recap – ions and ionic bonding
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Recap – Ions and Ionic Bonding. Cations are positively charged and formed from metals. Anions are negatively charged and formed from non-metals . Cations and anions are formed at the same time by electron transfer . - PowerPoint PPT PresentationTRANSCRIPT
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Recap – Ions and Ionic Bonding
• Cations are positively charged and formed from metals.
• Anions are negatively charged and formed from non-metals.
• Cations and anions are formed at the same time by electron transfer.
• An ionic bond is the electrostatic attraction between cations and anions.
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Ionic BondingCl
-ClNa + Na
+
• It takes energy to remove an electron from an atom.
• Electrostatic attraction between cations and anions supplies energy.
• Generally do not get very highly charges ions as too much energy is required to form them.
C C+ C2+ C3+ C4+ e- e- e- e-
2 360 kJ
1 090 kJ
4 630 kJ
6 230 kJ
Sharing of Electrons• In ionic compounds a Noble gas electron
configuration is obtained by transfer of electrons.
• In covalent compounds a Noble gas electron configuration is obtained by sharing of electrons.
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F F F F
Sharing of ElectronsH2
4
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Reason for Covalent Bonding
• Electrons are shared to achieve a Noble gas configuration for each atom.
• Electron density between the two atoms: the bond is directional.
• Only electrons from the outermost shell can be involved in bonding – valence electrons.
• Electrons tend to form pairs.
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Covalent Bonding: C and H
H
H
H
HC
• Carbon has 4 electrons in outer shell – needs 8
• Hydrogen has 1 electron in outer shell – needs 2
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Covalent Bonding - methane
CH4
H H
H
H
C
H
CH H
H
8
OH H
Covalent Bonding - water• Oxygen has 6 electrons in outer shell – needs
8• Hydrogen has 1 electron in outer shell – needs
2
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Covalent Bonding – H2O• We can identify bond pairs and
lone pairs (or non-bonding pairs) of electrons
OH H
OH H
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Covalent Bonding: N and H XXXX
XX
X
NXH
XXXX
XX
X
N
XH
X HXH
• Show only valence electrons
H N
H
H
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Valence• Valence electrons are used in bonding.• The valence of an atom is the size of the charge if
it forms an ion or the number of bonds it forms in a neutral molecule.
1 2 3 4 3 2 1
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• The diatomic elements (eg H2, N2, O2, F2) all have a similar formula but different bonding requirements.
Diatomic Molecules
X HXH
H H
F2Single Bond
H2Single Bond
XXXX
XF
XX
XX
XXXX
X F
XX
XX
F F
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• Double bonds occur where two electron pairs are shared between atoms.
Bonding Requirements
XXO
X
XXXO
X
X XXO
X
XXXO
X
X
O OO2
Double Bond
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• Triple bonds occur where three electron pairs are shared between atoms.
Bonding Requirements
XXN X
X
XXNX
XX X
X
X X
XXXN
X
XXX
XX NX
XX
X
N N
XX
N2
Triple Bond
• By the end of this lecture, you should:− understand the difference between ionic and
covalent bonding− be able to draw diagrams representing the
bonding in simple molecules− know the difference between a bond pair and
lone pair of electrons− know the valence of elements in groups 1, 2, 13
– 17− be able to predict the formula of simple covalent
compounds− appreciate the difference between a single,
double & triple bond
− be able to complete the worksheet (if you haven’t already done so…)
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Learning Outcomes:
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Questions to complete for next lecture:
1. Would the following pairs of elements form ionic or covalent bonds? H and O, Na and O, N and O, S and O.
2. Draw a diagram representing the molecule HCN.3. How many lone pairs does each of the following
molecules possess? H2, Cl2, H2S, HBr.4. Oxygen has a valence of 2. Give an example of
an ionic compound and a covalent compound containing oxygen that illustrates this concept.
5. Predict the formula of the simplest compounds formed between sulfur and fluorine, phosphorus and chlorine, magnesium and iodine.