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Transcript
Can you recall…
What is Matter?
Matter is anything that has mass and takes up
space.
Can you recall…
What is the kinetic particle theory?
Can you recall…
What is the kinetic particle theory?
The Kinetic Particle Theory states that matter is
made of tiny discrete particles (atoms or
molecules), which are in constant and random
motion.
So, what is an atom?
Atom!
gas
liquid
solid
So, what is an atom?
An atom is the smallest unit of an element,
having the properties of that element.
Do you think a copper atom is identical to a zinc
atom?
Are atoms like solid balls?
With nothing else inside?
Subatomic Particles
Atoms - made up of subatomic particles
positively charged
proton
neutron
nucleus
neutral
electron
negatively
charged
Note: The nucleus
consists of protons
and neutrons
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.
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.
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
12
are there in a 6C atom?
6 protons, 6 electrons and 6 neutrons.
Worksheet Time…
• Try Question 1 to 4
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
1st shell
2nd shell
3rd shell
4th shell
The electrons in an
atom are arranged
in shells (orbits) at
different distances
from the nucleus.
Note: Shells are
also called energy
levels.
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
Worksheet Time…
• Try Question 5
Advanced: 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: 2.5
2nd shell
1st 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
Thinking Time…
Based on what you have learnt in this topic,
describe how are the elements in the Periodic
Table being arranged?
Arrangement of elements in the order of
increasing proton (atomic) number.
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)
Worksheet Time…
• Try Question 6 to 8
Exercise
Charge of ion
Element
Name of ion
Symbol of ion
No. of electron gained
-2
Oxygen
Sulfur
Oxide
Sulfide
O2S2-
2
Fluorine
Chlorine
Fluoride
Chloride
FCl-
1
Hydrogen
Lithium
Sodium
Potassium
Hydrogen
Lithium
Sodium
Potassium
H+
Li+
Na+
K+
Beryllium
Magnesium
Calcium
Copper
Iron
Beryllium
Magnesium
Calcium
Copper (II)
Iron (II)
Be2+
Mg2+
Ca2+
Cu2+
Fe2+
Aluminium
Iron
Aluminium
Iron (III)
Al3+
Fe3+
-1
+1
+2
+3
No. of electron lost
1
2
3
Exercise
Do metals generally form cations or
anions?
cations
Do non-metals generally form cations or
anions?
anions