Topic 4

Describe ionic bonds

• An electrostatic attraction between oppositely charged ions

• a transfer of electrons from metallic to non-metallic elements

• electronegativity difference >1.8

What happens to metals in an ionic bond?

they loose electrons, becoming positive cations

Describe the strength of ionic bonds

Strong due to the powerful electrostatic attraction

Why are ionic compounds brittle?

when force is applied, like charges align and repel. This disrupts the structure and leads to breakage.

Why do ionic compounds have high boiling and melting points?

• the strong electrostatic force acts in all directions, keeping ions tightly together.

• the higher the charge, the lower the ionic radius, the greater the attraction between oppositely charged ions, the higher the melting point.

Are ionic compounds conductive?

• Only when molten or in a solution

• Free movement of electrons = conductivity

What type of bond occurs within a polyatomic ion?

covalent

Describe covalent bonding

• an electrostatic attraction between nuclei and shared valence electron

• Electrons are shared, not transferred

• Between non metals

• electronegativity difference <1/.8

What is it called when the electronegativity difference is 0

Pure covalent

What is it called when the electronegativity difference is 0.1-0.4

Non-polar/weakly covalent

What is it called when the electronegativity difference is 0.5-1.7

Polar covalent

Describe a coordinate covalent bond

one atom donates both shared electrons to create a bond with na electron-deficient atom.

Why is it not possible to create a quadruple bond?

The repulsive forces between the nuclei and the electrons are too great

Define bond energy

energy required to break bond between atoms (kj mol-)

What is the trend with bond energy

• the larger the bond energy, the stronger the covalent bond

• more bonds = higher energy

define bond length

the distance between the nuclei of the bonded atoms

What is the trend in bond length

• the greater the force of attraction, the shorter the bond length

• shorter bond = stronger

What are the incomplete octet examples

• H: 2

• Li: 2

• Be: 4

• B and Al: 6

What/why can elements for expanded octet?

• period 3 and below

• because they can expand into d subshell

What are resonance structures

Multiple possible lewis structures due to uncertainty in location of double bond

What are delocalized electrons?

Electrons not associated with a certain atom or bond

Explain VESPR

• valence shell electron pair repulsion theory

• electrons arrange themselves as far away as possible

• lone pairs repel more than bonding pairs

• multiple bonds behave like single bonds

Describe linear structure

• 180 degrees

• 2 electron domain : 2 bonding

describe trigonal planar structure

• 120 degrees

• 3 electron domain: 3 bonding

Describe bent trigonal planar structure

• 118 degrees

• 3 electron domain: 2 bonding, 1 non-bonding

Describe tetrahedral structure

• 109.5 degrees

• 4 electron domain: 4 bonding

describe trigonal pyramidal structure

• 107.3 degrees

• 4 electron domain: 3 bonding, 1 non-bonding

• electron domain geometry: tetrahedral

Describe bent tetrahedral structure

• 104.5 degrees

• 4 electron domain: 2 bonding, 2 non-bonding

• electron domain geometry: tetrahedral

How can a molecule with polar bonds be non polar

if the dipoles cancel out due to symmetrical structure

Which electrons are the most repulsive

• non-bonding with non-bonding

• non-bonding with bonding

• bonding with bonding

What are giant covalent structures?

A lattice of covalent bonds to satisfy bond capacity

Describe diamond giant covalent structure

• each C is bonded to 4 C

• poor conductor b/c no free electrons

• high melting and boiling points

• Extremely hard

describe graphite giant covalent structure

• each C is bonded to 3 C

• layers held by intermolecular forces

• atoms in layer held by covalent bonds

• conductive

• soft due to weak forces between layers

describe silicon grant covalent structure

• each Si is bonded to 4 Si

• high melting and boiling point

• poor conductor

describe Silicon dioxide giant covalent structure

• each Si bonded to 4 O

• hard

• poor conductor

• high melting and boiling points

Why are LDF temporary

Due to the continous movement of electrons

Describe LDF

• weak

• in every atom or molecule

What is the relationship between number of electrons and LDF and MP and BP

The higher the molar mass the higher the likelihood of distortion, the higher the frequency and intensity of temporary dipoles, the higher the melting and boiling point

What is the relationship between SA and LDF and BP and MP

the higher the SA, the more contact, the more LDF, the higher the melting and boiling points

Describe DD forces

• stronger than LDF

• permanent dipole

What is the relationship between DD, LDF,MP and BP

higher MP and BP than LDF

describe hydrogen bonding

• H directly attached to F,O,N

• strongest intermolecular force

• extremely high boiling point

• very electronegative

• highly polarized (H=+)

Describe the structure of metallic bonds

tightly packed lattice structure

What happens when force is applied to metallic structures

layer slide but do not break

Describe metallic bonding

• between metals

• High BP and MP: strong electrostatic force

• Conductive as solid or liquid

What is the relationship between charge and strength of metallic bonds

the higher the charge, the more electrons, the stronger the bond

What is the relationship between radius and strength of metallic bonds

the smaller the radius, the greater the attraction between delocalized electrons and nucleus, the stronger the bond

What is an alloy

a physical mixture of metals

what is an alllotrope

a different form of an element in the same state