Chemical Bonding Quiz

Chemical Bonding

• A compound is a substance made of two or more different elements combined chemically.
• Chemical bonds hold atoms together in a compound.
• The octet rule states atoms tend to gain, lose, or share electrons to achieve eight electrons in their outermost energy level (stable).
• Some elements (transition metals, hydrogen, lithium, and beryllium) do not follow the octet rule.
• An ion is a charged atom or group of atoms.
• Atoms form ions by gaining or losing electrons to achieve a noble gas configuration.
• Ionic bonding involves the complete transfer of electrons from one atom to another, forming oppositely charged ions that attract each other.
• Ionic compounds have high melting and boiling points, are usually solids at room temperature, hard and brittle, and conduct electricity when molten or dissolved in water.
• Formulae represent compounds’ elements and how many of each.
• Ionic compounds are formed between metals (groups I and II) and non-metals (groups VI and VII).
• A crystal lattice is a three-dimensional arrangement of ions.

Ionic Compounds - Formulas

• Elements in groups I and II tend to lose electrons to form positively charged ions (cations).
• Elements in groups VI and VII tend to gain electrons to form negatively charged ions (anions).
• Ionic compounds are overall neutral; thus, positive and negative charges must balance.
• The formula for any ionic compound is determined by ensuring the total positive charge equals the total negative charge.

Dot and Cross Diagrams

• Show the outer electrons of each atom.
• Represent atoms with dots or crosses (different symbols).
• Use an arrow to show electron transfer.

How to Write the Formulas of Ionic Compounds

• Represent atoms using symbols.
• Use numbers to show the number of atoms of each element.
• For Ionic compounds, determine the formulas by ensuring the total positive charge equals the negative charge.

Covalent Bonding

• Covalent bonds involve the sharing of electrons between atoms.
• Atoms share electrons to achieve a stable electron configuration.
• Molecules are groups of atoms joined together. The smallest particle of an element or compound.
• A sigma bond occurs when atomic orbitals overlap head-on.
• A pi bond occurs when p orbitals overlap sideways.

Types of bonds

• Single bonds consist of one sigma bond.
• Double bonds consist of one sigma and one pi bond.
• Triple bonds consist of one sigma and two pi bonds.
• Polar Covalent bond: Unequal sharing of electrons.
• Non-polar Covalent bond: Equal sharing of electrons.
• Electronegativity is the measure of an atom's attraction for shared electrons in a covalent bond.

Properties of Covalent Compounds

• Often soft solids, liquids, or gases at room temperature.
• Have low melting and boiling points.
• Do not conduct electricity, either as solids or in solution.

Shapes of Covalent Molecules

• VSEPR Theory (Valence Shell Electron Pair Repulsion) predicts the shape of molecules based on electron pair repulsion.
• The shape of a molecule depends on the number of bond pairs and lone pairs around the central atom.

Electronegativity

• Electronegativity is the relative attraction of an atom for the shared pair of electrons in a covalent bond.
• The electronegativity difference between two atoms determines if the bond is polar.
• Polar Bonds- When the electronegativity difference between atoms in a molecule is greater than 0.4 but less than 1.7.
• Non-polar Bonds- When electronegativity difference between atoms is less than or equal to 0.4.
• Ionic Bonds- When electronegativity difference is greater than 1.7.

Intermolecular Forces

• Intermolecular forces are forces between molecules.
• Van der Waals forces are weak attractive forces between non-polar molecules resulting from temporary dipoles.
• Dipole-dipole forces exist between polar molecules.
• Hydrogen bonding is a strong type of dipole-dipole attraction between molecules with hydrogen bonded to a highly electronegative element (N, O or F).

Differences between ionic and covalent compounds

• Ionic compounds have high melting and boiling points; covalent compounds have low melting and boiling points.
• Ionic compounds are usually hard and brittle; covalent compounds are usually soft and flexible or gases.
• Ionic compounds can conduct electricity in their molten or dissolved states; covalent compounds do not conduct electricity.