P- Bonding Flashcards by Katherine Choi

What is a coordinate/ dative covalent bond?

A shared pair of e- w/ both e- SUPPLIED by one atom

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Electronegativity

The power of an atom to attract the pair of e- in a covalent bond

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What is the way of drawing atoms showing e- w/o shells called?

Lewis structures

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What is electronegativity measured in?

Pauling scale (0-4)

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Describe the trend in electronegativity in the periodic table.

↓ down the group
∵ shielding ↑
↑ across the period
∵ nuclear charge ↑ (↑ + charge to pull e- )

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What is the atom that accepts the e- pair (slightly positive end of the molecule) called?

Electron deficient (/ delta positive)

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What is the bond between 2 atoms with an electronegativity difference?

Polar (covalent) bond

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How do we know whether 2 elements form covalent or ionic bonds?

electronegativity diff. < 1.7 – covalent
> 1.7 – ionic

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Octet rule

atoms are most stable when they have 8 outer e-
(esp. if they are in bonds)

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Why are molecular structures poor conductors of electricity?

they have an overall neutral charge
x charged particles to carry charge

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How are coordinate covalent bonds represented in a diagram?

Arrow pointing towards atom accepting e- pair

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Condition needed for the formation of a dative covalent bond

lone pair + incomplete octet –> dative covalent bond

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What is the name of the compound called when some very reactive molecules (eg. AlCl3) reacts with itself?

Dimer- ↑ reactive

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What is a dipole?

A covalent bond whose ends have opp. partial charges.

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Why is F more electronegative than Cl?

smaller atom
shared e- closer to nucleus when covalent bond forms

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Starter: How does sodium conduct electricity?

delocalised e-
move & carry charge THROUGH the structure
when potential difference is applied

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What are intermolecular forces?

Weak forces of attraction between 2 molecules

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Give one unusual physical property molecules with H bonds have compared to molecules that don’t.

Molceules w/ H bonds- ↑ bp

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2 conditions needed for H bonding

NEEDS BOTH!!!

N, O or F directly bonded to a H atom
Lone pair on N, O or F atom

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Examples where H bonding is seen

Ammonia (NH3)
- N is v. electronegative + has 1 lone pair
Water
- O has 2 lone pairs
Alcohol- O-H
Carboxylic acid- O-H
Amine- N-H
Protein- N-H

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Why does ice have a low density?

maximises amount of H bonds between molecules
open hexagonal structure w/ large spaces within crystal
melting–> liquid occupies ↓ space –> ↑ dense

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Why is a DNA molecule helical?

C=O bonds in long chains
H atoms + electronegative O atom –> H bond
molecule spirals

INTRAmolecular H bonds- attraction between H & electronegative atom on the SAME MOLECULE

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What kind of substances are affected by Van der Waals forces?

Atoms & molecules (x ions) apart from diamond & silicon dioxide (SiO2)

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How is a temporary dipole formed?

e- cloud in constant motion –> temp dipole when more at one pole
attraction between 2 molecules induces dipole on the other molecule–> VdW

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Factors increasing strength of VdW forces

1. ↑ e- cloud 2. ↑ Ar of atoms/ Mr of compounds 3. s.a.

How does shape of a molecule affect its boiling point?

- straight chains have ↑ bp (than spherical) ∵ ↑ s.a. for VdW forces ↑ interactions + stronger

Factors determining bp

1. Mr 2. Are there dipole-dipole/ H bonds as well as VdW? 3. Shape **H bonds= strongest IM--> high bp (eg. water- unusually high bp)

What is 'absolute zero'?

0 K- everything is solid

Explain why temp of water doesn't change during boiling/ melting.

Melting- energy is used to break SOME of the H bonds Boiling- ALL H bonds -- x IM forces in gas ∵ all H bonds broken when boiling

Explain what energy transferred is used for during melting of a substance.

To overcome SOME forces holding atoms/ ions/ molecules in proximity

Explain what energy transferred is used for during boiling of a substance.

To overcome ALL forces between atoms/ ions/ molecules in proximity ∴ x IM forces in gases

What is a crystal?

A substance in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating three-dimensional patterns. - most crystals are solids

What are the forces to overcome when a molecular crystal is heated?

1. the strongest type of IM force present 2. any other IM forces (Van der Waals, permanent dipole-dipole)

What are the forces to overcome when an ionic crystal is heated?

Ionic bonds x IM forces!!

What are the forces to overcome when a metallic crystal is heated?

Metallic bonds x IM forces!!

What are the forces to overcome when a macromolecular crystal is heated?

Covalent bonds x IM forces!!

Explain why hexane is a liquid at room temp while butane is a gas.

- hexane- larger molecule - ∴ ↑ e- - ↑ VdW between molecules

Explain why covalent molecules are gases, liquids, or solids with low melting points.

- covalent bonds only between the 2 atoms they bond - small attraction between individual molecules

Phosphorus (P4) has a mp of 317K while Sulfur (S8) has a mp of 386K. Explain this difference in terms of bonding.

- ↑ VdW - ∵ ↑ e-

Co-ordination no.

no. of bonds around a central atom

What kind of bond has the highest repulsion?

lone pair-lone pair -- to ↓ repulsion, outer e- spread out as far apart in space as poss.

What is VSEPR?

Valence shell electron repulsion theory

Name + bond angle w/ 2 bonding pairs

Linear- 180

Name + bond angle w/ 3 bonding pairs

Trigonal planar- 120

Name + bond angle w/ 4 bonding pairs

Tetrahedral- 109.5 -- achieved thru 3D!! (max 90 if 2D)

Name + bond angle w/ 5 bonding pairs

Trigonal bipyramidal- 90 &120

Name + bond angle w/ 6 bonding pairs

Octahedral- 90

How would the bond angle change when there are lone pairs on a tetrahedral (4 co-ordinate) shaped molecule?

Take off 2.5 for every lone pair

How would the bond angle change when there are lone pairs on a linear/ trigonal planar shaped molecule?

x affected by lone pairs

Explain the shape of an ammonia (NH3) molecule

- trigonal pyramid- 107 - bonding pairs attracted to H as well as N - vs lone pair only attracted to N - ∴ pulled closer - H-N-H angle ↓

What is different in bonding between a macromolecular and molecular crystal?

Molecular: - strong covalent bonds between atoms - weaker intermolecular forces between molecules vs Macromolecular: - all atoms are covalently bonded

Do ionic compounds conduct electricity?

yes when molten - ions x free to move in solids - free to move & carry charge when separated

Are ionic compounds soluble?

yes - ∂+ & ∂- ends of H2O attracted to ions

Why are ionic compounds brittle?

- layers slide--> same charges next to each other - repulsion cracks crystal

Melting points of monatomic substances

v. low - v. weak forces between ATOMS

Do monatomic substances conduct?

no - atoms are NEUTRAL - x mobile charged particles

Why are metallic compunds strong?

- layers can slide - while maintaining metallic bonding

Why does graphite conduct electricity?

- delocalised e- free to move - BETWEEN LAYERS

Why is graphite brittle?

- weak IM forces between layers (graphene) - can slide (pi-pi stacking interactions)

Describe the structure of ice

- 3D open structure - held tgt by covalently bonded H2O molecules (2 H bonds) - each O bonded to 4 H atoms - tetrahedral shape

mp & bp of ice

low - weak forces between H2O molecules

Why does ice have a lower density than water?

- molecules in a lattice ∵ H bonds - vs water molecules closer ∵ x in lattice

Why is a dative covalent bond represented by an arrow?

to show both e- come from the same atom

Why is Br in p block?

OUTER e- in p orbital

Explain why the bond angles in CH4 are all 109.5.

- so that 4 bond pairs can be - as far apart as poss. - as they repel equally

How do HCl and HF differ in appearance when drawn?

- bigger arrow showing dipole in HF ∵ bigger dipole - draw lone pairs on for F for H bonding - ∵ lone pair= one of the conditions for H bonding!!!

What does VSEPR mean?

- e- pairs repel - move as far apart in space as poss. - MINIMISE REPULSION l-l > l-b > b-b

Describe briefly strucutre of diamond

- rigid - tetrahedral - lattice

Describe briefly structure of graphite

- planar - hexagonal layered structure - layers held by weak IMF

What's the shape with 2 lone pairs and 3 bond pairs?

T-shape/ trigonal planar

Formula of hydrogencarbonate ion

HCO3-

Formula of nitrate ion

NO3- 2 single bonds + one double bond

Give 2 examples of polar molecules

1. Urea - lots of polar bonds 2. Ethanol ∵ has both polar & non-polar ends\ ∴ can dissolve both polar & non-polar substances

P- Bonding Flashcards

(73 cards)