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Atomic Structure – Notes

Approach of writing electronic configurations

1. First, write down the electronic configurations for the neutral atom.

2. Remember to add electrons to the 4s orbitals before the 3d orbitals.

3. Remove or add the relevant number of electrons to the electronic configuration of the neutral atom to get that of the cation or anion
respectively.

4. Remember to remove electrons from the orbitals with the highest energy.Thus remove electrons from the 4s orbitals before the 3d orbitals.

Some Definitions

Isoelectronic: species containing the same number of electrons

Isotopic: species containing the same number of protons

Isotonic: species containing the same number of neutrons

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Turning Effect of Forces

1. The moment of a force about a pivot is the product of the force F and the perpendicular distance d from the pivot to the line of action of the force.
Moment of a force = F x d

2. The SI unit for moment of a force is newton metre (N m).

3. Moment of a force is a vector. The direction of the moment of a force is either clockwise or anticlockwise about the pivot.

4. There are two conditions for an object in equilibrium:
(a) Net external force F = 0
(b) Net moment due to external forces = 0 (also known as the Principle of Moments)

5. The Principle of Moments states that when an object is in equilibrium, the sum of the clockwise moments equals the sum of the anticlockwise moments.

6. The centre of gravity of an object is the point at which its entire weight appears to act. The
centre of gravity of regular-shaped objects can be determined by geometrical symmetry. The centre of gravity of irregular-shaped objects can be determined by the plumb line experiment.

7. The stability of an object increases when the base area increases or when the centre of gravity is lowered.

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Condensation Polymerisation

1. In condensation polymerisation, small molecules such as water, are eliminated when monomers join together to form a polymer.

2. For condensation polymerisation to occur, each monomer must have two reactive groups. The polymer chain is formed by the removal of water molecules.
Example:
Dicarboxylic acid (two -COOH groups) + diamine (two -NH2 groups)
HOOC – X – COOH + NH2 – Y – NH2 polyamide + H2O
dicarboxylic acid diamine (e.g. nylon) water

3. There are two main groups of condensation polymers: polyamides and polyesters.

4. Nylon: a polyamide
(a) Nylon is made from two different monomers:
• Dicarboxylic acid (a molecule with two -COOH groups)
• Diamine (a molecule with two -NH2 groups)
(b) When the two monomers combine, the polymer, nylon, is formed and water molecules are eliminated.

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Turning Effect of Forces

1. The moment of a force about a pivot is the product of the force F and the perpendicular distance d from the pivot to the line of action of the force.
Moment of a force = F x d

2. The SI unit for moment of a force is newton metre (N m).

3. Moment of a force is a vector. The direction of the moment of a force is either clockwise or anticlockwise about the pivot.

4. There are two conditions for an object in equilibrium:
(a) Net external force F = 0
(b) Net moment due to external forces = 0 (also known as the Principle of Moments)

5. The Principle of Moments states that when an object is in equilibrium, the sum of the clockwise moments equals the sum of the anticlockwise moments.

6. The centre of gravity of an object is the point at which its entire weight appears to act. The
centre of gravity of regular-shaped objects can be determined by geometrical symmetry. The centre of gravity of irregular-shaped objects can be determined by the plumb line experiment.

7. The stability of an object increases when the base area increases or when the centre of gravity is lowered.

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O-Level Additional Mathematics Tuition Singapore

TRIGONOMETRY

1. GENERAL ANGLES

• General angles
• Basic angles

General angles

In a cartesian plane, for an angle A measured from the positive x-axis, A is a positive angle if it is measured in an anti-clockwise direction. A is a negative angle if it is measured in a clockwise direction.

Basic angles

The angle, a , which is the positive acute angle (an angle between 0° and 90°)made by the arm OP and the x-axis, is known as the basic angle, associated angle or the reference angle.

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O Level E Maths Tuition Singapore/Tuition O Level E Maths/Tutor

Percentages

1. A percentage is a fraction whose denominator is 100 and we use % to represent percent.

2. In general, y percent is defined as y parts per hundred.
Y% = Y/100

3. A percentage is converted to a fraction or decimal by dividing its value by 100.

4. Final percentage x Original value = New value

5. Increase/Decrease = percent increase/decrease x original value

6. % Profit = Profit/(CostPrice) x 100%
% Loss = Loss/(CostPrice) x 100%

7. Discount = Original Selling Price – Sale Price
Percentage Discount = (Discount/Market Price) x 100%

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A-Level Mathematics Tuition Singapore/JC Maths/H2 Math Tuition and Tutor

Hi A-Level/H2 Math Students

Poisson Distribution

A Poisson distribution is another special case of a discrete distribution.

Characteristics / Assumptions of a Poisson Distribution:

 The outcomes occur singly and randomly.
 Whether an event occurs in a particular point in time or space is independent of what happens elsewhere.
 At all points in time (or space), the probability of one event occurring within a small fixed interval of time (or space) is the same.
 There is no (or negligible) chance of 2 events occurring simultaneously at precisely the same point in time (or space).
 The distribution is commonly used to model rare events (discrete).

In a Poisson distribution, the random variable is a count of the number of occurrences of a random event in a given region of time and space when a mean number of occurrences, , is given for a particular interval of time and space.

Real-Life examples in which the Poisson distribution is a good model: The number of
 particles emitted in a minute by a radioactive substance.
 typographical errors in a randomly chosen page of a book.
 accidents in a factory in a randomly chosen day.

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A-Level Economics Tuition Singapore/H2/H1 Economics Tuition

Topic 2.2 Macroeconomic Aims, Problems/Issues, Consequences and Policies

Syllabus
Monetary Policy and its Effectiveness

Outcome
Explain monetary policy in a broader international context where interest rates and exchange rates are alternative instruments
Explain the external and domestic effects of changes in exchange rates and interest rates
Evaluate the effectiveness of monetary policy in achieving macroeconomic aims.

Macroeconomics Lecture 16 : Monetary Policy 2

16.1 Limitations of monetary policy

• Confidence (or lack of)

• If interest rate is high enough, borrower and spending will be deterred. But in times of an economic boom, businesses and households are very optimistic and hence high interest rate may not deter borrowing and spending. Instead, high interest rate may cause other macroeconomic problems (e.g. rapid appreciation of the currency) and lead to conflict with other objectives of government policy.

• On the other hand, low interest rates are not likely to be very effective as a stimulant when the economy is depressed. Borrowing and spending by firms are not likely to be encouraged when new investment offers little or no prospect of reasonable profits. When there is high unemployment, lower interest charges are not likely to lead to any significant increase in hire purchase borrowing in the markets for consumer goods.

• Liquidity Trap

When levels of interest rates are already very low such that any surplus money is simply channeled to idle balances. Hence interest rates also remain unchanged. With interest rates being stagnant despite the rise in money supply, investment, consumption and hence AD would also not increase.

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A-Level Physics Tuition Singapore/H2 Physics Tuition/JC Physics Tutor

Hi A-level/H2/JC Physics Tuition students

Mastering Qualitative Questions

Chapter 19 Lasers and Semiconductors Part 2

6. Explain what is meant by population inversion and why it is necessary to produce amplification of light. [3]

7. Give two reasons why a 1 W laser may appear brighter than a 10 W filament lamp. [2]

8. State two differences between p-type semiconductors and n-type semiconductors. [2]

9. A p-n diode is connected to an alternating supply. Explain with suitable diagrams how it works.

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A-Level Biology Tuition Singapore/H2 Biology Tuition/JC Biology Tutor

TOPIC 1: CELLULAR FUNCTIONS – Part 18

LEARNING OUTCOME

(r)Explain how meiosis and random fertilisation can lead to variation

KEY WORDS

• Chiasmata formation and crossing over during prophase I
• Independent assortment of chromosomes at metaphase I
• Independent assortment of chromatids at metaphase II
• Each gamete has a unique combination of genes

ESSAY ANSWER

Meiosis introduces genetic variation through producing new combination of alleles in gametes.

Chiasmata formation and crossing over during prophase I During prophase I, synapsis occurs and homologous chromosomes pair up to form bivalents.

As a result of chiasmata formation, crossing over between non-sister
chromatids of homologous chromosomes where breakage and rejoining
between the 2 non-sister chromatids resulting in the exchange of alleles. This leads to recombinant chromatids being formed. This results in new combinations of alleles on chromosomes of the gametes, causing genetic variation.

Independent assortment of homologous chromosomes at metaphase I
During metaphase I, each pair of homologous chromosomes aligns in 2 rows at the equator.

The arrangement of each pair of homologous chromosome is completely
independent of the other pairs of homologous chromosomes.

Subsequent separation of the homologous chromosomes during anaphase I will produce different combinations of chromosomes in the daughter cells at the end of meiosis I.

Independent assortment of chromatids at metaphase II
During metaphase II, there is independent assortment of non-identical sister chromatids. Subsequent separation of chromatids during anaphase II will further contribute to different combinations of chromosomes in the four daughter cells produced at the end of meiosis II.

Random fertilisation of an ovum by a sperm
Two gametes fuse to form a zygote.
Each gamete has a unique combination of genes.
Any male gamete can fertilise any female gamete, thus making each zygote
unique which contributes to genetic variation

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A Level GP/General Paper Tuition Singapore

Is Violence Against Women a Priority in Political Agendas?

The reality shows that it should be, according to United Nations, 7 out of 10 women experience physical or sexual violence in their lifetime – the majority by someone they know. Acts of violence against women aged between 15 to 44, cause more deaths and disabilities than cancer, malaria, traffic accidents and war combined. Despite its magnitude, this issue occupies a marginal space in public agendas around the world and in many places it continues to be considered a domestic – private – problem. Politicians have the responsibility to take measures that contributive to stop this global threat and citizens have the responsibility to reject it.

This is a problem that affects not only poor and underdeveloped countries, but also the richest nations in the world. In the United States, during the last decade 11,766 women were killed as a result of domestic violence – almost double of U.S. troops killed in Afghanistan and Iraq in the same period of time. Additionally, 1 in 4 women have reported intimate partner violence. In Europe, 25% of citizens know a woman within their circle of friends and family who has been a victim of domestic violence – in the case of Sweden, Finland and the UK this percentage is around 40%.

In Latin America, according to the Organization of American States, each day 460 persons are victims of rape – probably mostly women. Colombia has a daily average of 245 women who are victims of some kind of violence; in the last decade almost 400 thousand suffered some form of abuse. In Mexico, 5 out of 10 women aged 15 or older have suffered violence from their partner. Only in 2009, in the middle of the drug war, UN Women denounced the occurrence of 1.859 femicides in this country. In Brazil, 6 out of 10 citizens know a woman who has been a victim of domestic violence.

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Atomic Structure – Notes

2.1 Isotopes

(a) Isotopes are atoms of the same element which contain the same number of protons and electrons but different number of neutrons.

(b) Isotopes have the same number of electrons and therefore the same chemical properties.

(c) However, since they have different number of neutrons, they will have different masses and hence different physical properties such as melting point, density etc.

(d) They are found in all naturally occurring elements except F, Na, Al, P, Mn, Co, As.

Why do isotopes react similarly?
This is because in a chemical reaction, it is the electrons that are transferred between different atoms; atoms either gain, lose or share electrons

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Mass,Weight and Density

KEY TERMS AND CONCEPTS

1. The mass of an object is a measure of the amount of matter in the object. The SI unit of mass is kilogram (kg).

2. Inertia is the resistance of an object to a change in its state of motion or rest. The larger the mass, the greater is its inertia.

3. The attractive force between any two masses is known as gravitational force.

4. The gravitational field is a region in which a mass experiences
a gravitational force.

5. Gravitational field strength g is the gravitational force acting per unit mass. The unit for g is m s-2 or N kg-1. The gravitational field strength is also known as the acceleration due to gravity.
F = mg

6. Gravitational field strength g is usually taken to be a constant at 10 N kg-’ on the surface of the Earth. It varies slightly according to the location.

7. Weight is the gravitational force acting on an object. It is equal to the product of mass and gravitational field strength. The SI unit for weight is the newton (N).
W = mg

8. Density p of an object is its mass per unit volume.

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Addition Polymerisation

1. Addition polymerisation occurs when monomer units join together without losing any molecules or atoms.

2. Poly(ethene)
(a) At high pressure and temperature and in the presence of a catalyst, ethene undergoes addition polymerisation to form a long-chain molecule, poly(ethene).

(b) Ethene is called the monomer and poly(ethene) is called the polymer.

(c) Uses of poly(ethene)
Poly(ethene) is widely used as plastic bags, plastic bottles and cling films for wrapping food.

Condensation Polymerisation

1. In condensation polymerisation, small molecules such as water, are eliminated when monomers join together to form a polymer.

2. For condensation polymerisation to occur, each monomer must have two reactive groups. The polymer chain is formed by the removal of water molecules.

3. There are two main groups of condensation polymers: polyamides and polyesters.

4. Nylon: a polyamide
(a) Nylon is made from two different monomers:
• Dicarboxylic acid (a molecule with two -COOH groups)
• Diamine (a molecule with two -NH2 groups)
(b) When the two monomers combine, the polymer, nylon, is formed and water molecules are eliminated.

If you need help in the Organic Chemistry, please contact Angie @96790479 or Mr Ong 98639633

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O-Level Singapore/O-Level/Pure Physics Tuition/Physics Tutor

Mass,Weight and Density

KEY TERMS AND CONCEPTS

1. The mass of an object is a measure of the amount of matter in the object. The SI unit of mass is kilogram (kg).

2. Inertia is the resistance of an object to a change in its state of motion or rest. The larger the mass, the greater is its inertia.

3. The attractive force between any two masses is known as gravitational force.

4. The gravitational field is a region in which a mass experiences
a gravitational force.

5. Gravitational field strength g is the gravitational force acting per unit mass. The unit for g is m s-2 or N kg-1. The gravitational field strength is also known as the acceleration due to gravity.
F = mg

6. Gravitational field strength g is usually taken to be a constant at 10 N kg-‘ on the surface of the Earth. It varies slightly according to the location.

7. Weight is the gravitational force acting on an object. It is equal to the product of mass and gravitational field strength. The SI unit for weight is the newton (N).
W = mg

8. Density p of an object is its mass per unit volume.

If you need help in the above topics, please contact Angie @96790479 or Mr Ong @98639633

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