Substances and chemical bonds

important key words that seem unfamiliar :) DOES NOT INCLUDE THE NAMING OF COMPOUNDS

What are ionic bonds?

Atomic bonding where atoms transfer electrons, creating charges, which results in an electrostatic attraction that holds the ions together and forms the ionic bond.

What is a cation?

Positive ion, lost electrons

What is an anion?

Negative ion, gained electrons

What is needed for an ionic bond to form?

The electronegativity difference between elements has to be over 1.7.

What are 5 typical properties of ionic bonds?

• High melting and boiling points

• Hardness and brittleness

• Electrical conductivity 0 when solid

• Soluable in water (polar)

• Crystal shape (ionic crystal)

What is ionization energy? (ionization potential)

The amount of energy needed to remove an electron from an isolated atom or molecule

What is electron affinity EA?

A measure of the change of energy when an electron is added to a natural atom in the gas phase to form an anion

• basically the opposite to ionization energy

• high ea (negative ea) indicates a strong attraction for the extra electron and so on

• ea describes the atom’s system’s energy, so negative means that it’ll release energy to take..

What significance does electron affinity have?

1. Chemical Reactivity

   • Elements with high (more negative) electron affinities tend to be more reactive nonmetals

2. Predicting Ionic Bonds

   • Electron affinity helps predict the likelihood of an atom forming an anion

How are covalent bonds formed?

When atoms share electron pairs.

• goal is to attain the electron configuration of a noble gas ( a stable molecule )

What is a coordinate bond ( dative covalent bond )?

A covalent bond where both electrons in the shared bond come from the same atom

• two atoms of the same element bond together

What is electronegativity?

A measure of an atoms ability to attract and hold onto electrons in a covalent bond

What is polarity or nonpolarity in covalent bonds?

Polar = “unequal sharing” of the electrons, where there are regions of distinct partial positive or partial negative charges.

• electronegativity difference is 0.5 to 1.7

Nonpolar = equal sharing of the electrons, where the molecule is neutral in charge.

• electronegativity difference of 0 to 0.4

• the molecular geometry could cancel out charges, making it a nonpolar molecule.

What are the typical properties of covalent bonds?

• Low melting and boiling points, due to the intermolecular forces being generally weaker than the bonds themselves

• Polar covalent compounds are soluble in polar solvents (water)

• Nonpolar covalent compounds are soluble in nonpolar solvents (oil)

• Not conductive (exception of graphite in electrical conductivity)

• Molecular structures; each molecule is their own "unit" instead of a continuous lattice seen in ionic or metallic compounds.

What are intramolecular forces?

Forces that hold together atoms within a molecule

• very strong compared to intermolecular forces

• responsible for the chemical properties of a substance

• covalent, ionic, metallic

What are intermolecular forces?

Forces of attraction or repulsion between molecules

• determines the physical properties of a substance (melting and boiling point, vapor pressure, solubility)

• Van der Waals forces, hydrogen bonds

What are van der Waals forces and name the three types.

Bonds resulting from weak intermolecular forces between molecules or atoms

• significant in determining the physical properties of substances (boiling point, melting point, solubility)

• London dispersion forces

• dipole-dipole interactions

• dipole-induced dipole interactions

What are London dispersion forces, how do they come to be and what affects the strength?

Weak attractions due to temporary fluctuations in the electron distribution within atoms or molecules, regardless of the polarity.

Strength increases with the size and shape of the molecule, because of the larger area where the temporary dipoles can form.

What are dipole-dipole interactions?

Interactions between polar molecules due to electrostatic attractions

• generally stronger than London dispersion forces

What are dipole-induced dipole interactions?

A polar molecule can distort the electron cloud of a nearby nonpolar molecule, inducing a temporary dipole

• generally stronger than London dispersion forces, but weaker than dipole-dipole interactions

Rank intermolecular forces from strongest to weakest

1. Hydrogen bond

2. Dipole-dipole interactions

3. dipole-induces dipole interactions

4. London dispersion forces

What are hydrogen bonds?

strong type of dipole-dipole interaction

• A hydrogen atom is covalently bonded to a highly electronegative atom (most commonly nitrogen (N), oxygen (O) or fluorine (F)) which then interacts with a lone pair of electrons on another electronegative atom in a nearby molecule

  • Lone pair of electrons = pairs of valance electrons not shared with another atom and are not thus involved in bonding

    • Provide a region of negative charge