Elements and The Periodic Table

Question 1

Define an element.

Answer 1

Elements are basic substances that cannot be broken down chemically into simpler substances.

Question 2

Define a compound.

Answer 2

Compounds are made up of two or more atoms of elements.

Question 3

Define a mixture

Answer 3

Mixtures are various elements and compounds which are not chemically bonded.

Question 4

Give a brief description of the structure of elements, in relation to their subatomic particles.

Answer 4

Elements are composed of atoms, which have a central nucleus with protons, neutrons and electrons outside the nucleus.

Question 5

What does the atomic number of an element represent?

Answer 5

The atomic number is the number of protons in an atom of the element. It also represents how far down the periodic table the element is.

Question 6

What did the Ancient Greeks believe about elements?

Answer 6

• Empedocles defined elements as the basic substances from which all other material are made.
• He stated that the four elements were earth, air, fire and water.

Question 7

Name this Irish scientist that defined an element as a substance that cannot be broken down into simpler materials.

Answer 7

(Robert) Boyle.

(He regarded compounds as combinations of particular elements, that can be broken down into these elements.)

Question 8

Name this scientist who developed powerful new electrochemical techniques for breaking down compounds into elements.

Answer 8

(Humphry) Davy

(He electrolysed a moist solid sample of potassium hydroxide and produced potassium.

He did the same to sodium hydroxide and isolated sodium.

Later he isolated the element barium, strontium, calcium and magnesium.)

Question 9

Name this scientist who used x-rays to find that the atomic nucleus of each element had a characteristic positive charge.

Answer 9

(Henry) Moseley.

(He called this charge the atomic number.

The discovery of the atomic number made possible a more advanced definition of an element: a substance all of whose atoms have the same atomic number.

He discovered elements should be put in order according to the number of protons, not mass number, which explained why Mendeleev put tellurium before iodine.)

Question 10

Name this scientists that suggested that elements should fit together in groups of three called triads.

Answer 10

(Johann) Döbereiner

(The elements in a triad would have similar chemical properties, and the atomic weight of the middle element would be halfway between the other two eg. calcium, strontium and barium. This was the ‘Law of Triads’.)

Question 11

Name this scientist who arranged the elements in order of atomic weight, and found that properties seemed to repeat themselves every eight elements.

Answer 11

(John) Newlands.

(He tried to force elements to fit his ‘Law of Octaves’.)

Question 12

Name this scientist who is responsable for our current periodic table.

Answer 12

(Dmirti) Mendeleev

(Mendeleev, in his periodic table, listed separately in subgroups elements such as copper and silver, whose properties did not fit with those of the main groups.

In Mendeleev’s table, the first two horizontal periods contained seven elements, but the next two contained seventeen each.

He did not hesitate to put the elements iodine and tellurium out of the correct order of their atomic weights, because of their properties.

He left gaps in the table in order to make elements fit into proper groups.

He announced that the gaps represented undiscovered elements and choosing three gaps in particular, he described the properties the missing elements should have.

These elements (gallium, scandium and germanium) were soon discovered and were very close to Mendeleev’s predictions.)

Question 13

Give three difference between Mendeleev’s periodic table and our modern one.

Answer 13

Mendeleev

• Gaps left for undiscovered elements
• Group 0 elements missing
• Elements discovered since 1869 missing
• D-block elements in subgroups beside main group
• Elements in increasing atomic weight

Modern

• Gaps have been filled
• Group 0 elements filled
• Elements discovered since 1869 included
• D-block elements in subgroup in separate block
• Elements in increasing atomic number

Question 14

List the two elements that are liquids at room temperature.

Answer 14

Mercury and bromine.

Question 15

List the eleven elements that are gases at room temperature.

Answer 15

Noble gases, hydrogen, nitrogen, oxygen, chlorine, fluorine.

Question 16

Give three physical properties of alkali metals.

Answer 16

• They are soft metals
• They can be cut with a knife
• They have low densities: lithium, sodium and potassium each float in water.

Question 17

Give two chemical properties of alkali metals and give word equations to illustrate them.

Answer 17

• When they are freshly cut, they have a metallic shine, but this disappears rapidly due to reaction of the exposed metal surface with oxygen in the air.
• sodium + oxygen → sodium oxide*
• They react vigorously with water, forming a basic solution and hydrogen.
• sodium + water → sodium hydroxide + hydrogen*

Question 18

How are alkali metals stored, to prevent them from reacting with the oxygen and moisture in the air?

Answer 18

In oil.

Question 19

Does the reactivity of alkali metals increase going up or going down the group?

Answer 19

Reactivity increases going down. (More shells, screening effect, ect.)

Question 20

Give one physical property of alkali earth metals.

Answer 20

• They are harder than the corresponding alkali metals.
  *

Question 21

Give one chemical property of alkali earth metals and give a chemical equation for the reaction of one of them with water.

Answer 21

• They are less reactive than the corresponding alkali metals.

calcium + water → calcium hydroxide + hydrogen

Question 22

Does the reactivity of alkali earth metals increase going up or going down the group?

Answer 22

Reactivity increases going down. (More shells, screening effect, ect.)

Question 23

Give one physical property of halogens.

Answer 23

• They have low melting and boiling points.

Question 24

For the halogens; fluorine, chlorine, bromine and iodine, give their physical appearance at room temperature.

Answer 24

Fluorine and chlorine are yellow-green gases, bromine is a red liquid and iodine is a dark solid.

Question 25

Give two chemical property of halogens and give word equations to illustrate them.

Answer 25

• They react with hydrogen to form compounds which dissolve in water to form acidic solutions.
• hydrogen + chlorine → hydrogen chloride gas*
• hydrogen chloride gas + water → hydrochloric acid solution*
• They react vigorously with sodium (and other alkali metals), forming white salt.
• sodium + chlorine → sodium chloride*

Question 26

Does the reactivity of halogens increase going up or going down the group?

Answer 26

Reactivity increases going up.

Question 27

Give one physical property of noble gases.

Answer 27

• They are all gases at room temperature. The boiling point and density increase going down the group.

Question 28

Give one chemical property of noble gases.

Answer 28

• They are the least reactive of all elements.

Question 29

Comment on the densities, boiling and melting points and reactivity of s-block elements.

Answer 29

The elements in Groups I and II, that have lower densities, lower melting points and lower boiling points, and are more reactive than most other metals.

Question 30

Which groups of elements belong to the d-block?

Answer 30

Groups III, IV, V, VI, VII and 0 belong to the d-block.