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1.2 IONSUNDERSTANDING HOW THE ELECTRONS MOVE INSIDE AN ATOM ALLOWS SCIENTISTS TO CONTROL HOW ATOMS REACT WITH EACH OTHER.
VOCABULARY PREVIEW
Look up the following terms an provide a definition that you understand.
Anion
Cation
Ion
Ionic bond
Ionic compound
solubility
A negatively charged ion
A positively charged ion
An atom which has either gained or lost an electron
An attraction between two oppositely charged ions
When anions and cations come together (sodium chloride)
How easily something dissolves
USING VISUALS
Discuss why lithium is likely to form a cation (positive) when it only has one loose electron around it.
Compare this with oxygen or chlorine, which are more likely to gain an electron to complete their shells.
Cl
ATOMS AND IONS
Atoms are electrically neutral (what does this mean?)
If an electron is removed or added, the atom becomes charged and is now called an?
When an electron is removed from an atom, that atom becomes a charged ion.
A positive ion is known as a?
If an electron is added to an atom, that atom becomes a charged ion.
A negatively charged ion is known as a?
ion
They contain an equal number of positive protons and negative electrons.
positively
cation
negatively
anion
CATIONS
A cation is formed when an atom loses electrons.
Do you think the outermost shell would be mostly empty or mostly full?
The atom will usually lose all the electrons in the outermost shell so that only filled shells remain.
Almost all cations come from metal atoms, why is this? Page 14- Top Paragraph
Mostly empty
COMMON CATIONS
An important non-metallic cation comes from hydrogen (H). Hydrogen ions (H+) are formed whenever an acid is dissolved in water.
The symbols used to represent cations are made up of the atomic symbol and the charge of the ion.
For example: Since sodium (Na) loses one electron, the sodium ion has a charge of +1. This is represented by Na+. Magnesium (Mg) atoms lose two electrons and so the magnesium ion is represented as Mg2+
ANIONS
An anion is produced when an atom gains electrons. This will occur if the outermost electron shell of the atom is almost full. In that case, the atom gains additional electrons until the shell is filled, as seen below
ANIONS
The name of a cation is the same as the atom, however anions are named differently. The chemical name for an anion is similar to the name of the atom but ends in –ide.
What would the following atoms be called when they become anions?
Chlorine
Oxygen
Nitrogen
Iodine
Fluorine
Sulfur
Bromine
Chloride
Oxide
Nitride
Iodide
Fluoride
Sulfide
Bromide
IONIC COMPOUNDS
When anions and cations come together they form compounds made up of large crystal lattices. These compounds are known as ionic compounds.
RECAP
What is a
Anion - A negatively charged ion
Cation - A positively charged ion
Ion - An atom which has either gained or lost an electron
Ionic bond - An attraction between two oppositely charged ions
Ionic compound - When anions and cations come together (sodium chloride)
What ions are formed whenever an acid is dissolved in water? Hydrogen ions (H+)
CHEMICAL NAMES AND FORMULAS
Naming ionic compounds is very easy
Simply write the name of the cation followed by the name of the anion
Write the chemical name for the following compounds
1. Ca2+ and O2- = Calcium Oxide
2. Cu+ and Cl- = Copper Chloride
CHEMICAL FORMULAS
Writing chemical formulas is slightly more difficult.
When writing the formula for an ionic compound you must ensure that there is an equal number of positive and negative charges so that the total charge is zero.
Sodium(Na+) chloride (Cl-) the chemical formula us just NaCl
Magnesium (Mg2+) chloride (Cl-) the chemical formula becomes MgCl2
Charge is at the top, number of atoms is on the bottom.
WRITING IONIC FORMULAS
QUESTION TIME
IONIC BONDING
Cations and anions are attracted to each other because they have opposite electrical charges. When they come close to one another they stick together to form an ionic bond.
Ionic bonds holding crystal lattices together are very strong. Therefore, ionic compounds usually:
Are hard
Are brittle
Have high melting points
IONS IN SOLUTION Some ionic compounds are soluble(dissolve) in water, while others are insoluble (do not
dissolve)
19
NAMES OF SOME COMMON IONS
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
20
CHARGES OF REPRESENTATIVE ELEMENTS
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
21
Complete the names of the following ions. Ba2+ Al3+ K+
_________ __________ _________
N3 O2 F
_________ __________ _________
P3 S2 Cl
_________ __________ _________
LEARNING CHECK
22
Ba2+ Al3+ K+
barium aluminum potassium
N3 O2 F
nitride oxide fluoride
P3 S2 Cl
phosphide sulfide chloride
SOLUTION
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Formula Ions Name cation anion
NaCl Na+ Cl- sodium chloride
K2S K+ S2- potassium sulfide
MgO Mg2+ O2- magnesium oxide
CaI2 Ca2+ I- calcium iodide
Al2O3 Al3+ O2- aluminum oxide
EXAMPLES OF IONIC COMPOUNDS WITH TWO ELEMENTS
24
Write the names of the following compounds.
1) CaO ___________
2) KBr ___________
3) Al2O3 ___________
4) MgCl2 ___________
LEARNING CHECK
25
Write the names of the following compounds:
1) CaO calcium oxide
2) KBr potassium bromide
3) Al2O3 aluminum oxide
4) MgCl2 magnesium chloride
SOLUTION
26
LEARNING CHECK
Write the formulas and names for compounds of the following ions:
Br− S2− N3−
Na+
Al3+
27
SOLUTION
Br− S2− N3−
Na+
Al3+
NaBrsodium bromide
Na2S
sodium sulfide
Na3N
sodium nitride
AlBr3
aluminum bromide
Al2S3
aluminum sulfide
AlNaluminum nitride
IONS IN SOLUTION
When ions are in a solution they can move freely through the liquid meaning they can create a flow of electric charge and therefor conduct electricity.
Only liquids that contain ions will allow an electrical current to flow.
Liquids such as oil or kerosene do not contain ions and therefore do not conduct electricity.
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