Learning objectives

The electrons in a particular shell on an atom may be of different energies depending on their average distance from the nucleus. Electrons having the same energy are grouped in subshells.

The maximum number of subshells in a shell is equal to the shell number.
The subshells are labeled by the shell number and one of the letter s, p or d (for example 2s, 3p).

The maximum number of electrons in the three different types of subshells corresponds to the number of groups in the blocks of periodic table as shown below (s -2; p - 6 and d -10).

1	2
							1H										2He
3 Li	4 Be											5 B	6 C	7 N	8 O	9 F	10 Ne
11 Na	12 Mg											13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
19 K	20 Ca	21 Sc	22 Ti	23 V	24 Cr	25 Mn	26 Fe	27 Co	28 Ni	29 Cu	30 Zn	31 Ga	32 Ge	33 As	34 Se	35 Br	36 Kr
37 Rb	38 Sr	39 Y	40 Zr	41 Nb	42 Mo	43 Tc	44 Ru	45 Rh	46 Pd	47 Ag	48 Cd	49 In	50 Sn	51 Sb	52 Te	53 I	54 Xe
55 Cs	56 Ba	71 Lu	72 Hf	73 Ta	74 W	75 Re	76 Os	77 Ir	78 Pt	79 Au	80 Hg	81 Tl	82 Pb	83 Bi	84 Po	85 At	86 Rn
s-block 2		d-block 10 groups										p-block 6 groups

The electron configuration for an atom is a list of the occupied subshells. This list can be constructed using the periodic table as a guide.

The number of these electrons that are involved in bonding (valence electrons) for a particular atom can also be deduced from the position of that atom relative to the just previous noble gas.

On completion of this activity, you should be able to, using the periodic table,

write the full electron configuration for any of the first 20 elements
write an abbreviated electron configuration using the symbol of the appropriate noble gas
choose an element that has a given abbreviated electron configuration
identify the element that has a given configuration of the valence electrons
identify the atom that has a given number of valence electrons