1. CHAPTER 5 Atomic Structure
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2. Chapter 5 Atomic Structure
5.1 Inside Atoms
5.2 The Proton Number and Nucleon Number
5.3 Isotopes
5.4 Arrangement of Electrons in Atoms

3. What connects Everything?

4. In 465 BC, the teacher Democritus of Abdera, Greece; suggested tiny particles that are indivisible and indestructible. He called them atoms.

5. In 1787, an English teacher studied the ratios in which elements combine in chemical reactions. John Dalton came up with Dalton’s atomic theory.
Atoms of same element are identical
Atoms of different elements can physically mix.
Atoms can chemically combined.
Chemical reactions occur due to rearrangement of atoms.

6. In 1880, JJ Thomson discovered electrons with the help of positive rays. He noticed atoms can be divided concluding that atoms have a positive core and electrons within.

7. Ernst Rutherford, a student of Thomson, proved that the atom has a solid atomic nucleus.

8. In 1933, Niehls Bohr identified that the electrons are arranged by it’s energy levels.

9. 5.1 Inside Atoms Learning Outcomes
At the end of this section, you should be able to:
state the relative charges and masses of a proton, a neutron and an electron;
describe the structure of an atom. 9

10. 5.1 Inside Atoms What are Atoms Made up of?
Atoms are made up of 3 sub-atomic particles:
protons;
neutrons;
electrons. 10

11. 5.1 Inside Atoms Where are these Sub-Atomic Particles Found? Nucleus
protons (+ve)
neutrons (neutral)
Shells around the nucleus
electrons (–ve) 11

12. 5.1 Inside Atoms Proton Represented by the letter, p
Found in the nucleus
Relative mass = 1
Relative charge = +1

13. 5.1 Inside Atoms Neutron Represented by the letter, n
Found in the nucleus
Relative mass = 1
Relative charge = 0 13

14. 5.1 Inside Atoms Electron Represented by the letter, e
Found in shells surrounding nucleus
The relative mass of an electron is negligible.
Relative mass =
Relative charge = –1 14

15. 5.1 Inside Atoms Summary of Sub-Atomic Particles Particle Symbol
Relative mass
Relative charge
proton p 1 +1
neutron n
electron e –1

16. Chapter 5 Atomic Structure
5.1 Inside Atoms
5.2 The Proton Number and Nucleon Number
5.3 Isotopes
5.4 Arrangement of Electrons in Atoms

17. 5.2 The Proton Number and Nucleon Number
Learning Outcomes
At the end of this section, you should be able to:
define proton (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 ( ). 17

19. 5.2 The Proton Number and Nucleon Number
Proton Number (Z)
The number of protons in an atom is called its proton number.
It is also known as the atomic number.
Since an atom is electrically neutral (i.e. has no overall charge),
Proton number = number of electrons 19

20. 5.2 The Proton Number and Nucleon Number
Proton Numbers
Each element has a unique proton number.
Atoms of different elements have different proton numbers.
Emphasis should be on the proton number being unique for each element, like that of an identification (ID) number.
nucleus of a carbon atom
Example
Proton number of carbon = 6
Any atom with 6 protons must be a carbon atom. 20

21. 5.2 The Proton Number and Nucleon Number
Where is the proton number of an element found in the Periodic Table? 23 Na 11
Sodium
Help students locate proton number from Periodic Table – bottom left corner.
Proton number 21

22. 5.2 The Proton Number and Nucleon Number
Exercise
1. Find the proton number of the atoms of the following elements:
(a) Nitrogen
(b) Helium
(c) Sulfur
2. Which element has a proton number of
(a) 17?
(b) 3?
(c) 20? 7 2 16
1. (a) Nitrogen – 7; (b) Helium – 2; (c) Sulfur – 16.
2. ( a) 17 – Chlorine; (b) 3 – Lithium; (c) 20 – Calcium.
Chlorine
Lithium
Calcium 22

23. 5.2 The Proton Number and Nucleon Number
Nucleon Number (A)
The total number of protons and number of neutrons in an atom is called the nucleon number.
Nucleon number is also known as mass number.
The mass of an atom depends on the number of protons and neutrons.
Nucleon number (A) = number of protons + number of neutrons

24. Chapter 5 Atomic Structure
5.1 Inside Atoms
5.2 The Proton Number and Nucleon Number
5.3 Isotopes
5.4 Arrangement of Electrons in Atoms

25. 5.3 Isotopes Learning Outcome
At the end of this section, you should be able to:
define isotopes. 25

26. 5.3 Isotopes Isotopes of Hydrogen These are 3 atoms of hydrogen.
They each have one proton.
They have different numbers of neutrons.
What are the similarities and differences of these 3 atoms? 26

27. Cl 5.3 Isotopes What are Isotopes?
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
Although the mass of an atom is determined by the sum of protons and neutrons, the mass of an atom of an element is not always a whole number (eg. Cl – 35.5). The mass of an atom of an element is an average mass of the isotopes that make up the element. The percentage abundance is used to calculate the average mass.
Example 1 Cl 35 17 37
Chlorine gas consists of 75% chlorine-35, 25% chlorine-37. 27

28. C 5.3 Isotopes What are Isotopes? Example 214 6 12 13
Carbon consists of 98.93% carbon-12, 1.07% carbon-13, and trace amounts of carbon-14.

29. 5.3 Isotopes Properties of Isotopes
Isotopes have the same chemical properties but slightly different physical properties.
Same chemical properties are due to
the same number of electrons;
only electrons involved in chemical reactions.

30. 5.3 Isotopes Properties of Isotopes
Different physical properties are due to
different relative atomic masses;
result in different densities, melting and boiling points.

31. 5.3 Isotopes Uses of 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.

32. 5.3 Isotopes Uses of 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.

33. 5.3 Isotopes Protons, Neutrons, Electrons and Isotopes Review
Uses of Isotopes
Clicking on the URL button will link you to < a website with a video on protons, neutrons, electrons and isotopes. It reviews the chemical makeup of elements. (The video is approximately 4.5 minutes long.)
Clicking on the URL button will link you to < a website with a video on the uses of radioactive isotopes. It outlines the uses of common radioactive isotopes. (The video is approximately 3.4 minutes long.) 33

34. Chapter 5 Atomic Structure
5.1 Inside Atoms
5.2 The Proton Number and Nucleon Number
5.3 Isotopes
5.4 Arrangement of Electrons in Atoms

35. 5.4 Arrangement of Electrons in Atoms
Learning Outcome
At the end of this section, you should be able to:
use diagrams to describe atoms as containing:
– protons and neutrons in nucleus;
– electrons arranged in the electron shells (energy levels). 35

36. 5.4 Arrangement of Electrons in Atoms
Electronic Structure
Electrons move around the nucleus in regions
known as electron shells.
The 1st shell
is closest to the nucleus;
holds a maximum of 2 electrons;
is always filled first;
has the lowest energy level.

37. 5.4 Arrangement of Electrons in Atoms
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. 37

38. 5.4 Arrangement of Electrons in Atoms
Electronic Configuration/ Electronic Structure
Electronic configuration/structure is the arrangement of electrons in an atom.
Nucleus
12p, 12n
Magnesium atom (Z = 12)
1st shell: 2 electrons
2nd shell: 8 electrons
3rd shell: 2 electrons
To show the electronic structure of an atom:
Indicate the number of protons and neutrons.
Infer the number of electrons.
Fill electrons starting from the 1st shell.
Magnesium atom
Electronic configuration = 2, 8, 2 38

39. 5.4 Arrangement of Electrons in Atoms
Valence Shell and Valence Electrons
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.
Magnesium has 2 valence electrons
Valence shell/ outer shell
Magnesium atom

40. 5.4 Arrangement of Electrons in Atoms
Valence Electrons
The chemical properties of an element depend on the number of valence electrons.
Example 1
Sodium (2, 8, 1) and Potassium (2, 8, 8, 1)
have similar chemical properties;
each has 1 valence electron.
Example 2
Fluorine (2, 7) and Chlorine (2, 8, 7)
have similar chemical properties;
each has 7 valence electrons.

41. 5.4 Arrangement of Electrons in Atoms
The Periodic Table
Elements are arranged in order of increasing proton number.

42. 5.4 Arrangement of Electrons in Atoms
The Periodic Table
Horizontal rows of elements are called periods.
Vertical columns of elements are called groups.

43. 5.4 Arrangement of Electrons in Atoms
Valence Electrons and 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. 43

44. Chapter 5 Atomic Structure
Concept Map