2.2.2 - Bonding and Structure Flashcards
What does ionic bonding happen between?
A metal and a non metal.
Which way are electrons transferred?
From the metal atom to the non-metal atom.
What holds ionic compounds together?
Oppositely charged ions are formed, which are bonded together by strong electrostatic attraction.
In giant ionic lattices what is each ion surrounded by?
Oppositely charged ions.
How is a three dimensional giant ionic lattice formed?
Ions attract each other from all directions.
Can ionic compounds conduct electricity when solid?
No
Why can ionic compounds conduct electricity when in liquid state?
The ions are free to move around and conduct electricity.
What is ionic bonding?
electrostaic atracion between positive and negatively charged ions.
Why don’t ionic compounds conduct when solid?
Ions are in fixed position and cannot move to carry a charge.
Why can ionic compounds conduct when molten or in solution?
Ions are mobile and are therefore able to carry a charge.
Why do ionic compounds have high melting and boiling points?
Due to the strong electrostatic force of attraction between positively and negatively charged ions.
Why does MgO have require more energy to break down than NaCl?
Mg2+ and O2- bonds are stronger than Na- and Cl- bonds.
What do ionic lattices dissolve in?
Polar solvents, such as water.
What do polar bonds occur between?
Atoms that do not share electrons equally between them.
What is the result of a polar bond?
Results in the atom having very small charges on them.
What do polar water molecules do?
Attract the charged ions in the giant ionic lattice.
What is covalent bonding?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
What is a dative covalent bond?
A covalent bond in which the shared pair of electrons has been provided by one of the bonding atoms only.
What is an example of a substance which contains a dative covalent bond?
Ammonium ion. NH4+
What does the average bond enthalpy measure?
The energy required to break a covalent bond.
What does a greater average bond enthalpy mean?
The stronger the bond is, therefore more energy is required tot break it.
In shapes of molecules what angles are the biggest?
Lone pair lone pair angles
In shapes of molecules what angles are the smallest?
Bond pair - bond pair angles.
According to electron pair repulsion theory what happens to the bond angle when a lone pair is added?
The distances decreases by 2.5 degrees as the lone pair repels the bond pair.
In a linear molecule what is the bond angle?
180
If there are three bond pairs and no lone pairs what shape the molecule and what is its bond angle?
Trigonal planar and 120
What is the shape of a molecule and bond angle which has four bond pairs and no lone pairs?
Tetrahedral 109.5
What is the shape and bond angle of a molecule which has 3 bond pairs and 1 lone pair
Trigonal pyramidal 107
What is the shape and bond angle of a molecule which has two bond pair and two lone pairs?
Non linear 104.5
What is the shape and bond angle of water?
Non-linear 104.5
What is the shape and bond angle of a molecule with 5 electron pairs bonded around the central atom?
Trigonal bipyramidal 90
What is the shape and bond angle of a molecule with 6 electron pairs around the central atom?
Octahedral 90
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond.
What is the most electronegative element?
Fluorine
How does the Pauling scale work?
The higher the value the more electronegative the element is.
What makes a bond polar in covalent bonding?
The bonding electrons are pulled towards the more electronegative atom.
What is a dipole?
The difference in charge between the two atoms caused by a shift in electron density in the bond.
How is a bond more polar?
The greater the difference in electronegativity.
Why are diatomic gases non polar?
Because both atoms have equal negativity and so electrons are attracted equally to both nuclei.
Why are carbon and hydrogen ann-polar?
They have pretty similar electronegativity.
What do polar bonds have?
Permanent dipoles.
What does the arrangement of polar bonds in a molecule determine?
Whether or not the molecule will have an overall dipole.
In what instance do polar molecules cancel out?
When the polar bonds are symmetrical - overall no dipole so non-polar.
Example of cancelling out dipoles?
CO2
In what case does the molecule have an overall dipole?
If the polar bonds are arranged unevenly across the whole molecule.
Example of overall polar molecule?
H2O - negative charge is positioned more towards the oxygen atom.
When is a substance purely covalent?
Diatomic gases because the electronegativity difference is 0 and so the bonding electrons are arranged completely evenly within the bond.
How can you use electronegativity to predict the type of bonding?
The higher the difference in electronegativity, the more ionic in character the bonding becomes.
What are intermolecular forces?
Forces between molecules.
What is the strength of intermolecular forces?
They’re much weaker than covalent, ionic or metallic bonds.
What are the three types of intermolecular forces?
- London forces.
- Permanet dipole-dipole interactions.
- Hydrogen bonding
What is the strongest intermolecular force?
Hydrogen bonding
How is a temporary dipole formed in a charge cloud?
These clouds are moving really quick. At any particular moment, the electrons in an atom are likely to be more to one side than the other. This causes a temporary dipole.
What does a temporary dipole cause?
Another temporary dipole in the opposite direction on a neighboring atom.
How is the overall affect that the atoms are attracted to one another?
Dipoles are being constantly created and destroyed all the time as electrons are constantly moving.
What do stronger London forces mean?
Higher boiling points.
Why do larger molecules have stronger London forces?
They have a larger electron cloud.
What do molecules with a greater surface area have?
A stronger London force because they have a bigger exposed electron cloud.
What do molecules with stronger London forces have and why?
Higher boiling points as more energy is required to break the intermolecular forces.
What kind of intermolecular forces do polar molecules have?
Permanet dipole-dipole interactions.
When does hydrogen bonding occur?
When hydrogen is covalently bonded to fluorine, nitrogen or oxygen.
What do molecules have which have hydrogen bonding?
-OH or -NH groups.
How does hydrogen bonding affect the properties of a substance?
They are soluble in water and their density and viscosity are also affected.
How is ice less dense than water?
Ice has more hydrogen bonds than liquid water and since the hydrogen bonds are relatively long, this makes the ice less dense than water.
What is the main factor that determines the boiling point of a substance?
The strength of the induced dipole-dipole unless it has hydrogen bonds.
What else increases the strength of the induced dipole-dipole?
Number of electrons in the molecule.
Why are polar molecules soluble in water?
Water is a polar molecule, so only tends to dissolve other polar substances. Compounds with hydrogen bonds can from hydrogen bonds with water molecules so will be soluble.
Why don’t simple covalent compounds conduct electricity?
Covalent substances are uncharged.
Anomalous properties of water?
- Less dense when ice as there is an open lattice due to longer hydrogen bonds.
- Higher melting/boiling points than expected as hydrogen bonds require a larger amount of energy to overcome.
Metallic bonding?
The strong electrostatic attraction between positive ions and negatively charged delocalised electrons in a regular lattice.
