Atoms, Molecules and Stoichiometry Chemistry

Atoms, molecules and stoichiometry.

Kita akan belajar hari ini berkenaan:

1. Structure of the atom,

2. Basic calculation.

An atom is the smallest particle of an element, having the same chemical properties as the bulk element (zarah paling halus). 


What are the three fundamental particles of the atom?

Proton. A proton is a subatomic particle with a mass defined as 1 and a charge of +1 (positive charge).

Neutron. The neutron is a subatomic particle with a mass of 1 and charge of 0.

Electron. An electron is a stable subatomic particle with a negative electrical charge.

atomic structures

Now we want to differentiate these three things with some things below:



Mass/ Size (amu)

Charge deflection

Position in atom


amu = atomic mass unit because mass of an atom is very small.

1 amu = 1/12 x mass of one atom of C-12

distribution of mass charges within an atom locations

Particle: Proton

Symbol: p

Mass/ size: almost same as neutron.

Heavier than electron.

Charge: positive.

Deflection: towards to negative plate.

Position in atom:


Particle: Electron

Symbol: e

Mass/ size: smaller than prton and neutron.

Charge: negative

Deflection: towards to positive plate.

Position in atom:


Particle: Neutron

Symbol: n

Mass/ size: almost same as proton. Heavier than electron.

Charge: electrically neutral.

Deflection: none.

Position in atom:

electric field Charge negative positive deflection towards to positive plate

properties of protons neutrons electrons

The keyword is, electrons is very light, always surround the nucleus (protons + neutrons).

Proton and Neutron almost same mass, Rumusan untuk mass/size

e < p = n. proton dan neutron almost same mass.
electron lighter than both proton and neutron

Located in nucleus.

E is negligible mass (boleh diabaikan/ too tiny).

P + N known as nucleons
proton + neutron = nucleons



Atom = neutral
Ions are divided into cations (positive charge), anions (negative charge).

Cation = positively charge.
Anion = negatively charge.

proton number and nucleon number

it represents atoms with:

X is a symbol
A is the nucleons in the nucleus only. Does not include electrons because electrons are negligible.
Z is the proton number, also called the atomic number.

nucleons protons electrons

It’s easy for us to do this.



A = Z+N

Azan is muslim calling for prayer.

Nucleon number = proton number + neutron number.

electron is negligible.

determine-the-number-of-protons-neutrons-and-electrons present in both neutral and charged species of a given proton number and nucleon number

What causes an atom to be neutral?

Answer: An atom is neutral, number of protons = number of electrons.

the number of protons and the number of electrons are the same.

When a chemical reaction takes place only the valence electrons are involved, while the number of protons and neutrons in an atom remain unchanged. Thus, an ion has the same proton number and nucleon number as its atom.


RAM = JAR (jisim atom relatif)
RMM = JMR (jisim molekular relatif)
RIM = JIR (jisim isotop relatif)

RAM is Relative atomic mass.

RMM is Relative molecular mass.

RIM is Relative isotopic mass.


Sometimes we find the value of RAM is a decimal number

examples of RAM for Chlorine.

is 35.5.

why? Chlorine has an average mass of the isotopes. Cl-35 dan Cl-37.

different atomic numbers.

this type of 35 represents 75% of the total.
while type 37 represents 25% of the total


chlorine average mass isotopes 75 25 35 37


Boron. But this time it is not given in the form of %. have to calculate for yourself.

B-10 = 23,
B-11 = 100,

Find RAM of Boron.

have to find the percentage first

Example Exercise

1. A student needs 65.0 g of copper(II) chloride, CuCl2, for an experiment. How many atoms of copper are there in this sample?

Seorang pelajar memerlukan 65.0 g kuprum(II) klorida, CuCl2, dalam satu eksperimen yang dijalankan. Berapakah  atom kuprum di dalam sampel  ini?

[Relative atomic mass/ Jisim atom relatif Cu, 64, Cl, 35.5;  NA = 6.02 x 10 ^23 mol-1]

A. 2.89 x 10^23 atoms.

B. 3.91 x 10^25 atoms

C. 2.35 x 10^23 atoms

D. 4.70 x 10^23 atoms


2. If one Monster energy drink contains 0.16 g of caffeine, how many moles of caffeine do we consume when we drink 1 can? The chemical formula for caffeine is C8H10N4O2.

Dalam satu tin minuman ‘Monster energy’ mengandungi 0.16 g kafein. Berapakah bilangan mole kafein yang kita peroleh apabila kita minium satu tin minuman tersebut. Formula kimia bagi kafein adalah C8H10N4O2

[Relative atomic mass/ Jisim atom relatif: C, 12; H, 1; N, 14; O,16]

A. 194.19 moles

B. 1.07 moles

C. 0.00082 moles.

D. 1213.69 moles


3. Mylanta, a common antacid, contains magnesium hydroxide, Mg(OH)2. How many moles of magnesium hydroxide are in 75.0 g of magnesium hydroxide?

Mylanta merupakan satu jenis antasid yang mengandungi Mg(OH)2. Berapakah bilangan mol magnesium hydroksida bagi 75.0 g m sampel ini?

[Relative atomic mass/ Jiism atom relatif: H, 1;Mg, 24; ), 16]

A. 0.551 moles

B. 0.778 moles

C. 1.29 moles.

D. 1.82 moles


4. Which of the following has the most number of atoms?

Antara berikut, yang manakah mengandungi bilangan atom yang paling banyak?

[NA = 6.02 x 10^23 mol-1]

A. 1.5 moles of oxygen, O2

1.5 mol oksigen, O2

B. 1.0 mol of ammonia, NH3

1.0 mol ammonia, NH3.

C. 0.5 moles of sulpur dioxide, SO2

0.5 mol sulfur dioksida, SO2

D. 1.2 moles of carbon dioxide, CO2

1.2 mol karbon dioksida, CO2


5. What is the mass of nitrogen in 20.0 g of ammonium nitrate, NH4NO3?

Berapakah jisim nitrogen dalam 20.0 g ammonium nitrat, NH4NO3?

[Relative atomic mass / Jisim atom relatif: H, 1; N, 14; O, 16]

A. 3.5 g

B. 7.0 g.

C. 14.0 g

D. 56.0 g


6. What is the mass of carbon dioxide that contains the same volume as in 2 moles of sulphur dioxide?

Berapakah jisim karbon dioksida yang mengandungi isi padu yang sama banyak dengan 2 mol sulfur dioksida?

[ Relative atomic mass/ Jisim atom relatif: C,12; O, 16; S, 32]

A. 44

B. 88

C. 128.

D. 132


7. The formulae of barium carbonate and ammonium phosphate are BaCO3 and (NH4)3PO4 respectively. What is the formula of barium phosphate?

Formula bagi barium karbonat dan ammonium fosfat adalah BaCO3 dan (NH4)3PO4 masing-masing. Apakah formula bagi barium fosfat?

A. BaPO4

B. Ba2PO4

C. Ba(PO4)2

D. Ba3(PO4)2.


8. The formula for X oxide is X2CO3 and its relative formula mass is 106. What is the relative atomic mass of element X?

Formula bagi oksida X ialah X2CO3, jisim formula relatif baginya ialah 106. Berapakah jisim atom relatif bagi unsur X?

relative atomic mass/ Jisim atom relatif: C, 12; O, 16]

A. 23.

B. 30

C. 46

D. 60


9. 10.5 g of the oxide of metal M with the empirical formula of MO produces 7.5 g of M when it is reduced completely. What is the relative atomic mass of M?

10.5 g okida logam M dengan formula empirik MO menghasilkan 7.5 g M apabila diturunkan dengan lengkap. Berapakah jsisim atom relatif M?

[Relative atomic mass/ Jisim atom relatif: O = 16]

A. 5

B. 11

C. 14

D. 40.


10. 1.6 g of gas X occupies 560 cm3 at standard temperature and pressure ( s.t.p). What is the relative molecular mass of X?

1.6 g gas X menempati 560 cm3 pada suhu dan tekanan piawai ( stp). Berapakah jisim molekul telatif bagi X?

[molar volume of gas at s.t.p/ Isi padu molar gas pada s.t.p = 22.4 dm3 mol-1]

A. 4

B. 16

C. 32

D. 64.






1. Element : ………………….. ,

Atomic Number / number of protons / number of electrons : ………………….. ,

Neutron : ………………….. ,

Nucleon number / mass number (A) / atomic mass number  : ………………….. ,

RAM, relative atomic mass (gram per mole) : ………………….. ,

elements atom ag f he al cl sn fe ca na ne c mn

2. – Atomic Notation. Given the atomic notation for the following atoms, draw a diagram showing the arrangement of protons, neutrons, and electrons.

silver 109 47 fluorine 19 9

3. – Given the following diagram, indicate the nucleus using atomic notation.

Mn 55 25

4. – Nuclear Composition of Isotopes. State the number of protons and the number of neutrons in an atom of each of the following isotopes.

a. chlorine 37 17

b. mercury-202

5. – State the number of protons and the number of neutrons in an atom of each of the following isotopes.

a.Stanum sn 120 50

b. uranium-238

6. – Concept Exercise. Can atoms of different elements have the same mass number?

7. – Calculation of Atomic Mass. Silicon is the second most abundant element in Earth’s crust. Calculate the atomic mass of silicon given the following data for its three natural isotopes:

Silicon is the second most abundant element in Earths crust atomic mass of silicon isotopes

8. – Calculation of Atomic Mass. Calculate the atomic mass of copper given the following data:

isotopes cu copper 63 65 mass amu abundance

9. – Concept Exercise. A bag of marbles has 75 large marbles with a mass of 2.00 g each, and 25 small marbles with a mass of 1.00 g each. Calculate

(a) the simple average mass, and

(b) the weighted average mass of the marble collection.

10. – Nuclear Composition from the Periodic Table. Refer to the periodic table on the inside cover of this textbook and determine the atomic number and atomic mass for iron.

11. – Nuclear Composition from the Periodic Table. Refer to the periodic table on the inside cover of this text and determine the atomic number and mass number for the given radioactive isotope of radon gas.

12. – Concept Exercise. Which of the following is never a whole number value: atomic number, atomic mass, or mass number?

13. – Properties of Light. Considering blue light and yellow light,

which has the

(a) longer wavelength?

(b) higher frequency?

(c) higher energy?

14. – Concept Exercise. The energy of light (increases/decreases) as the wavelength increases. The energy of light (increases/decreases) as the frequency increases.



















































































ada nota putih di bawah

Belajar apa?

Atomic mass units


Molar mass

Equation balancing

Mole ratios


Berapa jisim gula untuk hasilkan minuman?

Tidak tahu berapa banyak, kene kira (stoichiometry = greek, measuring elements).

Kira bahan kimia yang masuk dan keluar melalui tindak balas.

Kira atom dan molekul dengan timbang jisim.

Saintis kata, ia berkaitan benda yang tidak dapat dikira dengan benda boleh kira.

Kaitan benda yang tidak nampak dengan benda boleh nampak (contoh, atom, molekul, sebatian).

Inilah fungsi kimia digunakan secara meluas.

Kira bahan-bahan dalam kimia ialah RAM.


C-12 98.89%,

C-13 1.11%,

C-14 0.000000001%,

dikira menjadi 12.01 amu untuk Carbon.

amu ialah untuk kira unit dipanggil ‘atomic mass unit’.

Oxygen O-16, O-17, O-18 ialah jisimnya bersamaan 1/12 the mass of an atom of 12-C.

C = 12.01 amu, O = 16 amu, H = 1.008 amu.

Berapa atom dan molekul untuk hasilkan secawan teh?

Berapa gula perlu dimasukkan supaya kekal badan slim dan sihat, tidak terlebih gula dalam minuman?

Mole = important unit measurement of chemistry, allows to express chemical atomic mass interms of grams.

Carbon-12, 6.022 x 1023  sebanyak bilangan atoms in 12 grams of 12-C.

Avogadro’s number. 1 mole roses = 6.022 x 1023. Translate atoms into grams.

Moles, molar mass (M) in grams = RAM in amu.

1 mole H = 1.008 g.

1 mole Fe = 55.85 g.

1 mole C = 12.01 g.

Molar mass = boleh kira apa sahaja sebatian.

Sucrose = C12H22O11

Carbon 12 mol x 12.01g / mol = 144.12 g

Hydrogen 22 mole x 1.008 g / mol = 22.176 g

Oxygen 11 mol x 16.00 g / mol = 172g


Mass of 1 mole sucrose = 342.296 g

Bakar gula yang saya makan melalui tindak balas (reaction).

Badan kita gunakan daripada glucose kepada sucrose –> hasilkan tenanga (create energy).

Reactants and products, C12H22O11 + O2 (reactants, left) => CO2 + H2O (products, right)

Number of atoms each elements remain the same, equation balancing = stoichiometry.

C12H22O11 +12O2 –> 12CO2 + 11H2O

12 CO2 molecules = 24 O atoms

11 H2O moles = 11 O atoms

= 35 O atoms

C12H22O11 +12O2 –> 12CO2 + 11H2O

1 mol sucrose (342.296 g) + 12 mol of O2 (348 g)

342.296 g sucrose / 384 g oxygen = 5 g sucrose / x g oxygen

5 g oxygen = 5.6 g oxygen = 35 nafas.





































Atoms, Molecules and Stoichiometry

1.1 Fundamental particles of an atom

Candidates should be able to:

(a) describe the properties of protons, neutrons and electrons in terms of their relative charges and relative masses; (b) predict the behaviour of beams of protons, neutrons and electrons in both electric and magnetic fields; (c) describe the distribution of mass and charges within an atom; (d) determine the number of protons, neutrons and electrons present in both neutral and charged species of a given proton number and nucleon number; (e) describe the contribution of protons and neutrons to atomic nuclei in terms of proton number and nucleon number; (f) distinguish isotopes based on the number of neutrons present, and state examples of both stable and unstable isotopes.

1.2 Relative atomic, isotopic, molecular and formula masses

Candidates should be able to:

(a) define the terms relative atomic mass, Ar, relative isotopic mass, relative molecular mass, Mr, and relative formula mass based on 12C; (b) interpret mass spectra in terms of relative abundance of isotopes and molecular fragments; (c) calculate relative atomic mass of an element from the relative abundance of its isotopes or its mass spectrum.

1.3 The mole and the Avogadro constant

Candidates should be able to:

(a) define mole in terms of the Avogadro constant; (b) calculate the number of moles of reactants, volumes of gases, volumes of solutions and concentrations of solutions; (c) deduce stoichiometric relationships from the calculations above.

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