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GSCI 163
Lecture 5
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Review
• Electrons in an atom are distributed in shells, orbitals and energy levels.
• When electrons absorb photons they jump to higher orbitals
• They move back up by emitting a photon whose energy correspond to the change in energy level
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Activity
• Finding the emission lines of different compounds.
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Chemistry
• Electrons in an atom are distributed in shells, orbitals and energy levels.
• The way electrons are shared will determine how elements combine with each other to form compounds.
• The highest or last shell of an atom is the valence shell
• The valence shell determines the chemistry and properties
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Various groups
• Metals and non-metals– Metals tend to lose
electrons in chemical reactions
– Non-metals tend to gain (or share) electrons in chemical reactions
Semi-metals have both metallic and non-metallic properties
– Most reactive metal Cesium– Most reactive non-metal Fluorine
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Noble gases
• The valence shell is full. Thus they almost never react.
– Argon gas (Ar) is used as an inert gas in light bulbs to prevent the filament, made of tungsten (W), from reacting under intense heat
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Other families• Alkali metals
– Only one valence electron; very soft metals– React so easily with Oxygen (O) and moisture that they need to be stored under oil
• Alkaline earth metals– Two valence electrons; harder than alkali metals– Not so reactive.
• Halogens– Seven electrons in the valence shell– Very active non-metals
• Fluorine – highly corrosive, • Chlorine – purifying agent, • Bromine – desinfectant
• Semi-metals (semi-conductors)– 3,4 or 5 electrons in the valence shell– Makes them behave both as metals and insulators
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Atomic size
• Increase when:– Add a new shell
(moving down a group) since electrons are farther away from the nucleus
– Number of protons decrease (across a period) since electrons are more loosely bound by electrostatic force
Cs ~ 0.47 nm He ~ 0.064 nm
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Ionization energy
• Energy required to remove one electron from the outer shell
H
He
Hardest elements to remove one electron from
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Octet rule
• Most common elements have electrons on the s and p orbitals of their outmost shells
• We can fit 2 electrons on s and 6 on p, with a total of 8 electrons
Octet rule: atoms will combine with other atoms in such a way that gives a full shell of 8 electrons
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Naming compounds
• We represent compounds with a chemical formula:
H2O
• Names are also used to identify the compound unambiguously
Symbol of the element
Number of atoms of the element
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Compounds with special names
There are no rules for these. Their names are learned individually
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Metal and a non-metal
• Groups 1A, 2A plus Aluminum (Al), Zinc (Zn) and Silver (Ag). They form only one ion.
• Rule for binary compounds:– Name of the metal + non-metal with ending –ide
Examples:NaCl – Sodium ChlorideAl2O3 –
Ca3N2 –
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Two non-metals
• Rule: – The less metallic element (farther left and/or farther down the
periodic table) comes first. The second is named with ending –ide .– For more than one element use Greek prefixes: di(2), tri(3),
tetra(4), penta (5), hexa (6), hepta (7), octa (8).
Examples:HCl – hydrogen chlorideCS2 –
PBr3 –
IF7 –
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Compounds with polyatomic ions
• Metal plus a polyatomic ion:Rule: name of the metal + the name of
of the polyatomic ion
Example:ZnSO4 – Zinc Sulfate
NaC2H3O2 –
Mg(NO3)2 –
K3PO4 –
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Next class
Calculating reactions
• To prepare for the class read:– Handout pages 17 to 20 (day 5)– Presentation by Rebecca Cross, Acids and Bases
• To prepare for the quiz read:– Handout pages 16 (day 4)– Power point for this class– Your class notes