1. Chapter 3: Matter and Atomic Structure
Unit 2: Composition of Earth
Covers 3.1 and 3.2

2. Matter and Elements All matter is made up of elements
Element – a substance that can’t be broken down into simpler substances
Periodic Table of Elements – 92 naturally occurring elements, others are produced in laboratory experiments.
Chemical symbol - the one- two- or three-letter abbreviation that identifies an element

3. Elements are made up of atoms
Each element has distinct characteristics
Elements are arranged on the periodic table of elements

4. Atoms
Atoms – smallest particle of an element that holds the characteristics of the element
Composed of:
Electrons – (-)
Protons – (+)
Neutrons – (0)
The protons and neutrons
are located in the center of the atom at the nucleus
the nucleus has a positive charge - + - + - + + -

6. Atoms cont. Atomic Number – number of protons
Mass Number – number of protons and neutrons
Number of protons = number of electrons
Number of neutrons – mass number – number of protons -
Atomic Number: 4 - x x -
Mass Number: = 8 x x
Number of Neutrons: 8 – 4 = 4 -

7. Chemical Symbols
Chemical Symbols – abbreviation or short representation for an element
Symbol
Element Na
Sodium Mg
Magnesium H
Hydrogen Ur
Uranium He
Helium C
Carbon O
Oxygen Fe
Iron K
Potassium Al
Aluminum Cu
Copper Au
Gold

8. Energy Levels
Energy level – indicates the area in which electrons are found
Valence electrons – electrons in the outermost energy level
The number of electrons fitting in the outer shells goes in a certain sequence
This sequence is 2:8:18:32

9. E1 – holds 2 electrons
E2 – holds 8 electrons
E3 – holds 18 electrons
E4 – holds 32 electrons

10. Energy Levels cont. Remember the sequence is 2:8:18:32
Electrons tend to occupy the lowest available energy level - - - - - - x
00000 x - - - x x
xxxxx - - - - -

11. Energy Levels cont. Remember: What are valence electrons?
_____________________________________________________________________.
Valence electrons determine the chemical behavior of the elements (bonding, reactions to other substances, etc.)
Valence electrons do all the work

12. Isotopes
All atoms of an element have the same number of protons, however the number of neutrons in the nucleus can vary.
Isotopes – when atoms of the same element have different mass numbers due to the different number of neutrons in the nucleus
Atomic mass – the average of the mass numbers of the isotopes of an element

13. Example of an Isotope
Chlorine has 17 protons, but may have a different number of neutrons (like 18 or 20).
This means chlorine could have a mass number of 35 (17 protons + 18 neutrons) or a mass number of 37 (17 protons + 20 neutrons)

14. Elements in the universe
Hydrogen and helium are the most abundant elements in the universe.
They account for 99% of the elements and trace elements account for the other 1%
Note: Elements in the Earth’s crust are different than those in the universe

15. Elements in the Crust
Oxygen is the most abundant element in the crust.