Bonding Flashcards
What is Ionic Bonding?
The electrostatic force of attraction between two oppositely charged ions formed by electron transfer
What is Covalent Bonding?
A shared pair of electrons
What is Dative Covalent Bonding?
Formed when the shared pair of electrons in the covalent bond come from only one of the bonding atoms.
What is Metallic Bonding?
The electrostatic force of attraction between the positive metal cations and the sea of delocalised electrons
What is electronegativity?
The relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond towards itself
What do the physical and chemical properties of a compound depend on?
The chemical bonds and intermolecular forces
How are positive ions formed?
The loss of electrons
How are negative ions formed?
The gain of electrons
What ions do metals usually form?
Positive ions
What ions do non metals usually form?
Negative ions
What is the name for a positive ion?
Cation
What is the name for a negative ion?
Anion
Give three properties of ionic compounds.
They have high melting and boiling points
They are soluble in water
They conduct electricity
Why do ionic compounds have high melting points?
There is a strong electrostatic attraction between the oppositely charged ions in the ionic lattice. It requires a large amount of energy to overcome.
Why is the melting point of MgCl greater than the melting point of NaCl?
Magnesium is a smaller ion (ionic radius)
Higher charge
Greater charge density
Stronger electrostatic attraction between oppositely charged ions
Stronger ionic bond
When do ionic compounds conduct electricity?
When molten or in solution
Why can ionic compounds conduct electricity when molten or in solution?
The ions are free to move and carry charge
Why are some ionic compounds soluble in water?
The water molecules hit the ionic lattice and knock off the ions.
The water molecules then surround the ions
Why are some ionic compounds insoluble in water?
The electrostatic attraction between the oppositely charged ions is too strong
What properties do compounds containing molecular ions exhibit?
The same properties as ionic compounds
What is necessary for a dative covalent bond to form between 2 atoms?
1 atom must have lone pair of electrons
1 atom must have empty orbital
How do you show a lone pair of electrons?
Two dots and a line around them
What is a dative covalent bond?
A shared pair of electrons with both donated/supplied by one atom
What is metallic bonding?
The electrostatic attraction between the delocalised electrons and positive metal ions
Arranged in a lattice
What does the strength of the metallic bond depend on?
The number of delocalised electrons and size of the positive metal ion
Why does electronegativity increase as you go across a period?
-The number of protons increased
-The atomic radius decreases because the electrons in the same shell are pulled in more
Why does electronegativity decrease as you go down a group?
-Distance between the nucleus and the outer electrons increases
-Shielding increases
Why aren’t the noble gases electronegative?
Because they don’t form bonds
Molecular Shapes: 2 electron pairs
Linear, 180 degrees
Molecular Shapes: 3 electron pairs
Trigonal Planar, 120 degrees
Molecular Shapes: 2 bonding pairs, 1 lone pair
Bent, 118 degrees
Molecular Shapes: 4 electron pairs
Tetrahedral, 109.5 degrees
Molecular Shapes: 3 bonding pairs, 1 lone pair
Trigonal Pyramidal, 107 degrees
Molecular Shapes: 2 bonding pairs, 2 lone pairs
Bent, 104 degrees
Molecular Shapes: 5 electron pairs
Trigonal Bipyramidal, 120 &90 degrees
How do you work out shapes?
-Write group number of central atom
-Add number of atoms around the central atom
-Add/Subtract charge (If charge is negative, add it & if charge is positive, subtract it)
-To find bonding pairs, divide step 3 by 2
-To find lone pair, subtract step 4 by the number of atoms around the central atoms
Describe the Intermolecular Forces: Van Der Waals Forces
Occur between all simple covalent molecules & the separate atoms in noble gases
As the electrons move, parts of the molecule can become more or less electronegative. These dipoles can induce dipoles in adjacent molecules.
Factors which affect the strength of VDW forces: Number of electrons in the molecule
The more electrons there are in the molecule, the higher the chance temporary dipoles will form. This means VDW forces will be stronger and boiling points will be greater.
Factors which affect the strength of VDW forces: Surface area of the molecules
The larger the surface area of a molecule, the more contact it will have with adjacent molecules. This means it has a greater ability to induce a dipole in an adjacent molecule and the VDW forces are stronger, and melting points and boiling points will be higher. Straight chain isomers have a larger S.A than branched isomers
Intermolecular Forces: Permanent Dipole-Dipole
Occur between polar molecules
Stronger than VDW forces, so boiling points are higher
Intermolecular Forces: Hydrogen Bonding
Occurs in compounds which have H attached to F, O, N which must have an available lone pair of electrons. There is a large difference between electronegativities
They have the highest boiling points as they’re the strongest intermolecular force
What is VSEPR - the electron pair repulsion theory
Bonding pairs and lone (non-bonding) pairs of electrons are charged clouds that repel each other. Pairs of electrons in the outer shell of atoms repel each other to arrange themselves as far apart as possible. Lone pair - lone pair repulsion is greater than lone pair-bond pair repulsion, which is greater than bond pair - bond pair repulsion.
What is simple molecular covalent bonding?
Strong covalent bonds between atoms, weak Van der Waal forces of attraction between molecules
Can simple covalent bonds conduct electricity? Why?
No because all the electrons are used up in bonding, so they aren’t free to move
Do simple molecular substances have a high or low boiling point? Why?
They have low melting and boiling points because of the weak Van der Waal forces of attraction between molecules that dont take up much energy to overcome.
Describe macromolecular covalent bonding
A lattice of many atoms held together by strong covalent bonds
Do substances with macromolecular covalent bonds have a high or low boiling points? Why?
High as it takes more energy to overcome many strong covalent bonds
Do substances with macromolecular covalent bonds conduct electricity?
Most dont as all electrons are used up in bonding
Describe the structure of diamond
3D tetrahedral structure of Carbon atoms, with each carbon atom bonded to 4 others
Describe the structure of graphite
Macromolecular covalent
Each carbon atom bonded to 3 other carbon atoms, so is in layers
Weak Van der Waals forces of attraction between layers means they can slide over each other.
One electron from each carbon is delocalised and can carry a charge so can conduct electricity.
Do metallic compounds have high or low melting and boiling points? Why?
High as the strong forces of attractions between positive metal ions and negatively charged sea of delocalised electrons
Do metallic compounds conduct electricity? Why?
Yes, the delocalised electrons can move throughout the electron to carry charge
How does the strength of metallic bonds change across the periodic table? Why?
Increases: higher melting and boiling points, stronger
Higher charge on metal ions
More delocalised electrons per ion
Stronger force of attraction between them
What affects electronegativity?
Nuclear Charge
Atomic Radius
Electron Shielding
What is the most electronegative element?
Fluorine (4.0 Pauling Scale)
Largest nuclear charge for its electron shielding, small atomic radius
How do you get a non polar bond?
Both bonding elements have the same electronegativities
When do you get a polar bond?
Both atoms have different electronegativities
What is the strongest type of intermolecular force?
Hydrogen Bonding
What is the weakest type of intermolecular force?
Van der Waals forces
Are Van der Waal forces greater in smaller or larger molecules? Why?
Larger - more electrons
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 they’re highly electronegative, H nucleus is left exposed. Strong force of attraction between H nucleus and lone pair of electrons on O,N,F
Why is ice less dense than liquid water?
In liquid water, hydrogen bonds constantly break and reform as molecules move about.
In ice, the hydrogen bonds hold the molecules in fixed positions; this makes them slightly further apart than in liquid water
What does the Electron Pair Repulsion theory state?
That electron pairs will take up positions as far away from each other as possible, to minimise the repulsive forces between them
Which experience the most repulsion?
●Lone pair-Lone pair
●Lone pair-Bonded pair
●Bonded pair-Bonded pair
LP-LP repulsion strongest
LP-BP repulsion middle
BP-BP repulsion weakest
Define the term Polar Bond
A covalent bond where the shared pair of electrons is displaced to one end
