2B. Bonding and Structure [SET 2] Flashcards by Zongqi Li

What are ions?

Charged particles that is formed when an atom loses or gains electrons

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What is the charge of the ion when electrons are gained?

Negative

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What are molecular ions?

Covalently bonded atoms that lose or gain electrons

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Which electrons are lost when an atom becomes a positive ion?

Electrons in the highest energy levels

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Do metals usually gain or lose electrons?

Lose electrons

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Which are the 4 elements that don’t tend to form ions and why?

The elements are beryllium, boron, carbon and silicon
Requires a lot of energy to transfer outer shell electrons

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What are the 3 main types of chemical bonds?

● Ionic
● Covalent
● Metallic

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Define ionic bonding

The electrostatic attraction between oppositely charged ions

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What determines the strength of an ionic bond?

Ionic radius and ionic charge
Ionic bonding is stronger and the melting points higher when the ions are smaller and/ or have higher charges.

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How to draw dot and cross diagram for ionic bonding

Brackets with charges outside with the outershell displayed on the inside

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Explain the trend in ionic radius down a group

Ionic radii increases going down the group. This is because down the group the ions have more shells of electrons and thus the outermost electron experience less pull from positive
nucleus.

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Explain the trend in ionic radius for this set of isoelectronic ions, N 3-, O 2-, F-, Ne, Na +, Mg 2+, Al 3+

There are increasing numbers of protons from N to F and then Na to Al but the same number of electrons. Therefore nuclear attraction between the outermost electrons and nucleus increases and ions get smaller

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What are the physical properties of ionic compounds?

*high melting points
*non conductor of electricity when solid
*conductor of electricity when in solution or molten
*brittle

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In a solution of CuCrO 4 with connected electrodes which electrode will the 2 ions migrate to?

Cu 2+ - migrates to negative electrode
CrO 4 2- - migrates to positive electrode

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Define covalent bonding

Electrostatic attraction between a shared pair of electrons and the nuclei

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Draw a dot and cross diagram for covalent molecules

Overlapping circles of outer shells

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Define metallic bonding

Electrostatic attraction between the positive metal ions and the sea of delocalised electrons

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Why does giant ionic lattices conduct electricity when liquid but not when solid?

In solid state the ions are in fixed positions and thus cannot move. When they are in liquid state the ions are mobile and thus can freely carry the charge

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Giant ionic lattices have high or low melting and boiling point?
Explain your answer

They have high melting and boiling point because a large amount of energy is required to overcome the electrostatic bonds

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In what type of solvents do ionic lattices dissolve?

Polar solvents
E.g water

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Why are ionic compounds soluble in water?

Water has a polar bond. Hydrogen atoms have a δ+ charge and oxygen atoms have a δ- charge. These charges are able to attract charged ions

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What is the effect of multiple covalent bonds on bond length and strength?

Double/triple bonds exert greater electron density therefore the attraction between nucleus and electron is greater resulting in a shorter and stronger bond.

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What is a dative covalent bond?

A bond where both of the shared electrons are supplied by one atom

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How are oxonium ions formed?

Formed when acid is added to water,
H 3 O +

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What does expansion of the octet mean?

When a bonded atom has more than 8 electrons in the outer shell

What are the types of covalent structure?

● Simple molecular lattice ● Giant covalent lattice

Describe the bonding in simple molecular structures?

Atoms within the same molecule are held by strong covalent bonds and different molecules are held by weak intermolecular forces

Why do simple molecular structures have low melting and boiling point?

Small amount of energy is enough to overcome the intermolecular forces

Can simple molecular structures conduct electricity?

No, they are non conductors.

Why do simple molecular structures not conduct electricity?

The have no free charged particles to move around

Simple molecular structures dissolve in what type of solvent?

Non polar solvents

Give examples of giant covalent structures

● Diamond ● Graphite ● Silicon dioxide, SiO

List some properties of giant covalent structures

● High melting and boiling point ● Non conductors of electricity, except graphite ● Insoluble in polar and non polar solvents

How does graphite conduct electricity?

Delocalised electrons present between the layers are able to move freely carrying the charge

Why do giant covalent structures have high melting and boiling point?

Strong covalent bonds within the molecules need to be broken which requires a lot of energy

Draw and describe the structure of a diamond

3D tetrahedral structure of C atoms, with each C atom bonded to four others

What does the shape of a molecule depend on?

Number of electron pairs in the outer shell Number of these electrons which are bonded and lone pairs

What is the shape, diagram and bond angle in a shape with 2 bonded pairs and 0 lone pairs?

Linear 180°

What is the shape, diagram and bond angle in a shape with 3 bonding pairs and 0 lone pairs?

Trigonal planar 120°

What is the shape, diagram and bond angle in a shape with 4 bonded pairs and 0 lone pairs?

Tetrahedral 109.5°

What is the shape, diagram and bond angle in a shape with 5 bonded pairs and 0 lone pairs?

Trigonal bipyramid 90° and 120°

What is the shape, diagram and bond angle in a shape with 6 bonded pairs and 0 lone pairs?

Octahedral 90°

What is the shape, diagram and bond angle in a shape with 3 bonded pairs and 1 lone pairs?

Pyramidal 107°

What is the shape, diagram and bond angle in a shape with 2 bonded pairs and 2 lone pairs?

Non linear / v shape 104.5°

What is the shape, diagram and bond angle for NH 4+

Tetrahedral 109.5°

By how many degrees does each lone pair reduce the bond angle?

2.5°

Define electronegativity

The ability of an atom to attract the pair of electrons (the electron density) in a covalent bond

What scale is electronegativity measured on?

Pauling scale

In which direction of the periodic table does electronegativity increase?

Top right, towards fluorine

What does it mean when the bond is non-polar?

The electrons in the bond are evenly distributed

How is a polar bond formed?

Bonding atoms have different electronegativities

Why is H 2 O polar, whereas CO 2 is non polar?

CO 2 is a symmetrical molecule, so there is no overall dipole

What are the 3 types of intermolecular forces?

● Hydrogen bonding ● Permanent dipoles ● London forces

Describe permanent dipole- induced dipole interactions

When a molecule with a permanent dipole is close to other non polar molecules it causes the non polar molecule to become slightly polar leading to attraction

Describe permanent dipole- permanent dipole interactions

Some molecules with polar bonds have permanent dipoles → forces of attraction between those dipoles and those of neighbouring molecules

Describe London forces

● London forces are caused by random movements of electrons ● This leads to instantaneous dipoles ● Instantaneous dipole induces a dipole in nearby molecules ● Induced dipoles attract one another

Are London forces greater in smaller or larger molecules?

Larger due to more electrons

Does boiling point increase or decrease down the noble gas group? Why?

Boiling point increases because the number of electrons increases and hence the strength of London forces also increases

What conditions are needed for hydrogen bonding to occur?

O-H, N-H or F-H bond, lone pair of electrons on O, F, N Because O, N and F are highly electronegative, H nucleus is left exposed Strong force of attraction between H nucleus and lone pair of electrons on O, N, F

Describe the diagram of a hydrogen bond

dotted line between a atom of a positive dipole and a negative dipole

Why is ice less dense than liquid water?

● In ice, the water molecules are arranged in a orderly pattern. It has an open lattice with hydrogen bonds. ● In water, the lattice is collapsed and the molecules are closer together.

Why does water have a melting/ boiling point higher than expected?

Hydrogen bonds are stronger than other intermolecular forces so extra strength is required to overcome the forces

What type of intermolecular forces do alkanes have? Why?

London force → induced dipole-dipole interaction, because the bonds are nonpolar

What happens to the boiling point as alkane chain length increases? Why?

The boiling point increases because there is more surface area and so more number of induced dipole- dipole interaction. Therefore more energy required to overcome the attraction

Does a branched molecule have lower or higher boiling point compared to equivalent straight chain? Why?

The branched molecule has a lower boiling point because they have fewer surface area and hence less induced dipole -dipole interactions.

Are alkanes soluble in water? Explain your answer.

Insoluble because hydrogen bonds in water are stronger than alkanes’ London forces of attraction

What kind of intermolecular forces do alcohols have? Why?

Hydrogen bonding, due to the electronegativity difference in the OH bond

How do alcohols’ melting point and boiling point compare to other hydrocarbons’ of similar C chain lengths? Why?

Higher, because they have hydrogen bonding (strongest type of intermolecular force) → stronger than London forces

Are alcohols soluble in water? Why does solubility depend on chain length?

Soluble when short chain - OH hydrogen bonds to hydrogen bond in water Insoluble when long chain - non-polarity of C-H bond takes precedence

Explain the trend of boiling temperatures of hydrogen halides HF to HI

There is a general increase of boiling point from HCl to HI which is caused by increasing London forces because of increasing number of electrons. There is a big drop in boiling point from HF to HCl because fluorine is very electronegative therefore the hydrogen bonding is much stronger.