Matter
1.1: Atoms and molecules
What is
matter?
■
Matter is anything that has mass and
occupies space.
■
For examples are metal, plastics, gas
■
All matters consist of tiny particles
called atoms
1.1.1 Atom
■
Atom is composed of 3 primary
particles:
i- proton, p
ii- electron, e
iii-neutron, n
Figure 1
electron
-
Proton
( positive charge)
nucleus
+
+
Neutron (neutral)
1.1 Figure of atom
■
Proton is a sub-atomic particles which
carries a single positive charges
■
Neutron is a subatomic particles which
carries no charges (neutral)
■
Electron cloud occupied by negative
charged populated surrounding the
nucleus
Summarized properties of these
particle:
Name
Electron (e)
Relative Mass (a.m.u) Mass (gram)
charge
-1
5.4 x 10 -4
9.1095 x 10-28
Proton (p)
+1
1.00
1.66 x 10-24
Neutron (n)
0
1.00
1.66 x 10-24
Nucleon
■
the particles that are found in the
nucleus
■
consist proton and neutron
■
By proton we can identified the element
1.1.2 Isotopic notation
Nucleon number
Atom or ion
Proton number
Definition
■
Proton number, Z, is total number of
protons in the nucleus
■
Nucleon number, A, is total number of
proton and neutron in the nucleus
Ex:
Number of protons = proton number
= 13
Number of neutrons = nucleon number – proton number
= 27 - 13
= 14
Number of electron = proton number – charge carried by
species
= 13 – ( +3)
= 10
Q: determine the number of proton, neutron
and electron in the following species.
solution
90
38
Sr
Sr
Number of protons = proton number
= 38
Number of neutrons = nucleon number – proton number
= 90 – 38
= 52
Number of electron = proton number (species is neutral)
= 38
35
17
Cl-
Number of protons = proton number
= 17
Number of neutrons = nucleon number – proton number
= 35 – 17
= 18
Number of electron = proton number – charge carried by
species
= 17 – (-1)
= 18
1.1.3 Isotopes
■
■
Two or more atoms of the same element
having same proton number but different
nucleon numbers
Ex:
species Protium
Deuterium Tritium
Proton
Neutron
electron
1
0
1
1
1
1
1
2
1
Isotopes of an element have the same:
1.
number of protons (proton number)
2.
charge of nucleus of the atoms (ionization
energy; electron affinity; size of the atom;
electronegativity are the same)
3.
number of electrons in a neutral atom
4.
electronic configuration (the number of valence
electrons)
5.
chemical properties
Isotopes of an element have different:
■
number of neutrons (nucleon number) in
the nucleus of the atoms
■
relative isotopic mass
■
physical properties (e.g boiling point /
melting point, density, effusion rate,…)
1.1.4 Molecule
■
A molecule consists of a small number of
atoms joined together by covalent bond.
■
Diatomic molecule: contains two atoms
(example: H2, Cl2, HCl, CO)
■
Polyatomic molecule: contains more
than two atoms (example: H2O, NH3)
1.1.5 Ion
■
An ion is a charged species formed from a neutral atom
or molecule when electrons are gained or lost as the
result of a chemical reaction.
■
Cation: a positively charged ion (number e < number p)
(example: Mg 2+, K +),)
■
Anion: a negatively charged ion (number e > number p)
(example: Cl−, OH−)
■
Monatomic ion: ion contains only one
nucleus (example: Fe3+ , S2−)
■
Polyatomic ion: ion contains more than
one nucleus (example: H3O+, CN−)
1.1.6 Relative Mass
a.
Relative Atomic Mass, Ar of an element
Ar = average mass of an atom of the element
1/12 x mass of one atom of 12C
b.
Relative Molecular Mass, Mr of a
molecular substance
Mr = mass of one molecule of the compound
1/12 x mass of one atom of 12C
or
= sum of the relative atomic masses of all
the atoms shown in the molecular
formula.
Explain why:
■
■
The mass of an atom is found mainly in its
nucleus?
Atom carries no charges.
Fill in the blanks :
Species
12
C
Proton
6
Electron
Neutron
6
6
35
Cl
17
18
17
226
Ra
88
138
88
238
U
92
17
18
92
92
19
18
20
20