Chemistry Fundamentals Quiz

Chemical Bonding: Chemical Formulas

• Most materials are combinations of elements
• Compounds are formed when two or more elements combine chemically
• Chemical bonds hold atoms together in compounds
• The octet rule states that atoms tend to gain or lose electrons to achieve a full outer electron shell (8 electrons)
• Noble gases are unreactive because they have stable electron configurations (full outer shells)
• Elements in Group 1 tend to lose one electron to form a positive ion
• Elements in Group 2 tend to lose two electrons to form a positive ion
• Elements in Groups 6 and 7 tend to gain electrons to form a negative ion
• Ionic bonds are formed by the attraction between oppositely charged ions
• Ions are charged atoms or groups of atoms
• Ionic compounds are usually formed between metals and non-metals
• Table salt (sodium chloride) is an example of an ionic compound
• Electron dot-and-cross diagrams show the transfer of electrons during the formation of an ionic bond.
• Examples of transition elements include iron, copper and chromium
• Transition metals can form more than one type of ion with various charges.
• Knowing the charges on the ions of elements in groups 1, 2 ,6, and 7 allows us to predict how many ions will combine
• Chemical formulas represent compounds using symbols for atoms and numbers to show how many of each type of atom are present.
• Examples of ionic compounds and how they form are shown
• Metals tend to lose electrons, forming positive ions. Non-metals tend to gain electrons, forming negative ions.
• The overall charge of an ionic compound has to be zero.
• Ionic compounds usually exist as solid crystals with a crystal lattice structure.

Sodium Chloride Crystal Structure

• X-ray studies determine the arrangement of ions in a crystal
• Sodium chloride has a cubic crystal structure.
• Ions in the crystal structure are surrounded by other ions.
• Sodium chloride is essential for life in various functions.

How to Write Chemical Formulas

• Ionic compounds are formed by a metal and a non-metal.
• The overall charge must be zero.
• Using the example of magnesium fluoride (Mg(F2) and calcium chloride (Ca(Cl2), the rules for writing correct formulas are demonstrated.
• Examples of compounds and chemical formulas are shown

Writing Formulas of Compounds with Group Ions

• Group ions are charged groups of atoms, such as sulfate, nitrate, and hydrogen carbonate.
• Knowing the charges of the group ions allows the prediction of ionic formulas

Characteristics of Ionic and Covalent Compounds

• Ionic compounds form crystals and are hard, have high melting points and boil at high temperatures. They conduct electricity in liquid or aqueous state.
• Covalent compounds form molecules and do not typically form crystals. Covalent compounds are soft, have low melting and boiling points. They typically do not conduct electricity except in liquid or aqueous form.

Shapes of Covalent Molecules

• Some covalent compounds exhibit unique shapes.
• Shapes of molecules can be predicted using the valence shell electron pair repulsion theory (VSEPR)

Electronegativity

• Electronegativity is the ability of an atom in a covalent bond to attract the electrons in the bond.
• Bonding character can be predicted using differences in electronegativity between elements.
• Electronegativity difference greater than 1.7 usually indicates ionic bonding; difference less than 0.4 indicates non-polar covalent bonds; difference between 0.4-1.7 usually indicates polar covalent bonds
• Polar molecules have oppositely charged ends (poles)

Intermolecular Forces

• Intermolecular forces are the forces of attraction between molecules.
• There are three types: van der Waals forces, dipole-dipole forces, and hydrogen bonding.
• Van der Waals forces are weak forces of attraction caused by temporary dipoles in molecules. These forces increase as the number of electrons or size of the molecules increases
• Dipole-dipole forces are attractions between permanent dipoles in polar molecules. These forces are stronger than van der Waals forces
• Hydrogen bonding is a strong type of dipole-dipole interaction between molecules containing a hydrogen atom bonded to a highly electronegative atom (O, N, F). Hydrogen bonds are much stronger than van der Waals or dipole-dipole forces.

Dissolving of Ionic and Covalent Compounds in Water

• Water is an excellent solvent for many ionic and polar covalent compounds.
• Water molecules are attracted to charged ions and other polar molecules. This attraction overcomes the forces holding the particles together in the solid or liquid state. The compounds dissolve in water.