Atomic Structure © 2013 Marshall Cavendish International (Singapore) Private Limited

Atomic Structure 1Inside Atoms 2The Proton Number and Nucleon Number 3Isotopes 4Arrangement 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

ParticleSymbolRelative massRelative charge protonp1+1 neutronn10 electrone–1 Summary of Sub-Atomic Particles 9 1 Inside Atoms

2The Atomic Number and Nucleon Number 3Isotopes 4Arrangement 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: 2The 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 2The 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 2The Atomic Number and Nucleon Number

Na Sodium Atomic number Where is the atomic number of an element found in the Periodic Table? The Atomic Number and Nucleon Number 11 23Mass 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? Chlorine Lithium Calcium 15 2The 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 2The 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

1Inside Atoms 2The Proton Number and Nucleon Number 3Isotopes 4Arrangement 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 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. ClCl ClCl What are Isotopes? Isotopes

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

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

Protons, Neutrons, Electrons and Isotopes Review Uses of Isotopes Isotopes

5.1Inside Atoms 5.2The Proton Number and Nucleon Number 5.3Isotopes 5.4Arrangement of Electrons in Atoms Chapter 5Atomic 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 1 st 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 2 nd shell can hold up to 8 electrons; has higher energy than 1 st shell. The 3 rd shell can usually hold up to 8 electrons; is filled up after the 2 nd shell. 5.4 Arrangement of Electrons in Atoms 31

Nucleus 12p, 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) 1 st shell: 2 electrons 2 nd shell: 8 electrons 3 rd 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 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. Valence Electrons 5.4 Arrangement of Electrons in Atoms 34

The Periodic Table Elements 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 5Atomic Structure 38