Grade 9 chemistry

Question 1

Alkali metals

Answer 1

Generally silver coloured, all of them are shiny and reactive. Always found bound with other elements in nature. React violently in water.

Question 2

Alkali safety

Answer 2

Pure Alkalis are stored in mineral oil so they do not react.

Question 3

Alkaline earth metals

Answer 3

Very similar to alkalis but alkaline earth metals do not have as strong reactions.

Question 4

Halogens

Answer 4

Include elements in all three states of matter. All are highly reactive and many are found in living organisms. In pure form, they can be harmful or even lethal.

Question 5

Chlorine

Answer 5

Its high reactivity = excellent disinfectant.
Kills off bacteria and other disease causing organisms.
It’s added to drinking water to purify it and swimming pools to kill bacteria.

Question 6

Noble gases (inert gases)

Answer 6

They are called noble because they don’t react with other elements.
All noble gases are: odourless, colourless, tasteless, and aren’t flammable.

Question 7

Non metals

Answer 7

Non metals are found over several groups of the periodic table. Halogens/noble gases= non metals.
Remaining non metals are found in groups 14, 15, 16.

Question 8

Metalloids

Answer 8

A cluster of elements found across several groups.
Difficult to classify.
Lie between the metals (g1-12) and the non metals (g14-18).
Metalloids’ properties make them useful in producing glass and semiconductors.

Question 9

Carbon

Answer 9

Carbon can be a soft, dull, grey powdery solid. It can also be compressed and heated to become diamond which is the hardest substance on earth.

Question 10

Reading the periodic table

Answer 10

Elements are arranged by atomic number

Question 11

Number of neutrons

Answer 11

Formula: # of neutrons=atomic weight - atomic number

E.g. Oxygen: 8 = 16 - 8

Question 12

Rows

Answer 12

Rows go by the number of electron shells, the further you go down in the periodic tables the more electron shells the elements have.

Question 13

What makes elements react?

Answer 13

Atoms react with other atoms because of the way the electrons in their shells interact with the electrons in the outer shell of other atoms. Protons are held more tightly by the atom. Atoms either give up electrons from or add electrons to their outer shell.

Question 14

Rule eight

Answer 14

Most electron shells can hold a maximum of eight electrons. The exception is the first shell which can hold only two.

Question 15

Metalloids

Answer 15

A cluster of elements found across several groups.
Difficult to classify.
Lie between the metals (g1-12) and the non metals (g14-18).
Metalloids’ properties make them useful in producing glass and semiconductors.

Question 16

Carbon

Answer 16

Carbon can be a soft, dull, grey powdery solid. It can also be compressed and heated to become diamond which is the hardest substance on earth.

Question 17

Reading the periodic table

Answer 17

Elements are arranged by atomic number

Question 18

Number of neutrons

Answer 18

Formula: # of neutrons=atomic weight - atomic number

E.g. Oxygen: 8 = 16 - 8

Question 19

Rows

Answer 19

Rows go by the number of electron shells, the further you go down in the periodic tables the more electron shells the elements have.

Question 20

What makes elements react?

Answer 20

Atoms react with other atoms because of the way the electrons in their shells interact with the electrons in the outer shell of other atoms. Protons are held more tightly by the atom. Atoms either give up electrons from or add electrons to their outer shell.

Question 21

Rule eight

Answer 21

Most electron shells can hold a maximum of eight electrons. The exception is the first shell which can hold only two.

Question 22

Compounds

Answer 22

A compound is a pure substance consisting of two or more different elements chemically bonded together.

Question 23

Ionic compound

Answer 23

A non-reactive compound consisting of elements that are highly reactive and potentially dangerous but when they are chemically bonded together they lose their high reactivity.

Question 24

Ions

Answer 24

Ions are atoms in which the total number of electrons is not equal to the total number of protons.

Question 25

Anions

Answer 25

When an atom gains electrons gain electrons and form anions. Since the number of protons has not changed, the charge in the nucleus remains the same, so the atom now has an overall negative charge. This process can be shown using a Bohr- Rutherford diagram.

Question 26

Cations

Answer 26

When an atom loses electrons, it loses negative charges. Since the number of protons has not changed, the charge in the nucleus remains the same. So the atom now has an overall positive charge.

Question 27

Notation

Answer 27

Chemists use specific notation to show the type of ions that forms. A superscript number is used to indicate the number of electrons transferred, and a “+” or “-“ is used to indicate the overall charge on the ion.
If the number of electrons transferred is one then the 1 is usually left out of the notation.

Question 28

Ionic bonds

Answer 28

Because of their charge imbalance, ions behave s if they’re sticky. Opposite charges attract.
For ionic compounds to form, one atom must give up its electrons, and another accepts the electrons. In general, atoms gain or lose electrons to have the same number of valence electrons as their nearest noble gas.

Question 29

Ionic bonds between a metal and a non metal

Answer 29

Since metals tend to lose electrons and non metals gain electrons, ionic bonds tend to form

Question 30

Properties of ionic compounds (4)

Answer 30

• Solid at room temperature
• Brittle
• High melting point
• High boiling point