5.3 Covalent bonding Flashcards

1
Q

What is covalent bonding

A

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

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2
Q

Where does covalent bonding occur

A

non-metallic elements, eg. H2 and O2
Compounds of non-metallic elements, for example H2O and CO2
Polyatomic ions for example NH4+

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3
Q

What units can form by covalent bonds

A

Small molecule - eg. H2
Giant covalent structure - eg. SiO2
Charged polyatomic ion - eg. NH4+

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4
Q

What is a covalent bond

A

An overlap of atomic orbitals each containing one electron to give a shared pair of electrons
Attraction is LOCALISED

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5
Q

How does a covalent bond , bond

A

The shared pair of electrons is attracted to the nuclei of both the bonding atoms
The bonding atoms often have outer shells with the same electron structure as the nearest noble gas

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6
Q

What is a molecule

A

The smallest part of a covalent compound that can exist while retaining the chemical properties of the compound

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7
Q

Difference between ionic and covalent bonding

A

In covalent bonding, electrons are shared but in ionic bonding, the electrons are transferred

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8
Q

What does the displayed formula show

A

The relative positioning of atoms and the bonds between them as lines
Ione pairs can also be added - eg. in H2O

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9
Q

What are Ione pairs

A

Paired electrons that are not shared

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10
Q

How many bonds are formed by carbon

A

4

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11
Q

How many bonds are formed by nitrogen

A

3

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12
Q

How many bonds are formed by oxygen

A

2

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13
Q

How many bonds are formed by hydrogen

A

1

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14
Q

When can ‘expansion of the octet’ take place

A

Only from the n=3 shell when a d-sub shell becomes available for the expansion
Example is sulfur hexafluoride

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15
Q

When does a multiple covalent bond exist

A

When two atoms share more than one pair of electrons

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16
Q

Where is the attraction in a double covalent bond

A

Electrostatic attraction is between two shared pairs of electrons and the nuclei of the bonding atoms

17
Q

Where is the attraction in a triple covalent bond

A

Between three shared pairs of electrons and the nuclei of the bonding atoms

18
Q

What is a dative covalent / coordinate bond

A

A covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only
In a dative covalent bond, the shared electron pair was originally a lone pair of electrons on one of the bonded atoms

19
Q

Example of a dative covalent bond

A

Formation of ammonium from ammonia and H+

Ammonia molecule donates its lone pair of electrons to a H+ ion
Dative covalent bond in NH4+ shown by a bond with an arrowhead -> to show that the nitrogen atom provides both electrons to the covalent bond
In an NH4+ ion, all four bonds are equivalent and you cannot tell which is the dative covalent bond. The arrow for the bond just helps with accounting for all electrons

20
Q

What is Average bond enthalpy

A

Serves as a measurement of covalent bond strength

The larger the value of the average bond enthalpy, the stronger the covalent bond