3.1.3 Bonding Flashcards
What is ionic bonding?
A type of chemical bonding that involves the electrostatic attraction between charged ions
Structure of ionic compound
Ions arranged in lattice
How happens during ionic bonding?
Outer shell electrons are transferred from metal atoms so non-metal atoms forming ionic bonds (metal cations and non-metals anions)
Properties of ionic compounds
Electrical conductivity- not when solid, when molten or dissolved (ions free to move + carry charge)
Melting/boiling point- high due to strong electrostatic forces so a lot of energy is required to overcome
Solubility in water- usually yes as water molecules are polar (part has small negative charge and part has small positive charge) so the water molecules pull metals away from ions + cause it to dissolve
How to work out formula of ionic compound
Work out how many electrons need to be lost or gained to form full outer shells (group number). Balance so that the number of electrons that need to be lost from a metal = number of electrons that need to be gained by a non-metal
How to form out formula of ions
Look at the group number of that element which indicates the amount of electrons in the outer shell. Use this to work out how many electrons need to be lost or gained to form a full outer shell. If it gains electrons, an anion is formed and if it loses electron, a cation is formed. The amount of electrons required indicates the size of the charge
Define the term elecronegativity
The power of an atom to attract a pair of electrons in a covalent bond
Explain how permanent dipole-dipole forces arise between hydrogen chloride molecules
Difference in electrogenativity leads to attraction between slight positive on one molecule and slight negative on the other.
Explain why sodium bromide has a melting point that is higher than that of sodium and higher than that of sodium iodide
Sodium bromide and iodide ionically bonded
Sodium atom donates 1 electron to bromine/iodine atom creating 2 oppositely charged ions.
The oppositely charged ions are electrostatically attracted and held together in a giant lattice
Sodium is metallically bonded by the electrostatic attraction between positive metal ions and delocalised electrons.
Sodium has a giant lattice structure
Ionic bonds are stronger than metallic bonds (stronger electrostatic attraction)
Br- is smaller than I-
What type of substance is an alloy?
Mixture
Describe a safe method for making pure crystals of copper sulfate from copper carbonate and dilute sulfuric acid
• sulfuric acid in beaker (or similar)
• add copper carbonate one spatula at a time
• until copper carbonate is in excess or until no more effervescence occurs *
• filter using filter paper and funnel
• filter excess copper carbonate
• pour solution into evaporating basin / dish
• heat using Bunsen burner
• leave to crystallise / leave for water to evaporate / boil off water
• decant solution
• pat dry (using filter paper)
• wear safety spectacles / goggles
Suggest why the electronegativity of the elements increases from lithium to fluorine.
More protons
Similar shielding
Suggest the type of crystal shown by OF2
Molecular
State how the bond between ammonia and boron trichloride is formed
Lone pair is donated to B(Cl3)
Why do metals melt over a larger temperature range than simple molecular molecules ?
Metals has forces of attraction in liquid
Explain how the value of the Cl-Al-Cl bond angle in AlCl3 changes, if at all, on
formation of the compound H3NAlCl3
Aluminium now surrounded by 4 electron pairs
Tetrahedral
Cl-Al-Cl bond angle decreases
Which elements can be hydrogen bonded
Nitrogen
Oxygen
Fluorine
Describe what happens when a reaction mixture is refluxed and why it is necessary.
A mixture of liquids is heated to boiling point for a prolonged time
Vapour is formed which escapes from the liquid mixture, is changed back into liquid and returned to the liquid mixture
Describe how you would obtain a sample of ethanal from a mixture of three compounds (higher bps). Include in your answer a description of the apparatus you would use and how you would minimise the loss of ethanal
Mixture heated in a suitable flask / container
With still head containing a thermometer Water cooled condenser connected to the still head and suitable cooled collecting vessel
Collect sample at the boiling point of ethanal
Cooled collection vessel necessary to reduce evaporation of ethanal
Explain why methanol is easy to liquefy
Hydrogen bonding
Strong enough force to keep molecules together in a liquid
Importance of hydrogen bonding in ice
Low density
Spacing of molecules (move further apart)
Ice can float
Increasing melting boiling point
Define macromolecular
Giant molecule with covalent bonds
Why does macromolecule have higher boiling point than simple molecules
M- contains covalent bonds that must be broken, strong bonds
S- contains VdW between molecules, weak forces
Describe the structure of and bonding in graphite and explain why the melting point of graphite is very high
Arranged in layers
Giant covalent
Strong covalent bonds
VdW between layers
Bond formed when H+ ion reacts with H2O + how
Dative
Lone pair of electron on O shared/donated to H+
Strongest IMF between 2 ammonia molecules
Large difference in electronegativity between N and H
Forms dipole (N partially - and H partially +)
Lone pair on N attracts H partially +
Why does NH3 have higher boiling point than AsH3
NH3 contains hydrogen bonding- strongest IMF
AsH3 contains VdW- weakest IMF
Hydrogen bonding stronger than VdW
How does hydrogen bonding cause anomalous melting and boiling points of some compounds
Hydrogen bonding is the strongest intermolecular force so the boiling/melting point will be higher than expected if present
You can describe bonding pairs and lone pairs of electrons as
Charge clouds that repel each other
How do pairs of electrons in the outer shell arrange themself
As far apart as possible to minimise repulsion
Suggest one reason why electron pair repulsion theory cannot be used to predict the
shape of the [CoCl4]2– ion
Too many electrons in d sub-shell
3 factors affecting electronegativity
Nuclear charge
Atomic radius
Electron shielding
Describe Van der Waals forces of attraction
Temporary dipoles created by the random movement of electrons
Induces dipole in neighbouring molecule
Temporary induced dipole-dipole attraction
Why are Van der Waals forces stronger in larger molecules
More electrons
How does hydrogen bonding arise
O-H, N-H, F-H bonds
Lone pairs of electrons on O,N,F
Highly electronegative
Leave H nucleus exposed
Strong force of attraction between H nucleus and lone pair on O,N,F
Why is ice less dense that liquid water
In water, hydrogen bonds constantly break + reform as molecules move about
Ice, hydrogen bonds hold molecules in fixed positions. Makes them slightly further apart than in liquid water
Electron repulsion theory
Electron pairs will take up positions as far away from each other as possible to minimise the repulsive forces between them
