AP CHEM - UNIT 2

Intramolecular forces

exist between the bonded atoms of a compound or a molecule

intermolecular forces

exist between molecules, i.e. hydrogen bonds between water molecules

Why do chemical bonds form?

To achieve a lower energy state.

Pure metallic

1 type of metal atom

Alloy

mixture of 2 or more different atoms (at least 1 is a metal)

What are metals considered in terms of their charge?

Metals are cations.

What does it mean that the electrons in metals are delocalized?

It means the electrons are more free

What is the electron

sea model?

How does the size of metallic cations affect the strength of metallic bonds?

The bond is stronger with smaller metallic cations.

What effect do more valence electrons have on metallic bonding?

More valence electrons lead to stronger metallic bonds.

Metallic Properties

Shiny (luster)

Malleable (hammer into sheets)

Ductile (stretch into wires)

Conduct heat and electricity

What are ionic solids commonly known as?

Salts

What occurs to electrons during ionic bonding?

Electrons are transferred from a cation to an anion.

What characterizes a cation in ionic bonding?

A cation is formed when an element with low ionization energy and low electron affinity gives up an electron.

What characterizes an anion in ionic bonding?

An anion is formed when an element with high ionization energy and high electron affinity gains an electron.

How is the transfer of electrons represented in Lewis structures?

Arrow(s) indicate the transfer of the electron(s).

What causes ionic bonds to form?

A large difference in electronegativity between a metal and a nonmetal, leading to electron transfer.

What is the nature of the attraction that holds ions together in ionic bonds?

The electrostatic attraction between the positively and negatively charged ions.

What is the role of Coulomb's law in ionic bonding?

Coulomb's law describes the electrostatic force that causes ions to bond.

What factor increases the strength of ionic bonds according to Coulomb's Law?

The strength of ionic bonds increases with larger charges on the ions.

How does the size of ions affect the strength of ionic bonds?

Smaller ions lead to stronger ionic bonds due to decreased distance between the centers of ions.

What is the relationship between charge and interaction strength in ionic bonds?

The strength of interaction is proportional to the charge on each ion; larger charges result in stronger interactions.

What does Coulomb's Law explain about ionic bonds?

Coulomb's Law explains that ionic bond strength is affected by the size of the ions and the magnitude of their charges.

Ionic Properties

Form crystal salts (lattice of positive and negative ions)

High melting and boiling points

Hard

Brittle (see bottom image)

Conduct electricity when dissolved and when molten (melted)

Good insulators as a solid

Properties of Covalent Molecules

Non

Low melting points and boiling points

Many compounds in this class are liquids or gases at room temperature

Soft or brittle solid forms

Poor electrical and thermal conductivity.

Polar covalent bond

Electrons are shared unequally.

Nonpolar covalent bond

Electrons are shared equally.

What does bond polarity measure?

Bond polarity measures how equally or unequally the electrons in a covalent bond are shared.

Can covalent bonds be polar or nonpolar?

Yes, covalent bonds can be either polar or nonpolar.

Are ionic bonds considered polar?

No, ionic bonds are never polar due to the transferring of electrons.

What type of bonds are associated with the term 'polar'?

The term 'polar' is associated only with covalent bonds, not ionic bonds.

What characterizes nonpolar covalent bonds?

They involve 'equal' sharing of electrons.

What is the electronegativity difference in nonpolar covalent bonds?

There is a small difference in electronegativity values.

When do nonpolar covalent bonds mainly occur?

They mainly occur between the same element.

What are diatomic elements that form nonpolar covalent bonds?

Diatomic elements include H2, N2, F2, O2, I2, Cl2, Br2.

What type of bonds between carbon and hydrogen are considered nonpolar?

Carbon to hydrogen bonds are always nonpolar.

What characterizes a polar covalent bond?

Unequal sharing of electrons between atoms.

How does electronegativity difference affect polarity in bonds?

The greater the difference in electronegativity, the more polar the bond.

What can be used to determine the polarity of a bond if electronegativity values are not available?

The distance between the elements on the periodic table; further apart means more electronegative.

Which element is the most electronegative?

Fluorine (F).

What charge does the pole with more electron density have in a polar covalent bond?

A partial negative charge (𝛅

What charge does the pole with less electron density have in a polar covalent bond?

A partial positive charge (𝛅+).

What is a dipole?

A measure of polarity formed when two opposite charges are separated by a distance.

What causes the formation of a dipole?

The separation of two opposite charges.

Bond order

number of bonds between 2 atoms

What is bond length in covalent bonding?

The distance between two bonded nuclei at the point of maximum attraction.

How does the number of shared electrons affect bond length?

As the number of shared electrons increases, the bond length decreases.

What is the relationship between bond length and bond strength?

The shorter the bond length, the stronger the bond.

Which type of covalent bond is the weakest?

Single bonds are weaker than double and triple bonds.

Which type of covalent bond is the strongest?

Triple bonds are stronger than double and single bonds.

What is bond enthalpy?

The amount of energy required to break a chemical bond, also known as dissociation energy.

Why is bond enthalpy always a positive value?

Because breaking bonds requires the input of energy, making it an endothermic process.

How does bond length affect bond enthalpy?

The shorter the bond length, the greater the energy required to break it, resulting in higher bond enthalpy.

What effect do larger atomic radii have on bond length and bond enthalpy?

Larger atomic radii increase bond length, which decreases bond enthalpy, particularly in single bonds.

How does bond order influence bond enthalpy?

Increasing the bond order (from single to double to triple bonds) increases bond enthalpy.

What is the relationship between electrons, bond length, and Coulombic attraction?

More electrons and shorter bond lengths result in greater Coulombic attraction, leading to higher bond enthalpy.

How do bonds between hydrogen and other atoms change as you move down a column in the periodic table?

Bonds become weaker as you go down the column (e.g., H

What trend is observed in bonds between like atoms as you move down a column?

Bonds between like atoms usually become weaker (e.g., C

What is notable about multiple bonds between carbon, oxygen, or nitrogen and period 3 elements?

They tend to be unusually strong, which is important in biological molecules like DNA.

Covalent bonds occur at the ____

lowest energy state.

Goldilocks zone

need to find optimal bond length (bottom of curve)

What is the energy required to separate ions in an ionic bond called?

Lattice energy

How does Coulomb's law relate to lattice energy?

Lattice energy is influenced by the charges of the ions and their radii, as described by Coulomb's law.

What effect do larger charges have on lattice energy?

Larger charges result in higher lattice energy, making the bond harder to break.

How does the size of ion radii affect lattice energy?

Smaller ion radii lead to higher lattice energy.

What does Coulomb's Law indicate about ionic bond strength?

Ionic bond strength can be estimated from Coulomb's Law, where higher ion charges result in stronger bonds.

Why does calcium oxide (CaO) have stronger bonds than sodium chloride (NaCl)?

CaO has Ca2+ and O2

What is the relationship between ionic charge and melting point?

Higher ionic charges lead to stronger bonds, resulting in a higher melting point.

Compare the bond lengths of sodium chloride (NaCl) and sodium bromide (NaBr).

NaCl has shorter bond lengths because Cl is smaller than Br, making NaCl stronger.

What is the implication of smaller atoms on ionic bond strength?

Smaller atoms result in stronger bonds, which contributes to a higher melting point.

What is the arrangement of cations and anions in an ionic solid called?

A crystal lattice

What type of forces are maximized in a crystal lattice arrangement?

Attractive forces

What type of forces are minimized in a crystal lattice arrangement?

Repulsive forces

What is the structure of the arrangement of ions in an ionic solid?

A systematic, repeating 3

What is dissociation in chemistry?

Dissociation is a type of dissolution where a compound breaks apart into its parts that can be recombined later.

What happens to ionic solids when they dissolve in water?

Ionic solids dissociate into ions when they dissolve in water.

Why do ionic solids dissolve in water?

Ionic solids dissolve in water because water is polar, and the partial positive and negative areas of polar molecules pull the ions apart.

What is the process called when water molecules attach to ions during dissolution?

The process is called hydration.

How do nonpolar solvents affect ionic compounds?

Nonpolar solvents have no effect on ionic compounds because they don't have charges to pull the ions apart.

What are mixtures of metals called?

Alloys

What type of alloy involves small atoms fitting between metal atoms?

Interstitial alloys

Which elements are often added to interstitial alloys?

Hydrogen (H), Boron (B), Carbon (C), and Nitrogen (N)

What characterizes substitutional alloys?

Atoms added have similar radii and replace atoms in the lattice.

What type of ions or molecules have an odd number of electrons?

Ions or molecules that do not follow the octet rule.

What is a characteristic of ions or molecules with less than an octet?

They do not follow the octet rule.

What is meant by an expanded octet?

Ions or molecules that have more than eight valence electrons.

What are resonance structures?

Resonance structures are different valid Lewis structures that can represent the same molecule when there are two or more accurate ways to draw it.

What do resonance structures represent in chemistry?

They represent different ways of arranging electrons in a molecule, showing that all structures exist simultaneously.