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Ozone. An allotrope of oxygen two forms of the same element that differ in their molecular and crystal structure, and hence their properties. Filtering Effect of the Ozone Layer. Subatomic Particles. There are many… more than 200! But 3 are most significant: Electrons Nucleus
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Ozone • An allotrope of oxygen two forms of the same element that differ in their molecular and crystal structure, and hence their properties
Subatomic Particles There are many… more than 200! But 3 are most significant: • Electrons • Nucleus Protons Neutrons
Properties of atoms Mainly due to the • the number and distribution of electrons
Properties of atoms Mainly due to the • the number and distribution of electrons Electrons are arranged in levels or shells around the nucleus
Properties of atoms Mainly due to the • the number and distribution of electrons Electrons are arranged in levels or shells around the nucleus The electrons in the innermost shell are most strongly attracted to the nucleus
Which type of electrons determines the “behavior” of atoms? the ones which can “interact” with other atoms. (not the ones closest to the nucleus, in the innermost shell)
Which type of electrons determines the “behavior” of atoms? the ones which can “interact” with other atoms. (not the ones closest to the nucleus, in the innermost shell) The most distant electrons (in the outermost shell) are the least attracted to the nucleus
The shells are associated with energy levels: Each energy level • has maximum electron capabilities
The shells are associated with energy levels: Each energy level • has maximum electron capabilities • becomes particularly stable when “filled”
The shells are associated with energy levels: Each energy level • has maximum electron capabilities • becomes particularly stable when “filled” • The innermost level, the lowest energy level, can hold a maximum of two electrons
How are molecules formed? • when atoms form “bonds” with one another
How are molecules formed? • when atoms form “bonds” with one another Covalent bonds: when two atoms “share” a pair of electrons
How to Write Lewis Structures Step 1: Count the number of outer electrons. For a neutral molecule this is equal to the number of outer electrons of the constituent atoms.
How to Write Lewis Structures Step 1: Count the number of outer electrons. For a neutral molecule this is equal to the number of outer electrons of the constituent atoms. Step 2: Connect the atoms by a covalent bond represented by a dash.
How to Write Lewis Structures Step 3: Distribute the remaining electrons not involved in bonding “in pairs” in such a way that as many atoms as possible have 8 electrons