Chemistry Notes

Atomic Structure

An atom is the smallest particle of an element that has the same chemical properties
of that element.

Atoms of the same element are identical

An atom is made up of Protons, Neutrons and Electrons

Nucleons = Protons + Neutrons

Electrons spin around the nucleus in fixed orbits

Subatomic Particle

Relative Mass

Relative Charge

(in atomic mass unit)

Proton

+1

Electron

0 (or !"#$)

-1

Neutron

Nuclide Notation

Mass number is the sum of protons and neutrons

Atomic number/Proton number is the number of protons

Number of Neutrons = Mass Number Atomic Number

In an electrically neutral atom, Number of Protons = Number of Electrons

A
Z

X refers to the symbol of the element

A refers to the mass number

Z refers to the atomic number

Isotopes

Isotopes are atoms of the same element with the same number of protons but different
number of neutrons.

In other words, isotopes of the same element have the same proton number but
different mass number

Chemistry Notes

Isotopes of the same element have similar chemical properties but different physical
properties (boiling point, melting point, density, etc.)

Arrangement of electrons (electronic configuration)

Electrons are arranged in groups of varying energy levels called electron shells

Bohrs Model: For the first 20 elements,

First shell: Maximum 2 electrons
Second shell: Maximum 8 electrons
Third shell: Maximum 8 electrons

Electron shells must be filled in order of increasing energy.

In other words, the first shell must be filled with the maximum number of electrons
before filling the next shell

Electronic Configuration: (eg) 2,8,2 OR 2.8.2

Valence Electrons

The outermost electron shell furthest away from the nucleus is called the valence shell

Electrons on this particular shell is called valence electrons

Chemical properties of an element is dependent on the number of valence electrons.

(Chemical Bonding)

Periodic Table

Elements in the periodic table are arranged in order of proton number

Vertical columns are call groups

Horizontal rows are called periods

Group I metals are also known as Alkali Metals

Reactivity of elements increase down the group
Melting/Boiling points of elements decrease down the group
Soft metals
Relatively low densities

Group VII elements are known as the halogens

Reactivity decreases down the group
Melting/Boiling points of elements increase down the group
Colour darkens down the group

Chemistry Notes

Group 0 elements are known as noble gases

Elements are in noble state configuration
Unreactive non-metals
Colourless gases

Atoms of elements in the same period have the same number of shells

Elements in the same group have the same number of electrons in their outer shells
(valence electrons)

From left to right, the elements change from metals to non-metals

Elements along the staircase separating the metals from the non-metals are
generally metalloids.

Size of atoms decrease down the groups Because the electronegativity of the
elements increase down the groups, thus attracting the electrons closer to the nucleus
and thus making the atoms smaller.

Fluorine is the most reactive element in the whole periodic table

Chemical Bonding and Structure

Atoms undergo chemical bonding to achieve the noble gas configuration, making
them stable chemically.

3 main types of bonding: Ionic, Covalent and Metallic* (not tested)

Ionic Bonding

Ionic compounds

Ions are held with strong electrostatic forces of attraction in a giant lattice structure

A high amount of energy is needed to overcome the bonds

Occurs between metals and non-metals

High melting point and boiling point Generally in the high hundreds

Most ionic compounds are soluble in water (exception(s): AgCl, etc.)

Ionic compounds tend not to be soluble in organic solvents

Electrical Conductivity
Solid NO
Liquid/Molten YES
Aqueous YES

Because ions are unable to move about freely

Free moving ions that can carry

electrical charge

Chemistry Notes
Property
Physical State at r.t.p.

Explanation

Hard, crystalline solids

Ions are held in their fixed

positions in a giant lattice
structure by very strong

Melting and Boiling points

High

ionic bonds, a lot of energy

is required to overcome the
strong electrostatic forces of
attraction

An ion is a charged particle formed from an atom or a group of atoms by the loss or
gain of electrons

Cations (Positive ions)

Atoms of metals tend to lose valence electrons to attain a noble gas configuration

Anions (Negative ions)

During ion formation, atoms of non-metals tend to gain electrons to attain a noble gas
configuration

Covalent Bonding

Simple covalent substances

Weak intermolecular forces of attraction between molecules

Little energy is needed to overcome the bonds

Occurs between non-metals

Low melting points and boiling points

Usually liquid/gas at r.t.p (25) EXCEPT for 1. Iodine 2.Sulfur

Most are insoluble in water EXCEPT for 1. HCl 2.Sugar (C6H12O6) 3. Alcohol

Electrical Conductivity
Cannot conduct electricity in ALL STATES
No free moving particles that can carry electrical charges

The covalent bond is a bond in which a pair of electrons are shared between 2 atoms
of non-metal elements. The shared electrons are attracted to both nuclei, thus holding
the atoms together.

Chemistry Notes

A molecule is made of 2 or more atoms held together by covalent bonds.

A molecule may contain atoms of the same element or atoms of different elements in
fixed ration/proportion

Covalent bonding involves only the valence shell electrons

Acids and Bases

Acids dissociate in water to produce hydrogen ions and negative ions

Eg.
HCl dissociation: HCl (aq) H+ (aq) + Cl- (aq)

Alkalis dissociate in water to produce positive ions and hydroxide ions

Eg.
NaOH dissociation: NaOH (aq) Na+ (aq) + OH- (aq)

pH = Power of Hydrogen

To measure the pH of a solution, some common methods are 1. Universal indicator 2.

pH meters 3. Litmus paper

Universal indicator
Useful to measure pH values of small amounts of solutions

pH meter
Although accurate, but the pH meter is difficult and time consuming when
calibrating and is also more inconvenient due to probabilities of contamination
and the pH meter has to be submerged in water every time.

Indicators include buffer solutions, methyl orange, bromothymol blue, etc.

Indicators are chemical substances that change colour in solutions of different pH

values

Universal Indicator
pH

Colour

Type of substance

0-3

Red

Strong Acid

4-6

Orange/Yellow

Weak Acid

Green

Neutral

8-10

Blue

Weak Alkali

11-14

Purple/Violet

Strong Alkali

Chemistry Notes

Litmus Paper
Acids turn [moist] blue litmus paper red
Alkalis turn [moist] red litmus paper blue

Chemical Formulae and Equations

Acid + Base Salt + Water (Neutralisation Exothermic Reaction [gives off heat])

Acid + Metal Carbonate Salt + Water + Carbon Dioxide

Acid + Metal Salt + Hydrogen gas

MUST MEMORISE

Ammonium NH4+

Ammonia NH3

Acids

Phosphoric Acid H3PO4

Sulphuric Acid H2SO4

Nitric Acid HNO3

Hydrochloric Acid HCl

Polyatomic ions

Sulphate SO42-

Carbonate CO32-

Nitrate NO3-

Phosphate PO43-

Transition Metals ions

Zinc Zn2+

Silver Ag+

The rest of the transition metals tested would have variable oxidation states

Copper (II) Cu2+

Etc.

Ions

Anions of elements usually end with ide

Chemistry Notes

Sulphide S2-

Nitride N3-

Fluoride F-

Oxide O2-

Phosphide P3-

Chloride Cl-

Unreactive Metals

Copper, Gold and Silver are unreactive metals

They do not react with acids

Writing Equations
1. Word equation
2. Formula of each chemical substance
3. Count the number of each atom on e=reactant and product sides
4. Add(normal-sized) numbers in front of the chemical formula of each substance if
necessary to balance the number of each atom on each side
5. Fill in the state symbols
Example:
Step 1: Hydrochloric Acid + Magnesium Carbonate Magnesium Chloride + Water +
Carbon Dioxide
Step 2: HCl + MgCO3 MgCl2
Step 3: 2HCl +

MgCO3 MgCl2

Step 4: 2HCl (aq) +

+ H2O + CO2
+ H2 O

+ CO2

MgCO3 (s) MgCl2 (aq) + H2O (l) + CO2 (g)

State Symbols

Salts are assumed aqueous (soluble) unless otherwise stated (eg. Precipitate)

Metal carbonates are taken to be solids, unless otherwise states

Metals are obviously solids

Metal hydroxides are insoluble, except those of ammonium, alkali metals and barium

Metal Oxides are insoluble, except those of ammonium, alkali metals, barium

Soluble oxides react with water to form the respective hydroxide