5: Electrons and bonding

Question 1

Number of electrons in each of the shells

Answer 1

Shell 1= 2 electrons
Shell 2= 8 electrons
Shell 3= 18 electrons
Shell 4= 32 electrons

Question 2

What is a shell

Answer 2

• A shell is an energy level
• As the energy increases the shell number also increases
• The shell number or energy level number is called the principal quantum number

Question 3

What is an atomic orbital?

Answer 3

• An atomic orbital is a region around the nucleus that can hold up to two electrons with opposite spins
• It is a region in space where there is a high probability of finding an electron

Question 4

S-orbitals
* What is it?
* How many electrons can it hold?
* Which shells contain s-orbitals?
* How does the shell number effect the s-orbital?

Answer 4

• In an s-orbital the electron cloud is within the shape of a sphere
• It can hold 1 or 2 electrons
• Every shell contains one s-orbital
• The greate the shell number, the greater radius of its s-orbital

Question 5

P-orbital
* What is it
* How many electrons can it contain?
* Which shells contain p-orbitals?
* How does the shell number effect the p-orbital?

Answer 5

• In a p-orbital, the electron clous is within the shape of a dumb-bell
• It can contain 1 or 2 electrons but there are 3 seperate p-orbitals at right angles to each other
• The 3 seperate p-orbitals are Px, Py and Pz
• Each shell from n=2 contains three p-orbitals
• The greate the shell number, the further the p-orbital is from the nucleus.

Question 6

d-orbitals and f-orbitals
* How many electrons can they contain
* Which shells are they found in

Answer 6

• Each shell from n=3 contains five d-orbitals (so it can contain 10 electrons)
• Each shell from n=4 contains seven f-orbitals (so it can contain 14 electrons)

Question 7

What are sub-shells

Answer 7

The sub-shell of a a shell different orbitals within a shell.
For example
Shell 2 has:
* 1 s-orbital and 3 p orbitals
* Within the shell it has 2s and 2p sub-shells

Question 8

How are orbitals filled?

Answer 8

Orbitals fill in order of increasing energy:
1. n=1, 1s
2. n=2, 2s
3. n=2, 2p
4. n=3, 3s
5. n=3, 3p
6. n=4, 4s
7. n=3, 3d
8. n=4, 4p
9. n=4, 4d
10. n=4, 4f

• The 3-d sub-shell is at a higher energy level than the 4s sub-shell
• The 4s sub-shell therefore fills before the 3d sub-shell
• So, the order of filling is 3p, 4s, 3d

Question 9

How are electrons paired?

Answer 9

• Electrons pair with oppsite spins
• As electrons are negatively charged, they repel each other. They have either up or down spin.
• Electrons in the same orbital must have opposite spins to help counteract the repulsion between the negative charges of the two electrons.

Question 10

How are orbitals within a sub-shell filled?

Answer 10

• Within a sub-shell, the orbitals have the same energy.
• One electron occupies each orbital before pairing starts
• This prevents any repulsion between paired electrons until there is no further orbital available at the same energy level

Question 11

What is the electron configuration of the noble gases?

Answer 11

• He= 1s2
• Ne= 1s2 2s2 2p6
• Ar= 1s2 2s2 2p6 3s2 3p6
• Kr= 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

Question 12

What are positive and negative ions called?

Answer 12

• Positive ions are called cations and are formed when atoms lose electrons
• Negative ions are called anions and are formed when atoms gain electrons

Question 13

What are the 3 blocks of the periodic table and where are they situated?

Answer 13

• s-block is (the left block of 2 groups) and the elements have their highest energy electrons in the s-sub-shell
• p-block is (the right block of 6 groups) and the elements have their highesest energy electrons in the p-sub-shell
• d-block is (the centre block of 10 groups) and the elements have their highest energy electrons in the d-sub-shell

Question 14

How are the 4s and 3d sub-shells emptied when atoms form positive ions?

Answer 14

• As the 4s sub-shell fills before the 3d sub-shell, the 4s sub-shell also empties before the 3d sub-shell

Question 15

What is ionic bonding?

Answer 15

Ionic bonding is the electrostatic attraction between positive and negative ions which occurs in all directions
It holds together cations and anions in ionic compounds.

Question 16

What is the structure of ionic compounds?

Answer 16

• Ionic compounds are arranged in giant ionic lattices (also called giant ionic structures)
• The type of lattice formed depends on the sizes of the positive and negative ions which are arranged in an alternating fashion
• The ionic lattice of MgO and NaCl are cubic

Question 17

Properties of ionic compounds: melting and boiling points

Answer 17

Most ionic compounds have high melting and boiling points
High temperatures are needed to provide enough energy to overcome the strong electrostatic attraction between the ions

Question 18

Why are most ionic compounds solids at room temperature?

Answer 18

• Almost all ionic compounds are solids at room temperature
• As, there is insufficient energy to overcome the strong electrostatic forces of attractions between the oppositely charged ions in the giant ionic lattice

Question 19

What types of ionic compounds have higher melting and boiling points?

Answer 19

• Lattices with ions with greater ionic charges have higher melting and boiling points.
• This is because their is stronger attraction between the ions

Question 20

Describe the solubility of ionic compounds

Answer 20

Many ionic compounds will dissolve in polar solvents, e.g. water

Solubility is dependent on two main factors:
1. Breaking down the ionic lattice
2. The polar molecules attracting and surrounding the ions

Polar molecules, such as water, can break down or disrupt the ionic lattice and surround each ion in solution:
1. The δ+ end of the polar molecule can surround the negative anion
2. The δ- end of the polar molecule can surround the positive cation

Question 21

What does the solubility of an ionic compound depend on?

Answer 21

The solubility of an ionic compound depends on the relative strength of the electrostatic forces of attraction within the ionic lattice and the** attractions between the ions and the polar molecule**

In general, the greater the ionic charge the less soluble an ionic compound

Question 22

What is the electrical conductivity of an ionic compound in a solid vs liquid/ molten (dissolved in water) state?

Answer 22

In the solid state:
* The ions are in a fixed position in the giant ionic lattice
* There are no mobile charge carriers
* So, the ionic compound is a non-conductor of electricity

In the liquid/molten state
* The solid ionic lattice breaks down
* The ions are now free to move as mobile charger carriers
* So, the ionic compund is a conductor of electricity in liquid and aqueous states

Question 23

Define covalent bonding

Answer 23

Covalent bonding is the strong electrostatic attraction between a shaired pair of electrons and the nuclei of the bonded atoms

Question 24

What does covalent bonding occur in?

Answer 24

It occurs been atoms in:
* Non-metallic elements
* Compunds of non-metallic elements
* Polyatomic ions

The atoms are bonded togather in a single unit- small molecule, giant covalent structure or charged polyatomic ion

Question 25

What is the orbital overlap in covalent bonding?

Answer 25

A covalent bond is the overlap of atomic orbitals, each containing 1 electron, to give a shared pair of electrons * The shared pair of electrons is attracted to the nuclei of both the bonding atoms

Question 26

Describe the localisation of a covalent bond

Answer 26

The attraction of a covalent bond is localised, acting solely between the shared pair of electrons and the nuclei of the 2 bonded atoms

Question 27

Can predictions of bonding be solely based on the configuaration of noble gases (use an example)?

Answer 27

Predictions for bonding cannot only be based on the configuration of the noble gas electronic structure. For example: * Boron has the electron configuration 1s2 2s2 2p1 so only 3 outer shell electrons can be paired. * Boron forms covalent compounds such as BF3 in which only 3 outer shell electrons are paired. * So the boron atom only has 6 electrons in its outer shell in the BF3 molecule

Question 28

What is the attraction between in double and triple covalent bonds?

Answer 28

* In a **double covalent bond**, the electrostatic attraction is between **two** shared pairs of electrons and the nuceli of the bonding atom * In a **triple covalent bond**, the electrostatic attraction is between **three** shared pairs of electrons and the nuceli of the bonding atom

Question 29

What happens in dative covalent bonding?

Answer 29

A dative convalent bond (also called a coordinate bond) is a bond in which the shared pair of electrons has been supplied by **only one** of the bonding atoms. * The shared electron pair was originally a **lone pair** of electrons on one of the bonded atoms

Question 30

What is bond energy and averagre bond enthalpy and how does it effect the strength of a bond?

Answer 30

**Bond energy** * The **bond energy** is the energy required to break one mole of a particular covalent bond in the gaseous states * The larger the bond energy, the stronger the covalent bond **Average bond enthalpy** Average bond enthalpy is also used as a measurement of the strength of a covalent bond * The average bond enthalpy term is the **average amount of energy** needed to break a **specific** type of bond, measured over a wide variety of different molecules

Question 31

Bond length * What is it * What effects it and how does bond length effect bond strength * Which bonds are the shortest and strongest

Answer 31

The bond length is the internuclear distance of two covalently bonded atoms The ** greater the forces of attraction** between electrons and nuclei, the more the atoms are **pulled closer** to each other This **decreases** the **bond length** of a molecule and **increases** the **strength** of the covalent bond Triple bonds are the shortest and strongest covalent bonds due to the large electron density between the nuclei of the two atoms

Question 32

What is meant by the term atomic orbital?

Answer 32

A region around the nucleus that can hold up to two electrons, with opposite spins.

Question 33

What is meant by the term bonded pair?

Answer 33

A pair of electrons shared between two atoms to make a covalent bond

Question 34

What is meant by the term coordinate bond?

Answer 34

A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only; also called a dative covalent bond.

Question 35

What is meant by the term covalent bond?

Answer 35

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

Question 36

What is meant by the term dipole?

Answer 36

A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule, has a small positive charge δ+ and the other has a small negative charge δ–.

Question 37

What is meant by the term electronegativity?

Answer 37

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.

Question 38

What is meant by the term giant covalent lattice?

Answer 38

A three-dimensional structure of atoms, bonded together by strong covalent bonds.

Question 39

What is meant by the term giant ionic lattice?

Answer 39

A three-dimensional structure of oppositely charged ions, bonded together by strong ionic bonds.

Question 40

What is meant by the term giant metallic lattice?

Answer 40

A three-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bonds.

Question 41

What is meant by the term metallic bond?

Answer 41

The electrostatic attraction between positive metal ions and delocalised electrons.

Question 42

What is meant by the term molecule?

Answer 42

The smallest part of a covalent compound that can exist while retaining its chemical identity, consisting of two or more atoms covalently bonded together.