Chemistry Chapter 6

Tetrahedral

4 atoms bonded to central atom, 0 lone pairs

Trigonal-bipyramid

5 atoms bonded to central atom, 0 lone pairs

Octahedral

6 atoms bonded to central atom, 0 lone pairs

What is the relationship between bond length and bond energy?

- The shorter the bond length, the greater the bond energy - so it's an indirect or inverse relationship - decrease bond length, increase bond energy; increase bond length, decrease bond energy

What is the relationship between size of the atoms and bond length?

- The smaller the size of the bonded atoms, the shorter the bond length - so it's a direct relationship - decrease size, decrease length; increase size, increase length

Linear

2 atoms bonded to central atom, 0 lone pairs

Bent or angular

2 atoms bonded to central atom, 1 lone pairs

Bent or angular

2 atoms bonded to central atom, 2 lone pairs

Trigonal-Planar

3 atoms bonded to central atom, 0 lone pairs

Trigonal-pyramid

3 atoms bonded to central atom, 1 lone pairs

Why do most atoms form chemical bonds?

By bonding the atoms with gain or lose electrons in an ionic bond or share electrons in a covalent bond to have 8 valence electrons (an octet) like the noble gases (except for H which likes 2 electrons to be like He). This makes them stable like the noble gases which lowers their potential energy.

Explain why ionic compounds do not conduct electricity in their crystalline form.

Electricity can only be conducted when ions are freely moving in separate positive and negative charges (as in the aqueous form and molten form). In their crystalline form, the ions in the ionic compound are locked tightly in one place and the positive and negative balance out to make the overall structure neutral.

How are the ionic bonds formed? The covalent bonds? The metallic bonds?

Ionic - a transfer of electrons from the metal to the nonmetal Covalent - a sharing of electrons between two nonmetals Metallic - the metals give up their valence electrons; the metal cations then become attracted to the sea of electrons which holds them together

What are the typical properties of an ionic bond? A covalent bond? A metallic bond?

Ionic - hard, brittle, high melting points Covalent - low melting points Metallic - malleable, ductile, reflect light and heat, (metals melting points vary)

Can metallic compounds conduct electricity? Ionic? Polar covalent? Nonpolar covalent?

Metallic - YES, because you have the (+) metal cations and (-) sea of electrons Ionic - YES, when molten and aqueous because the cations and anions have broken out of the crystal lattice and are moving about freely from each other; NO, when solid crystal because the cations and anions are in the crystal lattice in an alternation (+) and (-) pattern which makes the overall structure neutral (no charges to conduct an electric current) Polar Covalent - YES WEAKLY, because the molecule has partial (+) and partial (-) ends or poles Nonpolar Covalent - NO, because the molecule has no (+) or (-) poles; it is neutral

What is used to measure bond strength of metallic bonds, ionic bonds, and covalent bonds?

Metallic - heat of vaporization (the higher the heat of vaporization, the stronger the metallic bond) Ionic - lattice energy (the more negative the number, the more energy released, the stronger the bond) Covalent bonds - bond energy (the shorter the bond length, the stronger the bond, and the more energy it takes to break the bond)

What sign to lattice energy values have? Why?

Negative, because lattice energy is the energy RELEASED when one mole of an ionic compound forms into a crystal lattice. Therefore, the energy is exothermic. The negative sign indicates the direction of the energy, and that it is being taken away from the system (not added to the system, which would be endothermic and have positive values).

What two things determine the bond length of a covalent bond?

Size of the atoms and the distance between the two atoms at which potential energy is the lowest

Why do ionic compounds tend to be hard and brittle?

The cations and anions are locked tightly into place because of the attraction of their opposite charges - as a result, it's difficult to move the ions and the material is very hard. If you try to bend or shape an ionic crystal, you will cause a disruption in the crystal lattice causing like charges to touch and repel. This makes ionic compounds very brittle.

Why do metals and nonmetals usually form ionic compounds, whereas two bonded nonmetals are never ionic? Explain.

The difference in electronegativity between metals and nonmetals is high, meaning that it's very easy for the very electronegative nonmetals to take electrons from non-electronegative metals. If both elements were metals, or if both were nonmetals, the electronegativities would be too similar for one element to take electrons from the other.

Why is the formation of ionic compounds exothermic (hint: think about if energy i.e. potential energy increases or decreases?

The interaction of so many positive ions with negative ions gives ionic compounds considerable stability in the crystal lattice verses the individual elements. Because stable = lower in potential energy, this extra energy is given off as heat during the formation of ionic compounds.

Covalent compounds are composed of:

all nonmetals

Ionic compounds are composed of:

cations (usually metals, except for NH4+) and anions (nonmetals)

dipole

created by equal but opposite charges that are separated by a short distance

inter-molecular forces

forces of attraction between molecules

hybrid orbitals

orbitals of equal energy produced by the combination of two or more orbitals on the same atom

Strongest intermolecular forces exist between...

polar molecules

VSEPR theory

states that repulsion between the sets of valence-level electrons surrounding an atom causes these sets to be oriented as far apart as possible

London Dispersion

the inter-molecular attractions resulting from the constant motion of electrons and the creation of instanteous dipoles

hydrogen bonding

the inter-molecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule

hybridization

the mixing of two or more atomic orbitals of similar energies on the same atom to produce new hybrid atomic orbitals of equal energies