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

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

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

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 - + - + - + + -

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: 4 + 4 = 8 x x Number of Neutrons: 8 – 4 = 4 -

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

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

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

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 - - - - -

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

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

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)

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

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