Chemistry 2202 Unit 2Section 1Homework Portfolio - KEY (2006-2007)page 1
CHEMISTRY 2202
Unit 2Section 1Homework Portfolio Key
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(2)1.How is the distribution of electrons in the electron cloud of an atom related to the structure of the periodic table of the elements?
The periodic table of elements has elements arranged in vertical rows called groups. These groups contain elements whose atoms share a similar distribution of electrons in their valence orbitals. Elements in the same group possess the same number of valence electrons.
The periodic table is also arranged in rows called periods. The period number indicates the number of energy levels of an atom.
(2)2.Sketch an original Bohr energy level diagram for each atom.
(a) silicon(b) sulphur
(2)3.How does the modified Bohr model differ from the original Bohr model?
The modified Bohr Model differs from the original model in that it recognizes the advances of the quantum mechanical model by placing electrons in orbitals. Each energy level is replaced by orbitals, regions in which a maximum of two electrons can exist.
(2)4.Draw modified Bohr diagrams for each atom.
(a) silicon(b) sulfur
(1)5.(a)What is a valence electron?
A valence electron is an electron that is found in the outer energy levels (orbitals) of an atom.
(2)(b)Compare a lone pair and a bonding electron.
A lone pair of electrons represent a group of two electrons which fill a valence orbital. A bonding electron is a single electron that occupies a valence orbital. .
(8)6.Copy and complete this table:
Atom / # valence electrons / Lewis Diagram / # bonding electrons / # lone pairs / bonding capacityradium / 2 / / 2 / 0 / 2
cesium / 1 / / 1 / 0 / 1
aluminum / 3 / / 3 / 0 / 3
antimony / 5 / / 3 / 1 / 3
(1)7.(a)What is the electronegativity of an element?
Electronegativity is defined as the tendency of an atom to attract valence electrons.
(3)(b)List three trendsin electronegativity values in the periodic table.
(i) Electronegativity generally decreases as you move down a group.
(ii)Electronegativity generally decreases as you move left with a period.
(iii)Electronegativity is generally higher on the right side of the staircase line dividing elements into metals and nonmetals.
(3)(c)Use electronegativity values to predict the type of bonding that should occur between atoms in each pair.
(i) strontium (EN=1.0) and chlorine(EN=3.0): Ionic Bonding
(ii)nickel(EN=1.8) and silver (EN=1.9): Metallic Bonding
(iii) sulphur (2.5) and oxygen (EN=3.5): Covalent Bonding
8.Gold jewellery has been popular for millennia. Pure gold jewellery is rare and impractical because of the softness of pure gold metal. 18 carat gold is harder. It is an alloy of gold (70%), copper (20%), and silver (10%).
(2)(a) Sketch an electron sea model for the 18 carat gold.
In these proportions for every 10 atoms there will be 7 Au, 2 Cu, and 1 Ag. The Cu and Ag will be imbedded in the spaces between the Au
(2)(b)Why are metal alloys like 18 carat gold excellent conductors of electrical current?
Because of the low electronegativities of metals, the valence electrons are not held tightly, and are, for all intents and purposes, mobile. Electrons entering the metal from an outside source will cause the movement of these mobile electrons through the metal.