3.1.3 Bonding Flashcards
Define ionic bonding
Electrostatic force of attraction between oppositely charged ions formed by electron transfer
Ionic Bonding
Metal atoms ___ electrons to form ___ ions
Metal atoms lose electrons to form +ve ions
Ionic Bonding
Non-metal atoms ____ electrons to form ___ ions
Non-metal atoms gain electrons to form -ve ions
Simplest ions are…
single atoms which have lost/gained electrons to make full outer shell
What are compound ions?
Ions that are made up of groups of atoms with an overall charge
State the formula for a sulfate ion
SO42-
State the formula for a hydroxide ion
OH-
State the formula for a nitrate ion
NO3-
State the formula for a carbonate ion
CO32-
State the formula for an ammonium ion
NH4+
Name the structure of ionic crystals
Giant Ionic Lattice
Sodium nitrate contains Na+ (1+) and NO3- (1-) ions. State the fomula of the sodium nitrate.
Magnesium chloride contains Mg2+ (2+) and Cl- (1-) ions. State the fomula of the magnesium chloride.
Name 3 physical properties of ionic compounds
- Conduct electricity only when they’re molten or dissolved
- High melting points
- Tend to dissolve in water
Why can ions conduct electricity when they’re molten or dissolved?
∵ ions in liquid are free to move and carry a charge
Why can’t ions conduct electricity when they’re in a solid?
∵ ions are in fixed position by strong ionic bonds
Why do ionic compounds have high melting points?
- Giant ionic lattices
- Strong electrostatic forces of attraction between oppositely charged ions
- Takes a lot of energy to overcome these forces
Why do ionic compounds tend to dissolve in water?
- Water molecules are polar
- Part of molecule has a small negative charge and other bits have small positive charges
- Charged parts pull ions away from lattice = causing it dissolve
Ionic bonding is stronger and melting points are higher when ions are… (2x)
smaller and/ or have higher charges
When do molecules form and how are they held together?
- Form when 2 or more atoms bond together
- Held together by strong covalent bonds
What do single covalent bonds contain?
Shared pair of electrons
Describe covalent bonding
- Two atoms share electrons so they’ve both got full outer shells
- Both postive nuclei are attracted electrostatically to shared electrons
Multiple covalent bonds contain…
multiple shared pairs of electrons
Draw methane, represent the covalent bonds by drawing lines
Why can carbon form giant covalent structures?
∵ they can form 4 covalent bonds
Describe the structure of graphite
- Carbon atoms are arranged in sheets of flat hexagons covalently bonded with 3 bonds each
- 4th outer electron of each carbon atom is delocalised
- Sheets of hexagons are boned together by weak van der Waal forces
Name 5 properties of graphite
- Low density
- Dry lubricant/slippy
- Electrical conductor
- Insoluble in any solvent
- Very high melting point
Explain why graphite has a low density
Layers are quite far apart compared to the length of covalent bonds
Explain why graphite is an electrical conductor
‘Delocalised’ electrons aren’t attached to any particular carbon atoms & free to move along sheets carrying a charge
Explain why graphite is a dry lubricant/slippy
Weak bonds between layers in graphite = easily broken ∴ sheets can slide over each other
Explain why graphite has a very high melting point
Covalent bonds are very strong and require lots of energy to break
Explain why graphite is insoluble in any solvent
Covalent bonds in sheets are too strong to break
Describe the structure of diamond
- Each carbon atom is covalently bonding to 4 other carbon atoms (giant covalent structure)
- Tetrahedral shape
Name 5 properties of diamond
- Very high melting point
- Extremely hard
- Good thermal conductor
- Can’t conduct electricity
- Won’t dissolve in any solvent
Why is diamond a good thermal conductor?
Vibrations travel easily through stiff lattice
Why can’t diamond conduct electricity?
Outer electrons held in localised bonds
Why do diamond gemstones sparkle a lot?
Its structure makes it refract light a lot
What is dative covalent bonding (or co-ordinate bonding)?
When shared pair of electrons in covalent bond come from only one of the bonding atoms
Name an example of dative covalent bonding & explain how it is an example of this bonding
Ammonium ion (NH4+)
Forms when nitrogen atom in ammonia molecule donates a pair electrons to proton (H+)
Illustrate dative covalent bonding in an ammonium ion (NH4+)
Define metallic bonding
Metallic bonding is the electrostatic force of attraction between the positive metal ions and the delocalised electrons
Metals elements exist as…
giant metallic lattice structures
Describe metallic bonding
- Outer shell electrons of metal are delocalised
- Electrons free to move
- Leaves positive metal ion
- Positive metal ions attracted to delocalised negative electrons
- Form lattice of closely packed positively ions in sea of delocalised electrons
- This is metallic bonding
Name 4 properties of metals
- High melting points
- Good thermal conductors
- Good electrical conductors
- Insoluble (expect in liquid metals)
Why do metals have high melting points?
Strong electrostatic attraction between positive metal ions and delocalised sea of electrons
Why are metals good thermal conductors?
Delocalised electrons can pass kinetic energy to each other
Why are metals good electrical conductors?
Delocalised electrons can move and carry current
Why are metals insoluble?
Strong metallic bonds
Name 3 factors that affect the strength of metallic bonding
- Number of protons/strength of nuclear attraction
- Number of delocalised electrons per atom
- Size of ion
Metallic Bonding
More protons = ….
stronger bond
Metallic Bonding
More delocalised electrons per atom = ….
stronger bonding
Metallic Bonding
Smaller the ion = …
stronger the bond
Explain why Mg has stronger metallic bonding than Na and a higher melting point
- In Mg: more electrons in outer shell that are released to sea of electrons
- Mg ion is smaller and has more than one proton
- ∴ stronger electrostatic attraction between positive metal ions and delocalised electrons = higher energy is needed to break bonds
Illustrate a giant ionic lattice of sodium chloride
Illustrate metallic bonding in magnesium
What does the shape of a molecule depend on?
The number of pairs of electrons in outer shell of central atom
Bonding pairs and lone pairs electrons exist as ___ ____
charge clouds
What are charge clouds?
Area where you have really big chance of finding an electron pair
Why does a pair of electrons in an outer shell of an atom sit as far apart from each other as possible?
Electrons = negatively charged ∴ repel each other
Shape of charge cloud effects…
how much it repels other charge clouds
e.g. lone-pair charge clouds repel more than bonding-pair charge clouds
Why are the bond angles between bonding pairs reduced when lone pairs of electrons are added?
∵ they’re pushed together by lone-pair repulsion
_______ angles are the biggest
Lone-pair/lone-pair
_______ angles are the second biggest
Lone-pair/bonding-pair
_______ angles are the smallest
Bonding-pair/bonding-pair
Name the shape of a molecule with 2 electron pairs (& no lone pairs)
Linear
Draw BeCl2
State the bond angles of the molecule
2 electron pairs (& no lone pairs)
Name the shape of a molecule with 3 electron pairs (& no lone pairs)
Trigonal planar
Draw BF3
State the bond angles of the molecule
3 electron pairs (& no lone pairs)
Name the shape of a molecule with 4 electron pairs (& no lone pairs)
Tetrahedral
Draw NH4+
State the bond angles of the molecule
4 electron pairs (& no lone pairs)
Name the shape of a molecule with 3 electron pairs & 1 lone pair
Trigonal Pyramidal
Draw PF3
State the bond angles of the molecule
3 electron pairs & 1 lone pair
Name the shape of a molecule with 2 electron pairs & 2 lone pairs
Bent
Draw H2O
State the bond angles of the molecule
2 electron pairs & 2 lone pairs
Name the shape of a molecule with 5 electron pairs (& no lone pairs)
Trigonal Bipyramidal
Draw PCl5
State the bond angles of the molecule
5 electron pairs (& no lone pairs)
Name the shape of a molecule with 4 electron pairs & 1 lone pair
Seesaw
Draw SF4
State the bond angles of the molecule
4 electron pairs & 1 lone pair
Name the shape of a molecule with 3 electron pairs & 2 lone pairs
T-shaped
Draw ClF3
State the bond angles of the molecule
3 electron pairs & 2 lone pairs
Name the shape of a molecule with 6 electron pairs (& no lone pairs)
Octahedral
SF6
State the bond angles of the molecule
6 electron pairs (& no lone pairs)
Name the shape of a molecule with 4 electron pairs & 2 lone pairs
Square planar
Draw XeF4
State the bond angles of the molecule
4 electron pairs & 2 lone pairs
Describe how you can find out how many bonding and
lone electron pairs there are on central atom of molecule
- Find central atom (one that all other atoms are bonded to)
- Work out no. of electrons in outer shell of central atom (use periodic table)
- Add one to this number for every atom that central atom is bonded to
- Divide by 2 to find no. of electron pairs on central atom
- Compare no. of electron pairs to no. of bonds to find no. of lone pairs and no. of bonding pairs on central atom
Predict the shape of the molecule H2S (show all your steps)
Define Electronegativity
The power of an atom to attract a pair of electrons in a covalent bond
____ is most electronegative element
Fluorine
How are polar covalent bonds created?
In a covalent bond between 2 atoms of different electronegativities, bonding electrons will be pulled towards the more electronegative atom = makes bond polar
Covalent bond between 2 atoms of same element is ____
non-polar
Why is a covalent bond between 2 atoms of same element non-polar?
∵ atoms have equal electronegativities = electrons equally attracted to both nuclei
Some elements (e.g. C & H) have very similar electronegativities = bond essentially ____
non-polar
In a polar bond, difference in electronegativity between 2 atoms causes a ____ ___ to form
permanent dipole
What is a dipole?
Difference in charge between 2 atoms caused by shift in electron density in bond
Greater difference in electronegativity between atoms = …
more polar the bond
What makes a polar molecule?
When a molecule contains polar bonds that give an uneven distribution of charge across the whole molecule
When are molecules with polar bonds not polar and why is this?
When polar bonds are arranged symmetrically in molecule = charges cancel out & there’s no permanent dipole
Name 3 Intermolecular Forces
- Permanent dipole-dipole forces
- Van der Waals forces or induced dipole-dipole forces
- Hydrogen bonding
What type of molecules have permanent dipole-dipole forces?
Polar molecules
Describe how permanent dipole-dipole forces form
In a substance made from molecules with permanent dipoles = they’ll be weak electrostatic forces of attraction between δ+ and δ- charges on neighbouring molecules
Explain why if you put a charged rod next to a jet of polar liquid (e.g water), the liquid will move towards the rod
- ∵ polar liquids contain molecules with permanent dipoles
- (Doesn’t matter if rod is postively or negatively charged)
- Polar molecules in liquid can turn around so the opposite charged end is attracted towards the rod
Where are Van der Waals forces found?
Found between all atoms and molecules
Describe how Van der Waals forces form
- Electrons in charge clouds = always moving quickly
- At any moment, electrons in atom are likely to be more to one side than the other
- At this moment = atom has temporary dipole
- Dipole causes another temporary dipole in opposite direction on neighbouring atom
- 2 dipoles are attached to each other
- 2nd dipole causes another dipole in 3rd atom
- Dipoles are being created and destroyed constantly ∵ electrons are constantly moving
- Overall effect = atoms are attracted to each other
Van der Waals forces hold molecules together in ___
lattice
Describe and explain the structure of iodine at room temp
- Iodine atoms are held together in pairs by strong covalent bonds to from I2 molecules
- Molecules held together in molecular lattice arrangement by weak van der Waals attractions (this causes iodine to be solid at room temp.)
Name 3 factors that affect the strength of the Van der Waals forces
- Size of molecules
- Shape of molecules
- Number of electrons
Explain how the size of molecules affects the strength of van der Waal forces
Larger molecules = larger electron clouds = stronger van der Waals forces
Explain how the shape of molecules affects the strength of van der Waal forces
Long, straight molecules lie closer than branched ones = closer together 2 molecules get = stronger the forces between them are
When does hydrogen bonding occur?
When hydrogen is covalently bonded to fluorine, nitrogen or oxygen
Hydrogen Bonding is the _____ intermolecular force
Strongest
Describe hydrogen bonding
- F, N & O = very electronegative ∴ they draw bonding electrons away from hydrogen atom
- Bond is polarised + hydrogen has high charge density = hydrogen atoms form weak bonds with lone pair of electrons on F, N or O atoms or other molecules
Molecules with H-bonding usually contain ____ or ____ groups
-OH or -NH groups
Draw hydrogen bonding occuring in water
Draw hydrogen bonding occuring in ammonia
Substances with h-bond have ____ boiling/melting points than similar molecules
Substances with h-bond have higher boiling/melting points than similar molecules
Why do substances with h-bond have higher boiling/melting points than similar molecules?
∵ of extra energy needed to break h-bonds
Anomalously high boiling points of H2O, NH3 & HF are
caused by ___ ____ between molecules
Anomalously high boiling points of H2O, NH3 & HF are
caused by hydrogen bonding between molecules
Explain why ice is less dense than liquid water
- As liquid water cools to form ice, molecules make more h-bonds & arranged themselves into regular lattice structure
- In this structure, H2O molecules are further apart on average than molecules in liquid water
Explain why simple covalent compounds have lower melting/boiling points than macromolecules. (4)
- To melt/boil simple covalent compound = just need to overcome the van der Waals forces between molecules
- These forces are weak
- To melt/boil macromolecules = many covalent bonds have to be broken
- Covalent bonds = strong
Explain how the solubility of a substance in water depends on type of particles it contains
- Water = polar solvent
- ∴ substances that are polar or charged will dissolve in it
- Whereas non-polar or uncharged substances won’t
Fill in the blanks
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(3 examples)
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(3 examples)
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(3 examples)
Explain why CF4 has a bond angle of 109.5° (2)
- Around carbon = 4 bonding pairs of electrons
- ∴ these repel equally & spread as far apart as possible
State what is meant by macromolecular (1)
Means a giant molecule with covalent bonding
Predict the shape of AlCl4-. Draw a diagram of the specie to show its 3D shape. Name the shape and suggest a value for the bond angles. Explain your reasoning. (4)
Application Question
Perfume is a mixture of fragrant compounds dissolved in a volatile solvent. When applied to the skin the solvent evaporates, causing the skin to cool for a short time. After a while, the fragrance may be detected some distance away. Explain the observations. (4)
- Solvent has low boiling point or weak intermolecular forces
- Solvent needs energy, taken from the skin, to overcome intermolecular forces and evaporate
- Perfume molecule slowly spreads through the room
- By random diffusion of the perfume
Draw a diagram to show how 1 molecule of ammonia is attracted to 1 molecule of water. (3)
(hint h-bonding)
Draw NH3BCl3
What type of bonding does H3O+ have?
Dative Covalent Bonding
Fill in the blanks
Showing outer electrons only, draw a dot-and-cross diagram to indicate the bonding in calcium oxide (2)
Ionic Bonding
Explain why the boiling temperature of PH3 is greater than that of CH4 (3)
- PH3 has dipole-dipole
- between molecules
- stronger than in CH4
Explain why the H-F bond in HF is polar (2)
- Difference in electronegativity / F more electronegative than H
- Bonding pair of electrons attracted (drawn) towards F (nucleus) in the covalent bond
