Atomic Forces & Electron Configuration Atomic Forces Two atomic forces hold an atom together: • Nuclear force – holds the ‘nucleus’ together • Electromagnetic force – holds electrons & protons together Nuclear force – nucleus contains p+ and no . Since like charges repel each other, the neutrons act like a buffer between p+ to minimize this electrostatic repulsion. Thereby, helping to maintain stability.

Electromagnetic force – Since p+ and e- have opposite charges, they are attracted to each other. Therefore, the e- closer to the nucleus are moving slower than the e- further away from the nucleus. The closer they are to the nucleus, the stronger the electromagnetic force. This force gets weaker as you move further away from the nucleus. Therefore, the electrons in the outermost energy level have the most energy – their motion is much faster. Electron energy levels • We know electrons exist in an ‘electron cloud’ around the nucleus of an atom.

• ‘Energy levels’ are a region around the nucleus of an atom where electrons may be found.

• Electrons in these energy levels increase in energy as you move further away from the nucleus of an atom. • The ‘kinetic energy’ of matter comes from the motion of the electrons.

• They exist in three dimensions, and this requires coordinates to predict where they can be found. Three coordinates There are primary energy Levels & sublevels

• Each primary energy level is numbered 1,2,3,4, 5, 6, 7 as you move away from the nucleus of the atom. (there are maximum of 7 energy levels for a element– why?)

• Each primary energy level is divided into one or more sublevels. Sublevels • The maximum number of sublevels in a primary energy level equals the actual number of the primary energy level. However, there are a maximum of 4 sublevels

• So….. for energy level 1, there can be only 1 sublevel for energy level 2, there can be only 2 sublevels for energy level 3, there can be only 3 sublevels for energy level 4, there can be only 4 sublevels for energy level 5, there can be only 4 sublevels for energy level 6, there can be only 4 sublevels for energy level 7, there can be only 4 sublevels Sublevels • These sublevels are labeled with a number that represents the primary energy level and a letter - s, p, d, or f - that corresponds to the shape of the sublevel.

• energy level 1 the sublevel is 1s • energy level 2 the sublevels are 2s and 2p • energy level 3 the sublevels are 3s, 3p, and 3d • energy level 4 the sublevels are 4s, 4p, 4d, and 4f Energy levels beyond 4 have the same sublevel configuration Orbitals • Each primary energy level consists of one or more sublevels and each sublevel has a maximum number of electrons.

• s has a maximum of 2 electrons • p has a maximum of 6 electrons • d has a maximum of 10 electrons • f has a maximum of 14 electrons Writing electron configurations • An electron location is expressed by writing the primary energy level number (row number of the element) followed by the sublevel’s letter (s,p,d,f) with the number of electrons in each sublevel written as a superscript.

number of electrons 2 primary energy level number  3 s

sublevel letter • Examples: 3p2 (there are 2 electrons in the p sublevel of primary level 3) 4d7 (there are 7 electrons in the d sublevel of primary level 4) Example – Chlorine (Cl) • How many electrons does Chlorine have? • What row of the periodic table is Chlorine on? • The 17 electrons of Chlorine are distributed into three primary energy levels.

• Energy level 1 has 1 sublevel and 2 electrons -- 1s2 • Energy level 2 has 2 sublevels and 8 electrons-- 2s2 and 2p6 • Energy level 3 only needs 2 sublevels and 7 electrons – 3s2 and 3p5 • Therefore, the electron configuration of Chlorine is:

Chlorine 1s2 2s2 2p6 3s2 3p5 ( this is how the 17 electrons are distributed for a Chlorine atom) Electron configurations & the periodic table The shape of the periodic table shows energy levels, sublevels, and orbitals. Electron Configuration Summary There are a maximum of 7 primary energy levels corresponding to the 7 rows of the periodic table.

There are a maximum of 4 sublevels (s, p, d, f) corresponding to the 4 block shape of the periodic table.

There are a maximum number of electrons in each sublevel corresponding to the number of elements in each row of that block (s - 2 , p – 6, d – 10, f – 14). Checking electron configurations • Two ways to check an electron config

(1) The last notation in the electron configuration represents the location of the element on the periodic table. (gets tricky when you have d & f block elements) Example: Chlorine (Cl) is 1s2 2s2 2p6 3s2 3p5 the 3p5 indicates its location as the fifth square in the p sublevel on the third row of the periodic table. (2) The total of the superscripts equals the atomic number of the element. (# of electrons) Example: for Cl above, the total is 17 Electron filling order • Energy levels overlap in the d and f sublevels. • This means that the lowest-energy orbitals are filled before electrons are placed in the higher- energy orbitals. Valence Electrons & Valence

• Valence – the capacity to unite, react, or interact.

• Valence electrons are the only electrons that can participate in chemical bonds with other atoms. • The valence electrons are the number of electrons that the atom can gain, loose, or share in a chemical reaction with another atom of another element.

• An atom’s valence electrons are the electrons that are in the highest primary energy level of an atom; i.e. the energy level the farthest away from the nucleus. This corresponds to the period (row) where the element is located. • With a few exceptions, on the periodic table the number of valence electrons increases from left to right across a period (row).

• With a few exceptions, elements in a group (column) on the periodic table have similar properties because they all have the same number of valence electrons.

• Elements in column #1 all have 1 valence electron, elements in column #2 all have 2 valence electrons, elements in column 13 have 3, column 14 have 4, column 15 have 5, column 16 have 6, column 17 have 7, and column 18 have 8 (except He). • Columns 3 thru 12 all have 2 valence electrons (many exceptions in this section) Examples • Na 1s22s22p63s1 1 valence • Fe 1s22s22p63s23p64s23d6 2 valence • Br 1s22s22p63s23p64s23d104p5 7 valence

• Ba 1s22s22p63s23p64s23d104p65s24d105p66s2 2 valence • Ag 1s22s22p63s23p64s23d104p65s24d9 2 valence • Co 1s22s22p63s23p64s23d7 2 valence • I 1s22s22p63s23p64s23d104p65s24d105p5 7 valence