Can you recall…
What is Matter?
Matter is anything that has mass and takes up space.
What is matter made of?
Democritus
“…if one were to break up matter
into smaller and smaller piece,
there would come a point when it
could no longer be divided
further.”
He called this smallest indivisible
bit of matter ‘atom’ (from the
Greek word atomos which means
indivisible).
Greek Philosopher
(460 B.C. – 370 B.C.)
Particles that make up of matter
• Using a Scanning Tunneling Microscope (STM), scientists are
now able to observes the particles that make up matter.
Gold atoms
Scanning Tunneling Microscope
Particles that make up of matter
Iron on Copper
What is an atom?
An atom is the smallest unit of an element, having
the properties of that element.
Atom!
gas
liquid
solid
Given that…
an atom is the smallest unit of an element, having
the properties of that element…
Question for thought:
Is a copper atom identical to a zinc atom?
Let’s learn more about the
ATOM
Model of an Atom
Are atoms like solid balls?
With nothing else inside?
The Changing Model of the Atom
The history of atom:
•
•
•
•
•
•
•
•
•
Dalton model (Billiard Ball Model)
Thomson model (Plum Pudding Model)
Lewis model (Cubical Atom Model)
Nagaoka model (Saturnian Model)
Rutherford model (Planetary Model)
Bohr model (Rutherford–Bohr Model)
Bohr–Sommerfeld model (Refined Bohr Model)
Gryziński model (Free-fall Model)
Schrodinger model (Electron Cloud Model)
The Ever Changing Model…
Psy, psy, psy, psy, psy…
(Which model should I
learn?)
Presenting to you…
proton
neutron
nucleus
electron
The Bohr Model
Particles smaller than an atom…
Note:
Atoms - made up of subatomic particles
positively charged
proton
neutron
nucleus
neutral
electron
shell
negatively
charged
1. The nucleus
consists of
protons and
neutrons
2. Nucleus is
positively
charged. Why?
3. Electrons move
around very
rapidly. They
tend to occupy
layers or shells at
different
distances from
the nucleus.
Subatomic Particles
positively charged
proton
neutron
neutral
electron
negatively
charged
nucleus
Particle Symbol Relative Charge
Mass
Proton
p
1
1+
Neutron
n
1
0
Electron
e-
1/1836
1-
Thinking Time…
Particle
Why is the term
"relative mass"
used rather than
just mass?
Symbol
Relative
Mass
Charge
Proton
p
1
1+
Neutron
n
1
0
Electron
e-
1/1836
1-
Thinking Time…
Hints…
Mass of proton
≈ 1.67×10−27 kg
Mass of neutron
≈ 1.67×10−27 kg
Mass of electron
≈ 9.11×10−31 kg
Thinking Time…
Mass of proton, neutron and electron are too small
and inconvenient to work with.
By using relative mass, we do not have to remember
the exact value of the various masses.
Moving on…
The Periodic Table
The Periodic Table
Counting protons…
Proton Number
The number of protons in an atom is called the
proton number. Proton number is also known as the
Atomic Number.
From
Periodic
Table…
Counting protons & neutrons…
Nucleon Number
Nucleon number is the number of protons and
neutrons in the nucleus of an atom. Nucleon
number is also called the Mass Number.
Nucleon Number
Nucleon (Mass) number =
number of protons + number of neutrons
12
• Carbon atom in symbol form: 6 C.
• Can also be written as carbon-12.
Question
How many protons, electrons, and neutrons are
12
there in a 6 C atom?
6 protons, 6 electrons and 6 neutrons.
Thinking Time…
What is the proton number and nucleon
64
number of an atom of 29Cu?
Proton number: 29
Nucleon number: 64
Thinking Time…
What is the atomic number and mass number
40
of an atom of 20 Ca?
Atomic number: 20
Mass number: 40
Thinking Time…
Using the periodic table, identify
(a)the mass number of an atom of bromine
(b) the atomic number of an atom of boron
(c) the proton number of an atom of platinum
(d) the nucleon number of an atom of niobium
Thinking Time…
Using the periodic table, identify
(a)the mass number of an atom of bromine - 80
(b) the atomic number of an atom of boron - 5
(c) the proton number of an atom of platinum - 78
(d) the nucleon number of an atom of niobium - 93
Complete the table:
Element
Number of
protons
Number of
electrons
Number of
neutrons
1
1
H
23
11
Na
32
16
S
Complete the table:
Element
1
1
H
23
11
Na
32
16
S
Number of
protons
1
11
16
Number of
electrons
1
11
16
Number of
neutrons
0
12
16
Back to the Atomic Model…
protons
nucleus
neutrons
The centre of an atom is
called the nucleus which
contains the protons and
neutrons.
The Atomic Model…
protons
nucleus
neutrons
electron
The electrons in an atom
are arranged in shells
(orbits) at different
distances from the
nucleus.
Note: Shells are also
called energy levels.
1st shell
2nd shell
3rd shell
4th shell
The Atomic Model
Each shell can hold a certain
maximum number of electrons.
(a) 1st shell - 2 electrons
(b) 2nd shell - 8 electrons
(c) 3rd shell - 8 electrons
(1st 20 elements only)
1st shell
2nd shell
3rd shell
electron
4th shell
Advanced: For elements after calcium in
the 4th period, their third shell can hold
up to 18 electrons.
Question
An atom can be described as an electrically neutral entity
made up of a positively charged nucleus at its centre with
negatively charged electrons moving around the nucleus.
Question
An atom can be described as an electrically neutral entity made up of a
positively charged nucleus at its centre with negatively charged electrons
moving around the nucleus.
(a)
Why is the atom electrically neutral?
Number of electrons = number of protons. Equal positive and negative
charges
(b)
Why is the nucleus positively charged?
The nucleus contains protons and neutrons. Protons are positively
charged while neutrons are electrically neutral.
Differentiating different elements
How do I differentiate the atoms of one element
from the atoms of another element?
All atoms of the same element have the same
number of protons while those of different elements
contain different number of protons.
12
6
C
vs
23
11
Na
What are Isotopes?
• Isotopes are atoms of the same element with
different numbers of neutrons.
-> same proton number, different nucleon number
• E.g. carbon has 3 isotopes:
12
6
C
13
6
C
14
6
C
Electron Arrangement
• Nitrogen-14 atom has 7 electrons
7p
7n
Drawing the full electronic
configuration
Key
• - electron
p - proton
n - neutron
Note: full electronic configuration of
an atom shows the arrangement of
electrons in different shells.
Electron Arrangement
• Nitrogen-14 atom has 7 electrons
7p
7n
Key
• - electron
p - proton
n - neutron
shows arrangement of electrons in
different shells.
Writing the electronic configuration:
1st shell
2.5
2nd shell
separate the
2 shells
Electron Arrangement
• Argon-40 atom has 18 electrons
18 p
22 n
Key
• - electron
p - proton
n - neutron
electronic configuration of 2.8.8
Valence Shell
• Valence shell - farthest occupied shell from the
nucleus
• Valence electron - electron in the valence shell
7p
7n
Valence Shell
• Note: only valence electrons are involved in
chemical reactions.
7p
7n
Outer electronic structure
• only valence electrons are drawn
7p
7n
Key
• - electron
p - proton
n - neutron
Formation of Ions
• During chemical reactions, some atoms might lose/gain
electron(s). Atom becomes an ion (charged particle)
when it gains or loses electron(s).
Question
Why does an atom become a charged particle when
it gains or loses electron(s)?
An atom is electrically neutral because number of
electrons = number of protons (equal positive and
negative charges).
When it gains or loses electron(s), the positive and
negative charges are not balanced. Therefore, the
atom becomes a charged particle.
Formation of cations
• When an atom loses one or more electrons, it becomes a
positively charged particle called cation.
Lithium atom (Li)
3 electrons
3 protons
Net charge: 0
Lithium ion (Li+)
2 electrons
3 protons
Net charge: +1
Formation of anions
• When an atom gains one or more electrons, it becomes a
negatively charged particle called anion.
Fluorine atom (F)
9 electrons
9 protons
Net charge: 0
Fluoride ion (F-)
10 electrons
9 protons
Net charge: -1
Question for Thought
Why do atoms become ions?
To obtain a full valence shell
To obtain the same electronic structure of a noble
gas so as to be stable. (Note: this will be covered
under Chemical Bonding)
Fill up the blanks…
Charge
of ion
Element
Name of ion
Oxygen
Sulfur
Fluorine
Chlorine
Hydrogen
Lithium
Sodium
Potassium
Beryllium
Magnesium
Calcium
Copper
Iron
Aluminium
Iron
Oxide
Sulfide
Fluoride
Chloride
Hydrogen
Lithium
Sodium
Potassium
Beryllium
Magnesium
Calcium
Copper (II)
Iron (II)
Aluminium
Iron (III)
Symbol
of ion
O2S2FClH+
Li+
Na+
K+
Be2+
Mg2+
Ca2+
Cu2+
Fe2+
Al3+
Fe3+
No. of electron
gained
No. of electron
lost
Fill up the blanks…
Charge
of ion
-2
-1
+1
+2
+3
Element
Name of ion
Oxygen
Sulfur
Fluorine
Chlorine
Hydrogen
Lithium
Sodium
Potassium
Beryllium
Magnesium
Calcium
Copper
Iron
Aluminium
Iron
Oxide
Sulfide
Fluoride
Chloride
Hydrogen
Lithium
Sodium
Potassium
Beryllium
Magnesium
Calcium
Copper (II)
Iron (II)
Aluminium
Iron (III)
Symbol
of ion
O2S2FClH+
Li+
Na+
K+
Be2+
Mg2+
Ca2+
Cu2+
Fe2+
Al3+
Fe3+
No. of electron
gained
No. of electron
lost
2
1
1
2
3
Questions…
Do metals generally form cations or anions?
• cations
Do non-metals generally form cations or
anions?
• anions
The Periodic Table
• Scientists have classified all discovered elements into
a chart called the Periodic Table
The Periodic Table
• In the Periodic Table, elements are arranged in order
of increasing proton (atomic) number and are
classified according to Groups and Periods.
Vertical Row: Group
Elements in the same group have
similar chemical properties and
will undergo the same type of
chemical reactions
Horizontal Row: Period
As you move across a period,
the properties of the elements
will change gradually from
metallic to non-metallic
Group
• Groups are numbered from I to VII and then 0
Group
Alkali
metals
Noble
gases
Alkaline
earth
metals
Halogens
Transition
metals
Group
Elements in the same group have similar
chemical properties and will undergo the
same type of chemical reactions.
Elements in the Periodic Table
Li
Group I – Alkali Metals
– Lithium, Sodium, Potassium,
Rubidium, Cesium, Francium.
– Metals and solid at room
temperature.
– Very reactive.
Na
K
Rb
Cs
Fr
Elements in the Periodic Table
Be
Group II – Alkaline Earth Metals
Mg
– Beryllium, Magnesium, Calcium,
Strontium, Barium, Radium.
Ca
Sr
Ba
Ra
Elements in the Periodic Table
B
Group III
Al
– Boron, Aluminum, Gallium, Indium,
Thallium
– Except B, Group III elements are all
metals.
– B is a metalloid.
Ga
In
Tl
Elements in the Periodic Table
Group IV
– Carbon, Silicon, Germanium, Tin,
Lead
– Carbon is a non-metal.
– Si and Ge are metalloids.
– Sn and Pb are metals.
A metalloid is an element that has some of the
physical characteristics of a metal but some of the
chemical characteristics of a non-metal.
C
Si
Ge
Sn
Pb
Elements in the Periodic Table
N
Group V
P
– Nitrogen, Phosphorus, Arsenic,
Antimony, Bismuth.
– Non-metals (N, P) to metalloids (As,
Sb) to metals (Bi).
As
Sb
Bi
Elements in the Periodic Table
Group VI
O
S
– Oxygen, Sulfur, Selenium, Tellurium,
Polonium.
– Non-metals (O, S, Se) to metalloids
(Te) to metals (Po).
Se
Te
Po
Elements in the Periodic Table
Group VII – the Halogens
– Fluorine, Chlorine, Bromine, Iodine,
Astatine.
– All non-metals.
F
Cl
Br
I
At
Elements in the Periodic Table
He
Group 0 – the Noble Gases
Ne
– Helium, Neon, Argon, Krypton, Xenon, Ar
Radon.
– Least reactive elements.
Kr
– Also known as inert gases, or rare gases.
X
Rn
Elements in the Periodic Table
The Transition Elements
– All metals
Ti
Zr
V Cr Mn Fe
Ni
Rh
Cu Zn
Ag
Pt Au Hg
Period
1st
period
1st shell
fully
occupied
2nd
period
2nd shell
fully
occupied
3rd
period
Fill up the blanks.
Element
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Proton
number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1st shell
Number of electrons in
2nd shell
3rd shell
4th shell
Electronic
configuration
Period
Group
Fill up the blanks.
Element
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Proton
number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1st shell
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Number of electrons in
2nd shell
3rd shell
1
2
3
4
5
6
7
8
8
8
8
8
8
8
8
8
8
8
1
2
3
4
5
6
7
8
8
8
4th shell
1
2
Electronic
configuration
1
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.8.1
2.8.2
2.8.3
2.8.4
2.8.5
2.8.6
2.8.7
2.8.8
2.8.8.1
2.8.8.2
Period
Group
1
1
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
4
4
0
I
II
III
IV
V
VI
VII
0
I
II
III
IV
V
VI
VII
0
I
II
8 valence e-
1 valence e-
number of valence
electrons for each element
= group number
Group I
1 valence e-
Electronic
configuration – 2.1
Electronic
configuration – 2.8.1
Electronic
configuration – 2.8.8.1
elements with similar
electronic configurations
have similar chemical
properties
elements in the same group
have similar chemical
properties
Group I Reactivity
Metals vs Non-metals
Across the period, the properties of elements change from
metallic to non‐metallic.
Periodic Table: An organised table that consists of
all the elements discovered.
Periodic Table: An organised table
that consists of all the elements discovered.
Charges on ions
Charges on the ions formed are related to the group number and number
of valence electrons.
Element
Na
Mg
Al
Si
P
S
Cl
Ar
Group number
I
II
III
IV
V
VI
VII
0
Formula of ion
Na+
Mg2+
Al3+
-
P3-
S2-
Cl-
-
1
2
3
3
2
1
e- gain/lost
Charges on ions
Element
Na
Mg
Al
Si
P
S
Cl
Ar
Group number
I
II
III
IV
V
VI
VII
0
Formula of ion
Na+
Mg2+
Al3+
-
P3-
S2-
Cl-
-
1
2
3
3
2
1
e- gain/lost
• Metal
atoms lose their valence electrons to form cations
with charges corresponding to their group number.
• Non-metal atoms gain electrons to form anions. The
charges on the anions corresponding to the number of
electrons gained to fill their valence shells with eight
electrons.
Try this!
Draw a labelled diagram to show the full
electronic configuration in an atom of
32
(i) 16 S
Try this!
Draw a labelled diagram to show the full
electronic configuration in an atom of
40
(ii) 20 Ca