Chapter 20: Chemical Bonds
Combined Elements
Uncombined, elemental copper is a bright, shiny copper color.
Copper sulfate isn’t shiny and copper colored like elemental copper.
Chlorine is a poisonous greenish-yellow gas.
Formulas
Chemical Formula: tells what elements a compound contains and the exact number of the atoms of each element in a unit of that compound.
A subscript written after a symbol tells how many atoms of that element are in a unit of the compound.
If a symbol has no subscript, the unit contains only one atom of that element.
Atomic Stability
The electric forces between oppositely charged electrons and protons hold atoms and molecules together, and thus are the forces that cause compounds to form.
Atoms of noble gases are unusually stable.
An atom is chemically stable when its outer energy level is complete.
The noble gases are stable because they each have a complete outer energy level.
When you look at the elements in Groups 13 through 17, you see that each of them falls short of having a stable energy level.
Atoms with partially stable outer energy levels can lose, gain, or share electrons to obtain a stable outer energy level.
When the outer electron of sodium is removed, a complete inner energy level is revealed and now becomes the new outer energy level.
When atoms gain, lose, or share electrons, an attraction forms between the atoms, pulling them together to form a compound.
Chemical Bond: the force that holds atoms together in a compound.
Gain or Loss of Electrons
Atoms lose or gain to meet a standard—a stable energy level.
Ion: a charged particle because it now has either more or fewer electrons than protons.
Some of the most common compounds are made by the loss and gain of just one electron.
A lack of iodine causes a wide range of problems in the human body.
A neutral atom of potassium has one electron in its outer level.
When a potassium atom loses an electron, the atom becomes positively charged because there is one electron less in the atom than there are protons in the nucleus.
An iodine atom has seven electrons in its outer energy level.
The compound formed between potassium and iodine is called potassium iodide.
Ionic Bond: the force of attraction between the opposite charges of the ions in an ionic compound.
In an ionic bond, a transfer of electrons takes place.
The positive charge of the magnesium ion is exactly equal to the negative charge of the two chloride ions.
Ionic bonds usually are formed by bonding between metals and nonmetals.
Ionic compounds are often crystalline solids with high melting points.
Sharing Electrons
Some atoms of nonmetals are unlikely to lose or gain electrons.
Covalent Bond: The attraction that forms between atoms when they share electrons
Molecule: A neutral particle that forms as a result of electron sharing.
A single covalent bond is made up of two shared electrons.
A covalent bond also can contain more than one pair of electrons.
When each atom contributes three electrons to the bond, the bond contains six electrons, or three pairs of electrons.
Covalent bonds form between nonmetallic elements.
Electrons are not always shared equally between atoms in a covalent bond.
The strength of the attraction of each atom to its electrons is related to the size of the atom, the charge of the nucleus, and the total number of electrons the atom contains.
Each atom in the molecule attracts the electrons that they share.
The electrons being shared in a molecule are held more closely to the atoms with the stronger pull or larger nucleus.
The atom holding the electron more closely always will have a slightly negative charge.
Polar Molecule: one that has a slightly positive end and a slightly negative end although the overall molecule is neutral.
Non-polar Molecule: one in which electrons are shared equally in bonds.
Binary Ionic Compounds
Binary Compound: One that is composed of two elements.
Oxidation Number: tells you how many electrons an atom has gained, lost, or shared to become stable.
For ionic compounds the oxidation number is the same as the charge on the ion.
When naming these compounds, the oxidation number is expressed in the name with a roman numeral.
When writing formulas it is important to remember that although the individual ions in a compound carry charges, the compound itself is neutral.
A formula must have the right number of positive ions and the right number of negative ions so the charges balance.
Compounds with Complex Ions
Not all compounds are binary.
Polyatomic Ion: a positively or negatively charged, covalently bonded group of atoms.
Compounds with Added Water
Some ionic compounds have water molecules as part of their structure.
Hydrate: a compound that has water chemically attached to its ions and written into its chemical formula.
You can remove water from these crystals by heating them.
Naming Binary Covalent Compounds
Covalent compounds are those formed between elements that are nonmetals.
Some pairs of nonmetals can form more than one compound with each other.
Using oxidation numbers to write formulas, you can predict the ratio in which atoms of elements might combine to form compounds.
Combined Elements
Uncombined, elemental copper is a bright, shiny copper color.
Copper sulfate isn’t shiny and copper colored like elemental copper.
Chlorine is a poisonous greenish-yellow gas.
Formulas
Chemical Formula: tells what elements a compound contains and the exact number of the atoms of each element in a unit of that compound.
A subscript written after a symbol tells how many atoms of that element are in a unit of the compound.
If a symbol has no subscript, the unit contains only one atom of that element.
Atomic Stability
The electric forces between oppositely charged electrons and protons hold atoms and molecules together, and thus are the forces that cause compounds to form.
Atoms of noble gases are unusually stable.
An atom is chemically stable when its outer energy level is complete.
The noble gases are stable because they each have a complete outer energy level.
When you look at the elements in Groups 13 through 17, you see that each of them falls short of having a stable energy level.
Atoms with partially stable outer energy levels can lose, gain, or share electrons to obtain a stable outer energy level.
When the outer electron of sodium is removed, a complete inner energy level is revealed and now becomes the new outer energy level.
When atoms gain, lose, or share electrons, an attraction forms between the atoms, pulling them together to form a compound.
Chemical Bond: the force that holds atoms together in a compound.
Gain or Loss of Electrons
Atoms lose or gain to meet a standard—a stable energy level.
Ion: a charged particle because it now has either more or fewer electrons than protons.
Some of the most common compounds are made by the loss and gain of just one electron.
A lack of iodine causes a wide range of problems in the human body.
A neutral atom of potassium has one electron in its outer level.
When a potassium atom loses an electron, the atom becomes positively charged because there is one electron less in the atom than there are protons in the nucleus.
An iodine atom has seven electrons in its outer energy level.
The compound formed between potassium and iodine is called potassium iodide.
Ionic Bond: the force of attraction between the opposite charges of the ions in an ionic compound.
In an ionic bond, a transfer of electrons takes place.
The positive charge of the magnesium ion is exactly equal to the negative charge of the two chloride ions.
Ionic bonds usually are formed by bonding between metals and nonmetals.
Ionic compounds are often crystalline solids with high melting points.
Sharing Electrons
Some atoms of nonmetals are unlikely to lose or gain electrons.
Covalent Bond: The attraction that forms between atoms when they share electrons
Molecule: A neutral particle that forms as a result of electron sharing.
A single covalent bond is made up of two shared electrons.
A covalent bond also can contain more than one pair of electrons.
When each atom contributes three electrons to the bond, the bond contains six electrons, or three pairs of electrons.
Covalent bonds form between nonmetallic elements.
Electrons are not always shared equally between atoms in a covalent bond.
The strength of the attraction of each atom to its electrons is related to the size of the atom, the charge of the nucleus, and the total number of electrons the atom contains.
Each atom in the molecule attracts the electrons that they share.
The electrons being shared in a molecule are held more closely to the atoms with the stronger pull or larger nucleus.
The atom holding the electron more closely always will have a slightly negative charge.
Polar Molecule: one that has a slightly positive end and a slightly negative end although the overall molecule is neutral.
Non-polar Molecule: one in which electrons are shared equally in bonds.
Binary Ionic Compounds
Binary Compound: One that is composed of two elements.
Oxidation Number: tells you how many electrons an atom has gained, lost, or shared to become stable.
For ionic compounds the oxidation number is the same as the charge on the ion.
When naming these compounds, the oxidation number is expressed in the name with a roman numeral.
When writing formulas it is important to remember that although the individual ions in a compound carry charges, the compound itself is neutral.
A formula must have the right number of positive ions and the right number of negative ions so the charges balance.
Compounds with Complex Ions
Not all compounds are binary.
Polyatomic Ion: a positively or negatively charged, covalently bonded group of atoms.
Compounds with Added Water
Some ionic compounds have water molecules as part of their structure.
Hydrate: a compound that has water chemically attached to its ions and written into its chemical formula.
You can remove water from these crystals by heating them.
Naming Binary Covalent Compounds
Covalent compounds are those formed between elements that are nonmetals.
Some pairs of nonmetals can form more than one compound with each other.
Using oxidation numbers to write formulas, you can predict the ratio in which atoms of elements might combine to form compounds.
