Download - formula unit
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formula unit
Covalent Bonding:
Learning to Cooperate
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• describe a covalent bond • state the differences covalent and ionic bonds• explain the term molecule • describe a diatomic molecule
Key Wordscovalent compoundcovalent bonddiatomic molecule
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Covalent Compound:
Contains two or more NON-METAL atoms.
Formed by SHARING valence electrons to fill outer shell – octet rule.
· A molecule is the smallest unit of a covalent compound.
Non-metal + Non-metal = covalent bonding
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Fluorine atom:9 p+
9 e-
F
Fluorine atom:9 p+
9 e-
F
F2
covalent compound
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HH
Water H2O
1p
8p1p
O
A molecule has different properties than the atoms from which it is formed
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Methane CH4
C
H
H
H
H
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Ammonia NH3
NH
H
H
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O
Atoms can share one pair of electrons, or two or three pairs.
S
In the end – electrons must be arranged so that each atom has 8 electrons around it.
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Diatomic ElementsForming a Covalent Bond with Yourself
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No new substance is formed - the covalent bond forms a molecule of only one type of atom.
Diatomic elements are unstable as single atoms.
HH
They form covalent bonds with a same atom to make a stable molecule.
H2
molecule
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I H N Br O Cl F ave o ight r ever riends
Diatomic Elements:
2 2 2 2 2 2 2
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Element Symbol Diatomic MoleculeIodine I I2 (solid)
Hydrogen H H2 (gas)
Nitrogen N N2 (gas)
Bromine Br Br2 (liquid)
Oxygen O O2 (gas)
Chlorine Cl Cl2 (gas)
Fluorine F F2 (gas)
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OOO2
molecule (double bond)
F2
molecule(single bond)
FF
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Covalent Bonding:
Naming and Writing
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Same – covalent compounds are also named using the “ide” ending for last non-metal.
Different – covalent naming uses prefixes before the name of each element.
Prefixes show the number of atoms of that element in the formula for the molecule.
Diatomic Elements2
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Prefix Number of Atoms
mono
1
di 2
tri 3
tetra 4
penta 5
hexa 6
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Step 1: first non-metal is named with a prefix to show the number of atoms.
We do not use “mono” for the first non-metal.
nitrogen oxide
N O
Step 2: second non-metal is named with a prefix AND with the “ide” ending.
di
2 4
tetradinitrogen tetroxide
PrefixNumber of
Atoms
mono 1
di 2
tri 3
tetra 4
penta 5
hexa 6
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PrefixNumber of
Atoms
mono 1
di 2
tri 3
tetra 4
penta 5
hexa 6
sulfur oxide
SO
mono
3
trisulfur trioxide
carbon bromide
C Br
tri
3 6
hexa
tricarbon hexabromide
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Writing formulas
Step 1: Write the symbol of each element.
Step 2: Use a subscript to show the number of each type of atom given by the prefix.
Do not reduce covalent formulas.
phosphorus oxide
P O di
2 5
penta
PrefixNumber of
Atoms
mono 1
di 2
tri 3
tetra 4
penta 5
hexa 6
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nitrogen iodide
N I 3
triPrefix
Number of Atoms
mono 1
di 2
tri 3
tetra 4
penta 5
hexa 6carbon oxide
CO 2
di
silicon sulfide
Si S di
2 4
tetra
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**Always identify a compound as ionic (m + nm) or covalent (nm + nm) before doing anything.
Prefixes are used in naming covalent compounds ONLY.
Criss-crossing is only used in ionic compounds.
DO NOT reduce covalent compounds.
IMPORTANT POINTS:
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sulfur chlorideberyllium chloride
BeCl 2
Be
SCl
mono
2
di
metal non-metal non-metal non-metal
ionic covalent
Cl
Cl
+2
-
-
SCl
Cl