chemistry stpm chapter 1 by study smart

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STUDYSMART CHEMISTRY FORM 6

CHAPTER 1 : MATTER

1.1 Fundamental Particles of Atoms 1.2 Relative atomic masses and Relative molecular masses 1.3 Mass spectrometry 1.4 Mole Concept and Avogadro Constant 1.1 FUNDAMENTAL PARTICLES OF ATOMS

Particles in nucleus are called nucleons which are made up of proton and neutrons

Nucleus is surrounded by a cloud of electron

Effect of Electric Field and Magnetic Fields on Subatomic Particles

From the above diagram, electron deflected to positive plate because electron is negatively charged. Therefore it will deflect toward opposite charge plate (positive charge)

Proton deflected to negative plate because proton is positively charged. Therefore it will deflect toward opposite charge plate (negative charge)

Neutron does not deflect to positive or negative plate because neutron is neutral subatomic particles.

FUNDAMENTAL PARTICLES

@

SUBATOMIC PARTICLES

Electron

Proton Neutron

ELECTRIC FIELD

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The angle of deflection of electron, β is higher than deflection angle of proton, α. This is because, electron is far more lighter than proton making slightly bigger angle of deflection than proton

Proton Number and Nucleon Number

Proton number of an element is the number of proton in its atom

Nucleon number of an element is the total number of proton and neutrons in its atom

Charged Species

Atoms and Molecules does not contain charged, but ions contain charge example, Al3+. Therefore all ions are known as charged particles

Ions contain two charged, Positive Charge (Cations), an d Negative Charge (Anions)

Positive charged ions formed when an atom loses electron to achieve stable electron arrangements.

Negative charged ions formed when an atom accept electron to achieve stable electron arrangements.

The number stated in charge indicate the number of electron released or accepted

Examples of Cations Aluminium - Proton Number is 13 - Electron arrangement is 2.8.3 - In order to achieve stable electron arrangement, Aluminium atom loses 3 electron and becomes Al3+ ion

MAGNETIC FIELD

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Examples of Anions Chlorine - Proton Number is 17 - Electron arrangement is 2.8.7 - In order to achieve stable electron arrangement, Chlorine atom accept 1 electron and becomes Cl- ion

Some species of ions contain more than one atom in it. This is called polyatomic ions

Examples of polyatomic ions are OH—(hydroxide ion) NO3

- (nitrate ion) CO3

2- (carbonate ion) NH4

+ (ammonium ion) MnO4

2- (manganate ion) SO4

2- (sulphate ion) Isotopes

Isotopes are elements which have same number of proton but different number on nucleon and neutron

Example : isotopes of Hydrogen

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1 H 2

1 H 3

1 H

Hydrogen Deuterium Tritium

Isotopes have different physical properties such as melting point, boiling point, density and rate of diffusion

Some isotopes are unstable. These unstable isotopes are known as radioactive isotopes (Radioisotopes).

These isotopes disintegrate spontaneously by emitting alpha-particles ( 4

2 He2+ ), beta-particles

( 0

1 e ), and gamma-rays (γ rays). All these 3 rays are known as electromagnetic waves with very

short wavelength. This disintegration is known as radioactive decay.

Unstable nucleus will continuously undergo radioactive decay until it’s become stable. 1.2 RELATIVE ATOMIC MASSES AND RELATIVE MOLECULAR MASSES

Relative Atomic Mass Ar

A single atom is two small and light and cannot weighed directly

The best way to determine the mass of a single atom is to compare its mass to the mass of another atoms of an element that is used

Hydrogen was the first element to be chosen as the standard for comparing masses because the hydrogen is the lightest atom with a mass 1.0 a.m.u. (atomic mass unit)

Example

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The masses of 1 helium atom is 4 times larger than 1 hydrogen atom.Therefore the RAM of Helium is 4

On the hydrogen scale, the RAM of an elements mean the mass of one atom of the element compared to the mass of a single hydrogen atom.

Note that RAM does not have any units

The new standard used today is the carbon-12 atom. RAM based on carbon-12 scale is the mass of one atom of element compared to 1/12 mass of an atom of carbon-12

Example

RAM of Mg = 2 (The average mass of one atom of the element) 1/12 = 2 . 1/12 = 24

Relative Molecular Mass, Mr

RMM of a molecules = the average mass of one molecules . 1/12 x the mass of an atom of carbon-12

The relative molecular mass of molecules can be calculated by adding up the RAM of all atoms that are present in the molecules.

Relative Isotopic Mass

The carbon-12 isotopes is chosen as the standard for comparing the masses of other isotopes. This is known as carbon scale.

The Relative Isotopic Mass is defined as the ration of the mass of one atom of isotopes to 1/12 of mass of one atom of carbon-12 isotopes

SUBSTANCE RMM

Hydrogen Gas, H2 2 x Ar of H = 2 x 1 = 2

Ammonia, NH3 Ar of N + 3(Ar of H) = 14 + 3(1) = 17

Sodium Chloride, NaCl

Ar of Na + Ar of Cl = 23 + 35.5 = 58.5

Hydrated Magnesium

Sulphate, MgSO4.7H2O

Ar of Mg + Ar of S + 4(Ar of O) + 14(Ar of H) + 7(Ar of O) = 24 + 32 + 4(16) + 14(1) + 7(16) = 246

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1.3 MASS SPECTROMETRY

Stage 1: Ionisation The atom is ionised by knocking one or more electrons off to give a positive ion. This is true even for things which you would normally expect to form negative ions (chlorine, for example) or never form ions at all (argon, for example). Mass spectrometers always work with positive ions.

Stage 2: Acceleration The ions are accelerated so that they all have the same kinetic energy.

Stage 3: Deflection The ions are then deflected by a magnetic field according to their masses. The lighter they are, the more they are deflected. The amount of deflection also depends on the number of positive charges on the ion - in other words, on how many electrons were knocked off in the first stage. The more the ion is charged, the more it gets deflected.

Stage 4: Detection The beam of ions passing through the machine is detected electrically.

[adapted from http://www.chemguide.co.uk/analysis/masspec/howitworks.html ]

Isotopes abundance

Isotopes abundance is the abundance of each isotopes in the mixture

It can be expressed in term of fractional abundance or percentage abundance

It is also can be expressed in form of isotopic ratio

http://www.chemguide.co.uk/analysis/masspec/howitworks.html

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Interpreting Mass Spectra in term of Relative Abundance of Isotopes

The Mass Spectrum of Boron

The spectrum is also can be changed to line chart

From the diagrams, we can see two peaks at 10 m/e and 11 m/e. This shows that boron consist of two isotopes, 10B and 11B

In term of relative abundance, 10B is 20% while 11B is 80%. This shows that Boron-11 is 4 times more abundant than boron-10. Ratio of relative abundance of Boron-10 to Boron-11 is 1:4.

Interpreting Mass Spectra in term of Molecular Fragment

The mass spectrum of methane, CH4

From the above mass spectrum diagram, CH4+ ion is called the molecular ion (M) or the parent

ion of which have m/e value if 16, corresponding to the relative molecular mass of methane

The other lines (m/e values of 12,13,14,15) are caused by the ions or molecular fragments

In natural, 99% of carbon is carbon-12 isotopes and only 1% of carbon-13 which will show peak (M+1). The M+1 can be ignored in determining the Relative molecular mass of the compound

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Determining Relative Atomic Mass from Mass Spectrometry

Relative atomic mass (Ar) = ah1 + bh2 + ch3 + … h1 + h2 + h3 + …

Example 1 : To find relative atomic mass of X Therefore, the Relative Atomic Mass of X is, = (10 x 20) + (11 x 80) 20 + 80 = 10.80 With reference of the Periodic Table, the element X is Boron.

1.4 MOLE CONCEPT AND AVOGADRO CONSTANT

One mole = 12 grams of carbon-12

One mole contains 6.02 x 1023 numbers of atoms. This is known as Avogadro Constant

Molar mass = Relative atomic mass BUT, Relative atomic mass does not have any units, but molar mass have unit, g mol-1

Volume occupied by 1 mol of any gas is called the molar volume

There are 2 types of molar volume a) At s.t.p (Standard Temperature and Pressure) Molar volume = 22.4 dm3 The condition for s.t.p are 0°C and 1 atm pressure b) At r.t.p ( Room Temperature and Pressure) Molar volume = 24 dm3 The condition for s.t.p are 21°C and 1 atm pressure

General relationship in mole concept

x Molar Mass

÷ Molar Mass x NA

Number of Particles Number of mole Mass

Volume

÷ NA

÷ Molar Volume x Molar Volume

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Concentration of a solution can be measured as mass of solute per dm-3 of solution (g dm-3) or moles of solute per dm-3 (mol dm-3) [KNOWN AS MOLARITY OF SOLUTION]

Number of solute = MV 1000

For the reaction between A and B aA + bB Product MAVA a

MBVB b

For standard solution Thus, moles of solute before dilution = moles of solute after dilution M1 x V1 = M2 x V2

chemistry stpm chapter 1 by study smart

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