PAMANTASAN NG CABUYAO
KATAPATAN HOMES, BANAY-BANAY, CABUYAO LAGUNA
College of Arts and Sciences
LM 4 - ATOMIC STRUCTURE
Objectives:
1.
2.
3.
4.
State the modern concepts regarding the structure of an atom.
Explain the different facts about the atomic structure.
Explain the Hund’s Rule of Maximum Multiplicity and the Pauli’s Exclusion Principle.
Be able to write the electronic configuration of an atom using the atomic number.
Atomic Structure
Atom – smallest particle of an element that takes part in a chemical reaction.
The basic structure of an atom includes a tiny, relative massive nucleus, containing at least one
proton and usually one or more neutrons. Outside of the nucleus are energy levels (also called shells) which
contain one or more electrons.
The neutrons have the greatest mass and have no charge. The protons have slightly less mass than the
neutrons and are positively charge. The electrons have almost no mass and are negatively charged. The
electrons move around the nucleus in energy levels
3 Smaller sub – atomic particles of an atom:
1.
2.
3.
Proton (p+) – positively charge particle of an atom with a relative mass of 1.0073 amu.
Neutron (n0) – neutral particle of an atom with a relative mass of 1.0087 amu.
Electron (e – ) – negatively charge particle with a mass of 0.00055 amu.
Atom can be an isotopes, isotones, or isobars
Isotopes – two or more atoms with the same atomic number but different mass number.
1
Examples:
2
H,
1
3
H,
35
H
1
;
37
Cl ,
1
17
Cl
17
Isotones – any of two or more species of atoms or nuclei that have the same number of neutrons but different
number of protons.
27
Examples:
28
Al 14 ,
13
31
Si 14 ;
14
32
P 16 ,
15
S 16
16
Aluminum and silicon are isotones since they have the same number of neutrons which is 14; whereas,
phosphorus and sulfur have 16 neutrons.
Isobars – two or more atoms with the same mass number but different atomic number.
59
Examples:
Co ,
27
59
Ni
209
;
28
209
Bi ,
83
Po
84
Cobalt and nickel are isobars since they have the same mass of 59; whereas bismuth and polonium, the
mass number is both 209.
Facts about the Atomic Structure
1.
2.
3.
4.
5.
The protons and the neutrons are found inside the nucleus which is the central part of the atom.
The electrons are found outside the nucleus in shells or energy levels.
The number of protons in an atom is defined as the atomic number.
The nucleus is a very small part of an atom in terms of size, but it contains most of the atom’s
mass.
The number of protons + the number of neutrons is defined as the mass number which is
essentially equal to the atomic mass in amu; hence, the number of neutrons is equal to the mass
number minus the number of protons.
An atom is electrically neutral since it contains the same number of protons inside the nucleus
as there are electrons outside the nucleus.
Electron Distribution
The electron configuration of an atom is the representation of the arrangement of electrons
distributed among the orbital shells and subshells. Commonly, the electron configuration is used to describe
the orbitals of an atom in its ground state, but it can also be used to represent an atom that has ionized into
a cation or anion by compensating with the loss of or gain of electrons in their subsequent orbitals. Many
of the physical and chemical properties of elements can be correlated to their unique electron configurations.
The valence electrons, electrons in the outermost shell, are the determining factor for the unique chemistry
of the element.
Mnemonics in Organization of Electrons
1s
Note: following the arrow head, you will have
2s
2p
the correct arrangement of the subshells
3s
3p
3d
4s
4p
4d
4f
5s
5p
5d
5f
6s
6p
6d
7s
7p
8s
Subshells and Capacity of Each Main Shells
The electron configuration of each element is unique to its position on the periodic table. The energy level
is determined by the period number and the number of electrons is given by the atomic number of the
element where we can determine the number of valence electrons (electrons in the outermost shell).
The limit of two electrons per orbital is based on Pauli’s Exclusion Principle which states that
electrons occupying the same orbital must have their spins in opposite directions.
Example: Helium with atomic no. 2
1s2
Since helium has two electrons only based on the atomic number, electrons will occupy the first energy
level and on the same orbital, its electrons are arranged in opposite direction.
Hund’s Rule of Maximum Multiplicity – states that electrons entering a subshell containing more
than one orbital must be spread out over the available orbitals with their spins in the same direction.
Example. 1:
Draw the electronic configuration of oxygen atom with atomic no. 8, using the orbital and
the arrow box method:
1s2
2s2
2p4
-
orbital method
Example 2:
arrow-box method
Draw the electronic configuration of chlorine atom with atomic no. 17, using the orbital
and the arrow box method:
1s2
2s2
2p6
3s2
3p5
-
orbital method
-
Example 3:
arrow-box method
Draw the electronic configuration of calcium atom with atomic no. 20, using the orbital
and the arrow box method:
1s2
2s2
2p6
3s2
3s6
4s2
-
orbital method
- arrow-box method
References:
https://socratic.org
https://chem.libretexts.org/
Stoker, H. S. 2010. Exploring General, Organic, and Biological Chemistry
Seatwork: Draw the electronic configuration of the following elements using the orbital and arrow-box
1)
2)
3)
4)
30 Zn
18 Ar
Rb
56 Ba
37
Quizt #3: Atomic Structure
A. Choose the letter of the answer that best complete each statement.
_______ 1. Which scientist developed the atomic theory of matter?
a) Antoine Lavoisier
b) John Dalton
c) Aristotle
d) Rutherford
_______ 2. Which of the following represents an ion?
a) Ba
b) 4He
c) Na+
d) 40 Ca 20
_______ 3. A positive charge will
a) attract another positive
b) repel another positive charge
c) repel a negative charge
d) neither attract nor repel a negative charge.
_______ 4. Isotopes contain different numbers of
a) atomic number
b) atomic mass
c) neutrons
d) mass number
_______ 5. Isobars contain the same
c) atomic number
d) atomic mass
c) neutrons
d) mass number
_______ 6. The number of protons in an atom is called
a) atomic mass
b) mass number
c) atomic number
d) atomic weight
_______ 7. The d subshell has a maximum number of how many electrons?
a) 2
b) 6
c) 10
d) 14
_______ 8. Which of the following arrangement is correct?
a) 1s2 2s2 sp7
b) 3p6 3d10 4s2
c) 2s2 2p2 3p6
d) 3s23p6 4s2
_______ 9. Isotones contain the same number of
a) protons
b) Neutrons
c) electrons
d) nuclei
________ 10. Which of the following arrangement is incorrect?
a) 1s2 2s2 sp6
b) 3p6 4s3 3d10
c) 2s2 2p6 3s2
d) 3s23p6 4s2
B. Write true if the statement is correct, if it is false, change the underlined word or words to make
the statement correct.
___________________ 11. An atom’s mass number is the sum of its protons plus neutrons.
___________________ 12. A/An isotope is an atom or group of atoms having the same number of
neutrons but different numbers of protons
___________________ 13. The limit of two electrons per orbital is based on Hund’s Rule of Maximum
Multiplicity.
___________________ 14. In an atom, the 4th energy level has a maximum of 18 electrons.
___________________ 15. The number of protons in an atom is called the atomic mass.