variable charge
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© 2013 Pearson Education, Inc. Chapter 5, Section 1 1
Metals with Variable Charge
Most transition metals (3-12) and Group 4A (14) metals form 2 or more positive ions, except Zn2+, Ag+, and Cd2+, which form only one ion.
Metals with Variable Charge
The names of transition metals with two or more
positive ions (cations) use a Roman numeral after the
name of the metal to identify the ion charge.
Naming Ionic Compounds with Variable Charge Metals
Naming FeCl2
Step 1 Determine the charge of the cation from the anion. Analyze the Problem.
Naming FeCl2
Step 2 Name the cation by its element name and use a Roman numeral in parentheses for the charge.
Fe2+ = iron(II) Step 3 Name the anion by using the first syllable of its element name followed by ide . Cl− = chloride Step 4 Write the name for the cation first and the name for the anion second.
iron(II) chloride
© 2013 Pearson Education, Inc. Chapter 5, Section 1 6
Examples of Names of Compounds with Variable Charge Metals
Writing Formulas for Ionic Compounds
Writing the Formula for Iron(III) Oxide
Metal Nonmetal
Ion Iron(III) oxide
Group Transition 6A (16)
Symbol Fe3+ O2–
Learning Check
Write the correct name for CuO.
Write the correct formula for copper(I) nitride.
A polyatomic ion
is a group of atoms.
has an overall ionic charge.
Examples:
NH4+ ammonium OH− hydroxide
SO42−
sulfate CO32− carbonate
PO43− phosphate
Polyatomic Ions
© 2013 Pearson Education, Inc. Chapter 5, Section 1 11
Names and Formulas of Common Polyatomic Ions
Compounds Containing Polyatomic Ions
Polyatomic ions
must be associated with an ion of opposite charge.
form ionic bonds with ions of opposite charge to achieve charge balance.
Example:
Ca2+ NO3−
calcium nitrate ion
charge balance:
Ca(NO3)2
calcium nitrate
Step 1 Identify the cation and polyatomic ion (anion).
Cation: K+ Anion: SO42−
Step 2 Name the cation, using a Roman numeral if needed.
K+ = potassium ion
Step 3 Name the polyatomic ion.
SO42− = sulfate ion
Step 4 Write the name or the compound, cation first and the polyatomic ion second.
K2SO4 = potassium sulfate
Name K2SO4
Learning Check
Name each of the following compounds.
1. Cu(ClO3)2
2. PbCO3
3. Ba3(PO3)2
Solution
Step 1 Identify the cation and polyatomic ion (anion). cation polyatomic ion 1. Cu(ClO3)2 Cu2+ ClO3
−
2. PbCO3 Pb2+ CO32−
3. Ba3(PO3)2 Ba2+ PO33−
Step 2 Name the cation using a Roman numeral, if necessary. cation name 1. Cu(ClO3)2 copper(II)
2. PbCO3 lead(II) 3. Ba3(PO3)2 barium
Solution
Step 3 Name the polyatomic ion. polyatomic ion 1. Cu(ClO3)2 chlorate
2. PbCO3 carbonate 3. Ba3(PO4)2 phosphate
Step 4 Write the name or the compound, cation first
and the polyatomic ion second. compound name 1. Cu(ClO3)2 copper(II) chlorate
2. PbCO3 lead(II) carbonate 3. Ba3(PO3)2 barium phosphite
Write the Formula for Aluminium Hydroxide
Step 1 Identify the cation and polyatomic ion (anion). Al3+ and OH−
Step 2 Balance the charges. Step 3 Write the formula, cation first, using the subscripts from charge balance. Al(OH)3
Break Time!!
Covalence - Formation of H2
In the simplest covalent molecule, H2 , the H atoms
increase attraction as they move closer.
share electrons to achieve a stable configuration.
form a covalent bond.
© 2013 Pearson Education, Inc. Chapter 5, Section 1 20
Electron-Dot Formulas of Covalent Molecules
In a fluorine (F2) molecule, the F atoms
share one of their valence electrons.
acquire an octet.
form a covalent bond.
© 2013 Pearson Education, Inc. Chapter 5, Section 1 21
Elements That Exist as Diatomic Molecules
These seven elements share electrons to form diatomic, covalent molecules.
© 2013 Pearson Education, Inc. Chapter 5, Section 1 22
Electron-Dot Formulas for Some Covalent Compounds
© 2013 Pearson Education, Inc. Chapter 5, Section 1 23
Guide to Drawing Electron-Dot Formulas
Step 1 Determine the arrangement of atoms. In NH3, N is the central atom and is bonded to three H atoms. Step 2 Determine the total number of valence electrons. Total valence electrons for NH3 = 8 e−
Draw the Electron-Dot Formula for NH3
H N H
H
Step 3 Attach each bonded atom to the central atom with a pair of electrons.
Draw the Electron-Dot Formula for NH3
H N H
H
Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. 8 valence e− − 6 bonding e− = 2 e− remaining Use the remaining 2 e− to complete the octet around the N atom.
Draw the Electron-Dot Formula for NH3
H N H
H
H N H
H
or
© 2013 Pearson Education, Inc. Chapter 5, Section 1 27
Learning Check
Draw the electron-dot formula for CCl4.
Step 1 Determine the arrangement of atoms. In CCl4, C is the central atom and is bonded to four Cl atoms.
Solution
Cl Cl C Cl
Cl
Step 2 Determine the total number of valence electrons. Total valence electrons for
Solution
Step 3 Attach each bonded atom to the central atom with a pair of electrons.
Solution
Cl Cl C Cl
Cl
Step 4 Place the remaining electrons, using single or multiple bonds to complete the octets.
32 valence e− − 8 bonding e− = 24 e− remaining Use the remaining 24 e− to complete the octets around the Cl atoms.
Solution
Cl Cl C Cl
Cl
or
Cl Cl C Cl
Cl
Single and Multiple Bonds
In many covalent compounds, atoms share two or three pairs of electrons to complete their octets.
In a single bond, one pair of electrons is shared.
In a double bond, two pairs of electrons are shared.
In a triple bond, three pairs of electrons are shared.
Step 1 Determine the arrangement of atoms. In CS2, C is the central atom and is bonded to two S atoms.
Draw the Electron-Dot Formula for CS2
S C S
Step 2 Determine the total number of valence electrons. Total valence electrons for
Draw the Electron-Dot Formula for CS2
Step 3 Attach each bonded atom to the central atom with a pair of electrons. A pair of bonding electrons (single bond) is placed between each S atom and the central C atom.
Draw the Electron-Dot Formula for CS2
S C S
Step 4 Place the remaining electrons using single or multiple bonds to complete the octets.
16 valence e− - 4 bonding e− = 12 e− remaining
The remaining 12 electrons are placed as six lone pairs of electrons on both S atoms. However, this does not complete the octet for the C atom.
Draw the Electron-Dot Formula for CS2
S C S
Step 4 Continued: Double and Triple Covalent Bonds: To complete the octet for the C atom, it
needs to share an additional lone pair from each of the S atoms, forming a double bond with each S atom.
Draw the Electron-Dot Formula for CS2
S C S
or
S C S
S C S
© 2013 Pearson Education, Inc. Chapter 5, Section 1 38
A Nitrogen Molecule has a Triple Bond
In a nitrogen molecule, N2,
each N atom shares 3 electrons,
each N atom attains an octet, and
the sharing of 3 sets of electrons is called a triple bond.
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