Chapter 3. Chemical Bonding Flashcards
What is electronegativity
The tendency of an atom to attract electrons towards it
State and explain the trends in electronegativity on the elements of the periodic table
- Electronegativity decreases down a group because atoms get larger and the distance between the nucleus and the outer electrons gets increased and there is more shielding hence a decrease in electronegativity
- Electronegativity increases across a period because atoms become smaller and nuclear charge increases
What are the factors that electronegativity depends on
- Nuclear charge - the higher the charge the higher the electronegativity
- Atomic radii- the bigger the radius the lower the electronegativity
- Shielding - decreases nuclear charge
Exam tip
A difference in electronegativity of 2.1 is considered ionic bonding
What is covalent bonding
The electrostatic attraction between the nuclei of two atoms and a shared pair of electrons
What are the actual bond angles of ethene and explain why?
C-H-C 1180 and H-C-C 1210 because the four electrons in the double bond repel more than the two electrons in the single bond.
What is the shape and bond angles of NH3?
Triangular pyramid with 1070 N-H angle.
What is the shape and bond angles of water?
non-linear 104.50 bond angle.
What are the three van der Waals forces and order them in terms of increasing strength?
“1.London dispersion forces
2. Dipole-dipole forces
3. Hydrogen bonding”
How do dipole-dipole forces form?
If molecules with dipoles are not symmetrical they have a net charge on either sides so this are attracted to other molecules with dipoles aswell.
How do instantaneous dipole induced dipole forces form?
Electrons are not stationary hence their positions can change any time and when they are crowded one side they create a dipole while induces a dipole in the surrounding atoms/molecules creating a London dispersion forceforce.
What are the conditions necessary for a hydrogen bond to form?
A very electronegative atom
Why are hydrogen bonds stronger than dipole dipole forces?
There are lone pairs of electrons in hydrogen bonding and the hydrogen atoms are highly electron deficient as the other atoms has a high electro-negativity and the hydrogen atoms are small so they have a very strong electric field.
What is a covalent bond?
covalent bond is defined as the electrostatic attraction between the nuclei of two atoms and a shared pair of electrons.
State electron domains and their shape and their hybridisation type of the central atom
Electron Domains, Hybridisation of central atom, Electron domain geometry
2, sp, linear
3, sp2, trigonal planar
4, sp3, tetrahedral
5, sp3d, trigonal bipyramidal
6, sp3d2, octahedral
Define ionic bonding
The electrostatic attraction between oppositely charged particles.
What are the conditions required for ionic compounds to conduct electricity?
they have to be molten or dissolved
What does delocalised mean?
not tied to a particular atom.
Define metallic bonding
Positive ions in a sea of delocalised ions.
What holds covalent bonds?
Electrostatic force between the nuclei and shared electrons.
What are the two types molecular orbitals?
- Sigma orbital s to s, s to p and p to p.
- Pi orbital p to p parallelly. A double bond.
Explain how an sp3 is formed.
A 2s orbital raises its energy level to 2p. The 2p will be having two electrons only so the 2s brings 2 electrons and creates an sp3 orbital
What are the angles of the hybrid orbitals?
-sp3 109.50
-sp2 1200
-sp 1800
Which orbital is weaker and why?
A pi bond is weaker than a sigma bond because there is more overlap of orbitals in forming a sigma bond.
Which atoms are electronegative enough to form hydrogen bonds?
“Oxygen, Nitrogen and Fluorine.”
What is the shape of a hydrogen bond?
Linear because the electron in the covalent bond repel those in the hydrogen bond.
Why does water have a higher boiling point as compared to methane with a comparable Mr?
Water has hydrogen bonds.
Why is ice less dense than liquid water.
In liquid water the hydrogen bonds can easily be broken and reformed whereas in ice the molecules are not free to move about and the hydrogen bonds hold the molecules together in a 3-dimensional structure that resembles the structure of diamond. In order to fit into this structure the molecules are slightly less closely O packed than in liquid water which causes the ice to be less dense.
What are intramolecular forces?
Forces within molecules i.e covalent bonding. These govern the chemical properties of a compound
What are intermolecular forces?
relatively weak forces that exist between molecules. They govern the physical properties of a compound such as melting point
What is electronegativity?
Electronegativity is the ability of a particular atom
What are the trends of electronegativity?
It increases across a period and it decreases down a group
What is bond energy?
Bond energy is the average amount of energy absorbed when one mole of a particular bond is broken in 1 mole of gaseous molecules
What is bond length?
The covalent bond length is the distance between the nuclei of the two atoms in the bond
What is the range for polar covalent compounds in terms of electronegativity?
0.3 to 1.7
Factors that increase the strength of id-id forces?
- Increasing number of electrons per molecule.
- increasing number of contact points between the molecules.
Three facts to count when showing hydrogen bonding
(i) Show two dipoles
(ii) Show a lone pair of electrons on NOF
(iii) Show hydrogen bonding between the hydrogen atom and the lone pair.
