Unit 3
What are atoms ?
• Everything is made of ______________.
• There are different types of particles.
An _________ is the smallest part of an
element which can ever exist.
Basic Structure of an atom
Basic Structure of an atom
Basic structure of Atom
• An atom consists of three types of
subatomic particles : ____________,
___________, and ______________.
• ____________ and ___________ sit in the
nucleus of an atom.
• The ___________ move around the nucleus.
• Each proton carries a positive charge.(電荷)
• Each neutron has no charge.
• Each electron carries a negative charge.
• Protons and neutrons have the same mass.
• Electrons are very light.
Subatomic particles
Name
Position in
Symbol
atom
Inside the
nucleus
Inside the
nucleus
Moving
around the
nucleus
Relative
charge
Relative
mass
Atomic Number
Atomic number of an element
= number of protons in an atom.
Number of protons =
Number of electrons
For example
Hydrogen
The simplest atom.
Building up different atoms from
protons, neutrons and electrons.
• Different atoms have different numbers of
protons, neutrons and electrons.
Atom
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Symbol
H
He
Li
Be
B
C
N
O
Atomic Number
1
2
3
4
5
6
7
8
Atom
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phosphorus
Sulphur
Chlorine
Symbol
F
Ne
Na
Mg
Al
Si
P
S
Cl
Atomic Number
9
10
11
12
13
14
15
16
17
Atom
Symbol
Atomic Number
Argon
Ar
18
Potassium
K
19
Calcium
Ca
20
Mass Number
Mass number =
no. of protons + no. of neutrons
No. of neutrons = Mass number =
Standard Notation
• Do your classwork. P.26
Classwork 2
Atom
Atomic Mass
protons
number Number
neutrons Electrons Symbol
B
5
11
5
6
5
Na
11
23
11
12
11
Si
14
28
14
14
14
Cu
29
63
29
34
29
Fe
26
56
26
30
26
Isotopes
• Atoms of a particular element with the same
number of protons and electrons but a different
number of neutrons.
• E.g. hydrogen
Relative atomic mass
• 1/12 of the mass of a carbon-12 atom as one
unit, called
Atomic mass unit (a.m.u.)
Do classwork P.29
Arrangement of electrons in atom
Electron shell
Electronic arrangement
Atomic Number
Element
Electronic
arrangement
1
Hydrogen
1
2
Helium
2
3
Lithium
2,1
4
5
Electron diagram