Electrons

Question 1

What electrons in an atom are highest in energy

Answer 1

Those in the outermost shell as they are furthest away from the nucleus.

Those electrons closer to the nucleus are attracted more strongly to the nucleus so therefore are lower in energy.

Question 2

A shell

Answer 2

A group of orbitals with the same principle quantum number ( a number representing the relative overall energy of each orbital).

Question 3

How to calculate the number of electrons in each shell and the types of subshells present in each shell.

Answer 3

2nsquared
1st shell=2 (s)
2nd shell=8 (s , p)
3rd shell=18 (s , p , d)
4th shell=32 (s , p , d , f)

Question 4

orbitals

Answer 4

A region around the nucleus that can hold up to two electrons with opposite spins ( to minimise repulsion between electrons)

4 types: s , p, d and f

each type of orbital has a different shape.

atomic orbitals make up sub-shells.

Question 5

s orbital

Answer 5

• spherical shaped
• 1 orbital makes up the s subshell
  -holds 2 electrons

Question 6

p orbital

Answer 6

• dumb bell shaped
• 3 orbitals make up the p subshell
• 6 electrons

Question 7

d orbital

Answer 7

• 5 orbitals make up the d subshell
  -10 electrons

Question 8

f orbital

Answer 8

• 7 orbitals make up the f sub-shell
• 14 electrons

Question 9

Electron configuration using subshells

Answer 9

• electrons are added one at a time
• The lowest energy subshell is filled first (1s,2s,2p,3s,3p,4s,3d…)
• 4s is an exception to the rule as it is lower in energy than 3d.
• orbitals of the same energy in a particular subshell are filled singly until the subshell is half full ~ as electrons in the same orbital repel.
• The electrons are then paired with opposite spin
• each orbital can hold up to two electrons.

Question 10

subshell electron configuration examples & EXCEPTIONS

Answer 10

potassium - k19
1s2 2s2 2p6 3s2 3p6 4s1

Argon - Ar18
1s2 2s2 2p6 3s2 3p6

Scandium - Sc21 (short hand)
[Ar] 4s2 3d1

Exceptions:
Chromium - Cr24
1s2 2s2 2p6 3s2 3p6 [ 3d5 4s1] not 4s2 3d4

Copper- Cu29
1s2 2s2 2p6 3s2 3p6 [ 3d10 4s1] not 4s2 3d9

This is because the 3d subshell is more stable when either half full or completely full.

Question 11

Blocks in the periodic table

Answer 11

Each block is named after the subshell containing the highest energy electron for the element in that block.

example:
Mg- 1s2 2s2 2p6 3s2
this means it is int the s block, 3rd row.

Question 12

Ions of d-block elements

Answer 12

• The energies of the 4s and 3d subshell are very close together
• when forming d-block ions, the 4s subshell empties BEFORE the 3d subshell.
• This is because once the 4s subshell contains electrons , it now has a higher energy than the 3d subshell

Question 13

writing short hand configuration

Answer 13

Should not use this unless specified in the question, always use the long configuration.

• write out the normal configuration
• write out the configuration of the noble gas before this element.
• substitute the noble gas into the configuration.

example:

sulfur ~1s2 2s2 2p6 3s2 3p4

noble gas before sulfur is neon ~ 1s2 2s2 2p6

[ne] 3s2 3p4

Question 14

subshell

Answer 14

All of the orbitals of the same type in the same shell.

example ~ 1s, 2p , 3d

Question 15

electron configuration of ions

Answer 15

lose electrons = positive ions
gain electrons = negative ions

When atom lose or gain electrons the highest energy subshell is effected first.

Example :

sulfur atom (16 electrons) ~
1s2 2s2 2p6 3s2 3p4

sulfur ion (s2-) ~
1s2 2s2 2p6 3s2 3p6

Question 16

order of energy levels for atomic orbitals

Answer 16

1s
2s
2p
3s
3p
4s
3d
4p
5s
4d
5p
6s
4f
5d
6p
7s
5f
6d
7p

Question 17

As the distance from the nucleus increases …

Answer 17

the shells become closer in energy.

• Orbital overlap begins to take place from the third shell and beyond.

Question 18

Electron

Answer 18

• A cloud of negative charge
• has no exact location