6: The Periodic Table

Question 1

What are the characteristics of groups in the periodic table?

Answer 1

Groups in the periodic table are columns. Elements of the same group have similar chemical properties but differ in reactivity. Transition metals are between Group II and Group III.

Question 2

What are the characteristics of periods in the periodic table?

Answer 2

Periods in the periodic table are rows. From left to right across the period, elements are arranged from metals, semi-metals, to non-metals. Transition metals appear from period 4.

Question 3

What is the relationship between the group number and the electronic arrangement of an atom?

Answer 3

The group number of an element indicates the number of electrons in the outermost electron shell in the atom of an element.

Question 4

What is the relationship between the period number and the electronic arrangement of an atom?

Answer 4

The period number of an element indicates the number of occupied electron shells in an atom of the element.

Question 5

What is the name of elements in group I and why?

Answer 5

The elements in Group I are metals that react with water to form alkalis. Hence they are called alkali metals.

Question 6

What are the properties of alkali metals in aspects of hardness, density, and melting / boiling points?

Answer 6

Alkali metals are softer than other metals. They have low densities and low melting / boiling points relative to other metals. Their melting points, boiling points, and hardness decrease down the group while their densities increase down the group (exception: potassium)

Question 7

What are the typical chemical reactions by alkali metals?

Answer 7

1. Alkali metls react with oxygen to form oxides.
2. Alkali metals react with water to form hydroxides and hydrogen gas.
3. Alkali metals react with chlorine to form chlorides.

Question 8

What is the definition of tarnish?

Answer 8

Tarnishing refers to the process in which metals lose their lustre as a result of exposure to air or moisture.

Question 9

How can we show that the product of the reaction of alkali metals and water is alkaline?

Answer 9

The metal hydroxide turns universal indicator solution / pH paper blue. It also turns red litmus paper to blue, showing that it is alkaline.

Question 10

Describe 3 observations that can be made during potassium’s reaction with water.

Answer 10

1. It melts to form a silvery ball
2. It fizzes furiously on the water surface / smoke is produced
3. There is a lilac flame (hydrogen is ignited, and the high temerature excites the potassium ions to burn and give out a lilac flame.)

Question 11

How can we produce a flame when reacting sodium with water and why?

Answer 11

Put a piece of filter paper below the sodium metal. This is because originally, the energy given out in the reaction is quickly absorbed by the water nearby, lowering the temperature. Now, since the amount of water in contact with sodium decreases, the energy given out in the reaction is absorbed by the water at a lower rate, meaning that there is enough energy left for the sodium to burn with a golden yellow flame.

Question 12

How does the reactivity of alkali metals change down the group and why?

Answer 12

The reactivity of alkali metals increases down the group. This is because down the group, the size of the atom increases, meaning that the attraction force between the nucleus and the electron decreases. Therefore, the metals are more likely to lose the outermost electron by reacting with other substances.

Question 13

What is the name of elements in Group II and why?

Answer 13

The elements in Group II are metals found on the Earth that react with water to form alkaline substances. Hence they are called alkaline earth metals.

Question 14

What are the properties of alkaline earth metals in aspects of hardness, density, and melting/ boiling points?

Answer 14

Alkaline earth metals are hard. Their melting points and boiling points are higher than alkali metals, but still lower than most transition metals. Generally, their melting and boiling points decrease down the group. Their densities are all higher than 1, meaning that they sink in water, but they are not as dense as most other metals.

Question 15

What are the typical chemical reactions by alkaline earth metals?

Answer 15

1. They burn in oxygen to form oxides.
2. The metals from magnesium to barium reacts with water to form hydroxides and hydrogen gas. The hydroxides of alkaline earth metals are less soluble in wster than those of alkali metals.
3. They react with dilute hydrochloric acid to form chlorides and hydrogen gas.
4. They react with chlorine to form chlorides.

Question 16

Describe one observation of alkaline earth metals when heating them in air, thus suggest one usage of magnesium.

Answer 16

Alkaline earth metals burn brightly when heated in air. Hence magnesium is used in fireworks to produce brilliant white sparks.

Question 17

How does the reactivity of alkaline earth metals change down the group?

Answer 17

The reactivity of alkaline earth metals increases going down the group.

Question 18

What is the name of elements in group VII and why?

Answer 18

The elements in group VII are non-metals that react with most metals to form salts. Hence they are called halogens.

Question 19

What are the general physical properties and physical states of halogens?

Answer 19

1. They are toxic and have an irritating smell.
2. They occur in different states at rtp. Some examples are chlorine being a greenish yellow gas, bromine being a volatile reddish brown liquid, and iodine being a shiny black solid that sublimes to a purple vapour.
3. They have low melting and boiling points
4. They are poor conductors of heat and electricity.

Question 20

What are the trends in physical properties of halogens?

Answer 20

1. Their colours are darker down the group.
2. Their melting and boiling points increase down the group, changing from gases to liquids to solids at rtp.
3. They are less volatile down the group.

Question 21

How does the reactivity of halogens change down the group?

Answer 21

The reactivity of halogens decreases down the group.

Question 22

What is the name of elements in Group 0 and why?

Answer 22

The elements in Group 0 are non-metal gases that rarely react with other substances, or chemically inert. Hence they are called the noble gases.

Question 23

What are the general physical properties and trends in melting / boiling points of noble gases?

Answer 23

1. Noble gases are colourless.
2. They have very low melting and boiling points; they are all gases at rtp.
3. They have very low densities.
4. They are poor conductors of heat and electricity.
5. Their melting and boiling points increase down the group.

Question 24

Why are the noble gases chemically inert?

Answer 24

Each atom in Group 0 has a fully occupied outermost electron shell. An outermost shell of 8 electrons (exception: 2 for helium) is extremely stable, since it satisfies the octet rule (or duplet rule for helium). Thus, each of these atoms has little tendency to combine with other atoms to modify the electronis arrangement. As a result, they are very unreactive.

Question 25

List two usages of helium and explain why.

Answer 25

1. Helium is used to fill airships. Previously, airships are filled by hydrogen, which is flammable. After the Hindenburg disaster, airships are filled with helium instead since it is much lighter than air and non-flammable.
2. Helium is used to fill balloons.

Question 26

List two usages of argon and explain why.

Answer 26

1. Argon is denser than air. Therefore, it is added to the space above wine in wine barrels to stop oxygen in the air from reacting with the wine.
2. It is used to fill tungsten light bulbs because it does not react with tungsten even at high temperatures.

Question 27

List one usage of neon and explain why.

Answer 27

Neon produces a distinctive red-orange light when electricity is passed through it. This property makes it useful for making advertising signs.

Question 28

What is the definition of monoatomic ion?

Answer 28

When an atom loses or gains one or more electrons, a monoatomic ion is formed.

Question 29

What is an ion and what are the types of ions? How are they formed?

Answer 29

An ion is a charged counterpart of an atom. A positive ion, or cation, is formed when atoms lose electrons and the overall charge becomes positive. Meanwhile, a negative ion, or anion, is formed when atoms gain electrons and the overall charge becomes negative.

Question 30

What is the relationship between the elements and the number of electrons they lose to form ions?

Answer 30

Metals form cations with overall charge equal to the group number in the periodic table. Non-metals form anions with overall charge equal to the difference between 8 and their group number. Hydrogen is the only non-metal that forms cations.