Covalent bonding

Question 1

Covalent bond definition

Answer 1

The electrostatic force of attraction between the 2 nuclei of atoms and the shared pair of electrons in the bond

Question 2

How is a covalent bond formed?

Answer 2

When an atomic orbital with a single electron in it from one electron overlaps with an orbital of another atom that contains an electron

Question 3

What atomic orbitals overlap in covalent bonding?

Answer 3

Any 2

Question 4

4 ways an orbital can overlap in covalent bonding

Answer 4

2 ends of s orbitals overlap
2 ends of p orbitals overlap
Sideways overlap of p orbitals
End of s and p orbitals overlap

Question 5

What is a sigma bond?

Answer 5

When the ENDS of 2 atomic orbitals overlap eg 2s orbital ends or 2p orbitals end

Question 6

What is a pi bond?

Answer 6

When a sideways overlap is formed eg 2p orbitals bond sideways

Question 7

When can a pi bond be formed?

Answer 7

Can only be formed if sigma bond had already been formed = only in double or triple bonded atoms

Question 8

S orbital and p orbital overlap

Answer 8

Overlaps end on
Only those of DIFFERENT elements eg not Cl-Cl
Forms a polar covalent bond due to invariably of the elements

Question 9

Examples of formation of sigma bonds which result in covalent bonding

Answer 9

H2 because both electrons exist in 1s orbital
Ends of these overlap to form a new molecular orbital, and these electrons occupy this in the overlap
Therefore the highest electron density is between the 2 nuclei of the hydrogen

Question 10

Examples of formation of pi bonds which result in covalent bonding

Answer 10

In ethene where in C=C, one bond between carbon formed is a sigma bond whereas the other is pi, this is because of the way the p subshell is structured that a head on overlap between 2 p orbitals in different atoms (sigma bond) can result in up to 2 sideways overlaps (pi bonds)

Question 11

Electron density of a pi bond

Answer 11

highest above and below the molecule where the 2 orbitals overlap

Question 12

Bond length

Answer 12

Distance between between nuclei of 2 atoms that are covalently bonded together
This distance is the point where the repulsion between nuclei and attraction nuclei has to electrons is balanced

Question 13

Bond strength

Answer 13

Amount of energy required to break every bond in one mole of that bonded molecule when it’s in a gaseous state

Question 14

General relationship between bond strength and bond length between bonds of a similar nature

Answer 14

Higher the electron density (eg number of electrons in a bond) the stronger force of attraction the nucleus has to shared electrons
So higher bond enthalpy (more energy stored) and shorter bond chain because the higher forces pull nuclei closer

Question 15

Why is it important to only compare similar molecule with each other in terms of bond comparing strength and length?

Answer 15

Because there are extraneous reasons as to why a bond strength is weaker, rather than just a larger bond length ie a lone, non-bonded pair of electrons present repel each other = weaker bond

Question 16

Electronegativity

Answer 16

An atom’s electronegativity is its ability of an atom to attract a bonding pair of electrons

Question 17

Trend in electronegativity in periodic table

Answer 17

DECREASES going DOWN the group
INCREASES from LEFT to RIGHT

Question 18

Most electronegative element

Answer 18

Fluorine

Question 19

Electron density

Answer 19

Shows regions around nuclei in bonded atoms where the electrons are distributed (Eg in the overlap of orbitals)

Question 20

Electron density in identically bonded atoms

Answer 20

The distribution around the nuclei will be roughly symmetrical for each atom
Because it’s the same element = same electronegativity = so same ability to attract an element

Question 21

What is formed when 2 atoms of different electro-negatives bond?

Answer 21

A polar covalent bond

Question 22

Contour lines in a polar covalent molecule

Answer 22

the lines are closer packed to atom of higher electronegativity showing it has a higher density than the other

Question 23

Charges in a polar molecule

Answer 23

The atom with the largest electronegativity thus higher electron density becomes slightly negatively charged so represented as d-
Whereas atom with lower electron density near it becomes d+

Question 24

Ways of representing a polar bond in a stick diagram of a covalent bond

Answer 24

Have an arrow point in the direction of ‘electron drift’ so which has a higher electron density (so higher electronegativity)
Eg: H–>–Cl

Question 25

Polar covalent bond

Answer 25

A type of covalent bond between 2 atoms where bonding of electrons are unevenly distributed.
Therefore one atom carries slightly negative charge and other carries positive charge

Question 26

How can polar covalent bonds be separated on characteristics?

Answer 26

If they act purely (100%) covalent or (100%) ionic
Polar covalent bonds with a larger difference in electronegativity between both bonded elements have a higher % of ionic character

Question 27

Discrete (simple) molecule

Answer 27

A small molecule held together by covalent bonds

Question 28

Dot and cross diagrams

Answer 28

Represents covalently bonded molecule by showing the shared pairs outer shell electrons and lone pairs
Electrons from different atoms are represented using either x or o

Question 29

Bonding of carbon

Answer 29

Using orbital overlap theory it could only form 2 covalent bond as there is only 2 unpaired valence electrons
So carbon provides energy to close the energy gap between 2s and 2p
then a 2s electron is promoted to the empty 2p orbital = 4 unpaired electrons

Question 30

Why does the carbon atom use its energy to promote an electron?

Answer 30

Because energy released in forming 4 rather than 2 electrons compensates for original input of energy

Question 31

The octet rule

Answer 31

Shows that atoms share electrons with each other in order to achieve the outer shell electron config of a noble gas (8 electrons)

Question 32

What molecules can expand their octets (have more than 8 electrons in its outer shell due to bonding from other molecules)?

Answer 32

Elements from period 3 onwards such as Sulfur and phosphorus
Because they contain a d orbital which can accommodate these extra electrons

Question 33

Displayed formula

Answer 33

Representing covalent bonds as simple lines between elements of atoms that have bonded

Question 34

Dative covalent bond

Answer 34

Occurs when an empty orbital of an atom overlaps with an orbital containing a lone pair of electrons (so 2 unbounded electrons)

Question 35

How to represent a dative covalent bond

Answer 35

With an arrow from the atom with the lone pair of electrons to the atom with an empty orbitals which the electrons are being shared with

Question 36

Does AlCl3 have dative bonds?

Answer 36

No but it is a stable compound with 6 electrons in the outer shell of the middle (aluminium) atom

Question 37

Dative bonding in Al2Cl6

Answer 37

If 2 AlCl3 molecules combine,
Then because Al has room for 2 electrons (having only 6 in its outer shell) a chlorine atom from one molecule donates a pair to Al in both molecules

Question 38

Dative bonding in CO

Answer 38

Oxygen forms a dative bond by donating 2 electrons to carbon
As well as forming 2 normal covalent bonds with carbon
So a triple bond is formed