Download - Chapter 7 and 8 notes
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Chapter 7 and 8Ionic and Covalent Bonding
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7.1 Ions• Valence Electrons are the electrons in
the highest occupied energy level of an element’s atoms.
• The number of valence electrons determines the chemical properties of an element.
• To find the number of valence electrons in an atom of a representative element, look at the group number. (see table 7.1)
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Valence Electrons
• Valence electrons are usually the only electrons used in chemical bonds, so they are show in electron dot structures.
• In forming compounds, atoms tend to achieve the electron configuration of a noble gas.
• This is called the Octet Rule.
• All atoms want to have 8 electrons in their outer or valence shell.
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Formation of Cations
• Atoms of the metallic elements tend to lose their valence shell electrons leaving 8 in the next level down.
• An atom’s loss of valence of electrons produces a cation, or positively charged ion.
• Remember, an ion is a charged atom that has lost or gained electrons during the chemical bonding process.
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Na
Neutral Sodium Atom
+Whoa…I just got smaller…
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Cl
Neutral Chlorine Atom
-Now I’m bigger and stronger….
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Transition Metals
• For transition metals, the charges of cations may vary.
• For example, elements such as iron, nickel and copper may lose 1 to three electrons depending on the chemical compound.
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Formation of Anions• A anion is an atom or group of atoms with a
negative charge.
• The gain of a negatively charged electron by a neutral atom will create an anion.
• Non-metals typically form anions.
• The name of the anion is not the same as the name of the atom.
• It usually ends in –ide. (See table 7.2)
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Vocabulary Cards
• Valence electron
• Octet Rule
• Transition Metal
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SUM IT UPName the following ions properly.
F-
Cl-
Ca+2
O-2
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Electron Configurations
• An electron configuration is a way to show the electrons in a particular atom in the proper order.
• Since electrons are arranged in shells, each shell has a different name.
• Use the periodic table to figure out the electron configuration for any atom.
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LET’S PRACTICE!
1s2 2s1
1s2 2s2 2p5
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
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Vocabulary Cards
• Electron configuration
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POST IT UP
What is the electron configuration for carbon?
I GOT THIS! I NEED HELP!
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7.2 Ionic Bonds and Ionic Compounds
• Compounds composed of cations and anions are called ionic compounds.
• Ionic compounds are usually composed of a a metal and other nonmetals.
• Although they are composed of ions, they are electrically neutral…meaning no charges or their charges cancel out.
• Bonds that hold ionic compounds together are called ionic bonds.
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Formula Units
• A chemical formula shows the kinds and numbers of atoms in the smallest representative unit of a substance.
• A formula unit is the lowest whole-number ratio of ions in an ionic compound.
• The chemical formula is not always the lowest whole number ratio.
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Let’s Practice
• How many kinds of atoms are in each of these ionic compounds?
• NaCl
• MgCl2• Ca(OH)2
• Ca3(PO4)2
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Properties of Ionic Compounds
• Most ionic compounds are crystalline solids at room temperature.
• Ionic compounds generally have high melting points.
• Ionic compounds can conduct an electric current when melted or dissolved in water.
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Vocabulary Cards
• Ionic Bond
• Formula Unit
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SUM IT UP
How many kinds of each of these atoms are in this compound?
Ca (C2H6O2)2
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8.1 Molecular Compounds.• Some compounds are not ionic.• Instead of giving or taking electrons, these
compounds share electrons to complete their Octet.
• This is called a covalent bond.• A molecule is a neutral groups of atoms joined by
a covalent bond.• A diatomic molecule is a molecule consisting of
only two atoms.• A compound composed of molecules is called a
molecular compound.
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Molecular Formulas
• A molecular formula is the chemical formula of a molecular compound.
• It shows how many of each element a molecule contains.
• A molecular formula does not tell you about a molecule’s structure.
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8.2 The Nature of Covalent Bonding
• In forming covalent bonds, electron sharing usually occurs so that atoms attain the electron configuration of a noble gas.
• Combinations of nonmetallic elements in groups 4A, 5A, 6A and 7A are likely to form covalent bonds.
• They share electrons to achieve an octet like a noble gas.
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Diagrams• An electron dot diagram represents the
shared pairs of electrons in a molecule.
• Each bond is two electrons or two dots.
• A structural formula represents the covalent bonds by dashes and shows the arrangement of the atoms.
• Each dash will equal two electrons.
• A pair of valence electrons not shared between atoms is called an unshared pair, lone pair or nonbonding pair.
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Lone unshared pairs
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Polyatomic ions
• A polyatomic ion is a tightly bound group of atoms that has a positive or negative charge and behaves like a unit.
• A group of atoms may be covalently bonded as a polyatomic ion but since the whole unit has a charge, it can bond with other charged ions.
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Vocabulary Cards
• Covalent bond
• Molecule
• Polyatomic ion
• Unshared pair
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SUM IT UP
Draw the structural diagram for water.
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8.4 Polar Bonds and Molecules• Covalent bonds involve sharing between atoms.• However, some atoms are more electronegative
than others meaning they tend to attract more electrons than other atoms.
• When all the electrons are shared equally, it is a nonpolar covalent bond.
• When one atom attracts electrons more strongely than the other atom, a polar covalent bond forms.
• The atom that attracts more electrons become slightly negative while the other becomes slightly positive.
• This is NOT the same as an ionic bond with normal charges!
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Hydrogen Bonds• Hydrogen bonds occur when a hydrogen that
is covalently bonded to another atom will be weakly attracted to another atom on another molecule.
• The partial positive charge of the hydrogen in the polar molecule, gets attracted to the partially negative charge on another molecule.
• Water usually forms hydrogen bonds.
• As a result, life is possible.
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Vocabulary Cards
•Polar molecule
•Hydrogen bond
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POST IT UP
I GOT THIS! I NEED HELP!
Why is water polar?
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Science Swag
Create an accurate model for a chemical compound. Label the atoms and the bonds. Bigger models with more atoms get more points.