4.9.3 The Properties of Substances (Structured Questions)

Posted on December 10, 2014 by user

Question 1:
Diagram 1.1 and Diagram 1.2 show an experiment to study the electrical conductivity of lead(II) bromide.

(a)(i) Based on Diagram 1.2, what is your observation on the needle of the ammeter? [1 mark]

(ii) What is the reading of the ammeter in Diagram 1.2? [1 mark]

(b) State the variables I this experiment.
(i) Manipulated variable:
(ii) Responding variable:
[2 marks]

(c) State one inference for this experiment. [1 mark]

(d) Lead(II) bromide is an ionic compound.
State the operational definition for an ionic compound. [1 mark]

Answer:
(a)(i) The pointer of the ammeter is deflected.

(a)(ii) 0.4 A

(b)(i) The state of the lead(II) bromide or chemical compound

(b)(ii) The ammeter reading

(c) Lead(II) bromide in the molten state can conduct electricity.

(d) An ionic compound in the molten state will cause the pointer of the ammeter connected in a closed circuit to be deflected.

4.9.2 Proton Number and Nucleon Number (Structured Questions)

Posted on December 6, 2014 by user

Question 1:
Diagram 1.1 shows the structure of an atom.

(a) P and Q are subatomic particles.
Name P and Q. [2 marks]

(b) What is the charge of P? [1 mark]

(c) What is the nucleon number of this atom? [1 mark]

(d) Diagram 1.2 shows the structure of three atoms.
(i) Which atoms are isotopes? [1 mark]
Mark (\/) your answers in the box provided in Diagram 1.2.

(ii) Based on Diagram 1.2, complete the sentence below.
Isotopes are atoms of an element which have different number of nucleons but the same number of ______________. [1 mark]

Answer:
(a)
P: Electron
Q: Neutron

(b) Negative

(c) 13

(d)(i)

(d)(ii) Protons

4.9.1 Analysing Changes in the States of Matter (Structured Questions)

Posted on December 4, 2014 by user

Question 1:
Diagram below shows the changes in the state of matter of a substance.

Based on the Diagram,
(a) name the processes R, S and T using the following information. [3 marks]

(b) What happens to the kinetic energy of the particles in the substance during process R? [1 mark]

(c) What happens to the movement of the particles in the substance during process S? [1 mark]

(d) Draw the particle arrangement in X in the box provided below. [1 mark]

Answer:
(a)
R: Melting
S: Freezing
T: Condensation

(b) During melting, the kinetic energy of the particles increases.

(c) During freezing, the particles slowing down in their motion and form a pattern, becoming a solid.

(d)

4.5.2 Classification of Substances

Posted on October 14, 2014 by user

Classification of Substances

1. Types of substances:

2. The physical properties of substances depend on
(a) types of particles they contain,
(b) arrangement of the particles,
(c) forces of attraction between the particles.

Substances made of atoms (or Atomic substances)

1. Atomic substances are substances that consist of only atoms.

2. The atoms in atomic substances are arranged closely together in a fixed pattern and only can vibrate in their fixed positions.

3. Atomic substances have high melting and boiling points owing to strong metallic bond.

4. They are able to conduct electricity owing to presence of free electrons.

5. All metals are atomic substances such as iron, aluminium and calcium.

Substances made of molecules (or Molecular substances)

1. Molecular substances are made up of molecules which have two or more atoms of the same type or different types.

2. For example, two oxygen atoms combine to form one oxygen molecule. On the other hand, one nitrogen atom combines with three hydrogen atoms to form one ammonia molecule.

3. Examples of other molecular substances are hydrogen, nitrogen, carbon dioxide, sulphur dioxide, chlorine gas and iodine.

4. Molecules are held together by weak intermolecular force (or van der Waals forces) and have low melting and boiling points.

5. Molecules are made up of non-metal atoms which are poor conductors of electricity because there are no free electrons or ions in any state to carry electric charge.

Substances made of ions (or Ionic substances)

1. Substances that made up of ions are called the ionic compounds.

2. They are compounds of metal bonded with non-metal.

3. Examples of ionic compounds are sodium chloride, copper (II) sulphate, sodium hydroxide and lead (II) oxide.

4. Positive and negative ions are held together by strong ionic bonds. This strong bonding force makes ionic compounds has high melting and boiling points.

Arrangement of ions in a compound

5. All ionic compounds are crystalline solids at room temperature.

6. The solid crystals do not conduct electricity because the ions are not free to move to carry an electric current.

7. However, if the ionic compound is melted or dissolved in water, the liquid will now conduct electricity, as the ion particles are now free.

4.5 Properties of Substances Based on their Particle Content

Posted on October 10, 2014 by user

4.5 Properties of Substances Based on their Particle Content

1. Matter is anything that occupies space and has mass.

2. Matter can be divided into elements and compounds.

4.5.1 Atoms, Molecules and Ions

1. Substances are made of tiny particles called atoms, molecules and ions.

2. Atoms are the tiniest particles in an element.

3. A molecule consists of two or more atoms of the same type or of different types that are chemically combined together.

4. Ions are particles which carry positive or negative charges.

4.4 Classification of Elements in the Period Table

Posted on October 2, 2014 by user

4.4 Classification of Elements in the Period Table

4.4.1 The classification of Elements

1. In modern periodic table, the elements are arranged in ascending order of proton number.

Group

1. The vertical columns of the periodic table is called group.

2. There are 18 groups in the periodic table.

3. Elements in the same group have similar chemical properties.

Example:

Elements in Group 1 react violently with water to produce metal hydroxide, hydrogen and heat.

4. Elements in groups 1 and 2 are very reactive metals (except hydrogen).

5. Elements between groups 2 and 13 are called the transition elements.

6. Transition elements are metallic elements. Most of them are hard and shiny. All transition elements are good conductors of electricity.

7. The elements in group 17 are non-metals called halogens.

8. Group 18 consists of noble (inert) gases, which are inactive gases.

Period

1. The horizontal rows is called the period.

2. There are 7 periods in period table.

3. The first period has 2 elements only.

4. The second and third period consist of 8 elements, are called the short period.

5. The forth and the fifth period consist of 18 elements, are called the long period.

6. The sixth and the seventh period have 32 elements.

7. The chemical and physical properties of the elements are gradually changed when crossing periods.

4.4.2 Metals, Semi-metals and Non-metals

1. The elements in the Periodic Table are divided into metals, semi-metals and non-metals.

2. Most elements in group 1, 2, 13 and transition elements are metals.

3. Most non-metal elements are located in groups 16, 17 and 18.

4. Seven elements between metals and non-metals are semi-metals. Semi-metals possess certain properties of metals and non-metals.

5. When moving across a period from left to right, the properties of metal change gradually to those of semi-metal and finally non-metal.

6. The metals become increasingly active as they move down the table.

4.4.3 Importance of the Periodic Table

1. The periodic table enables us to study the elements in an orderly and systematic way.

2. It helps us to know the properties of elements that fall into a particular group.

3. It enables us to predict the properties, reactions and uses of the elements.

4.3.2 Isotopes

Posted on September 28, 2014 by user

4.3.2 Isotopes

1. Isotopes are atoms of certain elements which have the same number of protons but different number of neutrons in the nucleus of the atoms.

2. Isotopes of the same element have same chemical properties. For example, both carbon-12 and carbon-13 burn in oxygen to form carbon dioxide.

3. Physical properties of isotopes are different. For example, carbon-14 isotope has a melting point, boiling point and density that are higher than those of carbon-12 and carbon-13.

Examples of isotopes

4.3 Proton Number and Nucleon Number in Atoms of Elements

Posted on September 20, 2014 by user

4.3 Proton Number and Nucleon Number in Atoms of Elements

4.3.1 Proton Number and Nucleon Number

1. The proton number represents the number of proton found in nucleus of an atom. Sometime, it is also known as the atomic number.

2. Nucleons are the subatomic particles inside the nucleus of an atom,

Nucleon = protons and neutrons

3. Nucleon number represents the number of nucleons in an atom.

Nucleon Number = Number of protons + Number of neutrons

Example:

4. In a neutral atom contains an equal number of protons and electrons.

5. Atoms of certain elements can be represented by the following symbol:

Number of protons = 8

Number of electrons = 8

Number of neutrons = 16 – 8 = 8

6. Table below shows the proton number and nucleon number for some elements.

Atom	Proton Number	Nucleon Number	Amount of Proton	Amount of electron	Amount of Neutron
Helium	2	4	2	2	2
Oxygen	8	16	8	8	8
Sodium	11	23	11	11	12
Chlorine	17	35	17	17	18

Relationship between the number of subatomic particles, proton number and nucleon number

4.2 Structure of Atoms

Posted on September 16, 2014 by user

4.2 Structure of Atoms

Atoms

1. All matter consists of tiny units called atoms.

2. Atom is a basic unit of all matter.

4.2.1 Subatomic Particles

1. An atom is made up of particles that are even smaller called subatomic particles.

There are three types of subatomic particles, which are
(a) Protons
(b) Neutrons
(c) Electrons

Subatomic particles in an atom

4.2.2 Comparison between Subatomic Particles

1. Atoms of any element are neutral because the number of protons and the number of electrons in an atom are the same.

2. In a neutral atom, the number of protons is the same as the number of electrons.

4.1.c Changes of State of Matter and Energy

Posted on September 12, 2014 by user

Change in Heat and Kinetic Energy of Particles

1. The change in temperature will influences the kinetic energy or the speed of the motion of the particles.

2. When a substance is heated, the kinetic energy of the particles in the substance increases. This causes the particles to move or vibrate faster.

3. Likewise, when a substance is cooled, the kinetic energy of the particles in the substance decreases. This causes the particles to move or vibrate slower.

4. The kinetic energy of the particles in a substance is directly proportional to the temperature of the substance.

Inter-conversion between States of Matter

Melting	Definition Melting is the process where a solid changes to its liquid state at a certain temperature (called the melting point) and pressure when it is heated. Notes When a solid is heated, the particles obtain energy and vibrate at a faster rate. As the temperature increases, the vibration of the particles increases until they reach the melting point where the particles obtain enough energy to overcome the forces that hold them in their fixed positions.The solid then changes into a liquid. During melting, the temperature remains constant. This is because the heat energy is taken in by the particles to overcome forces between them instead of being used to raise the temperature. The freezing and melting points of a pure substance are the same.
Freezing	Definition Freezing is the process where a liquid changes to its solid state at a certain temperature (called freezing point) and pressure when it is cooled. Notes When a liquid is cooled, the temperature drops as heat energy is released to the surroundings. As heat energy is released, the kinetic energy of the particles in the liquid decreases, causing a slower movement of particles. The particles lose their energy and are pulled closer by the strong forces between the particles. As the temperature keep on dropping until it reach the freezing point, the liquid start changing into solid. The temperature stays constant while the liquid freezes because heat energy is released when the particles slow down to take up fixed and orderly positions in the solid.
Vaporization (Evaporation)	Definition Vaporization, also called evaporation is the process whereby atoms or molecules in a liquid state gain sufficient energy to enter the gaseous state. Boiling is the rapid vaporization of a liquid at a certain temperature (the boiling point) and pressure when heat is applied to it. Notes Evaporation Evaporation occurs below the boiling point of the liquid. The particles escape from the surface of the liquid to form gas. Evaporation differs from boiling in that it only takes place at the surface of the liquid and it is very slow. On the other hand, boiling takes place throughout the liquid and is very fast. Factors influencing rate of evaporation Humidity of the air. Temperature of the substance. Flow rate of air. Inter-molecular forces. The stronger the forces keeping the molecules together in the liquid or solid state the more energy that must be input in order to evaporate them. If conditions allow the formation of vapour bubbles within a liquid, the vaporization process is called boiling. Boiling When a liquid is heated, the particles gain energy and move faster. As heat energy is keep on supplying to the liquid, the particles will eventually obtain enough energy to completely break the forces in between molecule. The liquid then changes into a gas and particles are now able to move freely and are far apart. The temperature at which this happens is called the boiling point. The temperature remains constant during boiling because heat energy that is absorbed by the particles is used to break the forces holding them together.
condensation	Definition Condensation is the process by which a gas or vapor changes to liquid state at certain temperature and pressure when it is cooled. Notes When a gas is cooled, the particles lose kinetic energy. As a result they move slower and this will cause the forces between them grow stronger. At this point, the gas changes into liquid. During condensation, heat is given out to the surroundings. Condensation can occur at or below the boiling point of the substance
sublimation	Definition Sublimation is a process of conversion of a substance from the solid to the vapour state without its becoming liquid. Notes Some solids change directly into gas without becoming a liquid. This process is called sublimation. When heated, the particles of the solid gain enough energy to break the forces between them and move freely as a gas. When cooled, the gas changes straight back to solid. Examples of substances which sublime are solid carbon dioxide (dry ice), ammonium chloride and iodine.

Interesting Video:

Inter-conversion Between the 3 States of Matter