen and helium. Period 2 and Period 3 both have 8 elements. Other periods are longer. The periodic table can be used by chemists to observe patterns, and relationships between the elements.

questions

Mendeleev organized the elements based on their

a. atomic number.

b. number of protons.

-->  c. atomic mass.

d. number of neutrons.

In the modern periodic table, atomic number

a. increases from top to bottom within each period.

b. increases from left to right within each group.

c. is the same within each group but not between groups.

-->  d. none of the above

The shortest period in the periodic table is period

a. 18

b. 7

c. 6

-->  d. 1

All but one of the elements on the left side of the periodic table are

a. metalloids.

b. liquids.

-->  c. metals.

d. gases.

Which statement is true about any group in the periodic table?

a. It includes metals, metalloids, and nonmetals.

-->  b. It includes elements with similar properties.

c. It includes gases, liquids, and solids.

d. It contains 18 different elements.

number of protons in an atom

a. group

b. period

-->  c. atomic number

d. atomic mass

e. chemical symbol

f. Mendeleevs periodic table

g. modern periodic table

row of the periodic table

a. group

-->  b. period

c. atomic number

d. atomic mass

e. chemical symbol

f. Mendeleevs periodic table

g. modern periodic table

table based on the atomic number of elements

a. group

b. period

c. atomic number

d. atomic mass

e. chemical symbol

f. Mendeleevs periodic table

-->  g. modern periodic table

Mendeleev left spaces in his periodic table for unknown elements.

-->  a. true

b. false

how an element is represented in the periodic table

a. group

b. period

c. atomic number

d. atomic mass

-->  e. chemical symbol

f. Mendeleevs periodic table

g. modern periodic table

The modern periodic table is the same as Mendeleevs table but with more elements.

a. true

-->  b. false

table based on the atomic mass of elements

a. group

b. period

c. atomic number

d. atomic mass

e. chemical symbol

-->  f. Mendeleevs periodic table

g. modern periodic table

column of the periodic table

-->  a. group

b. period

c. atomic number

d. atomic mass

e. chemical symbol

f. Mendeleevs periodic table

g. modern periodic table

The modern periodic table has more than 100 elements.

-->  a. true

b. false

amount of matter in an atom

a. group

b. period

c. atomic number

-->  d. atomic mass

e. chemical symbol

f. Mendeleevs periodic table

g. modern periodic table

Elements called actinides are in period 7 of the periodic table.

-->  a. true

b. false

Elements in the same period of the periodic table have similar properties.

a. true

-->  b. false

Mendeleev developed his periodic table in the 1860s.

-->  a. true

b. false

Mendeleev named the columns of his table periods.

a. true

-->  b. false

Elements within a group of the periodic table are identical to each other.

a. true

-->  b. false

In Mendeleevs table, each period contains 18 elements.

a. true

-->  b. false

Mendeleevs used his table to predict unknown elements.

-->  a. true

b. false

The elements Mendeleev predicted were never discovered.

a. true

-->  b. false

Lanthanide elements are placed in period 2 of the modern periodic table.

a. true

-->  b. false

The chemical symbol for lead is Pb.

-->  a. true

b. false

Most elements in the modern periodic table are metalloids.

a. true

-->  b. false

Krypton is a gaseous metal in group 18 of the periodic table.

-->  a. true

b. false

Scientist first started looking for a way to organize the elements in the

-->  a. 1700s.

b. late 1800s.

c. early 1900s.

d. 1980s.

How many groups are there in Mendeleevs periodic table?

a. 18

b. 16

c. 12

-->  d. 8

Examples that illustrate the meaning of periodic include

a. phases of the moon.

b. day and night.

c. months of the year.

-->  d. all of the above

How many elements are represented in the modern periodic table?

a. fewer than 50

b. exactly 18

c. about 65

-->  d. more than 100

Which of the following could be the chemical symbol of an element?

a. SI

b. si

-->  c. Si

d. iS

Elements on the right side of the periodic table are

a. metals.

b. metalloids.

-->  c. nonmetals.

d. actinides.

Which sentence is true about periods of the periodic table?

a. All the periods are the same length.

b. There are a total of 18 periods.

-->  c. Some periods are longer than others.

d. two of the above

diagram questions

question_image

How many groups are there in the periodic table of elements?

a. 17

-->  b. 18

c. 15

d. 16

question_image

The noble gases are members of which group of the periodic table?

a. Group 2

-->  b. Group 1

c. Group 17

d. Group 18

question_image

What element comes between Pb and Po?

-->  a. Bi

b. Sb

c. Sn

d. Te

question_image

How many Boxes are in Group 1-1?

-->  a. 7

b. 3

c. 10

d. 8

question_image

How many lanthanides are there in the periodic table?

-->  a. 15

b. 12

c. 14

d. 16

question_image

Which letter(s) represent the element copper?

-->  a. Cu

b. Cr

c. Co

d. Au

question_image

What is Helium?

a. liquid

-->  b. metal

c. solid

d. Nonmetal

question_image

What element comes before the start of lanthanide series of elements?

a. Carbon

b. Ferrum

c. Aluminium

-->  d. Barium

question_image

How many nonmetals are there in the periodic table?

-->  a. 21

b. 15

c. 54

d. 2

question_image

What element corresponds for liquid metal?

-->  a. Hg

b. H

c. Nb

d. Mg

question_image

Elements under the group 8A of the periodic table are called what?

-->  a. Noble Gases

b. Metalloids

c. Halogens

d. Other Nonmetals

question_image

What group in the periodic table do halogens belong?

a. 3A

-->  b. 7A

c. 7B

d. 8A

question_image

What is an element that is a noble gas?

a. In

-->  b. Ar

c. O

d. H

question_image

How many Halogen elements are in the Periodic Table?

a. 15

b. 3

c. 10

-->  d. 6

question_image

How many Noble Gases are on the Periodic Table?

a. 11

-->  b. 7

c. 0

d. 6

question_image

Which group of elements are Noble Gases?

a. 6A

b. 1A

-->  c. 8A

d. 7A

question_image

How many groups does the periodic table have?

a. 19

b. 17

c. 16

-->  d. 18

question_image

What is the symbol for Iron?

a. Pt

b. I

c. Ir

-->  d. Fe

question_image

What is an example of a noble gas?

a. Li

-->  b. Ne

c. H

d. Cl

question_image

Which of the following periodic table elements are halogens?

a. Ag

-->  b. Cl

c. Fe

d. Ar

question_image

How many elements are in the Group 1 of the periodic table (excluding hydrogen)?

a. 8

b. 7

-->  c. 6

d. 5

question_image

How many lanthanides are there?

a. 14

-->  b. 15

c. 17

d. 16

question_image

What element in the periodic table represents Chromium?

-->  a. Cr

b. Cs

c. As

d. Li

question_image

Which element is a metalloid?

a. Helium

b. Hydrogen

-->  c. Arsenic

d. Lithium

question_image

What is an example of a nonmetal element?

a. Cr

b. Ba

-->  c. O

d. H

question_image

Which of the following periodic table elements are metalloids?

a. Rb

b. Kr

-->  c. Ge

d. Ga

question_image

How many elements have one electron?

a. 45

b. 5

-->  c. 1

d. 2

question_image

How many groups does the periodic table have?

-->  a. 18

b. 14

c. 12

d. 16

question_image

What represents the blue-colored elements?

-->  a. Nonmetals

b. Symbols

c. Metalloids

d. Metals

question_image

What is the atomic number of fluorine?

a. 6

b. 8

c. 7

-->  d. 9

question_image

What is the element with atomic number 47?

-->  a. Silver

b. Mercury

c. Gold

d. Helium

question_image

Which among the following has atomic mass greater than 'Cs' but less than 'Hf'?

a. Re

b. Ag

-->  c. Ba

d. Xe

question_image

How many elements are in the first column?

a. 8

b. 3

-->  c. 7

d. 20

question_image

What is the weight of one molecule of salt NaCl?

a. 48.7

b. 36.2

c. 65.5

-->  d. 58.4

question_image

What is the symbol of Lithium in the periodic table of elements?

-->  a. Li

b. H

c. Lh

d. Ni

question_image

What element has 18 protons?

a. Flourine

b. Krypton

c. Neon

-->  d. Argon

question_image

Which element is found in the fifth period and sixth group?

a. Na - Sodium

-->  b. Mo - Molydenium

c. Te - Tellurium

d. Ta - Tantalum

question_image

How many periods are in the Mendelevees table of the elements?

-->  a. 7

b. 18

c. 2

d. 5

question_image

How many groups does the periodic table have?

a. 16

b. 7

-->  c. 18

d. 111

question_image

What is the atomic number of Iron?

-->  a. 26

b. 16

c. 45

d. 39

question_image

In what group do Actinoids belong?

a. Nonmetals

b. Other Nonmetals

-->  c. Metals

d. Noble Gases

question_image

What is an example of an alkali metal?

-->  a. Li

b. P

c. S

d. Ne

question_image

Which of the following periodic table elements are noble gases?

a. Na

b. F

-->  c. He

d. Mg

question_image

How many Alkali metals are there?

a. 7

-->  b. 6

c. 8

d. 9

question_image

How many elements are classified as alkaline earth metals?

a. 15

b. 13

-->  c. 6

d. 7

question_image

What is the atomic number of fluor?

a. 11

-->  b. 9

c. 8

d. 10

question_image

How many elements are there?

a. One hundred three

b. One hundred two

-->  c. One hundred sixteen

d. Seventy one

question_image

What is the 3rd element in the periodic table?

-->  a. Lithium

b. Magnesium

c. Beryllium

d. Helium

question_image

How many elements have been discovered so far?

a. 103

-->  b. 116

c. 71

d. 115

question_image

Which is a noble gas?

a. Hydrogen

b. Chlor

c. Nitrogen

-->  d. Helium

question_image

Identify which column refers to the Alkali metals.

a. VB

b. IB

-->  c. IA

d. IIA

question_image

What element has an atomic number of 47?

-->  a. Silver

b. Gold

c. Carbon

d. Helium

question_image

Considering the periodic trend of electronegativity, which of the following elements has the most electronegative property?

a. bromine

-->  b. oxygen

c. helium

d. nitrogen

question_image

Which of the following periodic table elements are halogens?

-->  a. Br

b. Se

c. Kr

d. Ka

question_image

How many elements belong to the Noble Gases Group?

a. 37

b. 8

-->  c. 7

d. 6

question_image

How many groups are shown in the periodic table below?

-->  a. 16

b. 12

c. 10

d. 14

question_image

What is the symbol of Arsenic in the periodic table of elements?

-->  a. As

b. Ar

c. S

d. Ai

question_image

What is the atomic number of fluorine (F)?

-->  a. 9

b. 7

c. 6

d. 8

question_image

Which of the following elements is a halogen?

a. Boron

b. Hydrogen

c. Oxygen

-->  d. Chlorine

question_image

Which among the following is not an Actinoid?

-->  a. Na

b. Th

c. Pa

d. Ac

question_image

How many Alkali Metals are there?

a. 11

-->  b. 6

c. 9

d. 7

question_image

How many periods are there in the periodic table of elements?

a. 4

-->  b. 7

c. 5

d. 6

question_image

Will any of elements be affected if some elements are removed from the periodic table?

-->  a. Yes

b. No

c. Some elements only

d. Cannot determine

question_image

What is the symbol for Hydrogen?

a. Hy

b. He

c. Hd

-->  d. H

question_image

Which is the second element?

a. hydrogen

b. sodium

-->  c. helium

d. lithium

question_image

Which of the following periodic table elements are noble gases?

a. Be

b. Cl

-->  c. Ne

d. Pd

question_image

How many elements are in the leftmost column of the table?

a. 6

b. 5

-->  c. 8

d. 7

question_image

How many elements are on the last row of the periodic table?

a. 15

b. 20

c. 16

-->  d. 14

question_image

What is the atomic number of fluorine?

a. 8

b. 7

c. 6

-->  d. 9

question_image

What is the atomic number of fluorine?

a. 8

b. 7

-->  c. 9

d. 6

question_image

The alkali metals are members of which group of the periodic table?

a. 18

b. 2

c. 17

-->  d. 1

question_image

Which of the following periodic table elements are noble gases?

-->  a. Ar

b. Fe

c. P

d. H

question_image

Which one of these elements is NOT in group 18?

a. Argon

b. Neon

-->  c. Carbon

d. Krypton

question_image

How many groups are shown in the periodic table below?

a. 15

b. 5

-->  c. 7

d. 6

question_image

How many groups of elements are present in the Periodic Table?

a. 25

-->  b. 18

c. 11

d. 7

question_image

Which element is tetravalent?

a. Oxygen

-->  b. Carbon

c. Boron

d. Nitrogen

question_image

Which element has an atomic number of 11?

a. Magnesium

b. Iron

c. Helium

-->  d. Sodium

question_image

What does Fe stand for?

a. nitrogen

-->  b. iron

c. sodium

d. hydrogen

question_image

What element has atomic number of 2?

a. Boron

-->  b. Helium

c. Hydrogen

d. Carbon

question_image

What element has the lowest atomic weight?

a. Iron (Fe)

b. Boron (B)

-->  c. Hydrogen (H)

d. Xenon (Xe)

question_image

What element is an example of a halogen?

a. As

b. H

-->  c. Br

d. Ne

question_image

From the diagram, how many noble gases are there?

a. 7

b. 8

-->  c. 6

d. 5

question_image

How many nonmetals are there in the periodic table?

a. 25

-->  b. 18

c. 7

d. 45

question_image

If a few elements are removed from the periodic table, will it affect all the other elements or some elements?

-->  a. Some

b. All

c. Cannot answer

d. It won't affect any elements

question_image

What is the atomic number of fluorine?

a. 8

b. 6

c. 7

-->  d. 9

question_image

Identify the Nonmetal from the following.

a. Zn

-->  b. He.

c. Ga

d. B

question_image

What does N stand for?

a. hydrogen

-->  b. nitrogen

c. magnesium

d. sodium

question_image

Which element is after Be in the periodic table?

a. Carbon

b. H

-->  c. Boron

d. Lithium

question_image

Which noble gas has the least number of protons?

a. Hydrogen

b. Krypton

c. Nitrogen

-->  d. Argon

question_image

How many elements does lanthanide series have?

a. 18

b. 10

c. 12

-->  d. 15

question_image

What is the 44th element in the periodic table of elements?

a. rubidium

-->  b. ruthenium

c. rutherfordium

d. rodium

question_image

What is the name of the element with 76 protons?

-->  a. Osmium

b. Mercury

c. Radium

d. Strontium

question_image

What is the element with the lowest atomic mass?

a. Oxygen

b. Lithium

-->  c. Hydrogen

d. Titanium

question_image

What is the symbol of Oxygen in the periodic table of elements?

a. E

b. X

c. C

-->  d. O

question_image

Which among the following is a liquid?

a. Titanium

b. Sodium

c. Calcium

-->  d. Bromine

question_image

Which of the following elements is a liquid?

a. Lithium

-->  b. Mercury

c. Carbon

d. Hydrogen

question_image

How many elements are in Group 2 of the periodic table?

a. 8

b. 5

c. 7

-->  d. 6

question_image

How many noble gases are there?

a. 5

b. 8

c. 6

-->  d. 7

question_image

What is the symbol for Beryllium?

-->  a. Be

b. Mg

c. Bl

d. B