Transcript Atoms & Ions_RHo 2011

ATOMS & IONS
WHAT YOU NEED TO KNOW
 What
are ions
 Why
do atoms form ions
 How
are ions formed
 How
to interpret and analyse
information of atoms and ions
SUBATOMIC PARTICLES

-
-
In an atom, there are types of particles:
Proton, Neutron and Electron
Particle
Relative Mass
Relative
Electric Charge
proton
1
+1
neutron
1
0
electron
1/1840  0
-1
Protons and Neutrons are found together at the
nucleus
Importance of the
Proton – Gives the atom its identity
Neutron – Holds the protons together
Electron - Responsible for chemical
activities of the atom
STRUCTURE OF AN ATOM
Neutron
&
Proton
Electron
Electrons are negatively charged
Protons are positively charged
Neutrons are neutral
NUCLEON AND PROTON NUMBER
Relative Atomic
Mass (Nucleon
Number)
Atomic (Proton)
Number
Fluorine atom:
19
F
9
Fluorine
No. of Proton = 9
No. of Electron = 9
No. of neutron = 19 -9 =10

Proton number(also known as atomic number) is
define as the number of protons in an atom.

Nucleon number (mass number) is the total number
of protons and neutrons in an atom.
ISOTOPES

Isotopes: Atoms of the same element, but different
number of neutrons

Example:Hydrogen (1 electron, 1 proton, 0 neutron)

Hydrogen has 2 isotopes, Deuterium and Tritium

Deuterium: 1 electron, 1 proton, 1 neutron

Tritium: 1 electron, 1 proton, 2 neutrons
2
1
3
1
H
H
1
1
H
ARRANGEMENT OF ELECTRONS

Electron “Shell”

Example:
Ne
2nd shell holds up to 8
electrons
Shell 1 can have max 2 electrons
Shell 2 can have maximum 8 electrons
ARRANGEMENT OF ELECTRONS

Valence electrons: Electrons occupying the outer
most shell

Why are valence electrons important?
The chemical properties of an element depends
on the number of valence electrons
PERIODIC TABLE
Period
Group
Electronic Configuration of Noble Gases

All the Noble Gases have complete valence shells

Helium – 2 electrons (Duplet structure)

Neon and argon – 8 electrons (Octet structure)

Other elements try to achieve duplet or octet
structures during chemical reactions by gaining
or losing electrons
STABLE ELECTRONIC
CONFIGURATION
Noble gases

Completely filled outermost shell

Not reactive because of stable electronic
configuration (Octet configuration)

Applies to first 20 elements
e.g.
Helium  2
Neon  2, 8
Argon  2, 8, 8
IONS

1.
2.
3.
What are ions?
An ion is a charged particle formed when an atom has
gained or lost one or more electrons during a chemical
reaction.
Atoms are electrically neutral
When atoms loses or gain electrons, it forms an ion
When atoms gain electrons, gain negative charges
 form NEGATIVE IONS
(Anions)
When atoms lose electrons, gain positive charges
 form POSITIVE IONS
(Cations)
ARRANGEMENT OF ELECTRONS

-
Electronic configuration
Electronic configuration of Sodium (Na)
2, 8, 1
-
First shell will contain 2 eSecond shell will contain 8 eThird shell will contain 1 e-

Sodium atom has 1 valence electron
-
23
11
Na
Na
Sodium
2, 8, 1
IONS


23
Sodium atom loses 1 electron
to form positively charged
sodium ion
Sodium Atom, Na
Na
11
Sodium
Sodium Ion Na+ (Cation)
+
Sodium Atom is
Sodium Ion is
Electrically neutral
Positively charged
11 electrons & 11 protons 10 electrons & 11 protons
IONS


16
Oxygen atom gain 2 electrons
to form negatively charged
sodium anion
Oxygen Atom, O
O
8
Oxygen
Oxygen Ion O2- (Anion)
2-
Oxygen Atom is
Oxygen Ion is
Electrically neutral
Negatively charged
8 electrons & 8 protons 10 electrons & 8 protons
WORKSHEET SOLUTION
Atom
Proton
No.
No.
of e
Electronic
Configuration
No. of e
to be
LOST
No. of e
Left
No. of
e Less
Ion
12Mg
12
12
2.8.2
2
10
2
Mg2+
13Al
13
13
2.8.3
3
10
3
Al3+
19K
19
19
2.8.8.1
1
18
1
K+
20Ca
20
20
2.8.8.2
2
18
2
Ca2+
Q:
What is the relationship of proton
number and electron number in a neutral
atom?
A:
The number of positive charges
(protons) is the same as the number of
negative charges (electrons) in an atom.
Therefore, an atom is electrically
neutral.
Q:
What is the relationship between the
electronic configuration and the number
of electrons lost in a neutral atom?
A:
A neutral atom will lose or gain electrons
to achieve a duplet (Helium) or octet
electronic configuration.
Q:
Write general statement on formation of
positive ions.
A:
When there are more protons than
electrons in an atom, the atom becomes
positively charged (ion). The charge of
the ion is dependent on the number of
electron lost.
i.e. Lost of 1 e  +1
Lost of 2 e  +2
WORKSHEET SOLUTION
Atom
Proton
No.
No.
of e
Electronic
Configuration
No. of e
to be
GAINED
No. of e
Left
No. of
e More
Ion
16S
16
16
2.8.6
2
18
2
S2-
9F
9
9
2.7
1
18
1
F-
Q:
Write general statement on formation of
negative ions.
A:
When there are more electrons than
protons in an atom, the atom becomes
negatively charged (ion). The charge of
the ion is dependent on the number of
electron gained.
i.e. Gained of 1 e  -1
Gained of 2 e  +2
POSITIVE IONS
(CATIONS)
 Group
I elements loses 1
electron to form positive ions,
i.e. Na+
 Group
II elements loses 2
electrons to form positive ions
i.e. Ca2+
NEGATIVE IONS (ANIONS)
 Group
VI elements gain 2
electron to form positive
ions, i.e. O2-
 Group
VII elements gain 1
electrons to form positive
ions i.e. Cl-
GROUP VIII OR 0(NOBLE GASES)
 Either
 Stable
 Does
duplet or octet structure
– Chemically unreactive (inert)
not lose or gain electrons easily
SUMMARY
Ions are charged particles formed when
an atom loses or gains electrons.
 Atoms forms ions to achieve octet
electronic structure.
 Ions are present in many daily
applications. i.e. food

REVIEW QUESTIONS
The mass number of an atom is equal to
A. The
number of neutrons in the atom
B. The
number of protons in the atom
C. The
sum of the numbers of protons and electrons
in the atom.
D. The
sum of the numbers of protons and neutrons
in the atom
Answer: D
The atomic number of calcium is
20. The electronic structure of the
calcium ion can be represented as
A)2,
8, 4
B)2, 8, 8
C)2, 8, 8, 2
D)2, 8, 8, 4
Answer: B
Which of the following pairs contains
particles which have equal and
opposite charges?
A)A
neutron and an electron
B)A neutron and a hydrogen nucleus
C)A proton and an electron
D)A proton and a neutron
Answer: C
How many protons, neutrons and
electrons does the sodium ion
contain?
Protons
A) 10
B) 11
C) 11
D) 11
Answer: C
Neutrons
13
11
12
12
Electrons
10
12
10
11
IONS IN DAILY LIFE

Sodium ion

Potassium ion

Magnesium ion

Calcium ion

Chloride ion

Fluoride ion