Chemical Bonding I: Ionic vs Covalent Compounds
Content Review:
Links: Chemical Bonding This page contains PowerPoints that cover ionic and covalent bonding and a summary table.
For those of you that prefer PowerPoints, here they are:
Ionic Compounds Covalent Compounds Chemical Names & Formulas
Textbook Readings: Chapter 7, 8 & 9, respectively.
Student Missions:
Mission 1: Ions, Ions, Ions!
Mission Objectives. You should be able to...
1. Determine which elements form cations and which elements form anions.
2. Contemplate the structure of an ionic bond based on valence electrons.
3. Predict the name of an ionic compound and a covalent compound.
Recall that the group number on the periodic table represents the number of valence electrons in that group. Also recall that group 18, the noble gases, have stable octets. The objective for any element that is not a noble gas is to lose or gain electrons to have a noble gas configuration. Stability is key.
Elements in G1 will LOSE their valence electrons to form ions with a +1 charge. Elements in G2 will LOSE theirs to form ions with a +2 charge. Elements in G13 will lose theirs to form ions with a +3 charge. Any time an element LOSES a valence electron, a cation is formed. Cations are positively charged ions. Metallic elements form cations.
Conversely, elements in G15 will GAIN 3 electrons to form ions with a -3 charge. Elements in G16 will GAIN 2 electrons to form ions with a -2 charge, and elements in G17 will GAIN 1 electron to form an ion with a -1 charge. Any time an element GAINS a valence electron, an anion is formed. Anions are negatively charged ions. Nonmetals form anions.
This sweet little 10-second interactive shows what happens to the size of atoms when ions are formed. Make note of which elements will get smaller and which will get bigger.
For more on ion formation, see what David Weightman has to say about it. It's three minutes long.
Links: Chemical Bonding This page contains PowerPoints that cover ionic and covalent bonding and a summary table.
For those of you that prefer PowerPoints, here they are:
Ionic Compounds Covalent Compounds Chemical Names & Formulas
Textbook Readings: Chapter 7, 8 & 9, respectively.
Student Missions:
Mission 1: Ions, Ions, Ions!
Mission Objectives. You should be able to...
1. Determine which elements form cations and which elements form anions.
2. Contemplate the structure of an ionic bond based on valence electrons.
3. Predict the name of an ionic compound and a covalent compound.
Recall that the group number on the periodic table represents the number of valence electrons in that group. Also recall that group 18, the noble gases, have stable octets. The objective for any element that is not a noble gas is to lose or gain electrons to have a noble gas configuration. Stability is key.
Elements in G1 will LOSE their valence electrons to form ions with a +1 charge. Elements in G2 will LOSE theirs to form ions with a +2 charge. Elements in G13 will lose theirs to form ions with a +3 charge. Any time an element LOSES a valence electron, a cation is formed. Cations are positively charged ions. Metallic elements form cations.
Conversely, elements in G15 will GAIN 3 electrons to form ions with a -3 charge. Elements in G16 will GAIN 2 electrons to form ions with a -2 charge, and elements in G17 will GAIN 1 electron to form an ion with a -1 charge. Any time an element GAINS a valence electron, an anion is formed. Anions are negatively charged ions. Nonmetals form anions.
This sweet little 10-second interactive shows what happens to the size of atoms when ions are formed. Make note of which elements will get smaller and which will get bigger.
For more on ion formation, see what David Weightman has to say about it. It's three minutes long.
Ionic compounds are formed when a cation bonds with an anion through the transfer of valence electrons. Another way of saying this is that an ionic compound forms when a metal bonds with a nonmetal.
For example, the sodium atom will transfer its one valence electron to chlorine, an atom with seven valence electrons. Sodium does not need it's valence electron, and chlorine craves to have one more valence electron, so the ionic bond is easily formed between them. This pattern holds true for any G1 element bonding with a G17 element. The pattern also works for G2 and G16 elements, and G13 and G15 elements. I call these perfect pairings, because they result in 1:1 compounds.
Of course, nothing is perfect because any metal can bond with any nonmetal. So there are compounds with ratios greater than 1:1. It's not difficult because it's all about balancing charges. Tyler DeWitt talks you through it. It would be helpful to have your periodic table handy.
For example, the sodium atom will transfer its one valence electron to chlorine, an atom with seven valence electrons. Sodium does not need it's valence electron, and chlorine craves to have one more valence electron, so the ionic bond is easily formed between them. This pattern holds true for any G1 element bonding with a G17 element. The pattern also works for G2 and G16 elements, and G13 and G15 elements. I call these perfect pairings, because they result in 1:1 compounds.
Of course, nothing is perfect because any metal can bond with any nonmetal. So there are compounds with ratios greater than 1:1. It's not difficult because it's all about balancing charges. Tyler DeWitt talks you through it. It would be helpful to have your periodic table handy.
Practice with this interactive.
Mission 2: Sharing is Caring!
Mission Objectives. You should be able to...
1. Determine when covalent bonds are formed and which elements form them.
2. Predict the name of an ionic compound and a covalent compound.
Covalent bonds are the result of valence electrons being shared in order to achieve stable octets. If you think back...way back...to the short lesson on Lewis Dot, you'll recall that certain elements contained a certain number of dots that represented their valence electrons.
Mission 2: Sharing is Caring!
Mission Objectives. You should be able to...
1. Determine when covalent bonds are formed and which elements form them.
2. Predict the name of an ionic compound and a covalent compound.
Covalent bonds are the result of valence electrons being shared in order to achieve stable octets. If you think back...way back...to the short lesson on Lewis Dot, you'll recall that certain elements contained a certain number of dots that represented their valence electrons.
Anyhoo, if you take a look at groups 15, 16 & 17 (the nonmetals), this is where covalent bonding takes place. These elements can bond with themselves to share a pair (or two, or three) of electrons to form stable octets. Take a look below. Fluorine will share a pair of electrons with another fluorine and a single covalent bond is formed (represented by a line).
Group 16 elements will share two pairs of electrons (double covalent bond) and group 15 elements will share three pairs of electrons (triple covalent bond). Again, the goal is stability. The Octet Rule rules all.
There are seven elements that are found in nature covalently bonded to each other. They are called diatomic elements. A useful memory aid is HONI Bring Fried Clams. So when you're writing these elements in chemical equations, you need to make sure you write them correctly.
Polyatomic ions are a group of atoms that are tightly bound that behaves as a unit and has either a positive or negative charge. I gave you an ion reference chart, which contains a comprehensive list of polyatomic ions. You need to print a copy and keep it with your periodic table. Don't lose it.
Get familiar with covalent bonding using this interactive.
We will practice writing and naming ionic and covalent compounds.
There are seven elements that are found in nature covalently bonded to each other. They are called diatomic elements. A useful memory aid is HONI Bring Fried Clams. So when you're writing these elements in chemical equations, you need to make sure you write them correctly.
Polyatomic ions are a group of atoms that are tightly bound that behaves as a unit and has either a positive or negative charge. I gave you an ion reference chart, which contains a comprehensive list of polyatomic ions. You need to print a copy and keep it with your periodic table. Don't lose it.
Get familiar with covalent bonding using this interactive.
We will practice writing and naming ionic and covalent compounds.
Content Review:
Links: Intermolecular Forces
Student Missions:
Mission 3: What's Keeping Us Together Other Than Love??
Mission Objectives. You should be able to...
1. List and describe the types of intermolecular forces
2. Deduce the types of intermolecular forces present in substances based on their structure and chemical formulas.
3. Explain the relationship between physical properties of covalent compounds in terms of their structure and intermolecular forces.
Covalent bonds holds atoms together within molecules, but what forces hold molecules together? The answer depends on the polarity and size of the molecules involved, and so said intermolecular forces will vary. The strength of intermolecular forces determine the physical properties of a substance. Volatility, solubility, and conductivity can all be predicted and explained from knowledge of the nature of intermolecular forces.
Dispersion forces (aka London forces): These are weak forces of attraction that occur between opposite ends of two temporary dipoles, usually with nonpolar molecules. A dipole occurs when the density of an electron cloud at any one moment be greater in one region of a molecule or atom. These dipoles are called temporary or instantaneous because they do not last long. When temporary dipoles influence the electron behavior of a nearby atom or molecule, induced dipoles result.
Polarizability is the ease of distortion of the electron cloud. Remember, most molecules that are asymmetric are polar. This means that they have a clear negative and positive end.
Factors that affect dispersion (London) forces:
1. number of valence electrons: greater the number of electrons, the larger the distance between valence electrons and the nucleus.
2. volume of electron cloud: large electron clouds can be polarized more easily.
3. molecule shape: large areas of interaction allow the London forces to have a greater magnitude, which leads to higher boiling points.
Dipole-dipole forces: Polar molecules that have a permanent separation of charge within their bonds as a result of electronegative differences have dipole-dipole attractions. Water has a clear positive end and a clear negative end. This is called a permanent dipole. When it bonds with another water molecule, a dipole-dipole attraction results. The strength varies depending on the distance and orientation of the dipoles.
The umbrella term van der Waals includes both dipole-dipole and dispersion forces.
Hydrogen bonding: When a molecule contains hydrogen covalently bonded to a very electronegative atom (fluorine, oxygen, or nitrogen), these molecules are attracted to each other by a particularly strong force called a hydrogen bond. These are specific instances of dipole-dipole attraction. The large electronegativity difference results in the electron pair being pulled away from hydrogen. It now exerts a strong attractive force on a lone pair of electrons in a nearby molecule.
Hydrogen bonds are the strongest intermolecular force. As a result, they cause the boiling points of substances to be higher than normal.
Links: Intermolecular Forces
Student Missions:
Mission 3: What's Keeping Us Together Other Than Love??
Mission Objectives. You should be able to...
1. List and describe the types of intermolecular forces
2. Deduce the types of intermolecular forces present in substances based on their structure and chemical formulas.
3. Explain the relationship between physical properties of covalent compounds in terms of their structure and intermolecular forces.
Covalent bonds holds atoms together within molecules, but what forces hold molecules together? The answer depends on the polarity and size of the molecules involved, and so said intermolecular forces will vary. The strength of intermolecular forces determine the physical properties of a substance. Volatility, solubility, and conductivity can all be predicted and explained from knowledge of the nature of intermolecular forces.
Dispersion forces (aka London forces): These are weak forces of attraction that occur between opposite ends of two temporary dipoles, usually with nonpolar molecules. A dipole occurs when the density of an electron cloud at any one moment be greater in one region of a molecule or atom. These dipoles are called temporary or instantaneous because they do not last long. When temporary dipoles influence the electron behavior of a nearby atom or molecule, induced dipoles result.
Polarizability is the ease of distortion of the electron cloud. Remember, most molecules that are asymmetric are polar. This means that they have a clear negative and positive end.
Factors that affect dispersion (London) forces:
1. number of valence electrons: greater the number of electrons, the larger the distance between valence electrons and the nucleus.
2. volume of electron cloud: large electron clouds can be polarized more easily.
3. molecule shape: large areas of interaction allow the London forces to have a greater magnitude, which leads to higher boiling points.
Dipole-dipole forces: Polar molecules that have a permanent separation of charge within their bonds as a result of electronegative differences have dipole-dipole attractions. Water has a clear positive end and a clear negative end. This is called a permanent dipole. When it bonds with another water molecule, a dipole-dipole attraction results. The strength varies depending on the distance and orientation of the dipoles.
The umbrella term van der Waals includes both dipole-dipole and dispersion forces.
Hydrogen bonding: When a molecule contains hydrogen covalently bonded to a very electronegative atom (fluorine, oxygen, or nitrogen), these molecules are attracted to each other by a particularly strong force called a hydrogen bond. These are specific instances of dipole-dipole attraction. The large electronegativity difference results in the electron pair being pulled away from hydrogen. It now exerts a strong attractive force on a lone pair of electrons in a nearby molecule.
Hydrogen bonds are the strongest intermolecular force. As a result, they cause the boiling points of substances to be higher than normal.