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BondingIonic
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Valence Electrons
The number of valence electrons in an atom of an element determines the many properties of that element, including the ways in which the Atom can bond with other atoms
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electron shellsa) Atomic number = number of Electrons in a neutral atom
b) Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.
c) Electron shells determine how an atom behaves when it encounters other atoms
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Electrons are placed in shells according to rules:
1) The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.
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Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons
C would like to N would like toO would like to
Gain 4 electronsGain 3 electronsGain 2 electrons
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Why are electrons important?
1) Elements have different electron configurations different electron configurations mean different levels of
bonding As the number if protons (atomic number) increases, the number
of electrons also increases. As a result, the properties of the elements change in a predictable
way across a period.
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Bohr Model
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Lewis Electron Dot StructuresSymbols of atoms with dots to represent the valence-shell electrons
1 2 13 14 15 16 17 18
H He:
Li Be B C N O : F :Ne :
Na Mg Al Si P S :Cl :Ar :
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Learning Check
A. X would be the electron dot formula for
1) Na 2) K 3) Al
B. X would be the electron dot formula
1) B 2) N 3) P
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Chemical bonds: an attempt to fill electron shells
1. Ionic bonds
2. Covalent bonds
3. Metallic bonds
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Ions and Ionic BondsYou and a friend walk past a market that sells apples for 40 cents each and pears for 50 cents each. You have 45 cents and want an apple. Your friend also has 45 cents but wants a pear.
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Ions and Ionic BondsWhen an atom loses an electron, it loses a negative charge and become a positive ion. When an atom gains an electron, it gains a negative charge and becomes a negative ion.
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Ions and Ionic Bonds
Ions are atoms that have lost or gained electrons.
Ionic Bonds form as a result of the attraction between positive and negative ions
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Some Typical Ions with Positive Charges (Cations)
Group 1 Group 2 Group 13
H+ Mg2+ Al3+
Li+ Ca2+
Na+ Sr2+
K+ Ba2+
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Learning Check
Give the ionic charge for each of the following:
A. 12 p+ and 10 e-
1) 0 2) 2+ 3) 2-
B. 50p+ and 46 e-
1) 2+ 2) 4+ 3) 4-
C. 15 p+ and 18e-
2) 3+ 2) 3- 3) 5-
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Ionic Bond
Between atoms of metals and nonmetals with very different electronegativity
Bond formed by transfer of electrons
Produce charged ions all states. Conductors and have high melting point.
Examples; NaCl, CaCl2, K2O
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Formation of Ions from Metals
Ionic compounds result when metals react with nonmetals
Metals lose electrons to match the number of valence
electrons of their nearest noble gas
Positive ions form when the number of electrons are less
than the number of protons
Group 1 metals ion 1+
Group 2 metals ion 2+
Group 13 metals ion 3+
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Ions from Nonmetal Ions
In ionic compounds, nonmetals in 15, 16, and 17
gain electrons from metals
Nonmetal add electrons to achieve the octet
arrangement
Nonmetal ionic charge:
3-, 2-, or 1-
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Ionic Bonds: One Big Greedy Thief Dog!
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Ions and Ionic BondsIonic bonds form as a result of the attraction between positive and negative ions.
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1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.
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Properties of Ionic CompoundsIn general, ionic compounds are hard, brittle crystals that have high melting points.
When dissolved in
water or melted, they
conduct electricity.
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BondingCovalent
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2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.
Oxygen Atom Oxygen Atom
Oxygen Molecule (O2)
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Covalent Bond
Between nonmetallic elements of similar electronegativity.
(Between two nonmetals!)
Formed by sharing electron pairs
Stable, not conductors at any state
Examples; O2, CO2, C2H6, H2O, SiC
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How Covalent Bonds FormThe force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons.
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- Covalent Bonds
How Covalent Bonds FormCovalent bonds usually form between atoms of
nonmetals.CO2
H20
NH3
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- Covalent Bonds
How Covalent Bonds FormThe oxygen atom in water and the nitrogen atom in ammonia are each surrounded by eight electrons as a result of sharing electrons with hydrogen atoms.
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- Covalent Bonds
How Covalent Bonds Form
In covalent bonds, atoms share two or more pairs of electrons
Except for hydrogen, the number of covalent bonds that nonmetal atoms can form equal the number of electrons needed to make a total of 8
Hydrogen needs only two.
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- Covalent Bonds
How Covalent Bonds FormCovalent bonds can be double or triple bonds
Double bonds refer to two pairs of shared electrons. Triple bonds include three shared electrons
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- Covalent Bonds
How Covalent Bonds FormAn oxygen molecule contains one double bond, while a carbon dioxide molecule has two double bonds. A nitrogen molecule contains one triple bond.
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Equal and Unequal Sharing of Electrons
Nonpolar bonds: Electrons are equally shared.Fluorine forms a nonpolar bond with another fluorine atom.
Polar bonds: electrons are shared unequally In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does, so the bond formed is polar.
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Polar Covalent Bonds: Unevenly matched, but willing to share.
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Equal and Unequal Sharing of Electrons
A carbon dioxide molecule is a nonpolar molecule because of its straight-line shape. In contrast, a water molecule is a polar molecule because of its bent shape.
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- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
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Molecular CompundsA molecular compound contains atoms that are covalently bonded
Compared to ionic compounds, molecular compounds generally have lower melting and boiling points and do not conduct electricity when dissolved in water
- Covalent Bonds
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Comparing Molecular and Ionic Compounds
The table compares the melting points and boiling points of a few molecular compounds and ionic compounds..
- Covalent Bonds
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Comparing Molecular and Ionic Compounds
Melting points of molecular compounds are lower than those of ionic compounds.
Interpreting Data:
Describe what the table reveals about the melting points of molecular compounds compared to those of ionic compounds.
- Covalent Bonds
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Comparing Molecular and Ionic Compounds
Molecular compounds have weak attractive force between molecules, so less energy is needed to melt molecular compounds.
Inferring:
How can you account for the differences in melting points between molecular compounds and ionic compounds?
- Covalent Bonds
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Comparing Molecular and Ionic Compounds
Boiling points of molecular compounds are lower than those of ionic compounds.
Interpreting Data:
How do the boiling points of the molecular and ionic compounds compare?
- Covalent Bonds
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BondingMetallic
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Metallic Bonds: Mellow dogs with plenty of bones to go around.
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Metallic Bond
Formed between atoms of metallic elements
Electron cloud around atoms
Good conductors at all states, lustrous, very high melting points
Examples; Na, Fe, Al, Au, Co
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- Bonding in Metals
Metallic BondingA metal crystal consists of positively charged metal ions embedded in a “sea” of valence electrons.
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Ionic Bond, A Sea of Electrons
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Metals Form Alloys
Metals do not combine with metals to form compounds.They form an alloy, which is a solution of a metal in a metal.Examples are steel, brass, bronze and pewter.\
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Metals Form Alloys
Properties of AlloysConduct heat and electricityMalleableDuctileHave luster (shiny)Used in jewelry, mirrors, buildings, etc
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Bonding Summary
Ionic bonds – between metals and nonmetals
Covalent bonds – between two nonmetals
Metallic bonds – between metals
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Graphic Organizer
Attraction between oppositely charged ions
Feature Ionic BondPolar Covalent Bond
Nonpolar Covalent Bond
Metallic Bond
How Bond Forms
Charge on Bonded Atoms?
Example
Unequal sharing of electrons
Yes; positive or negative Yes; positive
O2 molecule
Equal sharing of electrons
Attraction between positive ions and surrounding electrons.
Yes, slightly positive or slightly negative
No
NaCl crystal (or other ionic compound)
H2O molecule (or other polar covalent molecule)
Calcium (or other metal)