Atomic Structure © 2013 Marshall Cavendish International (Singapore) Private Limited
Atomic Structure © 2013 Marshall Cavendish International (Singapore) Private Limited.
Dec 23, 2015
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Atomic Structure
© 2013 Marshall Cavendish International (Singapore) Private Limited
Atomic Structure
1 Inside Atoms
2 The Proton Number and Nucleon Number
3 Isotopes
4 Arrangement of Electrons in Atoms
2
1 Inside Atoms
Learning Outcomes
• state the relative charges and masses of a proton, a neutron and an electron;
• describe the structure of an atom.
At the end you should be able to:
3
What are Atoms Made up of?
Atoms are made up of 3 sub-atomic particles:
• protons;
• neutrons;
• electrons.
4
1 Inside Atoms
Where are these Sub-Atomic Particles Found?
Nucleus
• protons (+) Positive Charge
• neutrons (neutral) No Charge
Shells around the nucleus
• electrons (–) Negative Charge
5
1 Inside Atoms
• Relative mass = 1
• Relative charge = +1
• Represented by the letter, p
Proton
• Found in the nucleus
p
6
1 Inside Atoms
• Relative mass = 1
• Relative charge = 0
• Represented by the letter, n
• Found in the nucleus
n
7
Neutron
5.1 Inside Atoms
• Relative mass =
• Relative charge = –1
• Represented by the letter, e
• Found in shells surrounding nucleus
e
8
Electron
1 Inside Atoms
Particle Symbol Relative mass Relative charge
proton p 1 +1
neutron n 1 0
electron e –1
Summary of Sub-Atomic Particles
9
1 Inside Atoms
1 Inside Atoms
2 The Atomic Number and Nucleon Number
3 Isotopes
4 Arrangement of Electrons in Atoms
Atomic Structure
10
Learning Outcomes
• Define atomic number and nucleon (mass) number;
• deduce the number of protons, neutrons and electrons in an atom;
• interpret and use symbols that represent an element’s nucleon and proton numbers ( ).
At the end of this section, you should be able to:
XAZ
2 The Atomic Number and Nucleon Number
11
The number of protons in an atom is called its atomic number.
Atomic number = number of electrons
Atomic Number (Z)
Since an atom is electrically neutral (i.e. has no overall charge),
12
2 The Proton Number and Nucleon Number
nucleus of a carbon atom
Each element has a unique atomic number.
Atoms of different elements have different atomic numbers.
Atomic Numbers
Example
Atomic number of carbon = 6
Any atom with 6 protons must be a carbon atom.
13
2 The Atomic Number and Nucleon Number
NaSodium
Atomic number
Where is the atomic number of an element found in the Periodic Table?
14
5.2 The Atomic Number and Nucleon Number
11
23 Mass Number(Average atomic mass)
Exercise
1. Find the atomic number of the atoms of the following elements:(a) Nitrogen
(b) Helium
(c) Sulfur
2. Which element has an atomic number of(a) 17?
(b) 3?
(c) 20?
7
2
16
Chlorine
Lithium
Calcium15
2 The Atomic Number and Nucleon Number
The total number of protons and number of neutrons in an atom is called the mass number.
Mass Number(A)
Mass number (A) = number of protons + number of neutrons
The mass of an atom depends on the number of protons and neutrons.
16
2 The Atomic Number and Mass Number
Find the number of neutrons
17
To find the number of neutrons we only need to use our periodic tables.
Mass number – Atomic number = Number of neutrons
1 Inside Atoms
2 The Proton Number and Nucleon Number
3 Isotopes
4 Arrangement of Electrons in Atoms
Atomic Structure
18
Learning Outcome
• define isotopes.
At the end of this section, you should be able to:
5.3 Isotopes
19
These are 3 atoms of hydrogen.
What are the similarities and differences of these 3 atoms?
Isotopes of Hydrogen
Hydrogen-1 Hydrogen-2 Hydrogen-3
20
5.3 Isotopes
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
Example 1
Chlorine gas consists of 75% chlorine-35, 25% chlorine-37.
What are Isotopes?
21
5.3 Isotopes
Carbon consists of 98.93% carbon-12, 1.07% carbon-13, and trace amounts of carbon-14.
C14
6 C12
6C13
6
What are Isotopes?
Example 2
22
5.3 Isotopes
Isotopes have the same chemical properties but slightly different physical properties.
Properties of Isotopes
Same chemical properties are due to
• the same number of electrons;
• only electrons involved in chemical reactions.
23
5.3 Isotopes
Different physical properties are due to
• different relative atomic masses;
• result in different densities, melting and boiling points.
Properties of Isotopes
24
5.3 Isotopes
Isotopes that emit high-energy radiation are called radioisotopes.
They are radioactive substances. The radiation emitted is dangerous because it can damage living cells and cause cancer.
Uses of Isotopes
25
5.3 Isotopes
However, radioisotopes can have important applications and can be safely used if they are handled properly.
For example, smoke detectors use a radioisotope. Smoke entering the smoke detector absorbs the radiation. This sets off an alarm in the smoke detector.
26
5.3 Isotopes
Uses of Isotopes
Protons, Neutrons, Electrons and Isotopes Review
Uses of Isotopes
27
5.3 Isotopes
5.1 Inside Atoms
5.2 The Proton Number and Nucleon Number
5.3 Isotopes
5.4 Arrangement of Electrons in Atoms
Chapter 5 Atomic Structure
28
Learning Outcome
• use diagrams to describe atoms as containing:
– protons and neutrons in nucleus;
– electrons arranged in the electron shells (energy levels).
At the end of this section, you should be able to:
5.4 Arrangement of Electrons in Atoms
29
The 1st shell• is closest to the nucleus;• holds a maximum of 2 electrons;• is always filled first;• has the lowest energy level.
Electrons move around the nucleus in regions known as electron shells.
Electronic Structure
5.4 Arrangement of Electrons in Atoms
30
Electronic Structure
The 2nd shell• can hold up to 8 electrons;• has higher energy than 1st shell.
The 3rd shell• can usually hold up to 8
electrons;• is filled up after the 2nd shell.
5.4 Arrangement of Electrons in Atoms
31
Nucleus12p, 12n
Electronic configuration/structure is the arrangement of electrons in an atom.
Electronic configuration = 2, 8, 2
Electronic Configuration/ Electronic Structure
Magnesium atom
Magnesium atom (Z = 12)
1st shell: 2 electrons
2nd shell: 8 electrons
3rd shell: 2 electrons
5.4 Arrangement of Electrons in Atoms
32
The valence shell or outer shell of an atom refers to the shell that is furthest away from the nucleus of the atom.
Valence electrons are the electrons found in the valence
shell.
Valence shell/ outer shell
Valence Shell and Valence Electrons
Magnesium has 2 valence electrons
Magnesium atom
5.4 Arrangement of Electrons in Atoms
33
The chemical properties of an element depend on the number of valence electrons.
Example 1Sodium (2, 8, 1) and Potassium (2, 8, 8, 1) • have similar chemical properties; • each has 1 valence electron.
Example 2Fluorine (2, 7) and Chlorine (2, 8, 7)• have similar chemical properties;• each has 7 valence electrons.
Valence Electrons
5.4 Arrangement of Electrons in Atoms
34
The Periodic TableElements are arranged in order of increasing proton number.
5.4 Arrangement of Electrons in Atoms
35
Horizontal rows of elements are called periods.
Vertical columns of elements are called groups.
5.4 Arrangement of Electrons in Atoms
36
The Periodic Table
Elements with the same number of valence electrons belong to the same group in the Periodic Table.
Sodium (2, 8, 1) and potassium (2, 8, 8, 1) belong to Group I.
Fluorine (2, 7) and chlorine (2, 8, 7) belong to Group VII.
Hence, elements in the same group of the Periodic Table have similar chemical properties.
Valence Electrons and the Periodic Table
5.4 Arrangement of Electrons in Atoms
37
Concept Map
Chapter 5 Atomic Structure
38
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